High-order mode suppression device, waveguide filter device using them, spectrum analyzing device, signal analyzing device, signal generation device, high-order mode suppression control method, and filter construction 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 devices 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 with a frequency exceeding the upper limit frequency that can be measured by the device alone (for example, exceeding 60 GHz, such as exceeding 100 GHz), some use a downconverter as the front end and input the signal to be measured into this front end.

[0004] In the front stage of the front end that propagates electromagnetic waves in a frequency band exceeding 100 GHz, it is known to use a waveguide as the propagation path of the electromagnetic waves. In a spectrum analyzer with 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 waveguides connected in series are used as the propagation path of electromagnetic waves is made 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] JP 2020-137031 A Summary of the Invention [Problem to be solved by the invention]

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

[0008] When using a waveguide filter as an IF filter, it is common to operate it in the fundamental mode. However, today, there is an emerging demand for operation in a frequency band beyond the fundamental mode in response to the demand for higher analysis frequencies.

[0009] However, in conventional waveguide filters used as IF filters, when they are operated in a frequency band higher than the fundamental mode, higher-order modes (TE 20 There was a risk that a high reliability spectrum measurement could not be performed due to the occurrence of interference such as interference modes.

[0010] The frequency characteristics of this type of conventional waveguide filter are shown in Fig. 14. As shown in Fig. 14, when the conventional waveguide filter is operated in a frequency range that exceeds the fundamental mode frequency range of 34 to 52 GHz (for example, a frequency range of 66 to 80 GHz), the passage of unwanted frequency signals, which is a deterioration of the transmission characteristic S21 caused by the occurrence of higher-order modes, becomes noticeable.

[0011] In the case of a spectrum analyzer that employs a waveguide filter having the frequency characteristics as shown in FIG. 14 as an IF filter, for example, unnecessary frequency signals that pass through the IF filter in the frequency range of 66 to 80 GHz may result in the display of unnecessary components that are an obstacle to the measurement of spectrum characteristics, which may make it difficult to perform a highly reliable spectrum measurement.

[0012] As described above, there has been no conventional waveguide filter having an effective waveguide mode suppressor that suppresses higher-order modes when operating in a frequency range exceeding the fundamental mode. Further, in conventional devices such as a spectrum analyzer that employs a waveguide filter having no effective function for suppressing higher-order modes, it has been difficult to realize highly reliable measurements and the like due to the influence of higher-order modes.

[0013] The present invention has been made to solve such conventional problems, and it is possible to surely prevent the generated higher-order modes from passing through with a simple structure, and by applying the structure, highly reliable spectrum measurement, signal analysis, and signal generation that are not affected by higher-order modes can be realized. An object of the present invention is to provide a higher-order mode suppressor, 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.

Means for Solving the Problems

[0014] In order to solve the above problems, the higher-order mode suppressor according to claim 1 of the present invention is provided with a waveguide (51) penetrating in the longitudinal direction, and has a ridge waveguide section (50) having a ridge structure in which ridge portions (52a, 52b) are formed inside the waveguide, a first ridge-waveguide conversion section (60a) connected to one end face (53a) in the longitudinal direction of the ridge waveguide section, and having a ridge-waveguide conversion waveguide (61a) formed between the end face (63a) on the side opposite to the end face (64a) facing the one end face for relaying radio wave propagation between the waveguide of the ridge structure and the waveguide (71a) of the first waveguide (70a), a second ridge-waveguide conversion section (60b) connected to the other end face (53b) in the longitudinal direction of the ridge waveguide section, and having a ridge-waveguide conversion waveguide (61b) formed between the end face (63b) on the side opposite to the end face (64b) corresponding to the other end face for relaying radio wave propagation between the waveguide of the ridge structure and the waveguide (71b) of the second waveguide (70b). The ridge waveguide section is configured such that the inner diameter of the waveguide is narrower than the waveguides of the first waveguide and the second waveguide, and the first waveguide and the second waveguide are respectively connected to the end faces on the opposite sides of the first ridge-waveguide conversion section and the end faces on the opposite sides of the second ridge-waveguide conversion section. One of the first waveguide or the second waveguide is used as the input side and the other is used as the output side. When inputting a frequency band exceeding the fundamental frequency band from the input side, it is configured with dimensions such that the higher-order mode generated on the input side for a frequency band of twice or more the cut-off frequency is not allowed to pass.

[0015] With this configuration, the higher-order mode suppressor according to claim 1 of the present invention can surely prevent the higher-order mode generated on the input side by the input of a frequency band of twice or more the cut-off frequency from passing through with a very simple structure.

[0016] Further, the higher-order mode suppressor according to claim 2 of the present invention connects waveguides conforming to a predetermined waveguide standard as the first waveguide and the second waveguide, and the ridge waveguide section may be configured such that the inner diameter of the waveguide is a dimension through which the TE mode up to a desired frequency does not pass. 20 It may be configured.

[0017] With this configuration, the higher-order mode suppressor according to claim 2 of the present invention can prevent higher-order modes from passing through even when operating a waveguide with a predetermined waveguide standard in a frequency band higher than the fundamental frequency band, and can ensure good frequency characteristics.

[0018] In order to solve the above problems, in the higher-order mode suppressor according to claim 3 of the present invention, the ridge waveguide section may have a double-ridge structure in which the ridge section projects from the inner surfaces (51a, 51b) of the waveguide facing each other into the waveguide.

[0019] With this configuration, the higher-order mode suppressor according to claim 3 of the present invention can ensure the coupling between the fundamental frequency band and the ridge structure, and can avoid a situation where the fundamental frequency band does not pass through.

[0020] Further, in the higher-order mode suppressor according to claim 4 of the present invention, the first ridge-waveguide conversion section and the second ridge-waveguide conversion section are each provided inside the ridge-waveguide conversion waveguide, from the end face corresponding to one end face of the ridge waveguide section to the end face on the opposite side, and from the end face corresponding to the other end face of the ridge waveguide section to the end face on the opposite side, a tapered ridge section (62a1, 62a2, 62b1, 62b2) whose height gradually decreases may be further formed.

[0021] With this configuration, the higher-order mode suppressor according to claim 4 of the present invention can smoothly relay the radio wave propagation between the waveguide of the ridge structure and the waveguides of the first waveguide and the second waveguide while preventing higher-order modes from passing through.

[0022] Further, in the higher-order mode suppressor according to claim 5 of the present invention, the first ridge-waveguide conversion section and the second ridge-waveguide conversion section may each be configured by a tapered waveguide in which the dimensions of the openings continuously increase from the end face on the opposite side of the end face corresponding to one end face of the ridge waveguide section to the end face on the opposite side of the end face corresponding to the other end face of the ridge waveguide section.

[0023] With this configuration, the higher-order mode suppressor according to claim 5 of the present invention can more 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 passage of higher-order modes.

[0024] In order to solve the above problems, a waveguide filter device according to claim 6 of the present invention includes at least, as components, the higher-order mode suppressor (5, 81b) according to any one of claims 1 to 5 and a waveguide band-pass filter (81d) having a predetermined pass band, and has a waveguide section (80) in which a plurality of the components are continuously connected in the longitudinal direction to form one 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 frequencies exceeding the fundamental frequency band input from the input side, higher-order modes generated at the input side in a frequency band that is twice or more the cutoff frequency of the waveguide band-pass filter are prevented from passing through by the higher-order mode suppressor and are attenuated before reaching the waveguide band-pass filter.

[0025] With this configuration, the waveguide filter device according to claim 6 of the present invention can prevent higher-order modes from passing through by the higher-order mode suppressor even if higher-order modes occur in a frequency band that is twice the cutoff frequency by using a combination of the waveguide band-pass filter and the higher-order mode suppressor in the waveguide section, and can avoid a situation where unnecessary frequency components are not sufficiently attenuated. As a result, this waveguide filter device can perform a highly reliable band-pass filter operation in a wide frequency range from above the cutoff frequency to a frequency band that is twice or more the cutoff frequency.

