RF detector and high frequency module including same

Abstract

This RF detector or high-frequency module comprising same is provided to have a structure which maintains excellent conversion characteristics even at a frequency in a quasi-millimeter band or higher and has sufficient mechanical characteristics. For example, an RF detector 1 is composed of: a detection element 20 which detects a signal strength of an RF signal; and a print substrate 10 which is composed of a first conductive pattern that is electrically conducted with an input terminal of the detection element 20 and a second conductive pattern that is electrically conducted with an output terminal of the detection element 20, wherein the first conductive pattern and the second conductive pattern face each other with the detection element 20 interposed therebetween, thereby including a part capacitively coupled between the conductive patterns.

Description

[Technical field]

[0001] The present invention relates to an RF detector and a high-frequency module including the same. [Background technology]

[0002] Fig. 12 shows a typical configuration example of a high-frequency module having an RF detector (Radio Frequency Detector). In the high-frequency module 100 of Fig. 12, an RF signal obtained by attenuating out-of-band components of a signal received by an antenna ANT using an RF filter 101 is input to an RF detector 102. The RF detector 102 converts the input RF signal into a DC voltage corresponding to the signal strength (power) of the signal. The converted RF signal (DC voltage) is amplified by an amplifier 103 and then analog-to-digital converted by an A / D converter 104. A DSP (Digital Signal Processor) 105 outputs the digitally converted RF signal to a downstream electronic circuit as digital data representing the signal strength.

[0003] The RF detector 102 is a high-frequency component that includes a detection element such as a rectifier diode as a main component, and the ones disclosed in Patent Documents 1 and 2, for example, are known in the past. The RF detector disclosed in Patent Document 1 is used in the microwave band, and eliminates the characteristic variation of the rectifier diode by adding an impedance adjustment element. Silicon Schottky barrier diodes are mainly used as the rectifier diode.

[0004] The RF detector disclosed in Patent Document 2 includes a rectifier circuit that rectifies a 24 GHz RF signal, making it possible to suppress degradation of conversion characteristics when a higher frequency band is used. This rectifier circuit has two rectifier diodes connected in parallel between the output section and the ground (ground surface). Furthermore, by providing the output section with multiple sector-shaped open stubs (resonators), highly efficient power conversion over a wide band is made possible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-86666 A [Patent Document 2] JP 2014-209816 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, 5G (fifth generation mobile communication system) has been proposed as one of the next-generation communication standards. 5G is scheduled to use devices and systems in the quasi-millimeter wave band of 26 GHz, 28 GHz, or higher. Therefore, RF detectors that enable use in high frequency bands of quasi-millimeter wave or higher will be indispensable in the future for investigating the radio wave environment for 5G, product inspection, and checking the operation of products and parts. The quasi-millimeter wave band used in 5G is 24.25 to 27.5 GHz in the 26 GHz band, and 26.5 to 29.5 GHz in the 28 GHz band.

[0007] Although Patent Documents 1 and 2 do not disclose the material of the printed circuit board on which the high-frequency components are mounted, inexpensive FR (Flame Retardant)-4 grade printed circuit boards ("FR-4 boards") based on glass fiber are generally used for high-frequency components up to 1 to 10 GHz. The lower the dielectric constant ε of a printed circuit board, the faster the signal transmission speed becomes, and the higher the frequency band used, the greater the transmission loss becomes. For this reason, conventionally, for printed circuit boards used in the quasi-millimeter wave band, high-frequency boards using, for example, low-loss fluororesin as an insulator have been used, rather than FR-4 boards based on glass fiber, which has high loss and a high dielectric constant ε.

[0008] However, high-frequency boards are not only far more expensive than FR-4 boards, but also inferior to FR-4 boards in terms of processing productivity. When considering mechanical properties (strength and durability), it is desirable for the board (printed circuit board) to be thicker, but as the board becomes thicker, the line width of the signal line that conducts with the downstream electronic circuit becomes wider. When the line width becomes wider, it becomes even more difficult to achieve matching, and good conversion characteristics cannot be obtained. If each board is made thinner using a multi-layer structure, loss can be reduced and the conversion characteristics can be improved, but a multi-layer structure increases manufacturing costs.

[0009] Furthermore, silicon Schottky barrier diodes, which have traditionally been used as rectifier diodes, have a low forward potential difference and therefore can achieve relatively high conversion characteristics up to the 10 GHz band, but the conversion characteristics drop sharply at higher frequency bands. If silicon Schottky barrier diodes are used to forcibly achieve wideband matching, the conversion characteristics will be sacrificed. Mass production is difficult when trying to individually improve the characteristic variations of rectifier diodes.

