Higher-order mode suppressor, waveguide filter device using the same, spectrum analyzer, signal analyzer, signal generator, higher-order mode suppression control method, and filter configuration method.

Abstract

To provide a high-order mode suppression device, a waveguide filter device using them, a spectrum analyzing device, a signal analyzing device, a signal generating device, a high-order mode suppression control method, and a filter construction method, capable of surely preventing a high-order mode to be generated from being passed with a simple structure, and realizing a spectrum measurement, a signal analysis, and the generation of a signal with high reliability that are not receive an influence of the high-order mode by adopting the structure.SOLUTION: In a high-order mode suppression device 5, a ridge conductive pipe part 50 is constructed so that an inner diameter of a conductive path 51 is narrower than that of conductive path 71a and 71b of conductive pipes 70a and 70b, can be prevented from passing a high-order mode generated in an input side to a frequency band that is twice or more of a cutoff frequency when inputting the frequency band containing a basic frequency band from the input side.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a higher-order mode suppressor in a waveguide filter, a waveguide filter device using the same, a spectrum analyzer, a signal analyzer, a signal generator, a higher-order mode suppression control method, and a filter configuration method.

Background Art

[0002] With the development of the information society in recent years, the amount of information used in various communications has increased. For example, the analysis frequency required for devices such as spectrum analyzers used in performance tests of a device under test (DUT) has also shifted from the microwave band to the millimeter wave band or higher frequency bands.

[0003] In a spectrum analyzer, when analyzing a signal having a frequency exceeding the upper limit frequency (for example, 60 GHz) that can be measured by the device itself (such as exceeding 100 GHz), some use a downconverter as a front end and input the signal to be measured to this front end.

[0004] In the front stage of the front end for propagating electromagnetic waves in a frequency band exceeding 100 GHz, it is known to use a waveguide as the propagation path of the electromagnetic wave. In a spectrum analyzer having such a configuration, for the waveguide used for the propagation of electromagnetic waves, higher-order modes may occur depending on the connection method and operation, and in some cases, good frequency conversion may not be possible due to the influence.

[0005] As this type of spectrum analyzer, there has been conventionally known one in which the connection surface of one waveguide block in which different types of waveguides connected in series are adopted as the propagation path of electromagnetic waves is formed into a ridge structure to suppress the generation of higher-order modes and enable good frequency conversion (for example, Patent Document 1, etc.).

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-137031 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In devices such as spectrum analyzers described in Patent Document 1, waveguides may be used not only in the propagation path to the DUT, but also, for example, in the IF filter that filters the intermediate frequency band signal (IF signal) that has been frequency-converted by the front end.

[0008] While waveguide filters are typically used as IF filters in fundamental mode, there is a growing demand today for operation in frequency bands beyond the fundamental mode to accommodate higher analysis frequencies.

[0009] However, conventional waveguide filters used as IF filters, when operated at frequencies higher than the fundamental mode, produce higher-order modes (TE). 20 Modes (or similar issues) may occur, potentially preventing reliable spectrum measurements.

[0010] Figure 14 shows the frequency characteristics of this type of conventional waveguide filter. As shown in Figure 14, when conventional waveguide filters are operated in a frequency range beyond the fundamental mode frequency range of 34-52 GHz (for example, the frequency range from 66-80 GHz), the transmission of unwanted frequency signals, which is a degradation of the transmission characteristic S21 due to the generation of higher-order modes, becomes significantly apparent.

[0011] In the case of a spectrum analyzer that employs a waveguide filter with frequency characteristics as shown in Figure 14 as an IF filter, for example, unwanted frequency signals passing through the IF filter in the frequency range of 66 to 80 GHz may result in the display of unwanted components that interfere with the measurement of the spectrum characteristics, potentially making reliable spectrum measurements impossible.

[0012] As mentioned above, conventional waveguide filters lacked an effective higher-order mode suppression function (Waveguide Mode Suppressor) to suppress higher-order modes when operating in frequency ranges beyond the fundamental mode. Furthermore, conventional instruments such as spectrum analyzers employing waveguide filters without an effective higher-order mode suppression function were susceptible to the influence of higher-order modes, making it difficult to achieve reliable measurements.

[0013] The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a higher-order mode suppressor that can reliably prevent generated higher-order modes from passing through with a simple structure, and that can apply this structure to realize highly reliable spectrum measurement, signal analysis, and signal generation unaffected by higher-order modes, as well as a waveguide filter device, spectrum analyzer, signal analyzer, signal generator, higher-order mode suppression control method, and filter configuration method using the same. [Means for solving the problem]

[0014] To solve the above problems, the higher-order mode suppressor according to claim 1 of the present invention includes: a ridge waveguide section (50) having a ridge structure in which a waveguide (51) penetrating in the longitudinal direction is provided and ridge sections (52a, 52b) are formed inside the waveguide; a first ridge-waveguide conversion section (60a) connected to one longitudinal end face (53a) of the ridge waveguide section, and having a ridge-waveguide conversion waveguide (61a) formed between the end face (64a) opposite to the one end face and the opposite end face (63a) that acts as a bridge for radio wave propagation between the waveguide of the ridge structure and the waveguide (71a) of the first waveguide (70a); and a second ridge-waveguide conversion section (60a) connected to the other longitudinal end face (53b) of the ridge waveguide section, and having a ridge-waveguide conversion waveguide (61a) formed between the end face (64b) opposite to the other end face and the opposite end face (63b) that acts as a bridge for radio wave propagation between the waveguide of the ridge structure and the waveguide (71a) of the first waveguide (70a). The device includes a second ridge-waveguide conversion section (60b) having a ridge-waveguide conversion waveguide (61b) formed thereon, which acts as a bridge for radio wave propagation between the waveguides (71b) of the waveguide (70b), wherein the inner diameter of the waveguide of the ridge waveguide section is narrower than that of the waveguides of the first and second waveguides, and the first waveguide and the second waveguide are connected to the opposite end face of the first ridge-waveguide conversion section and the opposite end face of the second ridge-waveguide conversion section, respectively, with one of the first waveguide or the second waveguide as the input side and the other as the output side, and is sized to prevent higher-order modes generated on the input side from passing through to frequencies exceeding the fundamental frequency band when input from the input side, for frequencies more than twice the cutoff frequency. The first waveguide and the second waveguide are waveguides that conform to a predetermined waveguide standard, and the ridge waveguide section is configured such that the inner diameter of the waveguide is such that TE20 modes up to the desired frequency cannot pass through. It is characterized by having this feature.

[0015] With this configuration, the higher-order mode suppressor according to claim 1 of the present invention can reliably prevent higher-order modes generated on the input side due to inputs in a frequency band of twice or more the cutoff frequency from passing through with an extremely simple structure. Furthermore, the higher-order mode suppressor according to claim 1 of the present invention prevents higher-order modes from passing through even when a waveguide of a predetermined waveguide standard is operated at a frequency band higher than the fundamental frequency band, thereby ensuring good frequency characteristics.

[0018] To solve the above problems, the present invention 2In the high-order mode suppressor according to [the relevant content], the ridge waveguide portion may be configured to have a double-ridge structure in which the ridge portion protrudes from the inner surfaces (51a, 51b) of the waveguide facing each other into the waveguide.

[0019] With this configuration, the claim of the present invention 2 The high-order mode suppressor according to can ensure the coupling between the fundamental frequency band and the ridge structure, and avoid the situation where the fundamental frequency band cannot pass through.

[0020] Also, in the high-order mode suppressor according to the claim of the present invention 3 The first ridge-waveguide conversion portion and the second ridge-waveguide conversion portion each have a tapered ridge portion (62a1, 62a2, 62b1, 62b2) formed inside the respective ridge-waveguide conversion waveguides, the height of which changes gradually from the end face corresponding to one end face of the ridge waveguide portion to the end face on the opposite side, and from the end face corresponding to the other end face of the ridge waveguide portion to the end face on the opposite side. It may also be a configuration.

[0021] With this configuration, the claim of the present invention 3 The high-order mode suppressor according to can smoothly relay the radio wave propagation between the waveguide of the ridge structure, the first waveguide, and the waveguide of the second waveguide while preventing the high-order mode from passing through.

[0022] Also, in the high-order mode suppressor according to the claim of the present invention 4 The first ridge-waveguide conversion portion and the second ridge-waveguide conversion portion may each be configured by a tapered waveguide in which the dimensions of the openings continuously expand from the end face corresponding to one end face of the ridge waveguide portion to the end face on the opposite side, and from the end face corresponding to the other end face of the ridge waveguide portion to the end face on the opposite side.

[0023] With this configuration, the claim of the present invention 4The high-order mode suppressor according to [specific reference] can further smoothly relay the radio wave propagation between the waveguide of the ridge structure, the first waveguide, and the waveguide of the second waveguide while preventing the high-order mode from passing through.

[0024] In order to solve the above problems, the waveguide filter device according to claim 5 of the present invention includes at least, as components, the high-order mode suppressor (5, 81b) described in claim 1 and a waveguide band-pass filter (81d) having a predetermined pass band, and has a waveguide section (80) in which a plurality of the above components are continuously connected in the longitudinal direction to form a single waveguide (80a). One end of the waveguide section is used as the input side and the other end is used as the output side. During the filtering operation in the waveguide section for a fundamental frequency band input from the input side, the high-order mode generated at the input side for a frequency band of twice or more the cut-off frequency of the waveguide band-pass filter is prevented from passing through by the high-order mode suppressor and is attenuated before reaching the waveguide band-pass filter.

[0025] With this configuration, the waveguide filter device according to claim 5 of the present invention combines a waveguide band-pass filter and a high-order mode suppressor in the waveguide section. Even if a high-order mode occurs in a frequency band twice the cut-off frequency, the high-order mode suppressor can prevent the high-order mode from passing through, and a situation where unnecessary frequency components are not sufficiently attenuated can be avoided. As a result, this waveguide filter device can perform a highly reliable band-pass filter operation in a wide frequency range from exceeding the cut-off frequency to a frequency band of twice or more the cut-off frequency.