[0026] Further, the waveguide filter device according to claim 7 of the present invention is connected perpendicularly to the one end of the waveguide section with respect to the waveguide section, houses a coaxial cable (86a), and performs a coaxial waveguide conversion between the waveguide path at the one end of the waveguide section. A first coaxial waveguide converter (85a), and is connected perpendicularly to the other end of the waveguide section with respect to the waveguide section, houses a coaxial cable (86b), and performs a coaxial waveguide conversion between the waveguide path at the other end of the waveguide section. A second coaxial waveguide converter (85b), and the waveguide section, the first coaxial waveguide converter, and the second coaxial waveguide converter may constitute a coaxial waveguide conversion device.

[0027] With this configuration, the waveguide filter device according to claim 7 of the present invention can be operated as a waveguide filter device provided with a coaxial waveguide conversion device having a high-order mode suppression function, and is suitable for uses such as an IF filter or an RF filter of devices such as a spectrum analyzer, a signal analyzer, and a signal generator.

[0028] In order to solve the above problems, the spectrum analyzer according to claim 8 of the present invention supplies a measurement signal of a predetermined frequency component to a mixer (111) together with a local signal output from a local signal generator (112), and from the mixing output. A frequency conversion unit (100) having a filter (113) for extracting a signal in a predetermined intermediate frequency band, and a detector (120) for detecting the signal in the intermediate frequency band, and changing the frequency of the local signal according to the analysis target frequency. A spectrum analyzer (1) for obtaining the spectrum characteristics of the measurement signal, wherein the filter uses the waveguide filter device according to claim 6 or 7, and the waveguide section of the waveguide filter device inputs the mixing output, and while passing a frequency band corresponding to the pass band of the waveguide bandpass filter, the high-order mode generated in a high-frequency band of twice or more the cutoff frequency is not passed by the high-order mode suppressor.

[0029] With this configuration, the spectrum analyzer according to claim 8 of the present invention can widen the stop band up to a high frequency band that is twice or more the cutoff frequency while passing a frequency band corresponding to the pass band of the waveguide bandpass filter in the filter for extracting the IF signal, and can perform highly reliable measurement of spectrum characteristics targeting the millimeter wave band or a higher frequency band.

[0030] In order to solve the above problems, the signal analyzer according to claim 9 of the present invention provides a signal to be measured of a predetermined frequency component to a mixer (111B) together with a local signal output from a local signal generator (112B), and has a frequency conversion unit (100B) having a filter (113B) that extracts a signal in a predetermined intermediate frequency band from the mixing output, and a signal analysis unit (153B) that analyzes the waveform of the signal after converting the signal in the intermediate frequency band into a digital signal by an ADC (125). The signal analyzer (2) changes the frequency of the local signal according to the frequency to be analyzed and analyzes the waveform of the signal to be measured. The filter uses the waveguide filter device according to claim 6 or 7, and the waveguide section of the waveguide filter device inputs the mixing output and, while passing a frequency band corresponding to the pass band of the waveguide bandpass filter, prevents the higher-order mode generated in the high frequency band that is twice or more the cutoff frequency from passing through by the higher-order mode suppressor.

[0031] With this configuration, the signal analyzer according to claim 9 of the present invention can widen the stop band up to a high frequency band that is twice or more the cutoff frequency while passing a frequency band corresponding to the pass band of the waveguide bandpass filter in the filter for extracting the IF signal, and can perform highly reliable signal analysis targeting the millimeter wave band or a higher frequency band.

[0032] In order to solve the above problems, the signal generator according to claim 10 of the present invention passes a test signal in an intermediate frequency band output from a signal generation unit (130) through a filter (113B) that extracts a signal in a predetermined intermediate frequency band, and then supplies it to a mixer (111B) together with a local signal output from a local signal generator (112B), and has a frequency conversion unit (100B) that converts it into a signal in a millimeter wave band. The frequency of the local signal is changed according to a test target frequency for testing a device under test (DUT), and the signal after frequency conversion by the frequency conversion unit is sent as a test signal for the device under test. The filter uses the waveguide filter device according to claim 6 or 7. The waveguide unit of the waveguide filter device inputs the output from the signal generation unit, and while passing a frequency band corresponding to the pass band of the waveguide bandpass filter, the higher-order mode suppressor prevents higher-order modes generated in a high-frequency band that is twice or more the cutoff frequency from passing through.

[0033] With this configuration, the signal generator according to claim 10 of the present invention can expand the stop band to a high-frequency band that is twice or more the cutoff frequency while passing a frequency band corresponding to the pass band of the waveguide bandpass filter in the filter that extracts the IF signal, can send a highly reliable test signal in a millimeter wave band or a higher frequency band, and can improve the test quality of the DUT.

[0034] In order to solve the above problems, the high-order mode suppression control method according to claim 11 of the present invention is a high-order mode suppression control method using the high-order mode suppressor according to any one of claims 1 to 5, comprising: a step (S01) of connecting the first waveguide and the second waveguide to the opposite end faces of the first ridge-waveguide conversion part arranged on both sides of the ridge waveguide part and the opposite end faces of the second ridge-waveguide conversion part, respectively; a step (S02) of inputting a frequency band exceeding the fundamental frequency band from the input side; and a step (S03) of operating the ridge waveguide part so as not to allow a high-order mode to pass through by the waveguide having a ridge structure with respect to the input frequency band.

[0035] With this configuration, the high-order mode suppression control method according to claim 11 of the present invention can prevent a high-order mode generated when a frequency band higher than the recommended frequency band (fundamental frequency band) of the first waveguide and the second waveguide is input from passing through the narrow waveguide of the ridge waveguide part by a simple structure and simple processing steps.

[0036] In order to solve the above problems, the filter configuration method according to claim 12 of the present invention is a filter configuration method in the waveguide filter device (8) according to claim 7, wherein the first coaxial waveguide converter (85a) is connected to one end of the waveguide part, the second coaxial waveguide converter (85b) is connected to the other end of the waveguide part, and the first ridge-waveguide conversion part, the ridge waveguide part, and the second ridge-waveguide conversion part, which are elements of the high-order mode suppressor, are arranged in this order in the longitudinal direction between the side of the first coaxial waveguide converter and the side of the second coaxial waveguide converter, and the waveguide band-pass filter is arranged on the side opposite to the ridge waveguide part of at least one of the first ridge-waveguide conversion part and the second ridge-waveguide conversion part.

[0037] With this configuration, the filter configuration method according to claim 12 of the present invention can easily realize a waveguide filter device equipped with a coaxial waveguide conversion device with a high-order mode suppression function suitable as an IF filter or an RF filter of devices such as a spectrum analyzer, a signal analyzer, and a signal generator.

Advantages of the Invention

[0038] The present invention can prevent the generated high-order modes from surely passing through with a simple structure, and by applying its structure, it is possible to realize a highly reliable spectrum measurement, signal analysis, and signal generation that are not affected by high-order modes, a high-order mode suppressor, a waveguide filter device using the same, a spectrum analyzer, a signal analyzer, a signal generator, a high-order mode suppression control method, and a filter configuration method.

Brief Description of the Drawings

[0039]

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Figure 8

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Figure 12

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Figure 14

Embodiments for Carrying Out the Invention

[0040] Hereinafter, embodiments of a higher-order mode suppressor according to the present invention, 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 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 generated when a waveguide of a predetermined standard is operated at a frequency higher than the frequency band recommended for the waveguide.

[0042] The high-order mode suppressor according to the present invention can exist as a single functional component for suppressing high-order modes, and can also be used as a waveguide filter device having a high-order mode suppression function in combination with a waveguide filter. Further, the waveguide filter device having a high-order mode suppression function can be mounted, for example, as an IF filter or an RF filter in devices such as a spectrum analyzer, a signal analyzer, and a signal generator.