[0010] Also, for example, in a configuration in which rectifier diodes are connected in parallel, such as the RF detector disclosed in Patent Document 2, although sufficient current capacity can be ensured, matching is difficult due to the effect of the capacitance between the output section and ground, and in the case of mismatch, sufficient conversion characteristics cannot be obtained. Rectifier diodes used in the 24 GHz band are GaAs (gallium arsenide) diodes and planar-doped barrier diodes, which are several tens of times more expensive than silicon Schottky barrier diodes, have faster electron mobility, and can handle high frequencies.

[0011] For this reason, it has been difficult to reduce the cost and mass-produce RF detectors that can be used in the quasi-millimeter wave band or higher, or high-frequency modules that include such RF detectors.

[0012] One object of the present invention is to provide an RF detector or a high-frequency module having the same with a structure having sufficient mechanical properties while maintaining good conversion characteristics even at frequencies of the quasi-millimeter wave band or higher. Other objects of the present invention will become apparent from the description of this specification. [Means for solving the problem]

[0013] One aspect of the present invention is an RF detector having a detection element that detects the signal strength of an RF signal, and a printed circuit board on which a first conductive pattern that is conductive with an input terminal of the detection element and a second conductive pattern that is conductive with an output terminal of the detection element are formed, the first conductive pattern and the second conductive pattern facing each other across the detection element, and capacitive coupling is provided between the conductive patterns.

[0014] Another aspect of the present invention is a high-frequency module including an RF detector located on the surface of a printed circuit board whose back surface is a ground conductor and which detects the signal level of an input RF signal, the RF detector being the RF detector of the above-described aspect. Effect of the Invention

[0015] According to the above-mentioned aspects, it is possible to expand the usable frequency band without causing matching between the detection element and the first and second conductive patterns. Therefore, even when a detection element or a printed circuit board used in the microwave band is used in the quasi-millimeter wave band or higher, it is possible to maintain good conversion characteristics. This makes it possible to easily realize an RF detector and a high-frequency module that have sufficient mechanical characteristics and can also reduce costs. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a configuration diagram of an RF detector according to the first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram of dimensions and arrangement intervals of RF detectors according to the first embodiment. [Diagram 3] FIG. 4 is a conversion characteristic diagram of the RF detector according to the first embodiment. [Figure 4] FIG. 11 is a configuration diagram of an RF detector according to a second embodiment. [Diagram 5] FIG. 4 is a configuration diagram of an RF detector according to a comparative example. [Figure 6] FIG. 11 is a graph comparing output voltage (mV)-frequency (GHz) characteristics of the RF detector according to the second embodiment and an RF detector according to the comparative example. [Figure 7] FIG. 11 is a graph showing output voltage (mV)-frequency (GHz) characteristics of an RF detector according to a third embodiment. [Figure 8] FIG. 13 is a graph showing output voltage (mV)-frequency (GHz) characteristics of an RF detector according to the fourth embodiment. [Figure 9] FIG. 13 is a configuration diagram of an RF detector according to a fifth embodiment. [Figure 10] FIG. [Figure 11] FIG. 11 is an explanatory diagram of a second modified example. [Figure 12] FIG. 1 is a diagram showing an example of a general configuration of a high-frequency module. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] [First embodiment] Hereinafter, an embodiment in which the present invention is applied to an RF detector that detects the signal strength of an RF signal in the 28 GHz band (26.5 GHz to 29.5 GHz) will be described. Fig. 1 is a configuration diagram of an RF detector according to a first embodiment, and Fig. 2 is an explanatory diagram of its dimensions and arrangement intervals.

[0018] The RF detector 1 of the first embodiment has a printed circuit board 10 and a detection element 20 that detects an RF signal. The printed circuit board 10 is an FR-4 board (double-sided board) with a horizontal size W of 13 mm, a vertical size D of 8 mm, and a thickness T of 0.6 mm. On the surface of the printed circuit board 10, a plurality of conductive patterns are formed by patterning a conductor film with a thickness of about 18 μm. The conductor film is any one of copper foil, silver foil, and gold foil, and forms a microstrip line. The detection element 20 is a rectifier diode. In this embodiment, a silicon Schottky barrier diode is used as the detection element 20. As mentioned above, the FR-4 substrate with the thickness T and the silicon Schottky barrier diode are components that are not generally used at high frequencies above the quasi-millimeter wave band. However, in this embodiment, this is easily achieved by devising the shape and arrangement of the multiple conductive patterns. This will be explained below.