[0026] Also, the claim 6The waveguide filter device further comprises: a first coaxial waveguide converter (85a) connected perpendicularly to the waveguide section at one end of the waveguide section, housing a coaxial cable (86a), and performing coaxial waveguide conversion between the waveguide at the one end of the waveguide section and the waveguide; and a second coaxial waveguide converter (85b) connected perpendicularly to the waveguide section at the other end of the waveguide section, housing a coaxial cable (86b), and performing coaxial waveguide conversion between the waveguide at the other end of the waveguide section and the waveguide. The waveguide section, the first coaxial waveguide converter, and the second coaxial waveguide converter may constitute a coaxial waveguide converter.

[0027] This configuration allows the claims of the present invention to be made 6 The waveguide filter device described herein can be operated as a waveguide filter device equipped with a coaxial waveguide converter with a higher-order mode suppression function, and is suitable for applications such as IF filters or RF filters in equipment such as spectrum analyzers, signal analyzers, and signal generators.

[0028] To solve the above problems, the present invention 7 The spectrum analyzer relating to the claim comprises a frequency conversion unit (100) having a filter (113) that provides a signal to be measured of predetermined frequency components together with a local signal output from a local signal generator (112) to a mixer (111), and extracts a signal in a predetermined intermediate frequency band from the mixing output, and a detector (120) that detects the signal in the intermediate frequency band, and determines the spectral characteristics of the signal to be measured by changing the frequency of the local signal according to the frequency to be analyzed, wherein the filter is as described in the claim. 6 The waveguide filter device described above is used, and the waveguide section of the waveguide filter device receives the mixing output and allows the frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while the higher-order mode suppressor prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

[0029] This configuration allows the claims of the present invention to be made 7The spectrum analyzer in question can, in the filter that extracts the IF signal, allow the frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while extending the stopband to a high-frequency band of more than twice the cutoff frequency, enabling highly reliable measurement of spectral characteristics for the millimeter wave band or higher.

[0030] To solve the above problems, the present invention 8 The signal analyzer relating to the claim comprises a frequency conversion unit (100B) having a filter (113B) that feeds a signal to be measured of predetermined frequency components together with a local signal output from a local signal generator (112B) to a mixer (111B) and extracts a signal in a predetermined intermediate frequency band from the mixing output, and a signal analysis unit (153B) that converts the signal in the intermediate frequency band into a digital signal using an ADC (125) and then analyzes the waveform of the signal, and a signal analyzer (2) that changes the frequency of the local signal according to the frequency to be analyzed and analyzes the waveform of the signal to be measured, wherein the filter is as described in the claim. 6 The waveguide filter device described above is used, and the waveguide section of the waveguide filter device receives the mixing output and allows the frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while the higher-order mode suppressor prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

[0031] This configuration allows the claims of the present invention to be made 8 The signal analyzer in question can, in the filter that extracts the IF signal, allow the frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while extending the stopband to a high-frequency band of more than twice the cutoff frequency, enabling highly reliable signal analysis targeting the millimeter wave band or higher.

[0032] To solve the above problems, the present invention 9The signal generating device relating to the claim has a frequency conversion unit (100B) that passes the test signal in the intermediate frequency band output from the signal generating unit (130) through a filter (113B) that extracts a signal in a predetermined intermediate frequency band, and then feeds it together with the local signal output from the local signal generator (112B) to a mixer (111B) to convert it into a millimeter-wave band signal, and changes the frequency of the local signal according to the test target frequency for testing the device under test (DUT), and sends out the signal after frequency conversion by the frequency conversion unit as the test signal for the device under test, wherein the filter is as described in the claim. 6 The waveguide filter device described above is used, and the waveguide section of the waveguide filter device receives the output from the signal generation unit and allows the frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while the higher-order mode suppressor prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

[0033] This configuration allows the claims of the present invention to be made 9 The signal generator, in its filter for extracting the IF signal, can pass a frequency band equivalent to the passband of a waveguide bandpass filter while extending the stopband to a high-frequency band of more than twice the cutoff frequency, thereby enabling the transmission of highly reliable test signals in the millimeter-wave band or higher, and improving the test quality of the DUT.

[0034] To solve the above problems, the present invention 10 The higher-order mode suppression control method relating to the claim 1A method for controlling higher-order mode suppression using the higher-order mode suppressor described above, comprising the steps of: connecting the first waveguide and the second waveguide to the opposite end faces of the first ridge-waveguide conversion section and the opposite end face of the second ridge-waveguide conversion section, respectively, which are arranged on both sides of the ridge waveguide section (S01); inputting a frequency band exceeding the fundamental frequency band from the input side (S02); and operating the ridge waveguide section so as not to allow higher-order modes to pass through the waveguide having a ridge structure with respect to the input frequency band (S03).

[0035] This configuration allows the claims of the present invention to be made 10 The higher-order mode suppression control method, with its simple structure and simplified processing steps, can prevent higher-order modes generated when a frequency band higher than the recommended frequency band (fundamental frequency band) of the first and second waveguides is input from passing through the narrow waveguide section of the ridge waveguide.

[0036] To solve the above problems, the present invention 11 The filter configuration method relating to the claim 6 A filter configuration method for the waveguide filter device (8) described above, characterized in that a first coaxial waveguide converter (85a) is connected to one end of the waveguide section, a second coaxial waveguide converter (85b) is connected to the other end of the waveguide section, and the waveguide section is arranged such that a first ridge-to-waveguide converter, a ridge waveguide section, and a second ridge-to-waveguide converter, which are elements of the higher-order mode suppressor, are arranged sequentially in the longitudinal direction between the side of the first coaxial waveguide converter and the side of the second coaxial waveguide converter, and a waveguide bandpass filter is arranged on the side of at least one of the first ridge-to-waveguide converter or the second ridge-to-waveguide converter that is opposite to the ridge waveguide section.

[0037] This configuration allows the claims of the present invention to be made 11The filter configuration method described herein allows for the easy realization of a waveguide filter device equipped with a coaxial waveguide converter with a higher-order mode suppression function, which is suitable as an IF filter or RF filter for equipment such as spectrum analyzers, signal analyzers, and signal generators. [Effects of the Invention]

[0038] The present invention provides a higher-order mode suppressor that can reliably prevent generated higher-order modes from passing through with a simple structure, and by applying this structure, can realize highly reliable spectrum measurement, signal analysis, and signal generation that are unaffected by higher-order modes. It also provides a waveguide filter device, spectrum analyzer, signal analyzer, signal generator, higher-order mode suppression control method, and filter configuration method using the same. [Brief explanation of the drawing]

[0039] [Figure 1] This is a perspective view showing the external structure of a higher-order mode suppressor according to one embodiment of the present invention. [Figure 2] This figure shows the cross-sectional structure of a higher-order mode suppressor according to one embodiment of the present invention, as shown by line AA in Figure 1. [Figure 3] This figure shows the cross-sectional structure of a higher-order mode suppressor according to one embodiment of the present invention, where (a) is a cross-sectional view along line BB in Figure 2, and (b) is a cross-sectional view along line CC in Figure 2. [Figure 4] Figure 2 is an exploded perspective view of the cross-sectional structure, where (a) shows the structure of the left portion including the ridge waveguide section in Figure 2, and (b) shows the structure of the right portion including the ridge waveguide section. [Figure 5] This graph shows the frequency characteristics of a higher-order mode suppressor according to one embodiment of the present invention. [Figure 6] This is a flowchart showing the operational operation of a higher-order mode suppressor according to one embodiment of the present invention. [Figure 7] This figure shows the external configuration of a waveguide filter device using a higher-order mode suppressor according to one embodiment of the present invention. [Figure 8]Figure 7 is a graph showing the frequency characteristics of a waveguide filter device according to one embodiment of the present invention. [Figure 9] This figure shows the configuration of a spectrum analyzer using a waveguide filter device according to one embodiment of the present invention as an IF filter. [Figure 10] This flowchart shows the spectral characteristic measurement operation in a spectrum analyzer that uses a waveguide filter device according to one embodiment of the present invention as an IF filter. [Figure 11] This figure shows the configuration of a signal analyzer that uses a waveguide filter device according to one embodiment of the present invention as an IF filter. [Figure 12] This figure shows the configuration of a signal generator that uses a waveguide filter device according to one embodiment of the present invention as an IF filter. [Figure 13] This flowchart shows the signal transmission control operation in a signal generator that uses a waveguide filter device according to one embodiment of the present invention as an IF filter. [Figure 14] This graph shows the frequency characteristics of a conventional waveguide filter used as an IF filter in a spectrum analyzer. [Modes for carrying out the invention]

[0040] Hereinafter, embodiments of the higher-order mode suppressor, waveguide filter apparatus using the same, spectrum analyzer, signal analyzer, signal generator, higher-order mode suppression control method, and filter configuration method according to the present invention will be described with reference to the drawings.

[0041] The higher-order mode suppressor according to the present invention is used to suppress higher-order modes that occur when a waveguide of a predetermined standard is operated at a frequency higher than the frequency band recommended for that waveguide.

[0042] The higher-order mode suppressor according to the present invention can exist as a standalone functional component for suppressing higher-order modes, or it can be used in combination with a waveguide filter to form a waveguide filter device with higher-order mode suppression capabilities. Furthermore, the waveguide filter device with higher-order mode suppression capabilities can be implemented, for example, as an IF filter or RF filter in equipment such as spectrum analyzers, signal analyzers, and signal generators.

[0043] In recent years, there has been a growing demand for devices such as spectrum analyzers, signal analyzers, and signal generators to handle frequencies ranging from the microwave band to the millimeter wave band or higher. Consequently, IF filters in the IF signal path and RF filters in the RF signal path are also expected to support millimeter wave frequencies or higher.

[0044] In response to the above requirements, it is conceivable to implement waveguide filter devices equipped with the aforementioned higher-order mode suppressors as IF filters and RF filters for spectrum analyzers, signal analyzers, and signal generators.

[0045] One example of a waveguide used to implement a waveguide filter in combination with a higher-order mode suppressor is the WR19 waveguide. The WR19 waveguide functions as a high-pass filter that restricts the passage of signals with frequency components below the cutoff frequency (e.g., 31.4 GHz), and is not intended for use in frequency bands of more than twice the cutoff frequency (e.g., 60-80 GHz). In this invention, however, considering future applications in the millimeter-wave band or higher, the invention assumes a scenario where such a WR19 waveguide is operated in a frequency band of more than twice the cutoff frequency (e.g., 60-80 GHz), and aims to establish a technology that can efficiently suppress higher-order modes even when operating in high-frequency bands.