[0043] In recent years, there has been an increasing demand for frequencies handled by devices such as spectrum analyzers, signal analyzers, and signal generators to shift from the microwave band to the millimeter wave band or higher frequency bands. There is also a desire for IF filters provided in the IF signal path and RF filters provided in the RF signal path to support the millimeter wave band or higher frequency bands.

[0044] In response to the above requirements, for spectrum analyzers, signal analyzers, and signal generators, it is conceivable to implement a waveguide filter device equipped with the above-described high-order mode suppressor as an IF filter or an RF filter.

[0045] As an example of a waveguide for realizing a waveguide filter device in combination with a high-order mode suppressor, for example, a WR19 waveguide can be mentioned. The WR19 waveguide functions as a high-pass filter that restricts the passage of signals with frequency components below the cut-off frequency (for example, 31.4 GHz), and its use in a frequency band that is twice or more the cut-off frequency (for example, the 60-80 GHz band) is not originally assumed. In the present invention, such a WR19 waveguide is assumed to be operated in a frequency band that is twice or more the cut-off frequency (for example, the 60-80 GHz band) in consideration of future compatibility with the millimeter wave band or higher frequency bands, and an attempt is made to establish a technology that can efficiently suppress high-order modes even when operating in a high-frequency band.

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

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

[0048] In the higher-order mode suppressor 5, for example, as shown in FIGS. 2 and 3(a), a waveguide 51 having a rectangular cross-section penetrating along the longitudinal direction is formed inside the ridge waveguide section 50. Inside the waveguide 51, for example, ridge portions 52a and 52b that rise (project) inward from the positions of the upper surface 51a and the lower surface 51b facing each other and continuously extend in the longitudinal direction are provided. In this way, the ridge waveguide section 50 has a ridge structure. In the present embodiment, an example of a double-ridge structure in which the ridge waveguide section 50 has ridge portions 52a and 52b protruding inward from the positions of the upper surface 51a and the lower surface 51b of the waveguide 51 facing each other is given, but it is not limited to this, and a single-ridge structure may also be used. The upper surface 51a and the lower surface 51b each constitute the inner surface of the present invention.

[0049] The ridge waveguide section 50 has an inner diameter of the waveguide 51 that is narrower than the inner diameters 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 corresponding to the waveguides 70a and 70b. Specifically, when operating in a frequency band exceeding the recommended frequency band of the waveguides 70a and 70b (for example, a frequency that is two times or more the cut-off frequency), it has dimensions that enable suppression of higher-order modes (TE 20 modes, etc.).

[0050] In the higher-order mode suppressor 5, there is a significant difference in the size of the opening (inner diameter) between the waveguide 51 of the ridge waveguide section 50 and the waveguides 71a and 71b of the waveguides 70a and 70b to be arranged on both sides thereof. In order to mitigate the change in the opening (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-waveguide conversion sections 60a and 60b are provided between the ridge waveguide section 50 and the waveguide 70a, and between the ridge waveguide section 50 and the waveguide 70b, respectively.

[0051] As shown in FIGS. 2 and 4(a), the ridge-waveguide conversion section 60a is connected to one end face 53a in the longitudinal direction of the ridge waveguide section 50, and a ridge-waveguide conversion waveguide 61a for relaying the propagation of radio waves between the ridge-structured waveguide 51 and the waveguide 71a of the waveguide 70a is formed between the end face 63a on the side opposite to the end face 64a facing the one end face 53a. The ridge-waveguide conversion section 60a constitutes the first ridge-waveguide conversion section of the present invention, and the waveguide 70a constitutes the first waveguide of the present invention.

[0052] As shown in FIGS. 2 and 4(b), the ridge-waveguide conversion section 60b is connected to the other end face 53b in the longitudinal direction of the ridge waveguide section 50, and a ridge-waveguide conversion waveguide 61b for relaying the propagation of radio waves between the ridge-structured waveguide 51 and the waveguide 71b of the waveguide 70b is formed between the end face 63b on the side opposite to the end face 64b facing the other end face 53b. 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, as shown in FIGS. 2, 3(b), and 4(a), for example, the ridge-waveguide conversion section 60a is composed of a tapered waveguide 61a for ridge-waveguide conversion, in which the opening dimension continuously expands from an 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 waveguide 61a for ridge-waveguide conversion, for example, on the upper surface 61a1 and the lower surface 61a2, tapered ridge portions 62a1 and 62a2 are further formed, the height of which changes gradually lower from the end face 64a corresponding to one end face 53a of the ridge waveguide section 50 to the opposite end face 63a. Here, the waveguide 61a for ridge-waveguide conversion does not necessarily have to be a tapered waveguide, and may be a waveguide with a uniform inner diameter having the ridge portions 62a1 and 62a2. Also, the waveguide 61a for ridge-waveguide conversion is not limited to the double-ridge structure as in this example, and may have a single-ridge structure.

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

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

[0056] Accordingly, as an operation mode of the higher - order mode suppressor 5, for example, a waveguide 70a is connected to the end face 63a of the ridge - waveguide converter 60a on the left side of FIG. 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 FIG. 2 by its end face 73b for operation.

[0057] In this operation mode, as the waveguides 70a and 70b connected to the higher - order mode suppressor 5, for example, a WR19 waveguide is adopted. Under this assumption, in the higher - order mode suppressor 5 according to the present embodiment, the waveguides 70a and 70b can be operated up to a frequency band that is twice or more the cut - off frequency (for example, exceeding 80 GHz), and moreover, the generation of higher - order modes is suppressed at that time.

[0058] In the rectangular waveguide standard, the WR19 waveguide is defined to have an inner diameter of 4.775×2.388 (mm). Therefore, in the higher - order mode suppressor 5 according to the present embodiment, the ridge waveguide section 50 has a waveguide 51 with an inner diameter smaller than that of the WR19 waveguide (waveguides 70a and 70b), and the dimensions of the waveguide 51 are formed such that unnecessary modes (higher - order modes: TE 20 modes, etc.) do not exist even when operating in a required frequency band, for example, a frequency band exceeding 80 GHz.

[0059] Here, the fact that unnecessary modes do not occur in the required frequency band, that is, a frequency band that is twice or more the cut - off frequency, means that in lower modes, the fundamental mode (for example, TE 10Neither the (mode) will pass through. Therefore, the ridge waveguide section 50 has a waveguide 51 with a ridge structure, and this ridge structure realizes a structure through which the fundamental frequency band of the waveguide can pass.

[0060] Next, the suppression function of the higher-order mode in the higher-order mode suppressor 5 according to the present embodiment will be verified. The inventor of the present case performed an electromagnetic field simulation of the frequency characteristics assuming a case where, for example, a WR19 waveguide is used as the waveguides 70a and 70b for the higher-order mode suppressor 5 (see FIGS. 1 to 4) having the above-described configuration.

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

[0062] As described above, according to the higher-order mode suppressor 5 according to the present embodiment, the narrow waveguide 51 of the ridge waveguide section 50 is, for example, a frequency of twice or more the cutoff frequency (frequency exceeding 60 GHz) of the waveguides 70a and 70b to be connected via the ridge-waveguide conversion sections 60a and 60b. It is formed in such dimensions that unnecessary modes do not occur (higher-order modes do not pass through) even when operating. Thereby, in the higher-order mode suppressor 5 according to the present embodiment, the generated higher-order mode can be surely prevented from passing through with an extremely simple structure. Further, in the higher-order mode suppressor 5 according to the present embodiment, since the waveguide 51 of the ridge waveguide section 50 has a ridge structure, it is possible to avoid a situation where the fundamental mode (fundamental frequency band) does not pass through at a low frequency.

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

[0064] In the above operation, first, a higher-order mode suppressor 5 having the structure shown in FIG. 1 is prepared. As shown in FIG. 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, sandwiching the ridge waveguide section 50 (step S01).