[0019] In this specification, for convenience of explanation, three orthogonal axes, the X-axis, the Y-axis, and the Z-axis, are defined in Figures 1 and 2. In these three orthogonal axes, the +Z direction may be referred to as the vertically upward direction of the printed circuit board 10, the -Z direction as the vertically downward direction of the printed circuit board 10, the +X direction as the direction in which the RF signal is input, the -X direction as the direction in which the RF signal is output, the +Y direction as the left direction as viewed from the +X direction, and the -Y direction as the right direction as viewed from the +X direction. In addition, the surface including the X-axis and the Y-axis may be referred to as the front surface, back surface, or horizontal surface of the printed circuit board 10.

[0020] An input terminal section to which the input end (e.g., anode) of the detection element 20 is connected, and an output terminal section to which the output end (e.g., cathode) of the detection element 20 is connected are formed approximately in the center of the surface of the printed circuit board 10. When the anode of the detection element 20 is connected to the input terminal section and the cathode of the detection element 20 is connected to the output terminal section, the conversion characteristic is a positive output. Conversely, when the cathode of the detection element 20 is connected to the input terminal section and the anode of the detection element 20 is connected to the output terminal section, the conversion characteristic is a negative output.

[0021] In this embodiment, in order to miniaturize and simplify the structure of the RF detector 1, direct conversion is made possible, which converts an RF signal directly into a voltage. In this embodiment, a matching function, a filter function, and a conversion characteristic adjustment function are realized by a plurality of conductive patterns. A portion of the plurality of conductive patterns that includes an input terminal portion is called a "first conductive pattern." Also, a portion of the plurality of conductive patterns that includes an output terminal portion is called a "second conductive pattern." The RF detector 1 of this embodiment also achieves the function of blocking a set frequency on the low frequency side by the first conductive pattern. Also, the second conductive pattern also achieves the function of blocking a set frequency on the high frequency side. These functions will be described in detail later.

[0022] The first conductive pattern includes an input signal line 30 to which an RF signal is input, a short stub 32 for grounding, and an open stub 34. The input signal line 30 is a strip line with a characteristic impedance set to 50Ω. The line width W1 of the strip line to which the RF signal is input is 1.1 mm. This line width W1 is seven times or more wider than the line width of other signal lines described later. Of this wide input signal line 30, the portion where the above-mentioned input terminal part is formed acts as a matching stub 31 whose line width further expands toward the input terminal part to become an expanded open end. The reflection of the input RF signal near the detection element 20 is suppressed by the matching action in cooperation with the expanded open end of the matching stub 31 and a matching stub 41 described later. As a result, an RF signal of the operating frequency as designed is input to the detection element 20.

[0023] The matching stub 31 has a symmetrical shape with respect to the line axis (the central axis perpendicular to the line width, the same below) of the input signal line 30 including the input terminal portion to which the input end of the detection element 20 is connected. The outer edge between the ends of the expanded open end is formed in a non-linear shape. In the example of Figs. 1 and 2, the outer edge between the ends of the expanded open end (the "coupling region") is formed unevenly and symmetrically with respect to the line axis of the input signal line 30. At least one of the protruding parts forms an acute angle. The acute angle is made to facilitate adjustment work for matching, and also to facilitate capacitive coupling with the matching stub 41 described later.

[0024] The short stub 32 is a conductive pattern with a width of 0.15 mm that attenuates the RF signal propagating through the input signal line 30 at a low-set frequency. The short stub 32 is arranged at a location where grounding does not affect the matching in the operating frequency band. In the figure, the ground terminal is shown in an annular shape at the tip of the short stub 32. The length L1 of the short stub 32 is set to 1.52 mm, which is 1 / 4 or approximately 1 / 4 of the wavelength of the center frequency of the operating frequency band in this example. The open stub 34 is a conductive pattern with a width of 0.15 mm that extends from near the center of the short stub 32 by a length L2 (1.49 mm). The open stub 34 is arranged to approach and run along the input signal line 30. Under the condition that (L1 / 2) < L2 is satisfied, the length of (L1 / 2) + L2 is 1 / 4 or approximately 1 / 4 of the wavelength of the cutoff frequency of 24.0 GHz. The open stub 34 configured in this way operates as a notch filter. Thereby, steep attenuation characteristics can be obtained on the low-frequency side of the 28 GHz band.