[0046] Based on the points mentioned above, the following will sequentially describe one embodiment of the higher-order mode suppressor 5 according to the present invention (see Figures 1 to 6), an embodiment of a waveguide filter device 8 using the higher-order mode suppressor 5 (see Figures 7 and 8), an embodiment of a spectrum analyzer 1 using the waveguide filter device 8 (see Figures 9 and 10), an embodiment of a signal analyzer 2 using the waveguide filter device 8 (see Figure 11), and an embodiment of a signal generator 3 using the waveguide filter device 8 (see Figures 12 and 13).

[0047] (Higher-order mode suppressor) As shown in Figure 1, the higher-order mode suppressor 5 according to this embodiment comprises a ridge waveguide section 50 composed of a waveguide having a ridge structure, and ridge-waveguide conversion sections 60a and 60b connected to both sides of the ridge waveguide section 50 in the longitudinal direction (Z direction).

[0048] In the higher-order mode suppressor 5, the ridge waveguide section 50 has a waveguide 51 with a rectangular cross-section that penetrates the waveguide 51 longitudinally, as shown in Figures 2 and 3(a). Inside the waveguide 51, there are ridge sections 52a and 52b that protrude inward from mutually opposing positions on the upper surface 51a and the lower surface 51b, and extend continuously in the longitudinal direction. Thus, the ridge waveguide section 50 has a ridge structure. In this embodiment, an example is given in which the ridge waveguide section 50 has a double ridge structure in which the ridge sections 52a and 52b protrude inward from mutually opposing positions on the upper surface 51a and the lower surface 51b of the waveguide 51, but it is not limited to this and may also have a single ridge structure. The upper surface 51a and the lower surface 51b each constitute the inner surface of the present invention.

[0049] In the ridge waveguide section 50, the inner diameter of the waveguide 51 is narrower than the inner diameter of the waveguides 71a and 71b of the waveguides 70a and 70b connected via the ridge-waveguide conversion sections 60a and 60b. The inner diameter of the waveguide 51 of the ridge waveguide section 50 is predetermined in correspondence with waveguides 70a and 70b, and specifically, when waveguides 70a and 70b are operated at frequency bands exceeding the recommended frequency band (for example, frequencies more than twice the cutoff frequency), higher-order modes (TE) are produced. 20 The dimensions are designed to allow for the suppression of modes, etc.

[0050] In the higher-order mode suppressor 5, the waveguide 51 of the ridge waveguide section 50 and the waveguides 71a and 71b of the waveguides 70a and 70b, which are to be placed on either side of it, have significantly different aperture (inner diameter) sizes. To mitigate the change in aperture (inner diameter) between the waveguide 51 of the ridge waveguide section 50 and the waveguides 71a and 71b of the waveguides 70a and 70b, ridge-to-waveguide conversion sections 60a and 60b are provided between the ridge waveguide section 50 and waveguide 70a, and between the ridge waveguide section 50 and waveguide 70b, respectively.

[0051] As shown in Figures 2 and 4(a), the ridge-to-waveguide converter 60a is connected to one longitudinal end face 53a of the ridge waveguide section 50, and a ridge-to-waveguide converter waveguide 61a is formed between the end face 64a facing the one end face 53a and the opposite end face 63a, which acts as a bridge for radio wave propagation between the waveguide 51 of the ridge structure and the waveguide 71a of the waveguide 70a. The ridge-to-waveguide converter 60a constitutes the first ridge-to-waveguide converter of the present invention, and the waveguide 70a constitutes the first waveguide of the present invention.

[0052] As shown in Figures 2 and 4(b), the ridge-waveguide conversion section 60b is connected to the other longitudinal end face 53b of the ridge waveguide section 50, and a ridge-waveguide conversion waveguide 61b is formed between the end face 64b facing the other end face 53b and the opposite end face 63b, which acts as a bridge for radio wave propagation between the waveguide 51 of the ridge structure and the waveguide 71b of the waveguide 70b. The ridge-waveguide conversion section 60b constitutes the second ridge-waveguide conversion section of the present invention, and the waveguide 70b constitutes the second waveguide of the present invention.

[0053] More specifically, the ridge-waveguide conversion section 60a is configured such that, as shown in Figures 2, 3(b), and 4(a), the ridge-waveguide conversion waveguide 61a is a tapered waveguide in which the opening size continuously increases from one end face 64a corresponding to one end face 53a of the ridge-waveguide conversion section 60a to the opposite end face 63a. Inside the tapered waveguide of the ridge-waveguide conversion waveguide 61a, for example, on the upper surface 61a1 and the lower surface 61a2, tapered ridge sections 62a1 and 62a2 are further formed, with the height gradually decreasing from one end face 64a corresponding to one end face 53a of the ridge waveguide section 50 to the opposite end face 63a. Here, the ridge-waveguide conversion waveguide 61a does not necessarily have to be a tapered waveguide; it may be a waveguide with a uniform inner diameter having the ridge sections 62a1 and 62a2. Furthermore, the waveguide 61a for ridge-to-waveguide conversion is not limited to a double-ridge structure as in this example, but may also be a single-ridge structure.

[0054] Similarly, in the ridge-waveguide conversion section 60b, for example as shown in Figures 2 and 4(b), the ridge-waveguide conversion waveguide 61b is composed of a tapered waveguide in which the opening dimension is continuously increased from the end face 64b corresponding to the other end face 53b of the ridge waveguide section 50 to the opposite end face 63b. Inside the tapered waveguide of the ridge-waveguide conversion waveguide 61b, for example, on the upper surface 62b1 and the lower surface 62b2, tapered ridge sections 61b1 and 61b2 are further formed, in which the height gradually decreases from the end face 64b corresponding to the other end face 53b of the ridge waveguide section 50 to the opposite end face 63b. The ridge-waveguide conversion waveguide 61b does not necessarily have to be a tapered waveguide, but may also be a waveguide with a uniform inner diameter having ridge sections 62b1 and 62b2. Furthermore, the waveguide 61a for ridge-to-waveguide conversion is not necessarily a double-ridge structure, but may also be a single-ridge structure.

[0055] By connecting the ridge-waveguide conversion unit 60a, the ridge waveguide unit 50, and the ridge-waveguide conversion unit 60b, which have the above-described configuration, a series of waveguides 55 are formed in the higher-order mode suppressor 5, for example, as shown in Figure 2, by the tapered ridge-waveguide conversion waveguide 61a of the ridge-waveguide conversion unit 60a, the waveguide 51 of the ridge waveguide unit 50, and the tapered ridge-waveguide conversion waveguide 61b of the ridge-waveguide conversion unit 60b.

[0056] As a result, the higher-order mode suppressor 5 can be operated in a configuration in which, for example, a waveguide 70a is connected to the end face 63a of the ridge-waveguide converter 60a on the left side of Figure 2 by its end face 73a, and on the other hand, a waveguide 70b is connected to the end face 63b of the ridge-waveguide converter 60b on the right side of Figure 2 by its end face 73b.

[0057] In this operational configuration, for example, WR19 waveguides are used as waveguides 70a and 70b connected to the higher-order mode suppressor 5. Under this assumption, the higher-order mode suppressor 5 according to this embodiment is designed to allow waveguides 70a and 70b to be operated up to a frequency band of more than twice their cutoff frequency (for example, above 80 GHz), and moreover, to suppress the generation of higher-order modes even in that case.

[0058] In the rectangular waveguide standard, the inner diameter of a WR19 waveguide is specified as 4.775 × 2.388 (mm). Therefore, in the higher-order mode suppressor 5 according to this embodiment, the ridge waveguide section 50 has a waveguide 51 with an inner diameter narrower than the inner diameter of the WR19 waveguide (waveguides 70a, 70b), and the dimensions of the waveguide 51 are such that it suppresses unnecessary modes (higher-order modes: TE) even when operating in the required frequency band, for example, a frequency band exceeding 80 GHz. 20 The dimensions are designed so that modes (or similar features) cannot exist.

[0059] Here, the fact that no unwanted modes are generated in the required frequency band, i.e., the frequency band more than twice the cutoff frequency, means that in lower modes, the fundamental mode (for example, TE) is not generated. 10This also prevents the transmission of certain modes. For this reason, the ridge waveguide section 50 has a waveguide 51 with a ridge structure, and this ridge structure allows the fundamental frequency band of the waveguide to pass through.

[0060] Next, we will verify the higher-order mode suppression function of the higher-order mode suppressor 5 according to this embodiment. The inventors performed electromagnetic field simulations of the frequency characteristics of the higher-order mode suppressor 5 (see Figures 1 to 4) having the above-described configuration, assuming that waveguides 70a and 70b are, for example, WR19 waveguides.

[0061] The measurement results in that case are shown in Figure 5. The simulation results shown in Figure 5 indicate that there is no decrease in transmission characteristics S21 even when operating in the 60-80 GHz frequency band, which is above the 40-60 GHz operating frequency band of the WR19 waveguide.

[0062] Thus, according to the higher-order mode suppressor 5 of this embodiment, the narrow waveguide 51 of the ridge waveguide section 50 is formed with dimensions such that unwanted modes are not generated (higher-order modes are not allowed to pass) even when the waveguides 70a and 70b, which are to be connected via the ridge-waveguide conversion sections 60a and 60b, are operated at a frequency of, for example, twice or more the cutoff frequency (a frequency above 60 GHz). As a result, the higher-order mode suppressor 5 of this embodiment can reliably prevent the generated higher-order modes from passing through with an extremely simple structure. Furthermore, because the waveguide 51 of the ridge waveguide section 50 of the higher-order mode suppressor 5 of this embodiment has a ridge structure, it is possible to avoid a situation where the fundamental mode (fundamental frequency band) is not allowed to pass through at low frequencies.

[0063] (Higher-order mode suppression control method using higher-order mode suppressor 5) In this embodiment, the higher-order mode suppressor 5 can achieve the higher-order mode suppression function by operating it according to the following procedure. The operation will be explained with reference to the flowchart shown in Figure 6.