[0065] The waveguides 70a and 70b are composed of, for example, WR19 waveguides, and are capable of receiving a frequency higher than the frequency band (basic frequency band) recommended for waveguides of that standard (for example, a frequency of 2 times or more the cut-off frequency).

[0066] In the state where the waveguides 70a and 70b are connected as described above (see step S01), a frequency band including the basic frequency band is input to the higher-order mode suppressor 5 (step S02). Specifically, a frequency band including the basic frequency band (including a frequency band of 2 times or more the cut-off frequency) is input from port P1 to the waveguide 70a, propagated through the waveguide 55 to the waveguide 70b, and then output from the waveguide 70b to port P2 (step S02).

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

[0068] Thus, according to the high-order mode suppression control method using the high-order mode suppressor 5 according to this embodiment, in the first ridge-waveguide conversion unit 60a and the second ridge-waveguide conversion unit 60b arranged on both sides of the ridge waveguide unit 50, the step of connecting the first waveguide 70a and the second waveguide 70b respectively (S01); the step of inputting a frequency band including the fundamental frequency band from the input side (including a frequency band that is two times or more the cut-off frequency) (S02); and the step of operating the ridge waveguide unit 50 so as not to pass the high-order mode through the waveguide 51 having the ridge structure for the input frequency band (S03). By this process, even when a frequency band higher than the recommended frequency band (fundamental frequency band) of the waveguides 70a and 70b is input, the high-order mode generated at that time can be prevented from passing through the narrow waveguide 51 of the ridge waveguide unit 50.

[0069] As described above, the higher-order mode suppressor 5 according to the present embodiment is provided with a waveguide 51 penetrating in the longitudinal direction, and has a ridge waveguide section 50 having a ridge structure in which ridge portions 52a and 52b are formed inside the waveguide 51; a first ridge-waveguide conversion section 60a connected to one end face 53a in the longitudinal direction of the ridge waveguide section 50, and having a ridge-waveguide conversion waveguide 61a formed between the end face 63a on the side opposite to the end face 64a facing the one end face 53a for relaying the radio wave propagation between the waveguide 51 of the ridge structure and the waveguide 71a of the first waveguide 70a; a second ridge-waveguide conversion section 60b connected to the other end face 53b in the longitudinal direction of the ridge waveguide section 50, and having a ridge-waveguide conversion waveguide 61b formed between the end face 63b on the side opposite to the end face 64b corresponding to the other end face 53b for relaying the 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 an inner diameter of the waveguide 51 that is narrower than 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 respectively connected to the end face on the side opposite to the first ridge-waveguide conversion section 60a and the end face on the side opposite to the second ridge-waveguide conversion section 60b. One of the first waveguide 70a and the second waveguide 70b is used as the input side and the other as the output side. When inputting a frequency band exceeding the fundamental frequency band from the input side, it is configured with dimensions such that the higher-order mode generated on the input side with respect to the frequency band that is twice or more the cut-off frequency is not allowed to pass.

[0070] With this configuration, the higher-order mode suppressor 5 according to the present embodiment can surely prevent the higher-order mode generated on the input side by the input of the frequency band that is twice or more the cut-off frequency from passing through with a very simple structure.

[0071] Further, for the higher-order mode suppressor 5 according to the present embodiment, waveguides conforming to a desired waveguide standard (for example, WR19) may be connected as the first waveguide 70a and the second waveguide 70b, and the ridge waveguide section 50 may be configured with an inner diameter of the waveguide 51 such that the TE20 mode up to a desired frequency (for example, 80 GHz) does not pass through.

[0072] With this configuration, the higher-order mode suppressor 5 according to the present embodiment prevents higher-order modes from passing through even when the waveguides 70a and 70b of a standard such as WR19 are operated in a frequency band higher than the fundamental frequency band, and good frequency characteristics can be ensured.

[0073] Further, in the higher-order mode suppressor 5 according to the present embodiment, the ridge waveguide section 50 has a double-ridge structure in which ridge sections 52a and 52b project from the upper surface 51a and the lower surface 51b of the waveguide 51 facing each other into the waveguide 51.

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

[0075] Further, in the higher-order mode suppressor 5 according to the present embodiment, in the respective ridge-waveguide conversion waveguides 61a and 61b of the first ridge-waveguide conversion section 60a and the second ridge-waveguide conversion section 60b, 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, ridge sections (62a1, 62a2, 62b1, 62b2) having a tapered shape in which the height gradually decreases are further formed.

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

[0077] In addition, in the higher-order mode suppressor 5 according to the present embodiment, the first ridge-waveguide conversion unit 60a and the second ridge-waveguide conversion unit 60b may be configured by tapered waveguides in which the respective ridge-waveguide conversion waveguides 61a and 61b have continuously expanding opening dimensions 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.

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

[0079] (Waveguide filter device using the higher-order mode suppressor 5) A configuration example of a waveguide filter device 8 according to an embodiment of the present invention using the higher-order mode suppressor 5 is shown in FIG. 7.

[0080] As shown in FIG. 7, the waveguide filter device 8 according to the present embodiment includes a waveguide section 80 and coaxial waveguide converters 85a and 85b that are connected to both ends of the waveguide section 80 in the length direction (Z direction) at right angles to the waveguide section 80. The coaxial waveguide converters 85a and 85b are connection circuit elements that convert coaxial lines and waveguides having different propagation modes into appropriate propagation modes, respectively.

[0081] In the waveguide filter device 8 according to the present embodiment, the waveguide section 80 is configured by connecting, in order in the length direction from the coaxial waveguide converter 85a side to the coaxial waveguide converter 85b side, a waveguide 81a, a higher-order mode suppressor 81b, a waveguide 81c, a waveguide band-pass filter (hereinafter referred to as a band-pass filter) 81d, and a waveguide 81e. As the higher-order mode suppressor 81b, the above-described higher-order mode suppressor 5 (see FIGS. 1 to 4) can be used. In the waveguide section 80, a waveguide 80a is formed by connecting the waveguides of the waveguide 81a, the higher-order mode suppressor 81b, the waveguide 81c, the band-pass filter 81d, and the waveguide 81e in series.

[0082] On the other hand, the coaxial waveguide converters 85a and 85b each accommodate coaxial cables 86a and 86b. At the tip of the coaxial cables 86a and 86b, the covering of the core wire is removed by a predetermined length, and the core wire with the removed covering protrudes upward.

[0083] In the waveguide section 80, in the waveguide 80a of the waveguides 81a and 81e provided corresponding to the coaxial waveguide converters 85a and 85b, the core wires with the removed coverings of the coaxial cables 86a and 86b accommodated in the coaxial waveguide converters 85a and 85b are inserted as probes, respectively.

[0084] The coaxial waveguide converters 85a and 85b are connected to ports P1 and P2, respectively, at the ends of the accommodated coaxial cables 86a and 86b on the side opposite to the core wires as probes. In the configuration shown in FIG. 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 above-described configuration, between port P1 and port P2, conversion is performed from the coaxial mode to the waveguide mode, and propagation is performed from the waveguide 81a side to the waveguide 81e side in the waveguide 80a of the waveguide section 80. Here, in the coaxial waveguide converter 85b corresponding to the waveguide 81e, the radio wave is converted from the waveguide mode to the coaxial mode and output to port P2 via the coaxial cable 86b.

[0086] In the waveguide filter device 8 that performs the coaxial waveguide conversion processing operation between port P1 and port P2 as described above, as elements of the waveguide section 80 that constitutes the waveguide 80a, a higher-order mode suppressor 81b and a band-pass filter 81d are adopted. Thereby, in the waveguide filter device 8, even if the band-pass filter 81d is operated at a frequency twice or more the cutoff frequency, the coaxial waveguide conversion processing operation in a state where the higher-order mode is suppressed can be realized by the higher-order mode suppression function of the higher-order mode suppressor 81b.