[0025] Providing an open stub type notch filter on the input signal line 30 is a frequently adopted configuration. However, when adjusting the shape and size of the input signal line 30, the position and size change due to restrictions on the arrangement location, or when there is an addition such as another stub in the vicinity, the matching is disturbed and losses occur, and large attenuation cannot be obtained. Considering this point, the short stub 32 is provided in this embodiment. By providing this short stub 32, the factors causing the above-mentioned disturbance of matching and losses are eliminated, large attenuation can be obtained, and the loss of the RF signal can be minimized.

[0026] The second conductive pattern includes a matching stub 41 that faces the matching stub 31 of the first conductive pattern across the detection element 20. The matching stub 41 is a conductive pattern with a short side of 0.65 mm and a long side of 1.8 mm. The matching stub 41 is provided to achieve wideband matching by capacitive reactance generated by tip coupling of the outer edge (the "coupling region") that faces the matching stub 31. The length of the long side of the matching stub 41 is ¼ or approximately ¼ of the set wavelength of the cutoff frequency on the high frequency side, and it also acts as a reflection stub at the cutoff frequency on the high frequency side.

[0027] The second conductive pattern also includes a first output signal line 40, a first reflection stub 42, a second output signal line 43, a second reflection stub 44, a third output signal line 45, and an open stub 46, which extend from the center of the outer edge (the "high impedance line region") of the matching stub 41 opposite the coupling region with the matching stub 31. The first and second output signal lines 40 and 43 are conductive patterns with a width W2 of 0.15 mm. These lines act as high impedance signal lines for the frequency band used. The first reflection stub 42 is a conductive pattern with a short side of 0.65 mm by a long side of 1.8 mm. The length of the long side of the first reflection stub 42 is ¼ or approximately ¼ of the set wavelength of the cutoff frequency on the high frequency side. The first reflection stub 42 does not have to have a shape as shown in the figure as long as it can reflect the high frequency cutoff frequency. The second reflection stub 44 is a triangular conductive pattern that is easier to mold and process than a fan-shaped one. The second reflection stub 44 has a minimum width of 0.15 mm and a maximum width not exceeding 1.8 mm.

[0028] From the base end (the part with the smallest width) of the second reflection stub 44, the third output signal line 45 extends, and further from it, the open stub 46, the capacitor component (C) 47 and the resistor component (R) 48, which serve as loads, and the fourth output signal line 49 extend. The third output signal line 45 and the fourth output signal line 49 act as high impedance signal lines for the frequency band used. The third output signal line 45 and the fourth output signal line 49 are conductive patterns with a width W3 of 0.15 mm. The load is a passive element for stabilizing the operation, and the resistor component (R) 48 and the capacitor component (C) are connected in parallel to the ground terminal shown in a circular ring shape. In this example, the resistor component (R) 48 is 510 kΩ, and the capacitor component (C) 47 is 100 pF. The open stub 46 is a conductive pattern for matching, but can be omitted.

[0029] The length L3 from the outer edge of the matching stub 41 opposite the coupling region to the base end (the part with the smallest width) of the second reflecting stub 44 is 3 / 4 or approximately 3 / 4 of the wavelength of the center frequency of 28 GHz. In this example, it is 4.3 mm. The length L4 from the outer edge of the matching stub 41 opposite the coupling region to the opposing outer edge of the first reflecting stub 42 is 2.5 mm in this example.

[0030] The RF signal that has passed through the matching stub 41 is reflected by the first output signal line 40 and the first reflection stub 42 at a set frequency on the high frequency side, and is further reflected by the second output signal line 43 and the second reflection stub 44 in the operating frequency band. Since the reflection point (the position where reflection occurs) is away from the output end of the detection element 20, phase adjustment is easy, and cancellation of the input signal at the input end of the detection element 20 and the reflected signal at the output end does not occur. Even if harmonic components that cause deterioration of the original conversion characteristics due to reconversion by the detection element 20 are generated, these harmonic components are largely attenuated by the input signal line width 30, which is wider than that of the conventional general one. Therefore, high conversion characteristics can be obtained.