[0064] In the above operation, first, a higher-order mode suppressor 5 having the structure shown in Figure 1 is prepared, and as shown in Figure 4, waveguides 70a (first waveguide) and 70b (second waveguide) are connected to the end face 63a of the first ridge-waveguide conversion section 60a and the end face 63b of the second ridge-waveguide conversion section 60b, respectively, with the ridge waveguide section 50 in between (step S01).

[0065] Waveguides 70a and 70b are constructed using, for example, WR19 waveguides, and are designed to accept frequencies higher than the frequency band recommended for waveguides of that standard (e.g., frequencies more than twice the cutoff frequency).

[0066] As described above, with waveguides 70a and 70b connected (see step S01), a frequency band including the fundamental frequency band is input to the higher-order mode suppressor 5 (step S02). Specifically, a frequency band including the fundamental frequency band (including a frequency band of more than twice the cutoff frequency) is input from port P1 to waveguide 70a, propagated through waveguide 55 to waveguide 70b, and then output from waveguide 70b to port P2 (step S02).

[0067] Furthermore, during the radio wave propagation operation, the ridge waveguide section 50 is operated so as not to allow higher-order modes to pass through the waveguide 51 having a ridge structure (step S03).

[0068] As described above, according to the higher-order mode suppression control method using the higher-order mode suppressor 5 of this embodiment, the process includes the steps of: connecting the first waveguide 70a and the second waveguide 70b to the first ridge-waveguide conversion unit 60a and the second ridge-waveguide conversion unit 60b, respectively, which are arranged on both sides of the ridge waveguide section 50 (S01); inputting a frequency band including the fundamental frequency band (including a frequency band of twice or more the cutoff frequency) from the input side (S02); and operating the ridge waveguide section 50 so that higher-order modes do not pass through the waveguide 51 having a ridge structure with respect to the input frequency band (S03). As described above, even if a frequency band higher than the recommended frequency band (fundamental frequency band) of waveguides 70a and 70b is input, the higher-order modes generated at that time can be prevented from passing through the narrow waveguide 51 of the ridge waveguide section 50.

[0069] As described above, the higher-order mode suppressor 5 according to this embodiment includes a ridge waveguide section 50 having a ridge structure with a waveguide 51 penetrating in the longitudinal direction and ridge sections 52a and 52b formed inside the waveguide 51; a first ridge-to-waveguide conversion section 60a connected to one end face 53a in the longitudinal direction of the ridge waveguide section 50, with a ridge-to-waveguide conversion waveguide 61a formed between the end face 64a facing the one end face 53a and the opposite end face 63a, which acts as a bridge for radio wave propagation between the waveguide 51 of the ridge structure and the waveguide 71a of the first waveguide 70a; and a first ridge-to-waveguide conversion section 60a connected to the other end face 53b in the longitudinal direction of the ridge waveguide section 50, with a ridge-to-waveguide conversion waveguide 61a formed between the end face 64b corresponding to the other end face 53b and the opposite end face 63b, which acts as a bridge for radio wave propagation between the waveguide 51 of the ridge structure and the waveguide 71b of the second waveguide 70b. The ridge waveguide section 50 has a second ridge-waveguide conversion section 60b in which a ridge-waveguide conversion waveguide 61b is formed to act as a relay for radio wave propagation. The inner diameter of the waveguide 51 of the ridge waveguide section 50 is narrower than that of the waveguides 71a and 71b of the first waveguide 70a and the second waveguide 70b. The first waveguide 70a and the second waveguide 70b are connected to the opposite end face of the first ridge-waveguide conversion section 60a and the opposite end face of the second ridge-waveguide conversion section 60b, respectively. One of the first waveguide 70a or the second waveguide 70b is the input side and the other is the output side. The dimensions are such that when a frequency band exceeding the fundamental frequency band is input from the input side, higher-order modes generated on the input side are not allowed to pass through for frequency bands of twice or more the cutoff frequency.

[0070] With this configuration, the higher-order mode suppressor 5 according to this embodiment can reliably prevent higher-order modes generated on the input side from passing through due to inputs in a frequency band of twice or more the cutoff frequency, using an extremely simple structure.

[0071] Furthermore, the higher-order mode suppressor 5 according to this embodiment may connect waveguides conforming to a desired waveguide standard (e.g., WR19) as the first waveguide 70a and the second waveguide 70b, and the ridge waveguide section 50 may be configured such that the inner diameter of the waveguide 51 is such that TE20 modes up to a desired frequency (e.g., 80 GHz) cannot pass through.

[0072] With this configuration, the higher-order mode suppressor 5 according to this embodiment prevents higher-order modes from passing through waveguides 70a and 70b conforming to standards such as WR19, even when operated at frequencies higher than the fundamental frequency band, thereby ensuring good frequency characteristics.

[0073] Furthermore, in the higher-order mode suppressor 5 according to this embodiment, the ridge waveguide section 50 has a double ridge structure in which ridge sections 52a and 52b protrude from the mutually opposing upper surface 51a and lower surface 51b of the waveguide 51 toward the interior of the waveguide 51.

[0074] With this configuration, the higher-order mode suppressor 5 according to this embodiment can ensure coupling between the fundamental frequency band and the ridge structure, and avoid situations where the fundamental frequency band does not pass through.

[0075] Furthermore, in the higher-order mode suppressor 5 according to this embodiment, the first ridge-waveguide conversion section 60a and the second ridge-waveguide conversion section 60b each have tapered ridge sections (62a1, 62a2, 62b1, 62b2) formed inside the respective ridge-waveguide conversion waveguides 61a, 61b, such that the height gradually decreases from the end face 64a corresponding to one end face 53a of the ridge waveguide section 50 to the opposite end face 63a, and from the end face 64b corresponding to the other end face 53b of the ridge waveguide section 50 to the opposite end face 63b.

[0076] With this configuration, the higher-order mode suppressor 5 according to this embodiment can smoothly facilitate the intermediate propagation of radio waves between the ridge-structured waveguide 51 and the waveguides (61a, 61b) of the first waveguide 70a and the second waveguide 70b, while preventing higher-order modes from passing through.

[0077] Furthermore, in the higher-order mode suppressor 5 according to this embodiment, the first ridge-waveguide conversion section 60a and the second ridge-waveguide conversion section 60b may be configured as tapered waveguides in which the ridge-waveguide conversion waveguides 61a and 61b, respectively, have an opening that continuously expands from one end face 64a corresponding to one end face 53a of the ridge waveguide section 50 to the opposite end face 63a, and from the other end face 64b corresponding to the other end face 53b of the ridge waveguide section 50 to the opposite end face 63b.

[0078] With this configuration, the higher-order mode suppressor 5 according to the present invention can further facilitate the transition of radio wave propagation between the ridge-structured waveguide 51 and the waveguides (71a, 71b) of the first waveguide 70a and the second waveguide 70b, while preventing higher-order modes from passing through.

[0079] (Waveguide filter device using higher-order mode suppressor 5) Figure 7 shows an example of the configuration of a waveguide filter device 8 according to one embodiment of the present invention using a higher-order mode suppressor 5.

[0080] As shown in Figure 7, the waveguide filter device 8 according to this embodiment is configured to include a waveguide section 80 and coaxial waveguide converters 85a and 85b connected perpendicularly to the waveguide section 80 at both ends in the longitudinal direction (Z direction) of the waveguide section 80. The coaxial waveguide converters 85a and 85b are connection circuit elements that convert coaxial lines and waveguides with different propagation modes to their respective appropriate propagation modes.

[0081] In the waveguide filter device 8 according to this embodiment, the waveguide section 80 is configured by connecting a waveguide 81a, a higher-order mode suppressor 81b, a waveguide 81c, a waveguide bandpass filter (hereinafter referred to as a bandpass filter) 81d, and a waveguide 81e in order along the length from the coaxial waveguide converter 85a side to the coaxial waveguide converter 85b side. The higher-order mode suppressor 5 described above (see Figures 1 to 4) can be used as the higher-order mode suppressor 81b. The waveguide section 80 has a waveguide 80a formed by connecting the waveguides of waveguide 81a, higher-order mode suppressor 81b, waveguide 81c, bandpass filter 81d, and waveguide 81e into a single waveguide.

[0082] On the other hand, the coaxial waveguide converters 85a and 85b house the coaxial cables 86a and 86b, respectively. At the ends of the coaxial cables 86a and 86b, the insulation of the core wire is removed to a predetermined length, and the core wire from which the insulation has been removed protrudes upward.

[0083] In the waveguide section 80, the core wires of coaxial cables 86a and 86b, which are housed in the coaxial waveguide converters 85a and 85b, respectively, with their insulation removed, are inserted as probes into the waveguides 80a of the waveguides 81a and 81e, which are provided in correspondence with the coaxial waveguide converters 85a and 85b.

[0084] The coaxial waveguide converters 85a and 85b house coaxial cables 86a and 86b, respectively, with the opposite ends of the core wires acting as probes connected to ports P1 and P2. In the configuration shown in Figure 7, the coaxial waveguide converters 85a and 85b constitute the first coaxial waveguide converter and the second coaxial waveguide converter of the present invention, respectively.

[0085] In the waveguide filter device 8 having the configuration described above, the coaxial mode is converted to waveguide mode between port P1 and port P2, and the signal is propagated through the waveguide 80a of the waveguide section 80 from the waveguide 81a side to the waveguide 81e side. Here, the coaxial waveguide converter 85b corresponding to waveguide 81e converts the radio waves from waveguide mode to coaxial mode and outputs them to port P2 via coaxial cable 86b.

[0086] As described above, in the waveguide filter device 8 that performs coaxial waveguide conversion processing between port P1 and port P2, a higher-order mode suppressor 81b and a bandpass filter 81d are employed as elements of the waveguide section 80 that constitute the waveguide 80a. As a result, even if the bandpass filter 81d is operated at a frequency of more than twice the cutoff frequency in the waveguide filter device 8, the higher-order mode suppression function of the higher-order mode suppressor 81b enables coaxial waveguide conversion processing in a state where higher-order modes are suppressed.

[0087] This section examines the higher-order mode suppression function in the waveguide filter device 8 according to this embodiment. In the waveguide filter device 8 according to this embodiment, the higher-order mode suppressor 81b constituting the waveguide 80a corresponds to, for example, a WR19 waveguide, and an example of the measurement results of the frequency characteristics when a WR19 waveguide is applied as the bandpass filter 81d is shown in Figure 8. Let's compare the frequency characteristics shown in Figure 8 with the frequency characteristics of a conventional waveguide filter of this type (see Figure 14).