[0087] Verify the high-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 high-order mode suppressor 81b constituting the waveguide 80a corresponds to, for example, a WR19 waveguide. As a band-pass filter 81d, FIG. 8 shows an example of the measurement result of the frequency characteristics when a WR19 waveguide is applied. Compare the frequency characteristics shown in FIG. 8 with the frequency characteristics of this type of conventional waveguide filter (see FIG. 14).

[0088] According to the configuration of the waveguide filter device 8 according to this embodiment (see FIG. 7), the high-order mode is generated in the coaxial waveguide converter 85a on the input side. Conventionally, since there was no high-order mode suppression function (high-order mode suppressor 81b), the high-order mode directly entered the band-pass filter 81d. Here, since the band-pass filter 81d normally operates only in the fundamental mode, it cannot block the high-order mode generated in the high-frequency band and will be output as it is. In FIG. 14, it can be seen that an abnormal bulge appears in the frequency band of 60 to 80 GHz (a frequency band more than twice the cut-off frequency of 31.4 GHz of WR19) due to the output of the high-order mode that cannot be blocked by the band-pass filter 81d.

[0089] On the other hand, in the waveguide filter device 8 according to this embodiment, as a component of the waveguide section 80, a high-order mode suppressor 81b is adopted together with the band-pass filter 81d. Therefore, in the waveguide filter device 8 according to this embodiment, the high-order mode generated in the coaxial waveguide converter 85a on the input side is greatly attenuated by the high-order mode suppression function of the narrow ridge waveguide section 50 of the high-order mode suppressor 81b before reaching the band-pass filter 81d. In FIG. 8, the signal in the same frequency band (60 to 80 GHz) as that described for FIG. 14 is greatly attenuated for this reason (due to the attenuation effect of the high-order mode suppression function).

[0090] In FIGS. 8 and 14, it is a desirable operation that the attenuation is small in the frequency band of 32 to 52 GHz. 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 is possible to pass through the preset passband (32 to 52 GHz) without problems (with small attenuation), and significantly attenuate unnecessary signals in the frequency band of twice the cutoff frequency (63 GHz or higher).

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

[0092] In the waveguide filter device 8 according to the present embodiment, a configuration example is given in which a WR19 waveguide is applied 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 a configuration using a bandpass filter 81d of other standards (rectangular waveguide standards) other than WR19, or a high-pass filter or the like can be similarly realized. Also, the waveguide filter device 8 according to the present embodiment can be operated as a waveguide filter device having a higher-order mode suppression function even with the waveguide section 80 alone in which the bandpass filter 81d and the higher-order mode suppressor 81b are provided.

[0093] A waveguide filter system 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 a spectrum analyzer. Even if a higher-order mode occurs in a frequency band that is twice or more the cutoff frequency, the higher-order mode is not allowed to pass through, and an operation can be performed such that 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 corresponding to the higher-order mode suppressor 5 (see FIG. 1) described in the above embodiment and a waveguide bandpass filter 81d having a predetermined passband as 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. During the filtering operation in the waveguide section 80 for a frequency band exceeding the basic frequency band input from the input side, the higher-order mode generated on the input side for a frequency band that is twice or more the cutoff frequency of the waveguide bandpass filter 81d is prevented from passing through by the higher-order mode suppressor 81b and is attenuated before reaching the waveguide bandpass filter 81d.

[0095] With this configuration, the waveguide filter device 8 according to this embodiment can prevent the higher-order mode suppressor 81b from passing through the higher-order mode even if a higher-order mode occurs in the frequency band that is twice the cutoff frequency by using a combination of the bandpass filter 81d and the higher-order mode suppressor 81b (corresponding to the higher-order mode suppressor 5) in the waveguide section 80, and can avoid a situation where the transmission characteristic S21 is not sufficiently attenuated. As a result, the waveguide filter device 8 can perform a highly reliable bandpass filter operation in a frequency band exceeding the cutoff frequency and within a range that is twice or more the cutoff frequency.

[0096] In addition, the waveguide filter device 8 according to the present embodiment is connected perpendicularly to one end of the waveguide section 80, houses the coaxial cable 86a, and performs coaxial waveguide conversion with the waveguide 80a at one end of the waveguide section 80. A first coaxial waveguide converter 85a, and a second coaxial waveguide converter 85b that is connected perpendicularly to the other end of the waveguide section 80, houses the coaxial cable 86b, and performs coaxial waveguide conversion with the waveguide 80a at the other end of the waveguide section 80. Further provided, the waveguide section 80, the first coaxial waveguide converter 85a, and the second coaxial waveguide converter 85b constitute a coaxial waveguide conversion device.

[0097] With this configuration, the waveguide filter device 8 according to the present embodiment can be operated as a waveguide filter device provided with a coaxial waveguide conversion device having a higher-order mode suppression function, and is suitable for applications such as an IF filter or an RF filter of devices such as a spectrum analyzer, a signal analyzer, and a signal generator.

[0098] As described above, the first coaxial waveguide converter 85a is connected to one end of the waveguide section 80, the second coaxial waveguide converter 85b is connected to the other end of the waveguide section 80, and the waveguide section 80 is connected to the first coaxial waveguide converter 85a. A first ridge-waveguide conversion section 60a, a ridge waveguide section 50, and a second ridge-waveguide conversion section 60b, which are elements of the higher-order mode suppressor 5, are arranged in order in the longitudinal direction between the side of the second coaxial waveguide converter 85b, and a waveguide bandpass filter 81d is arranged at least at the tip (opposite side to the ridge waveguide section 50) of either the first ridge-waveguide conversion section 60a or the second ridge-waveguide conversion section 60b. According to the filter configuration method of the present embodiment, a waveguide filter device 8 provided with a coaxial waveguide conversion device having a higher-order mode suppression function suitable as an IF filter or an RF filter of devices such as a spectrum analyzer 1, a signal analyzer 2, and a signal generator 3 can be easily realized.

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

[0100] FIG. 9 is a diagram showing the configuration of a spectrum analyzer 1 according to an 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 is provided with a filter bank circuit 10 in front of the frequency conversion unit 100.

[0102] The frequency conversion unit 100 includes a mixer 111, a local signal generator 112, and a filter 113. The filter bank circuit 10 provided in front of the mixer 111 constitutes a front-end circuit 101 together with the local oscillation signal source 9, the mixer 111, the local signal generator 112, and the filter 113.

[0103] In the front-end circuit 101, the filter bank circuit 10 has a plurality of filters and a switching switch for selectively switching a filter that passes a signal in a desired frequency band from among the plurality of filters, and has a configuration in which the switching of the filter path by the switching switch can be controlled by a filter switching control unit 151.

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

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

[0106] Filter 113 inputs the IF signal frequency-converted by mixer 111, allows only the signal of the frequency components in a preset band of the input IF signal to pass through, and is a filter function unit that inputs it to detector 120. As filter 113, a waveguide filter system with a high-order mode suppression function such as the above-described waveguide filter device 8 (see FIG. 7) is adopted.

[0107] Detector 120 is a processing circuit that detects the intensity of the signals (IF) in each band that pass through filter 113 and are input.

[0108] In addition to the control function of overall controlling the entire spectrum analyzer 1 including filter bank circuit 10, control unit 150 has a filter switching control unit 151, a frequency sweep control unit 152, and a spectrum data acquisition unit 153.

[0109] Filter switching control unit 151 electronically switches and controls the changeover switch so that the filter path of the filter corresponding to the desired frequency among the plurality of filters provided in filter bank circuit 10 is selected.

[0110] Frequency sweep control unit 152 is a functional unit that executes frequency sweep control to change the frequency of the local signal output from local oscillator 112 to mixer 111 within a specified frequency range based on the local signal (reference signal) input from local oscillator signal source 9.

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

[0112] The operation unit 160 has input means such as various keys, switches, buttons, etc., and is operated by the user when performing various settings related to the measurement of the signal to be measured. The display unit 161 is a functional unit configured by, for example, a liquid crystal display, etc., and displays a setting screen related to the measurement of the signal to be measured, the measurement result, etc.