[0031] 3 is a diagram showing the conversion characteristics of the RF detector 1 of the first embodiment. The horizontal axis represents the strength of the input RF signal (RF_Level: dBm), and the vertical axis represents the voltage output (mV). As shown in the diagram, the RF detector 1 of this embodiment provides sufficient conversion characteristics in the 28 GHz band, even when using a detection element 20 and a printed circuit board 10 that have conventionally only been used in the microwave band of around 1 to 10 GHz. The reason why sufficient conversion characteristics can be obtained even in the 28 GHz band is that matching is achieved in both the first conductive pattern at the input end of the detection element 20 and the second conductive pattern at the output end of the detection element 20. Therefore, it is no longer necessary to provide a separate matching stub on the input signal line 30 as in the conventional case, the conductive pattern is simplified, and costs are reduced and mass production is facilitated.

[0032] [Second embodiment] 4 is a configuration diagram of an RF detector 2 according to the second embodiment. The same components as those described in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. The RF detector 2 according to the second embodiment does not include the open stub 46 of the RF detector 1, and adds an open stub 36 having a length L5 (1.9 mm) of ¼ or approximately ¼ of the wavelength of the notch setting cutoff frequency to the input signal line 30 on the side opposite the short stub 32. The open stub 36 extends downward from the input signal line 30, then changes its angle and extends parallel to the input signal line 30. The open stub 36 configured in this way acts as a narrow-band notch filter, and can make the attenuation on the low-frequency side steeper than that of the RF detector 1 described in the first embodiment. Because of the narrow band, it is less susceptible to the effects of mismatching.

[0033] [Comparative Example] The present inventors have created an RF detector 5 as a comparative example of the RF detectors 1 and 2 of the first and second embodiments. This RF detector 5 is configured using high-frequency components and design techniques that are widely used in the quasi-millimeter wave band at the time of filing this application, and operates in the 28 GHz band. A configuration diagram of the RF detector 5 is shown in FIG. The RF detector 5 is similar to the RF detectors 1 and 5 in that it uses an FR-4 board as the printed circuit board 50 and that a plurality of conductive patterns are formed in microstrips on the printed circuit board 50. However, the detection element 60 is a GaAs diode.

[0034] An input signal line 70 is connected to the input end of the detection element 60. The input signal line 70 has a narrower signal line width than the input signal line 30 of the first and second embodiments, and the portion close to the input terminal of the detection element 60 is tapered. Tapering the portion of the narrow signal line close to the input terminal in this manner has been a common matching method used up until now. The input signal line 70 is grounded by a short stub 71 provided at a position that is not affected by the frequency band used. In the illustrated example, a reflection stub 72 is provided to suppress reflection from the ground end, which is shown as a ring. The reflection stub 72 is fan-shaped so that the distance from the base end to the outer edge is equal. The detection element 60 is subject to reflection from the input terminal. Therefore, a matching stub 74 is required near the portion of the input signal line 70 that is conductive with the input terminal and where the RF signal is input.

[0035] A reflecting stub 80, whose length is set to ¼ or approximately ¼ of the wavelength of the center frequency of the frequency band used, is disposed close to the output end of the detection element 60. The reflecting stub 80 is shaped like a fan, and an output signal line 81, which has high impedance as a load with a resistance component (R) 87 and a capacitance component (C) 88, is connected near the base end, and a voltage that becomes a conversion signal is output from an output signal line 89.

[0036] Fig. 6 shows a comparison diagram of the output voltage (mV) vs. frequency (GHz) characteristics of the RF detector 2 according to the second embodiment and the RF detector 5 according to the comparative example. In Fig. 6, a straight dashed line 600 indicates the practical specification reference value, that is, the value of the output voltage that is a practical level. Furthermore, a solid line 601 indicates the output voltage of the RF detector 2 according to the second embodiment, and a dashed line 602 indicates the output voltage of the RF detector 5 according to the comparative example.

[0037] 6, the RF detector 2 of the second embodiment uses a silicon Schottky diode as the detection element 20, and even if a thick FR-4 board is used for the printed circuit board 10, it can obtain a higher output voltage than the RF detector 5 using an expensive detection element 60 with a conventional design technology on an FR-4 board. It can also be seen that a sufficient output voltage can be obtained over a wide band of about 3 GHz. Furthermore, the RF detector 2 has steep band characteristics in the low and high frequencies. The low frequency portion is steeply attenuated by the notch filter consisting of the open stub 36, the short stub 32, and the open stub 34. The high frequency portion is reflected by the first reflecting stub 42 and is steeply attenuated. Therefore, the RF detector 2 can improve the conversion characteristics in the required band significantly more than the RF detector 5 according to the comparative example.