[0088] According to the configuration of the waveguide filter device 8 in this embodiment (see Figure 7), higher-order modes are generated in the input-side coaxial waveguide converter 85a. Conventionally, since there was no higher-order mode suppression function (higher-order mode suppressor 81b), the higher-order modes entered the bandpass filter 81d directly. Here, since the bandpass filter 81d only functions normally in the fundamental mode, it cannot block the higher-order modes generated in the high-frequency range, and they are output as is. In Figure 14, it can be seen that an abnormal peak appears in the 60-80 GHz frequency band (a frequency band more than double the WR19 cutoff frequency of 31.4 GHz) due to the output of higher-order modes that cannot be blocked by the bandpass filter 81d.

[0089] On the other hand, in the waveguide filter device 8 according to this embodiment, a higher-order mode suppressor 81b is employed as a component of the waveguide section 80 along with the bandpass filter 81d. Therefore, in the waveguide filter device 8 according to this embodiment, higher-order modes generated in the input-side coaxial waveguide converter 85a are greatly attenuated before reaching the bandpass filter 81d by the higher-order mode suppression function of the narrow ridge waveguide section 50 of the higher-order mode suppressor 81b. This is why, in Figure 8, signals in the same frequency band (60-80 GHz) as those described in Figure 14 are greatly attenuated (due to the attenuation effect of the higher-order mode suppression function).

[0090] Furthermore, in Figures 8 and 14, the low attenuation in the 32-52 GHz frequency band is desirable. This is because the bandpass filter 81d is designed to pass through this frequency band and attenuate other frequencies. In short, by using the bandpass filter 81d in combination with the higher-order mode suppressor 81b, it becomes possible to pass through a preset passband (32-52 GHz) without problems (with little attenuation) while significantly attenuating unwanted signals in the frequency band above twice the cutoff frequency (63 GHz).

[0091] Thus, in the waveguide filter device 8 according to this embodiment, by incorporating a higher-order mode suppression function (using a combination of a bandpass filter 81d and a higher-order mode suppressor 81b), for example, when operating in a frequency range of 36 to over 80 GHz, even if a higher-order mode occurs in a frequency band twice the cutoff frequency (in the case of WR19, a frequency band of 31.4 × 2 ≈ 63 GHz or higher), the higher-order mode suppressor 81b can prevent that higher-order mode from passing through, thus avoiding a situation where the transmission characteristic S21 is not sufficiently attenuated due to the occurrence of higher-order modes.

[0092] In this embodiment, the waveguide filter device 8 is shown as an example in which a WR19 waveguide is used as the bandpass filter 81d of the waveguide section 80. However, the present invention is not limited to this, and it goes without saying that configurations using bandpass filters 81d of other standards (square wave waveguide standards) or high-pass filters can also be realized in the same way. Furthermore, the waveguide filter device 8 in this embodiment can be operated as a waveguide filter device with a higher-order mode suppression function even if the waveguide section 80 alone, which is equipped with a bandpass filter 81d and a higher-order mode suppressor 81b, is not limited to this.

[0093] Waveguide filter systems having a higher-order mode suppression function, such as the waveguide filter device 8 according to this embodiment, can be mounted on various devices, including spectrum analyzers, to prevent higher-order modes from passing through even if they occur in a frequency band of more than twice the cutoff frequency, thereby enabling operation in which the transmission characteristic S21 is sufficiently attenuated.

[0094] As described above, the waveguide filter device 8 according to this embodiment includes at least a higher-order mode suppressor 81b, which corresponds to the higher-order mode suppressor 5 (see Figure 1) mentioned in the above embodiment, and a waveguide bandpass filter 81d with a predetermined passband set as its components. The waveguide section 80 has a plurality of components connected continuously in the longitudinal direction to form a single waveguide 80a. One end of the waveguide section 80 is the input side and the other end is the output side. When filtering is performed by the waveguide section 80 for frequency bands exceeding the fundamental frequency band input from the input side, the higher-order mode suppressor 81b prevents higher-order modes generated on the input side for frequency bands of twice or more the cutoff frequency of the waveguide bandpass filter 81d from passing through, and the higher-order mode suppressor 81b attenuates them before they reach the waveguide bandpass filter 81d.

[0095] With this configuration, the waveguide filter device 8 according to this embodiment uses a combination of a bandpass filter 81d and a higher-order mode suppressor 81b (corresponding to the higher-order mode suppressor 5) in the waveguide section 80. This allows the higher-order mode suppressor 81b to prevent higher-order modes from passing through even if they occur in a frequency band twice the cutoff frequency, thus avoiding a situation where the transmission characteristic S21 is not sufficiently attenuated. As a result, the waveguide filter device 8 can perform reliable bandpass filtering in a frequency band exceeding the cutoff frequency and more than twice the cutoff frequency.

[0096] Furthermore, the waveguide filter device 8 according to this embodiment further comprises a first coaxial waveguide converter 85a connected perpendicularly to the waveguide section 80 at one end of the waveguide section 80, housing a coaxial cable 86a, and performing coaxial waveguide conversion with the waveguide 80a at one end of the waveguide section 80, and a second coaxial waveguide converter 85b connected perpendicularly to the waveguide section 80 at the other end of the waveguide section 80, housing a coaxial cable 86b, and performing coaxial waveguide conversion with the waveguide 80a at the other end of the waveguide section 80, and the waveguide section 80, the first coaxial waveguide converter 85a, and the second coaxial waveguide converter 85b constitute a coaxial waveguide converter device.

[0097] With this configuration, the waveguide filter device 8 according to this embodiment can be operated as a waveguide filter device equipped with a coaxial waveguide converter with a higher-order mode suppression function, and is suitable for applications such as IF filters or RF filters in equipment such as spectrum analyzers, signal analyzers, and signal generators.

[0098] As described above, a first coaxial waveguide converter 85a is connected to one end of the waveguide section 80, and a second coaxial waveguide converter 85b is connected to the other end of the waveguide section 80. The waveguide section 80 has a first ridge-to-waveguide converter 60a, a ridge waveguide section 50, and a second ridge-to-waveguide converter 60b, which are elements of the higher-order mode suppressor 5, arranged sequentially in the longitudinal direction between the side of the first coaxial waveguide converter 85a and the side of the second coaxial waveguide converter 85b. According to the filter configuration method of this embodiment, in which a waveguide bandpass filter 81d is placed at the end of at least one of the conversion unit 60a or the second ridge-waveguide conversion unit 60b (opposite the ridge waveguide unit 50), it becomes easy to create a waveguide filter device 8 equipped with a coaxial waveguide conversion device with a higher-order mode suppression function that is suitable as an IF filter or RF filter for equipment such as a spectrum analyzer 1, a signal analyzer 2, or a signal generator 3.

[0099] (Spectrum analyzer) A waveguide filter system such as the waveguide filter device 8 (see Figure 7) according to the above embodiment can be applied, for example, to a spectrum analyzer that performs spectrum measurements.

[0100] Figure 9 shows the configuration of a spectrum analyzer 1 according to one embodiment of the present invention. The spectrum analyzer 1 is assumed to have a signal analysis function in the millimeter wave band.

[0101] This spectrum analyzer 1 includes a frequency conversion unit 100, a detector 120, a control unit 150, an operation unit 160, and a display unit 161, and also has a filter bank circuit 10 in front of the frequency conversion unit 100.

[0102] The frequency conversion unit 100 comprises a mixer 111, a local signal generator 112, and a filter 113. The filter bank circuit 10, which is located before the mixer 111, together with the local oscillator signal source 9, the mixer 111, the local signal generator 112, and the filter 113, constitutes the front-end circuit 101.

[0103] In the front-end circuit 101, the filter bank circuit 10 has a plurality of filters and a changeover switch that selectively switches which filter allows a signal of a desired frequency band to pass through from among the plurality of filters, and the switching of the filter path by the changeover switch is controlled by the filter switching control unit 151.

[0104] In the frequency conversion unit 100, the mixer 111 is a functional unit that converts the signal under test from an RF frequency to an IF frequency signal (IF signal) by mixing the signals of each frequency component (RF frequency) with spurious waves suppressed, output from the filter bank circuit 10, with the local signal input from the local signal generator 112, and outputs it.

[0105] The local signal generator 112 generates a local signal for transmission to the mixer 111 based on the local signal (reference signal) input from the local oscillator signal source 9.

[0106] The filter 113 is a filtering unit that receives the IF signal frequency-converted by the mixer 111, passes only the frequency components of the input IF signal within a preset band, and inputs it to the detector 120. As the filter 113, a waveguide filter system with a higher-order mode suppression function, such as the waveguide filter device 8 (see Figure 7) described above, is employed.

[0107] The detector 120 is a processing circuit that detects the intensity of each input band signal (IF) that has passed through the filter 113.

[0108] In addition to a control function that comprehensively controls the entire spectrum analyzer 1, including the filter bank circuit 10, the control unit 150 also includes a filter switching control unit 151, a frequency sweep control unit 152, and a spectrum data acquisition unit 153.

[0109] The filter switching control unit 151 electronically controls the switching switch so that the filter path of the filter corresponding to the desired frequency is selected from among the multiple filters provided in the filter bank circuit 10.

[0110] The frequency sweep control unit 152 is a functional unit that performs frequency sweep control, which changes the frequency of the local signal output by the local signal generator 112 to the mixer 111 within a specified frequency range, based on the local signal (reference signal) input from the local oscillator signal source 9.

[0111] The spectrum data acquisition unit 153 acquires spectrum data including the intensity of signal components in a desired frequency band within the analysis target frequency range detected by the detector 120, and performs display control and other operations on the display unit 161.

[0112] The operation unit 160 has input means such as various keys, switches, and buttons, and is operated by the user when making various settings related to the measurement of the signal under test. The display unit 161 is a functional unit that is composed of, for example, a liquid crystal display and displays setting screens and measurement results related to the measurement of the signal under test.