[0113] In the spectrum analyzer 1 shown in FIG. 9, a millimeter-wave band signal to be measured (input signal) is given to the mixer 111 of the frequency conversion unit 100 via the filter bank circuit 10, and is mixed with the local signal output from the local signal generator 112. A signal in a predetermined IF frequency band is extracted from the mixing output by the filter 113. The frequency of the local signal is sweep-variable corresponding to a desired analysis target frequency range by the frequency sweep control unit 152 of the control unit 150, and the signal components in the 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. Here, for the sake of easy explanation, an example in which the frequency conversion process (heterodyne conversion) of the frequency conversion unit 100 is performed only once is shown. However, when accurately analyzing a high-frequency signal such as in the millimeter-wave band, the frequency conversion process is performed multiple times to convert it into an IF frequency band in which digital processing is possible.

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

[0115] At this time, the filter switching control unit 151 performs switching control to switch the switching switch in the filter bank circuit 10 according to the analysis target frequency, and switches to a filter having a pass band including the analysis target frequency.

[0116] Further, the frequency sweep control unit 152 performs sweep control of the frequency corresponding to the pass band of the filter selected according to the analysis target frequency at that time in accordance with the above switching control by the filter switching control unit 151.

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

[0118] In FIG. 9, the control unit 150 may be the control unit of the spectrum analyzer 1 main body, or may be configured with a separately attached device such as a PC (personal computer).

[0119] Next, the signal measurement control operation in the spectrum analyzer 1 according to the present embodiment will be described with reference to the flowchart shown in FIG. 10.

[0120] In this example, the spectrum analyzer 1 inputs, for example, a signal to be measured in the millimeter wave band (110 to 170 GHz band), extracts a signal in a preset desired frequency band from the signal to be measured by a corresponding filter among a plurality of filters in the filter bank circuit 10, converts the extracted frequency component to an IF frequency, inputs it to the detector 120, measures the frequency spectrum, and performs a measurement operation of displaying the measurement result on the display unit 161.

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

[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] Subsequently, the control unit 150 sets the path of the switch corresponding to the path of the filter to be selected described above and 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 switch based on the path setting in step S41, and in accordance with this, the frequency sweep control unit 152 performs control of frequency sweep for the local signal generator 112 based on the LO setting in step S41 (step S4).

[0125] In accordance with the above sweep control, in the control unit 150, the IF signal from the mixer 111 is filtered by the filter 113 and output to the detector 120 (step S5).

[0126] The control unit 150 sends the detection result of the detector 120 to the spectrum data acquisition unit 153, and here, measurement is performed with the filter selected in step S3 (step S6).

[0127] During the series of measurement processing operations shown in FIG. 10, in step S5, filtering processing in which the generation of higher-order modes is suppressed by the filter 113 constituted by the waveguide filter device 8 (see FIG. 7) is executed.

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

[0129] Here, as the filter 113, for example, the waveguide filter device 8 (see FIG. 7) described above is adopted. In this case, in the filter 113, for example, an IF signal in the frequency band of 30 to 50 GHz is passed through and sent to the detector 120, while the passage of other frequency bands (including 60 to 80 GHz) generated in the mixing process is blocked. In short, in the filter 113 adopting the waveguide filter device 8, the passband of the bandpass filter 81d does not change compared with the conventional one, but the stopband can be expanded to a high-frequency band twice or more the cut-off frequency by the higher-order mode suppressor 5 used in combination with the bandpass filter 81d.

[0130] Thereby, the spectrum analyzer 1 according to the present embodiment, as the filter 113, without combining with a higher-order mode suppression function, can expand the stopband to a high-frequency band twice or more the cut-off frequency by preventing the passage of higher-order modes while passing a preset passband, compared with the conventional configuration that simply uses a bandpass filter. Therefore, in the spectrum analyzer 1 according to the present embodiment, by suppressing the passage of unnecessary frequency signals caused by the generation of higher-order modes and expanding the stopband, highly reliable measurement of spectral characteristics in the millimeter-wave band or higher frequency bands can be realized.

[0131] As described above, the spectrum analyzer 1 according to this embodiment includes a waveguide filter system (waveguide filter device 8 (see FIG. 7)) having a waveguide section 80 that includes a band-pass filter 81d (see FIG. 7) with a predetermined passband and a higher-order mode suppressor 5 (see FIG. 1) as a filter 113 that extracts a predetermined IF signal from the mixing output of the signal under measurement (RF signal exceeding 110 GHz) and the local signal. The waveguide section 80 inputs the mixing output, and has a configuration that allows a frequency band corresponding to the passband of the band-pass filter 81d to pass through, while preventing the higher-order mode generated in a high-frequency band that is twice or more the cut-off frequency from passing through by the higher-order mode suppressor 5.

[0132] With this configuration, the spectrum analyzer 1 according to this embodiment can widen the stop band up to a high-frequency band that is twice or more the cut-off frequency while allowing a frequency band corresponding to the passband of the band-pass filter 81d to pass through in the filter 113 that extracts the IF signal, enabling highly reliable (displaying no unwanted components) measurement of spectrum characteristics targeting millimeter-wave bands or higher frequency bands in the future.

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

[0134] FIG. 11 is a diagram showing the configuration of a signal analyzer 2 according to an embodiment of the present invention. This signal analyzer 2 includes 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 provided with a filter bank circuit 10 equivalent to the spectrum analyzer 1 in the preceding stage of the frequency conversion unit 100A. The filter bank circuit 10 constitutes a front-end circuit 101 together with a local oscillation signal source 9 and a frequency conversion unit 100.

[0135] In the front-end circuit 101, the frequency conversion unit 100A is configured to include a mixer 111A, a local signal generator 112A, and a filter 113A.

[0136] The mixer 111A mixes the signal of each frequency component (RF frequency) with suppressed spurious waves output from the filter bank circuit 10 and the local signal input from the local signal generator 112A, thereby converting the signal to be measured from the RF frequency to an IF frequency signal and outputting it.

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

[0138] The filter 113A is a filter function unit that inputs the IF signal frequency-converted by the mixer 111A, allows only the signal of the frequency components in a preset band of the input IF signal to pass through, and inputs it to the ADC 125. Here, an overlap band is set so that the signal of the frequency components in a preset band of the IF signal (the signal to be measured) is not lost in the filter bank circuit 10. That is, the overlap band needs to pass a band wider than this IF band signal.

[0139] The ADC 125 converts the signal (the signal to be measured) that has passed through the filter bank circuit 10 and has been frequency-converted by the frequency conversion unit 100A from an analog signal to a digital signal.

[0140] The control unit 150A has 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 that provided in the control unit 150 of the spectrum analyzer 1 (see FIG. 8).

[0141] The frequency control unit 152A performs control to set the local frequency so that it can receive signals within the analysis target frequency range specified during the frequency conversion of the signal to be measured in the frequency conversion unit 100A. The local signal generator 112A that constitutes the frequency conversion unit 100A has a configuration that can vary the local frequency according to the received RF frequency. Therefore, the frequency control unit 152A may be configured to control the local signal generator 112A and perform sweep control of the local frequency.

[0142] The signal analysis unit 153A performs processing to analyze the waveform of the signal (signal to be measured) converted into a digital signal by the ADC 125. Specifically, it performs waveform analysis data for performing waveform display such as a spectrum on the digital signal and analysis of the modulation signal, and executes processing to generate a modulation analysis result.

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

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

[0145] Subsequently, the control unit 150A sets the path of the switch corresponding to the filter to be selected calculated in the above calculation process, and then the filter switching control unit 151A performs switching control of the switch so as to select the filter to be selected. This processing corresponds to the processing in step S3 and a part of the processing in step S4 (excluding sweep control) in the spectrum analyzer 1.

[0146] As a result, in the filter bank circuit 10, the input measurement signal to be measured passes through the filter calculated by the above-described calculation process switched by the above switching control and is output, and the passed frequency components are input as analysis targets to the frequency conversion unit 100A.