[0038] In addition, since the first reflection stub 42 is located away from the output end of the detection element 20, it is difficult for the matching to be disturbed. The output voltage exceeds the practical specification reference value of 600, and is at a level that does not pose any practical problems even on an FR-4 board.

[0039] [Effects of the above embodiment] According to the first and second embodiments, even if a silicon Schottky barrier diode and an FR-4 substrate are used, a quasi-millimeter wave band RF detector that exhibits high conversion characteristics and filter performance over a wide band and is compatible with 5G at low cost can be realized. In addition, since the input signal line 30 can be made thick, it can be used with a thick printed circuit board. By making the input signal line 30 thicker, heat generation is also suppressed. In addition, since the printed circuit board 10 can be made thicker, the mechanical characteristics (strength and durability) are increased without the need for a multi-layer structure.

[0040] In conventional general RF detectors, a reflected signal is generated from the input terminal of the detection element to the input signal line in any frequency band. Therefore, in order to prevent the input RF signal from being canceled out by the reflected signal, a stub (for example, stub 74 in Fig. 5) may be provided separately. However, this often results in unnecessary reactance loss, sacrificing the conversion characteristics. In contrast, in the RF detectors 1 and 2 of the first and second embodiments, the first conductive pattern at the input end of the detection element 20 and the second conductive pattern at the output end of the detection element 20 face each other across the detection element 20, so that the reflected signal from the input end of the detection element 20 is absorbed by the inductive reactance of each conductive pattern and the capacitive reactance generated by capacitive coupling between the conductive patterns, and therefore the conversion characteristics are not sacrificed.

[0041] In particular, the first conductive pattern includes a matching stub 31 whose line width increases toward the input end of the detection element 20 to form an expanded open end, and the outer edge between the ends of the expanded open end is formed in a non-linear shape, so that it is possible to achieve matching over a wide band while suppressing unnecessary reflections with the thick signal line 30. In addition, a protrusion that shortens the distance to the opposing second conductive pattern is formed on the outer edge between the ends of the expanded open end, resulting in a structure that facilitates capacitive coupling.

[0042] Furthermore, since the shapes of the enlarged open end of matching stub 31, the input end of detection element 20, the output end of detection element 20, and the second conductive pattern are all symmetrical with respect to the central axis of input signal line 30, imbalance in the high-frequency current on printed circuit board 10 is eliminated, and well-balanced matching can be achieved.

[0043] In both of the RF detectors disclosed in Patent Document 1 and Patent Document 2, attenuation outside the band is required, and therefore an RF filter must be added. RF filters require attenuation over a wide range, and are difficult to use in narrow bands such as notch filters. In addition, in RF filters, costs increase due to size expansion and additional parts, and insertion loss increases, sacrificing conversion characteristics. In contrast, in the RF detectors 1 and 2 of the first and second embodiments, a short stub 32 is formed at a predetermined portion of the input signal line 30, an open stub 34 extends to a predetermined portion of the short stub 32, and the sizes of the short stub 32 and the open stub 34 form a filter in which the cutoff frequency on the low side of the high frequency signal input to the detection element 20 is lower than the frequency band used. Therefore, there is no need to provide a separate RF filter.

[0044] Also, a narrow-band notch filter can be formed when an open stub 36 having a length of approximately 1 / 4 of the wavelength of the low-pass cutoff frequency is formed in a predetermined portion of the input signal line 30 on the opposite side to the portion where the short stub 32 is formed. This makes it possible to make the low-pass portion even steeper.

[0045] In addition, the first and second reflecting stubs 42 and 44 do not need to have sector-shaped outer edges with uniform distances from the base ends, as in the RF detector 5 according to the comparative example, and therefore can be easily manufactured, processed, and finely adjusted. This also makes design easier.

[0046] [Third embodiment] A third embodiment will be described. In the RF detector of the third embodiment, the open stub 34, the first reflection stub 42, and the open stub 36 are omitted from the RF detector 2 of the second embodiment. Therefore, they are not shown in the drawings. FIG. 7 shows the output voltage (mV)-frequency (GHz) characteristics of an RF detector with such a configuration. Referring to FIG. 7, the RF detector of the third embodiment has almost the same effect of wideband matching as the RF detector 2 of the second embodiment, and the output voltage increases on the low-frequency side, improving the conversion characteristics, but sacrificing a little the conversion characteristics in the high frequency range.