[0113] In the spectrum analyzer 1 shown in Figure 9, the millimeter-wave signal to be measured (input signal) is supplied to the mixer 111 of the frequency conversion unit 100 via the filter bank circuit 10, and mixed with the local signal output from the local signal generator 112. From the mixed output, a signal in a predetermined IF frequency band is extracted by the filter 113. The frequency of the local signal is swept and varied by the frequency sweep control unit 152 of the control unit 150 to correspond to the desired analysis target frequency range. The signal components in that desired analysis target frequency range are extracted as signals in the IF frequency band over time, and their intensity is detected by the detector 120. For the sake of simplicity, this example shows the frequency conversion process (heterodyne conversion) of the frequency conversion unit 100 performed only once. However, when accurately analyzing high-frequency signals such as those in the millimeter-wave band, the frequency conversion process is performed multiple times to convert them into an IF frequency band that can be digitally processed.

[0114] In the control unit 150, the spectrum data acquisition unit 153 stores the signal intensity detected by the detector 120 for each analysis target frequency, according to the analysis target frequency set by the operation unit 160, as spectrum data, and displays this on the display unit 161.

[0115] At this time, the filter switching control unit 151 controls the switching switches in the filter bank circuit 10 according to the frequency to be analyzed, and performs switching control to switch to a filter that has a passband that includes the frequency to be analyzed.

[0116] Furthermore, the frequency sweep control unit 152 performs frequency sweep control corresponding to the passband of the filter selected according to the frequency to be analyzed at that time, in accordance with the switching control by the filter switching control unit 151.

[0117] In the configuration of the spectrum analyzer 1 shown in Figure 9, the signal to be measured (RF Input) as the input signal to the front-end circuit 101 is, for example, a signal in the frequency range of 110 to 170 GHz (f RF ) and the signal under test as the output signal (IF Output) is, for example, a signal in the 30-80 GHz band (f IF The spectrum analyzer 1 according to this embodiment can take in received signals received from, for example, mobile phones (5G, LTE, XG-PHS, W-CDMA, CDMA2000, GSM, etc.) and various wireless communications (WLAN, Bluetooth, GPS, ISDBT, etc.) as input signals (RF Input), suppress spurious waves with the filter bank circuit 10 in the front-end circuit 101, and measure the spectral characteristics of each desired frequency component.

[0118] In Figure 9, the control unit 150 may be the control unit of the spectrum analyzer 1 main unit, or it may be configured as a separate device such as a PC (personal computer).

[0119] Next, the signal measurement and control operation in the spectrum analyzer 1 according to this embodiment will be explained with reference to the flowchart shown in Figure 10.

[0120] In this example, the spectrum analyzer 1 receives, for example, a signal to be measured in the millimeter-wave band (110-170 GHz band), extracts signals in a predetermined desired frequency band from the signal to be measured using the corresponding filter from among multiple filters in the filter bank circuit 10, converts the extracted frequency components into IF frequencies, inputs them to the detector 120, measures the frequency spectrum, and performs a measurement operation to display the measurement result on the display unit 161.

[0121] To perform the measurement operation, the user, for example, sets the sweep frequency range (analysis target frequency range) of the spectrum analyzer 1 on the operation unit 160 (step S1). Examples of parameters set here include the center frequency and sweep frequency span, start frequency and stop frequency, and start frequency and sweep frequency span.

[0122] Next, the control unit 150 calculates the filter to be selected and the LO setting (local frequency setting condition) from the sweep frequency range set in step S1 (step S2).

[0123] Next, the control unit 150 sets the path of the changeover switch corresponding to the filter path to be selected as described above, and also sets the local frequency (LO frequency) (step S3).

[0124] Next, in the control unit 150, the filter switching control unit 151 performs switching control of the changeover switch based on the path setting in step S41, and in conjunction with this, the frequency sweep control unit 152 performs frequency sweep control for the local signal generator 112 based on the LO setting in step S41 (step S4).

[0125] In accordance with the sweep control described above, the control unit 150 filters the IF signal from the mixer 111 using the filter 113 and outputs it to the detector 120 (step S5).

[0126] The control unit 150 sends the detection result from the detector 120 to the spectrum data acquisition unit 153, where it performs measurement with the filter selected in step S3 (step S6).

[0127] During the series of measurement operations shown in Figure 10, in step S5, a filtering process is performed in which the generation of higher-order modes is suppressed by the filter 113 configured by the waveguide filter device 8 (see Figure 7).

[0128] Specifically, in this spectrum analyzer 1, for example, the signal with a frequency extracted by the filter bank circuit 10 from the input signal (signal under measurement) in the range of 110 to 170 GHz is mixed with the local signal from the local oscillator signal source 9 by the mixer 111 in the frequency conversion unit 110, converted to an IF frequency, and input to the filter 113.

[0129] Here, for example, the waveguide filter device 8 (see Figure 7) described above is used as the filter 113. In this case, the filter 113 allows, for example, IF signals in the 30-50 GHz frequency band to pass through and send them to the detector 120, while blocking the passage of other frequency bands (including 60-80 GHz) that occur during the mixing process. In short, in the filter 113 employing the waveguide filter device 8, the higher-order mode suppressor 5 used in combination with the bandpass filter 81d allows the passband of the bandpass filter 81d to remain unchanged from the conventional method, but the stopband can be extended to a high-frequency band of more than twice the cutoff frequency.

[0130] As a result, the spectrum analyzer 1 according to this embodiment, compared to conventional configurations that simply use a bandpass filter as the filter 113 without combining it with a higher-order mode suppression function, can extend the stopband to a high-frequency band of more than twice the cutoff frequency by allowing a preset passband to pass while preventing higher-order modes from passing. Therefore, the spectrum analyzer 1 according to this embodiment can suppress the passage of unwanted frequency signals caused by the generation of higher-order modes and expand the stopband, thereby enabling highly reliable measurement of spectral characteristics in the millimeter-wave band or higher.

[0131] As described above, the spectrum analyzer 1 according to this embodiment is equipped with a waveguide filter system (waveguide filter device 8 (see Figure 7)) which has a waveguide section 80 that includes a bandpass filter 81d (see Figure 7) with a predetermined passband and a higher-order mode suppressor 5 (see Figure 1), as a filter 113 that extracts a predetermined IF signal from the mixing output of the signal to be measured (RF signal exceeding 110 GHz) and the local signal. The waveguide section 80 receives the mixing output and allows the frequency band corresponding to the passband of the bandpass filter 81d to pass through, while the higher-order mode suppressor 5 prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

[0132] With this configuration, the spectrum analyzer 1 according to this embodiment can extend the stopband to a high-frequency band of more than twice the cutoff frequency while allowing the IF signal to pass through a frequency band corresponding to the passband of the bandpass filter 81d in the filter 113 that extracts the IF signal. This enables reliable measurement of spectral characteristics (without displaying unwanted components) targeting the millimeter wave band or higher in the future.

[0133] (Signal analyzer) The waveguide filter device 8 (see Figure 7) according to the above embodiment is applicable not only to the spectrum analyzer 1 shown in Figure 9, but also to signal analyzers that analyze signals in a predetermined frequency band.

[0134] Figure 11 shows the configuration of a signal analyzer 2 according to one embodiment of the present invention. This signal analyzer 2 has a frequency conversion unit 100A, an analog-to-digital converter (ADC) 125, a control unit 150A, an operation unit 160, and a display unit 161, and is equipped with a filter bank circuit 10 equivalent to that of a spectrum analyzer 1 in front of the frequency conversion unit 100A. The filter bank circuit 10, together with the local oscillator signal source 9 and the frequency conversion unit 100, constitutes a front-end circuit 101.

[0135] In the front-end circuit 101, the frequency conversion section 100A comprises a mixer 111A, a local signal generator 112A, and a filter 113A.

[0136] Mixer 111A converts the signal under measurement from an RF frequency to an IF frequency signal by mixing the signals of each frequency component (RF frequencies) with spurious waves suppressed, output from the filter bank circuit 10, with the local signal input from the local signal generator 112A, and outputs it.

[0137] The local signal generator 112A generates a local signal for transmission to the mixer 111A based on the local signal (reference signal) input from the local oscillator signal source 9.

[0138] Filter 113A is a filtering unit that receives the IF signal frequency-converted by mixer 111A, passes only the frequency components of a predetermined band of the input IF signal through, and inputs it to ADC 125. Here, an overlap band is set so that the frequency components of a predetermined band of the IF signal (the signal under test) are not lost in the filter bank circuit 10. In other words, the overlap band needs to pass through a band wider than this IF band signal.

[0139] The ADC125 converts the signal (the signal under measurement), which has passed through the filter bank circuit 10 and frequency-converted by the frequency conversion unit 100A, from an analog signal to a digital signal.

[0140] The control unit 150A includes a filter switching control unit 151A, a frequency control unit 152A, and a signal analysis unit 153A. The filter switching control unit 151A is equivalent to the one provided in the control unit 150 of the spectrum analyzer 1 (see Figure 8).

[0141] The frequency control unit 152A controls the setting of the local frequency so that it can receive signals within the specified analysis frequency range when the frequency conversion unit 100A converts the frequency of the signal under measurement. The local signal generator 112A, which is part of the frequency conversion unit 100A, has a configuration that allows the local frequency to be varied according to the received RF frequency. Therefore, the frequency control unit 152A may be configured to control the local signal generator 112A and sweep the local frequency.

[0142] The signal analysis unit 153A performs the process of analyzing the waveform of the signal (the signal under measurement) converted from a digital signal by the ADC 125. Specifically, it performs the process of analyzing the waveform analysis data and modulated signal for displaying the digital signal as a spectrum, and generates the modulation analysis results.

[0143] In the signal analyzer 2 having the above configuration, in order to perform signal analysis processing, for example, the frequency to be analyzed is set by a predetermined setting operation on the operation unit 160. This process corresponds to the process of step S1 (see Figure 10) in the spectrum analyzer 1.

[0144] Next, the control unit 150A performs a process to calculate the filter to be selected in the filter bank circuit 10 based on the set analysis frequency. This process corresponds to the process in step S2 (see Figure 10) in the spectrum analyzer 1.

[0145] Next, the control unit 150A sets the route of the changeover switch corresponding to the filter to be selected, which was calculated in the above calculation process, and then the filter switching control unit 151A controls the changeover switch to select the filter to be selected. This process corresponds to the process in step S3 and part of the process in step S4 (excluding sweep control) in the spectrum analyzer 1.