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

[0148] The ADC 125 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 performs waveform analysis data for performing waveform display such as a spectrum and analysis of the modulation signal from the digital signal input from the ADC 125, and executes a process of generating a modulation analysis result. Further, 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] Thus, the signal analyzer 2 according to the present embodiment provides a measurement signal of a predetermined frequency component 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. It has a frequency conversion unit 100A having a filter 113A and a signal analysis unit 153A that analyzes the waveform of the signal after converting the signal in the IF frequency band into a digital signal by the ADC 125, and changes the frequency of the local signal according to the analysis target frequency, and analyzes the waveform of the measurement signal to be measured.

[0150] Here, as the filter 113A of the frequency conversion unit 100A, for example, the waveguide filter device 8 (see FIG. 7) described above is adopted. In this case, in the filter 113A, for example, an IF signal in the frequency band of 30 to 50 GHz is passed through and sent to the ADC 125, while the passage of other frequency bands (including 60 to 80 GHz) generated in the mixing process is blocked. In short, in the filter 113A that adopts the waveguide filter device 8, the passband of the band-pass filter 81d does not change compared with the conventional one, but the stopband can be expanded to a high-frequency band that is twice or more the cutoff frequency by the higher-order mode suppressor 5 used in combination with the band-pass filter 81d.

[0151] As a result, the signal analyzer 2 according to the present embodiment, as the filter 113A, can expand the stopband to a high-frequency band that is twice or more the cutoff frequency by preventing the passage of higher-order modes while passing a preset passband, compared with the conventional configuration that simply uses a band-pass filter without combining with a higher-order mode suppression function. Therefore, in the signal analyzer 2 according to the present embodiment, by suppressing the passage of unnecessary frequency signals caused by the generation of higher-order modes and expanding the stopband, reliable signal analysis in the millimeter-wave band or higher frequency bands can be realized.

[0152] As described above, the signal analyzer 2 according to the present embodiment uses the waveguide filter device 8 (see FIG. 7) having the waveguide section 80 including the band-pass filter 81d (see FIG. 7) with a predetermined passband and the higher-order mode suppressor 5 (see FIG. 1) as the filter 113A for extracting a predetermined IF signal from the mixing output of the signal under measurement (RF signal exceeding 110 GHz) and the local signal. The waveguide section 80 inputs the mixing output and has a configuration that allows the passage of a frequency band corresponding to the passband of the band-pass filter 81d while preventing the passage of higher-order modes generated in a high-frequency band that is twice or more the cutoff frequency by the higher-order mode suppressor 5.

[0153] With this configuration, the signal analyzer 2 according to the present embodiment can widen the stopband up to a high-frequency band that is twice or more the cut-off frequency while passing through the frequency band corresponding to the passband of the band-pass filter 81d in the filter 113A that extracts the IF signal, enabling reliable signal analysis (where no unwanted components are displayed) targeting the millimeter-wave band or a higher frequency band.

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

[0155] FIG. 12 is a diagram showing the configuration of a signal generator 3 according to an embodiment of the present invention. As the signal generator 3, a test signal generator that generates a test signal for performing a reception sensitivity test of a millimeter-wave band signal for the DUT is assumed.

[0156] This signal generator 3 includes, in addition to a frequency conversion unit 100B, a signal generation unit 130, a control unit 150B, an operation unit 160, and a display unit 161, a filter bank circuit 10B provided at the subsequent stage of the frequency conversion unit 100B. The filter bank circuit 10B constitutes a front-end circuit 101 together with the local oscillation signal source 9 and the frequency conversion unit 100B.

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

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

[0159] When the frequency conversion unit 100B converts the test signal filtered by the filter 113B as described above into a signal in the millimeter wave band, the frequency of the local signal is changed by the frequency control unit 152B according to the test target frequency set by, for example, the operation unit 160 in order to test the DUT, and the signal after frequency conversion is sent to the subsequent filter bank circuit 10B as a test signal for the DUT.

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

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

[0162] At this time, in the control unit 150B, the filter switching control unit 151B performs switching control on the switching switch to which the signal after frequency conversion is input according to the set test target frequency. By this switching control, the path of the filter corresponding to the test target frequency is selected, and the signal after frequency conversion passes through the filter having the corresponding passband and is extracted as a test signal. The extracted test signal is to be sent from an RF transmission unit (not shown) toward the DUT.

[0163] The signal transmission control operation in the signal generator 3 for the test of the DUT described above is performed according to the flowchart shown in FIG. 13. In order to perform the signal transmission control in the signal generator 3 for the test of the DUT, for example, the frequency, that is, 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 local frequency setting condition (LO setting) based on the set test target frequency (step S12).

[0165] Subsequently, the control unit 150B performs path setting of the switching switch corresponding to the filter to be selected calculated in step S12, and then the filter switching control unit 151B performs switching control on the switching switch so as 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 switching switch passes through the filter switched by the above switching control (calculated by the above calculating process) and is output from the output unit of the switching switch. The control unit 150B controls to send the signal of the frequency component output from the output unit of the switching switch as a test signal (step S14).

[0167] As described above, the signal generator 3 according to this embodiment filters the test signal in the IF frequency band output from the signal generation unit 130 with the filter 113B, and then supplies it to the mixer 111B together with the local signal output from the local signal generator 112B, and has a frequency conversion unit 100B that converts it into a signal in the millimeter wave band. 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 as a test signal for the DUT.

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

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

[0170] Here, as the filter 113B, for example, the waveguide filter device 8 (see FIG. 7) described above is adopted. In this case, in the filter 113B, for example, an IF signal in the frequency band of 30 to 50 GHz is passed through and sent to the mixer 111B, while the passage of other frequency bands (including 60 to 80 GHz) is blocked. In short, in the filter 113B that adopts the waveguide filter device 8, the passband of the bandpass filter 81d does not change from the conventional one, but the stopband can be expanded to a high-frequency band that is twice or more the cutoff frequency.

[0171] As a result, the signal generator 3 according to the present embodiment, as the filter 113B, can widen the stopband to a high-frequency band that is twice or more the cutoff frequency or higher without combining with the higher-order mode suppression function, compared to the conventional configuration that simply uses a bandpass filter. Therefore, in the signal generator 3 according to the present embodiment, by suppressing the passage of unnecessary frequency signals caused by the generation of higher-order modes and expanding the stopband, a reliable test signal transmission function capable of handling millimeter-wave bands or higher frequency bands can be realized.

[0172] In this way, the signal generator 3 according to the present embodiment uses a waveguide filter device 8 (see FIG. 7) having a waveguide section 80 that includes a bandpass filter 81d (see FIG. 7) with a predetermined passband and a higher-order mode suppressor 5 (see FIG. 1) as the filter 113B that extracts a signal in a predetermined IF frequency band from the test signal output from the signal generation section 130. The waveguide section 80 inputs the output from the signal generation section 130 and is configured to pass a frequency band corresponding to the passband of the bandpass filter 81d while preventing the higher-order modes generated in a high-frequency band that is twice or more the cutoff frequency from passing through by the higher-order mode suppressor 5.

[0173] With this configuration, the signal generator 3 according to the present embodiment can widen the stopband to a high-frequency band that is twice or more the cutoff frequency or higher while passing a frequency band corresponding to the passband of the bandpass filter 81d in the filter 113B that extracts the IF signal, and can transmit a reliable (with sufficient attenuation of unnecessary components) test signal in a millimeter-wave band or higher frequency band, thereby improving the test quality of the DUT.

Industrial Applicability

[0174] As described above, the present invention can surely prevent 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 not affected 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.