[0047] [Fourth embodiment] A fourth embodiment will be described. In the RF detector of the fourth embodiment, the open stubs 34, 36 are omitted from the RF detector 2 of the second embodiment. Therefore, illustration is omitted. The output voltage (mV)-frequency (GHz) characteristics of an RF detector with such a configuration are shown in FIG. 8. Referring to FIG. 8, the RF detector of the fourth embodiment has almost the same effect of wideband matching as the RF detector 2 of the second embodiment, and the output voltage increases on the high frequency side, improving the conversion characteristics, but sacrificing a little steepness in the low frequency range.

[0048] [Fifth embodiment] A fifth embodiment will be described. Fig. 9 is a configuration diagram of an RF detector 3 according to the fifth embodiment. The same components as those described in the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted. The RF detector 3 according to the fifth embodiment differs from the RF detector 1 of the first embodiment and the RF detector 2 of the second embodiment in the following points.

[0049] The ground terminals G1 and G2 are quadrilateral-shaped. The white circles are via holes for electrical connection to the ground terminal on the opposite side of the substrate 10. The open stub 34 faces in the X direction, i.e., toward the input side. The shape of the matching stub 41 has been changed. That is, the shape of the coupling region 41a of the matching stub 41 has been changed to a shape corresponding to the unevenly shaped coupling region on the matching stub 31 side, and the high-impedance line region 41b has been changed to a C-chamfered shape. 1 is triangular in shape and has substantially the same area as the second reflecting stub 44, and is disposed parallel to the second reflecting stub 44. The shape of the open stub 46 may be fan-shaped instead of triangular. In other words, the width of the portion of the open stub 46 that is connected to the third output signal line 45 gradually decreases to approach the width W3 of the third output signal line 45.

[0050] Since the open stub 34 faces the input side, coupling with the matching stub 31 is avoided, which facilitates impedance adjustment between the matching stub 31 and the matching stub 41. In addition, ripples in the used frequency band are improved.

[0051] Also, by changing the coupling region 41a of the matching stub 41 as shown in the figure, the interval between the coupling region of the matching stub 31 and the end portion becomes almost uniform. That is, not only is there a local coupling (e.g., lumped constant coupling) between the input end vicinity of the matching stub 31 side to which the detection element 20 is connected and the output end vicinity of the matching stub 41 side, but there is also a planar coupling (e.g., distributed constant coupling) over almost the entire area of ​​the coupling region of the matching stub 31 and the coupling region 41a of the matching stub 41. Therefore, the degree of coupling between the matching stubs 31 and 41 is increased, and a broadband is possible. This makes it possible to expand the options for the detection element 20 that can be used. Also, there is no need to make the interval between the matching stubs 31 and 41 minute, which is advantageous in terms of manufacturing and processing.

[0052] Furthermore, by gradually decreasing the width of the portion of open stub 46 that is connected to third output signal line 45 so as to approach width W3 of third output signal line 45, the planar coupling (e.g., distributed constant coupling) with third output signal line 45 becomes local coupling (e.g., lumped constant coupling), making impedance adjustment easier.

[0053] [Other embodiments] In the first to fifth embodiments, an example in which an FR-4 board is used for the printed circuit board 10 has been described. Since the printed circuit board 10 is a dielectric, there is a factor called a dielectric loss tangent (tanσ). The dielectric loss tangent indicates the degree to which a part of the electrical energy is converted into heat and lost in the dielectric part of the printed circuit board when an AC electric field is applied to the printed circuit board. In other words, as the frequency used increases, the action of converting the electrical energy into heat in the circuit of the printed circuit board increases, and the signal transmission loss increases. The dielectric loss tangent of the FR-4 board is about 0.02 per 1 GHz, but since there are FR-4 boards with small dielectric loss tangents, it is desirable to use them, but in applications where transmission loss is important, a glass fluororesin board or the like may be used instead of the FR-4 board.

[0054] Furthermore, the above-mentioned RF detectors 1, 2, and 3 can be implemented as a single high-frequency module usable in the quasi-millimeter wave band together with other high-frequency components, such as the amplifier 103, A / D converter 104, DSP 105, or antenna ANT shown in FIG.