[0146] As a result, in the filter bank circuit 10, the input signal to be measured passes through the filter calculated by the calculation process, which is switched by the switching control, and the output is generated. The frequency components that have passed through the filter are then input to the frequency conversion unit 100A as the target for analysis.

[0147] In the frequency conversion unit 100A, the frequency components (signal under measurement) input from the filter bank circuit 10 and the local signal input from the local signal generator 112A are mixed in the mixer 111A to convert them into an IF frequency band. From the mixed output, a signal in a predetermined IF frequency band is extracted by the filter 113A and sent to the ADC 125. This process corresponds to the process in step S5 of the spectrum analyzer 1 (see Figure 10).

[0148] The ADC125 converts the frequency-converted signal from an analog signal to a digital signal and inputs it to the signal analysis unit 153A. The signal analysis unit 153A analyzes the digital signal input from the ADC125 to generate waveform analysis data for displaying waveforms such as a spectrum, and modulated signals, and performs processing to generate modulation analysis results. Furthermore, the control unit 150A performs control for signal analysis, such as displaying the waveform analysis data generated by the signal analysis unit 153A on the display unit 161.

[0149] As described above, the signal analyzer 2 according to this embodiment has a frequency conversion unit 100A that has a filter 113A that feeds the signal to be measured with predetermined frequency components to the mixer 111A together with the local signal output from the local signal generator 112A and extracts a signal in a predetermined IF frequency band from the mixing output, and a signal analysis unit 153A that converts the signal in the IF frequency band into a digital signal with the ADC 125 and then analyzes the waveform of the signal, and analyzes the waveform of the signal to be measured by changing the frequency of the local signal according to the frequency to be analyzed.

[0150] Here, as the filter 113A of the frequency conversion unit 100A, for example, the waveguide filter device 8 (see Figure 7) described above is used. In this case, the filter 113A allows, for example, IF signals in the 30-50 GHz frequency band to pass through and send to the ADC 125, while blocking the passage of other frequency bands (including 60-80 GHz) that occur during the mixing process. In short, in the filter 113A employing the waveguide filter device 8, the higher-order mode suppressor 5 used in combination with the bandpass filter 81d allows the passband of the bandpass filter 81d to remain unchanged from the conventional one, but the stopband can be extended to a high-frequency band of more than twice the cutoff frequency.

[0151] As a result, the signal analyzer 2 according to this embodiment, compared to conventional configurations that simply use a bandpass filter as filter 113A without combining it with a higher-order mode suppression function, can extend the stopband to a high-frequency band of more than twice the cutoff frequency by allowing a preset passband to pass while preventing higher-order modes from passing. Therefore, the signal analyzer 2 according to this embodiment can suppress the passage of unwanted frequency signals caused by the generation of higher-order modes and expand the stopband, thereby enabling highly reliable signal analysis in the millimeter-wave band or higher.

[0152] As described above, the signal analyzer 2 according to this embodiment uses a waveguide filter device 8 (see Figure 7) as a filter 113A that extracts a predetermined IF signal from the mixing output of the signal to be measured (RF signal exceeding 110 GHz) and the local signal. The waveguide device 80 has a configuration in which the waveguide section 80 includes a bandpass filter 81d (see Figure 7) with a predetermined passband set and a higher-order mode suppressor 5 (see Figure 1), and the waveguide section 80 receives the mixing output and passes the frequency band corresponding to the passband of the bandpass filter 81d, while the higher-order mode suppressor 5 prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

[0153] With this configuration, the signal analyzer 2 according to this embodiment can pass the IF signal through a frequency band corresponding to the passband of the bandpass filter 81d in the filter 113A, while extending the stopband to a high-frequency band of more than twice the cutoff frequency. This enables highly reliable signal analysis (without displaying unwanted components) targeting the millimeter wave band or higher.

[0154] (Signal generator) A waveguide filter system like the waveguide filter device 8 (see Figure 7) according to the above embodiment can be implemented not only in the spectrum analyzer 1 and signal analyzer 2, but also in a signal generator that generates test signals for the DUT.

[0155] Figure 12 shows the configuration of a signal generator 3 according to one embodiment of the present invention. The signal generator 3 is assumed to be a test signal generator that generates a test signal for performing a reception sensitivity test of millimeter-wave band signals to the DUT.

[0156] This signal generator 3 includes a frequency conversion unit 100B, a signal generation unit 130, a control unit 150B, an operation unit 160, a display unit 161, and a filter bank circuit 10B located downstream of the frequency conversion unit 100B. The filter bank circuit 10B, together with the local oscillator signal source 9 and the frequency conversion unit 100B, constitutes the front-end circuit 101.

[0157] In the front-end circuit 101, the frequency conversion unit 100B comprises a mixer 111B, a local signal generator 112B, and a filter 113B. The control unit 150B comprises a filter switching control unit 151B, a frequency control unit 152B, and a signal generation control unit 153B.

[0158] In the signal generator 3, the frequency conversion unit 100B receives a test signal in the IF frequency band output from the signal generator 130 under the control of the signal generation control unit 153B. The frequency conversion unit 100B filters the input test signal with filter 113B and then feeds it to the mixer 111B along with the local signal output from the local signal generator 112B to convert it into a millimeter-wave band signal. As the filter 113B, a waveguide filter system with a higher-order mode suppression function, such as the waveguide filter device 8 (see Figure 7) described above, is employed.

[0159] As described above, when the frequency conversion unit 100B converts the test signal filtered by the filter 113B into a millimeter-wave signal, it changes the frequency of the local signal using the frequency control unit 152B according to the test target frequency set by the operation unit 160, for example, in order to test the DUT, and sends the frequency-converted signal to the subsequent filter bank circuit 10B as the test signal for the DUT.

[0160] As the filter bank circuit 10B, a filter bank circuit equivalent to the filter bank circuit 10 implemented in the spectrum analyzer 1 and signal analyzer 2 according to the above embodiment can be used.

[0161] In testing the DUT using the signal generator 3, after setting the target frequency in the operation unit 160, the test signal generated from the signal generator 130 that satisfies the set conditions is frequency-converted into an RF signal by the frequency conversion unit 100B under the control of the signal generation control unit 153B, and then input to the input of the changeover switch in the filter bank circuit 10B.

[0162] In this process, the control unit 150B controls the filter switching control unit 151B to switch a selector switch to which the frequency-converted signal is input, according to the set test target frequency. This switching control selects the filter path corresponding to the test target frequency, and the frequency-converted signal passes through a filter having the corresponding passband and is extracted as a test signal. The extracted test signal is sent to the DUT from an RF transmission unit (not shown).

[0163] The signal transmission control operation of the signal generator 3 for the DUT test described above is performed according to the flowchart shown in Figure 13. In order to perform signal transmission control of the signal generator 3 for the DUT test, for example, the frequency, i.e., the test target frequency, is set by a predetermined setting operation on the operation unit 160 (step S11).

[0164] Next, the control unit 150B calculates the filter to be selected in the filter bank circuit 10B and the setting conditions for the local frequency (LO setting) based on the set test frequency (step S12).

[0165] Next, the control unit 150B sets the route of the changeover switch corresponding to the filter to be selected, which was calculated in step S12, and then the filter switching control unit 151B controls the changeover switch to select the filter to be selected (step S13).

[0166] As a result, in the filter bank circuit 10B, the test signal input to the changeover switch passes through the filter switched by the changeover control (calculated by the calculation process described above) and is output from the output section of the changeover switch. The control unit 150B controls the frequency component signal output from the output section of the changeover switch to be sent out as a test signal (step S14).

[0167] As described above, the signal generator 3 according to this embodiment has a frequency conversion unit 100B that filters the IF frequency band test signal output from the signal generator 130 with a filter 113B and then feeds it to the mixer 111B together with the local signal output from the local signal generator 112B to convert it into a millimeter-wave band signal. The frequency of the local signal is changed according to the test target frequency for testing the DUT, and the signal after frequency conversion by the frequency conversion unit 100B is sent out as the test signal for the DUT.

[0168] During the test signal transmission processing operation described above, the frequency conversion unit 100B performs filtering processing in which the generation of higher-order modes in the input signal (test signal) is suppressed by the filter 113B configured by the waveguide filter device 8 (see Figure 7) described above.

[0169] More specifically, in this signal generator 3, for example, an IF signal (IF Input) in the frequency band necessary to transmit a test signal in the 110-170 GHz range as an RF signal (RF Output) is input to the frequency converter 100B. In the frequency converter 100B, the filter 113B filters the input signal (IF signal), and the mixer 111B mixes the filtered signal with a local signal from the local signal generator 112B, converts it into an RF signal, and transmits it.

[0170] Here, for example, the waveguide filter device 8 (see Figure 7) described above is used as filter 113B. In this case, filter 113B allows IF signals in the frequency band of 30-50 GHz to pass through and send them to mixer 111B, while blocking the passage of other frequency bands (including 60-80 GHz). In short, in filter 113B employing the waveguide filter device 8, the higher-order mode suppressor 5 used in combination with the bandpass filter 81d allows the passband of the bandpass filter 81d to remain unchanged from the conventional one, but the stopband can be extended to a high-frequency band of more than twice the cutoff frequency.

[0171] As a result, the signal generator 3 according to this embodiment, compared to conventional configurations that simply use a bandpass filter as the filter 113B without combining it with a higher-order mode suppression function, can extend the stopband to a high-frequency band of more than twice the cutoff frequency by allowing a preset passband to pass through while preventing higher-order modes from passing through. Therefore, the signal generator 3 according to this embodiment can suppress the passage of unwanted frequency signals caused by the generation of higher-order modes and expand the stopband, thereby realizing a highly reliable test signal transmission function that can handle millimeter-wave bands or higher frequency bands.