Description of Reference Numerals

[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 Waveguide 51a Upper Surface (Inner Surface) 51b Lower Surface (Inner Surface) 52a, 52b, 62a1, 62a2, 62b1, 62b2 Ridge Sections 53a One End Face 53b Other End Face 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-Waveguide Conversion 61a1, 61b1 Upper Surfaces 61a2, 61b2 Lower Surfaces 63a, 63b, 64a, 64b End Faces 70a Waveguide (First Waveguide) 70b Waveguide (Second Waveguide) 71a, 71b Waveguides 72a, 72b, 73a, 73b End Faces 80 Waveguide Section 80a Waveguide 81a, 81c, 81e Waveguides 81b High-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 generator 113, 113A, 113B Filter 120 Detector 125 ADC 130 Signal generation section 150, 150A, 150B Control section 151, 151A, 151B Filter switching control section 152 Frequency sweep control section 152A, 152B Frequency control section 153 Spectrum data acquisition section 153A Signal analysis section 153B Signal generation control section 160 Operation section 161 Display section

Claims

1. A ridge waveguide section (50) having a ridge structure in which a waveguide (51) penetrating in the longitudinal direction is provided and ridge portions (52a, 52b) are formed inside the waveguide, A first ridge-waveguide conversion section (60a) connected to one end face (53a) in the longitudinal direction of the ridge waveguide section, and a ridge-waveguide conversion waveguide (61a) for relaying radio wave propagation between the waveguide of the ridge structure and the waveguide (71a) of the first waveguide (70a) is formed between the end face (63a) on the side opposite to the end face (64a) facing the one end face, A second ridge-waveguide conversion section (60b) connected to the other end face (53b) in the longitudinal direction of the ridge waveguide section, and a ridge-waveguide conversion waveguide (61b) for relaying radio wave propagation between the waveguide of the ridge structure and the waveguide (71b) of the second waveguide (70b) is formed between the end face (63b) on the side opposite to the end face (64b) corresponding to the other end face, and has, The ridge waveguide section is configured such that the inner diameter of the waveguide is narrower than the waveguides of the first waveguide and the second waveguide, and the first waveguide and the second waveguide are respectively connected to the end faces on the opposite sides of the first ridge-waveguide conversion section and the second ridge-waveguide conversion section. When one of the first waveguide or the second waveguide is used as the input side and the other is used as the output side, and when inputting a frequency band exceeding the fundamental frequency band from the input side, it is configured with dimensions such that higher-order modes generated on the input side are not passed through for a frequency band that is twice or more the cutoff frequency. A higher-order mode suppressor characterized by this.

2. Connect waveguides conforming to a predetermined waveguide standard as the first waveguide and the second waveguide, The ridge waveguide section is configured such that the inner diameter of the waveguide has dimensions through which a TE ２０ mode does not pass up to a desired frequency. The high-order mode suppressor according to claim 1, characterized in that.

3. The ridge waveguide section according to claim 1, characterized in that it has a double-ridge structure in which the ridge portion projects from the inner surfaces (51a, 51b) of the waveguide facing each other into the waveguide.

4. The first ridge-waveguide conversion unit and the second ridge-waveguide conversion unit each have a tapered ridge portion (62a1, 62a2, 62b1, 62b2) formed inside the ridge-waveguide conversion waveguide, the height of which gradually decreases 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. The high-order mode suppressor according to claim 3, characterized in that it is formed.

5. The first ridge-waveguide conversion unit and the second ridge-waveguide conversion unit are each configured such that the ridge-waveguide conversion waveguide is a tapered waveguide in which the opening dimension continuously increases 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. The high-order mode suppressor according to claim 4, characterized in that it is formed.

6. A waveguide filter device comprising at least a high-order mode suppressor (5, 81b) according to any one of claims 1 to 5 and a waveguide bandpass filter (81d) having a predetermined passband as components, and a plurality of the components are continuously connected in the longitudinal direction to form a single waveguide (80a). having a waveguide section (80), With one end of the waveguide section as the input side and the other end as the output side, during the filtering operation in the waveguide section for frequencies exceeding the 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 cutoff frequency of the waveguide bandpass filter is passed by the high-order mode suppressor. A waveguide filter device characterized in that it is attenuated before reaching the waveguide bandpass filter.

7. A first coaxial waveguide converter (85a) connected perpendicularly to the waveguide section at the one end of the waveguide section, accommodating a coaxial cable (86a), and performing coaxial waveguide conversion between the waveguide section and the waveguide at the one end of the waveguide section; A second coaxial waveguide converter (85b) connected perpendicularly to the waveguide section at the other end of the waveguide section, accommodating a coaxial cable (86b), and performing coaxial waveguide conversion between the waveguide section and the waveguide at the other end of the waveguide section; Furthermore, the waveguide section, the first coaxial waveguide converter, and the second coaxial waveguide converter constitute a coaxial waveguide conversion device. The waveguide filter device according to claim 6, characterized in that it is formed.

8. A frequency conversion unit (100) that supplies a measurement signal of a predetermined frequency component to a mixer (111) together with a local signal output from a local signal generator (112), and has 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 a spectrum analyzer (1) that changes the frequency of the local signal according to the analysis target frequency to obtain the spectrum characteristics of the measurement signal, wherein the filter uses the waveguide filter device according to claim 6 or 7, and the waveguide section of the waveguide filter device inputs the mixing output and passes a frequency band corresponding to the pass band of the waveguide bandpass filter, while the high-order mode suppressor prevents high-order modes generated in a high-frequency band that is twice or more the cutoff frequency from passing through. The spectrum analyzer is characterized by this.

9. A frequency conversion unit (100B) that supplies a measurement signal of a predetermined frequency component to a mixer (111B) together with a local signal output from a local signal generator (112B), and has a filter (113B) that extracts a signal in a predetermined intermediate frequency band from the mixing output; and a signal analysis unit (153B) that analyzes the waveform of the signal after converting the signal in the intermediate frequency band into a digital signal by an ADC (125), and a signal analyzer (2) that changes the frequency of the local signal according to the analysis target frequency to analyze the waveform of the measurement signal, wherein the filter uses the waveguide filter device according to claim 6 or 7, and the waveguide section of the waveguide filter device inputs the mixing output and passes a frequency band corresponding to the pass band of the waveguide bandpass filter, while the high-order mode suppressor prevents high-order modes generated in a high-frequency band that is twice or more the cutoff frequency from passing through. The signal analyzer is characterized by this.

10. A signal generator (3) for testing a device under test (DUT), which passes a test signal in an intermediate frequency band output from a signal generation unit (130) through a filter (113B) that extracts a signal in a predetermined intermediate frequency band, and then supplies it to a mixer (111B) together with a local signal output from a local signal generator (112B) to convert it into a signal in a millimeter wave band. The frequency of the local signal is changed according to the test target frequency for the device under test, and the signal after frequency conversion by the frequency conversion unit is sent as a test signal for the device under test. The filter uses the waveguide filter device according to claim 6 or 7. The waveguide section of the waveguide filter device inputs the output from the signal generation unit, and while passing a frequency band corresponding to the pass band of the waveguide bandpass filter, the high-order mode suppressor prevents high-order modes generated in a high-frequency band that is twice or more the cutoff frequency from passing through. A signal generator characterized by this.

11. A high-order mode suppression control method using the high-order mode suppressor according to any one of claims 1 to 5, Connecting the first waveguide and the second waveguide to the opposite end faces of the first ridge-waveguide conversion section and the opposite end faces of the second ridge-waveguide conversion section arranged on both sides of the ridge waveguide section, respectively (step S01); Inputting a frequency band exceeding the basic frequency band from the input side (step S02); Operating the ridge waveguide section so as not to pass high-order modes through the waveguide having a ridge structure for the input frequency band (step S03); A high-order mode suppression control method characterized by including this.

12. A filter configuration method for the waveguide filter device (8) according to claim 7, 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, and The waveguide section has the first ridge-waveguide conversion section, the ridge waveguide section, and the second ridge-waveguide conversion section, which are elements of the high-order mode suppressor, arranged in order 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 opposite to at least one of the ridge waveguide portions of the first ridge-waveguide conversion portion or the second ridge-waveguide conversion portion.

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