[0172] As described above, the signal generator 3 according to this embodiment uses a waveguide filter device 8 (see Figure 7) as a filter 113B that extracts a signal in a predetermined IF frequency band from the test signal output from the signal generator 130. The waveguide device 80 has a waveguide section 80 that includes a bandpass filter 81d (see Figure 7) with a predetermined passband and a higher-order mode suppressor 5 (see Figure 1). The waveguide section 80 receives the output from the signal generator 130 and allows the signal to pass through the frequency band corresponding to the passband of the bandpass filter 81d, while the higher-order mode suppressor 5 prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

[0173] With this configuration, the signal generator 3 according to this embodiment can extend the stopband to a high-frequency band of more than twice the cutoff frequency while passing a frequency band corresponding to the passband of the bandpass filter 81d through the filter 113B that extracts the IF signal. This enables the output of highly reliable test signals (with unwanted components sufficiently attenuated) in the millimeter-wave band or higher, thereby improving the test quality of the DUT. [Industrial applicability]

[0174] As described above, the present invention has the effect of reliably preventing the generated higher-order modes from passing through with a simple structure, and by applying this structure, it is possible to realize highly reliable spectrum measurement, signal analysis, and signal generation that are unaffected by higher-order modes. It is useful for higher-order mode suppressors, waveguide filter devices using the same, spectrum analyzers, signal analyzers, signal generators, higher-order mode suppression control methods, and filter configuration methods in general. [Explanation of Symbols]

[0175] 1. Spectrum analyzer 2. Signal Analyzer 3. Signal Generator 5. Higher-order mode suppressor 8 Waveguide filter device 9. Local oscillator signal source 10, 10B filter bank circuit 50 Ridge waveguide section 51 Waveguides 51a Top surface (inner surface) 51b Bottom surface (inner surface) 52a, 52b, 62a1, 62a2, 62b1, 62b2 Ridge section 53a One end face 53b Other end surface 60a Ridge-Waveguide Conversion Section (First Ridge-Waveguide Conversion Section) 60b Ridge-Waveguide Conversion Section (Second Ridge-Waveguide Conversion Section) 61a, 61b Waveguides for ridge-to-waveguide conversion 61a1, 61b1 top surface 61a2, 61b2 bottom surface 63a, 63b, 64a, 64b end face 70a Waveguide (First Waveguide) 70b Waveguide (Second Waveguide) 71a, 71b waveguide 72a, 72b, 73a, 73b end face 80 Waveguide section 80a waveguide 81a, 81c, 81e waveguide 81b Higher-order mode suppressor 81d waveguide bandpass filter 85a Coaxial waveguide converter (First coaxial waveguide converter) 85b Coaxial waveguide converter (second coaxial waveguide converter) 86a, 86b coaxial cable 100, 100A, 100B frequency conversion section 101 Front-end circuit 111, 111A, 111B Mixer 112, 112A, 112B Local Signal Generators 113, 113A, 113B filters 120 Detector 125 ADC 130 Signal generation unit 150, 150A, 150B control unit 151, 151A, 151B Filter switching control unit 152 Frequency sweep control unit 152A, 152B Frequency Control Unit 153 Spectrum data acquisition unit 153A Signal analysis section 153B Signal Generation Control Unit 160 Operation section 161 Display section

Claims

1. A ridge waveguide section (50) is provided with a waveguide (51) that penetrates in the longitudinal direction, and a ridge structure is formed in which ridge sections (52a, 52b) are formed inside the waveguide, A first ridge-waveguide conversion section (60a) is connected to one longitudinal end face (53a) of the ridge waveguide section, and a ridge-waveguide conversion waveguide (61a) is formed between the end face (64a) facing the one end face and the end face (63a) opposite to it, which acts as a bridge for radio wave propagation between the waveguide of the ridge structure and the waveguide (71a) of the first waveguide (70a), The second ridge-waveguide conversion section (60b) is connected to the other longitudinal end face (53b) of the ridge waveguide section, and a ridge-waveguide conversion waveguide (61b) is formed between the end face (64b) corresponding to the other end face and the end face (63b) opposite to it, which acts as a bridge for radio wave propagation between the waveguide of the ridge structure and the waveguide (71b) of the second waveguide (70b), The ridge waveguide section has an inner diameter narrower than that of the waveguides of the first and second waveguides, and the first waveguide and the second waveguide are connected to the opposite end face of the first ridge-waveguide conversion section and the opposite end face of the second ridge-waveguide conversion section, respectively, with one of the first waveguide or the second waveguide being the input side and the other being the output side, and is configured with dimensions that prevent higher-order modes generated on the input side from passing through to frequencies exceeding the fundamental frequency band when input from the input side, for frequencies more than twice the cutoff frequency. Connect the first waveguide and the second waveguide, which are waveguides conforming to a predetermined waveguide standard. The ridge waveguide section is characterized in that the inner diameter of the waveguide is configured such that TE20 modes up to a desired frequency cannot pass through, thus providing a higher-order mode suppressor.

2. The higher-order mode suppressor according to claim 1, characterized in that the ridge waveguide portion has a double ridge structure in which the ridge portion protrudes toward the interior of the waveguide from the mutually opposing inner surfaces (51a, 51b) of the waveguide.

3. The higher-order mode suppressor according to claim 2, characterized in that the first ridge-waveguide conversion section and the second ridge-waveguide conversion section each have tapered ridge sections (62a1, 62a2, 62b1, 62b2) formed inside the respective ridge-waveguide conversion waveguides, such that the height gradually decreases from one end face corresponding to one end face of the ridge waveguide section to the opposite end face, and from the other end face corresponding to the other end face of the ridge waveguide section to the opposite end face.

4. The higher-order mode suppressor according to claim 3, characterized in that the first ridge-waveguide conversion unit and the second ridge-waveguide conversion unit are each composed of a tapered waveguide in which the diameter of the opening is continuously increased from the end face corresponding to one end face of the ridge waveguide to the opposite end face, and from the end face corresponding to the other end face of the ridge waveguide to the opposite end face.

5. The waveguide section (80) includes, as components, at least a higher-order mode suppressor (5, 81b) as described in claim 1 and a waveguide bandpass filter (81d) having a predetermined passband, wherein a plurality of the above components are continuously connected in the longitudinal direction to form a single waveguide (80a), A waveguide filter device characterized in that, one end of the waveguide section is the input side and the other end is the output side, and during filtering operation in the waveguide section that exceeds the fundamental frequency band input from the input side, higher-order modes generated on the input side for frequency bands of twice or more the cutoff frequency of the waveguide bandpass filter are prevented from passing through by the higher-order mode suppressor and are attenuated before reaching the waveguide bandpass filter.

6. A first coaxial waveguide converter (85a) is connected perpendicularly to the waveguide section at one end of the waveguide section, houses a coaxial cable (86a), and performs coaxial waveguide conversion between the waveguide at the one end of the waveguide section and the waveguide, A second coaxial waveguide converter (85b) is connected perpendicularly to the waveguide section at the other end of the waveguide section, houses a coaxial cable (86b), and performs coaxial waveguide conversion between the waveguide at the other end of the waveguide section and the waveguide, The waveguide filter device according to claim 5, further comprising the waveguide section, the first coaxial waveguide converter, and the second coaxial waveguide converter, wherein the waveguide section, the first coaxial waveguide converter, and the second coaxial waveguide converter constitute a coaxial waveguide converter.

7. A spectrum analyzer (1) has a frequency conversion unit (100) that provides a signal to be measured with predetermined frequency components together with a local signal output from a local signal generator (112) to a mixer (111), and a filter (113) that extracts a signal in a predetermined intermediate frequency band from the mixing output, and a detector (120) that detects the signal in the intermediate frequency band, and changes the frequency of the local signal according to the frequency to be analyzed to determine the spectral characteristics of the signal to be measured, The spectrum analyzer is characterized in that the filter is a waveguide filter device as described in claim 6, and the waveguide section of the waveguide filter device receives the mixing output and allows a frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while the higher-order mode suppressor prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

8. A signal analyzer (2) comprises a frequency conversion unit (100B) that provides a signal to be measured with predetermined frequency components together with a local signal output from a local signal generator (112B) to a mixer (111B), and a filter (113B) that extracts a signal in a predetermined intermediate frequency band from the mixing output; and a signal analysis unit (153B) that converts the signal in the intermediate frequency band into a digital signal using an ADC (125) and then analyzes the waveform of the signal, and analyzes the waveform of the signal to be measured by changing the frequency of the local signal according to the frequency to be analyzed, The signal analyzer is characterized in that the filter is a waveguide filter device as described in claim 6, and the waveguide section of the waveguide filter device receives the mixing output and allows a frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while the higher-order mode suppressor prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

9. The signal generator (3) has a frequency conversion unit (100B) that passes the intermediate frequency band test signal output from the signal generator (130) through a filter (113B) that extracts a signal in a predetermined intermediate frequency band, and then feeds it together with the local signal output from the local signal generator (112B) to a mixer (111B) to convert it into a millimeter-wave band signal, and changes the frequency of the local signal according to the test target frequency for testing the object under test (DUT), and sends out the signal after frequency conversion by the frequency conversion unit as the test signal for the object under test, The filter is a waveguide filter device as described in claim 6, and the waveguide section of the waveguide filter device receives the output from the signal generation unit and allows a frequency band corresponding to the passband of the waveguide bandpass filter to pass through, while the higher-order mode suppressor prevents higher-order modes that occur in a high-frequency band of more than twice the cutoff frequency from passing through.

10. A method for controlling higher-order mode suppression using the higher-order mode suppressor described in claim 1, Step (S01) involves connecting the first waveguide and the second waveguide to the opposite end faces of the first ridge-waveguide converter and the opposite end face of the second ridge-waveguide converter, respectively, which are arranged on both sides of the ridge waveguide section. The steps include: (S02) inputting a frequency band exceeding the fundamental frequency band from the input side, Step (S03) of operating the ridge waveguide section so as not to allow higher-order modes to pass through the waveguide having a ridge structure with respect to the input frequency band, A method for suppressing higher-order modes, characterized by including the following:

11. A method for configuring a filter in a waveguide filter device (8) according to claim 6, The first coaxial waveguide converter (85a) is connected to one end of the waveguide section. The second coaxial waveguide converter (85b) is connected to the other end of the waveguide section, The waveguide section is arranged such that the first ridge-to-waveguide converter, the ridge waveguide section, and the second ridge-to-waveguide converter, which are elements of the higher-order mode suppressor, are arranged sequentially in the longitudinal direction between the side of the first coaxial waveguide converter and the side of the second coaxial waveguide converter. A filter configuration method characterized in that the waveguide bandpass filter is arranged on the side of at least one of the first ridge-waveguide conversion unit or the second ridge-waveguide conversion unit that is opposite to the ridge waveguide unit.

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