[0055] [Variations] The combination of shapes of the matching stub 31 and the matching stub 41 surrounding the detection element 20 can be changed as shown in Fig. 10 and Fig. 11. In "Modification 1-1" in Fig. 10, the coupling region 311 at the open end of the matching stub 31 is chamfered (chamfered to round the corners) with a fine surface (fine chamfer) or a large surface (large chamfer). In "Modification 1-2", the coupling region 312 at the open end of the matching stub 31 is chamfered (chamfered at an angle) with a fine surface or a large surface. In "Modification 1-3", the width of the coupling region 313 at the open end of the matching stub 31 is increased. In "Modification 1-4", the outer end of the coupling region 314 at the open end of the matching stub 31 is extended in the direction of the second conductor pattern. In "Modification 1-5", the outer end of the coupling region 315 at the open end of the matching stub 31 is extended in an oblique direction.

[0056] In addition, in the "Modification 2-1" of FIG. 11, the coupling region 411 of the matching stub 41 is projected toward the concave region of the open end of the matching stub 31 along the concave shape of the concave region. In the "Modification 2-2", the coupling region 412 of the matching stub 41 is projected toward the coupling region of the open end of the matching stub 31 at an acute angle. In the "Modification 2-3", the high impedance line region 413 of the matching stub 41 is chamfered into a C-shape. In the "Modification 2-4", the high impedance line region 414 of the matching stub 41 is chamfered into a D-shape. In the "Modification 2-5", the high impedance line region 415 of the matching stub 41 is chamfered into a trapezoidal shape. Note that the shapes of FIG. 10 and FIG. 11 are merely examples, and other chamfer shapes may be used. Also, a combination of the shapes of FIG. 10 and FIG. 11 may be used.

[0057] In the above-described embodiments, examples of RF detectors 1, 2 and high-frequency modules used in the 28 GHz band have been described. However, the present invention can be similarly applied to RF detectors and high-frequency modules used in frequencies below the 26 GHz band or above the 28 GHz band, with only the dimensions of each component being changed.

[0058] [Field of Use] The above-mentioned RF detectors 1, 2, and 3 can be used to detect RF signals in a variety of fields, including surveillance (security and nursing care), IoT (content distribution, etc.), AI (autonomous driving, etc.), and medicine and healthcare.

[0059] According to the present specification, the following aspects are provided. (Aspect 1) A first aspect is an RF detector comprising: a detection element that detects the signal strength of an RF signal; and a printed circuit board on which a first conductive pattern that is electrically connected to an input terminal of the detection element and a second conductive pattern that is electrically connected to an output terminal of the detection element are formed, the first conductive pattern and the second conductive pattern facing each other across the detection element, thereby providing capacitive coupling between the conductive patterns. According to the first aspect, since the first conductive pattern and the second conductive pattern face each other with the detection element therebetween, the reflection from the input end of the detection element is absorbed by the inductive reactance of each conductive pattern and the capacitive reactance generated by the capacitive coupling between the conductive patterns, and therefore the conversion characteristics are not sacrificed. Since the width of the usable frequency band can be expanded without causing matching between the detection element and the first and second conductive patterns, detection elements and printed circuit boards used in the microwave band can be used in the quasi-millimeter wave band or higher. Therefore, an RF detector with sufficient mechanical characteristics and cost reduction can be easily realized.

[0060] (Aspect 2) A second aspect is the RF detector according to the first aspect, wherein the detection element is a rectifier diode that directly converts an input RF signal. According to the second aspect, a quasi-millimeter wave band RF detector compatible with, for example, 5G can be provided at low cost.

[0061] (Aspect 3) Aspect 3 is an RF detector according to aspect 1 or 2, in which the first conductive pattern includes an input signal line whose line width increases toward the input end of the detection element to form an enlarged open end, and an outer edge between the ends of the enlarged open end is formed in a non-linear shape. According to the third aspect, capacitive coupling is facilitated between the expanded open end of the first conductive pattern and a part of the second conductive pattern. In addition, the matching action caused by the cooperation between the expanded open end of the first conductive pattern and a part of the second conductive pattern suppresses reflection near the detection element, and matching can be achieved over a wide band, so that the frequency of use as designed is input to the detection element. Therefore, unlike the conventional case, it is no longer necessary to separately provide a matching stub on the input signal line, and the pattern is simplified, which reduces costs and facilitates mass production.

[0062] (Aspect 4) A fourth aspect is the RF detector according to the third aspect, wherein a protrusion is formed on an outer edge between the ends of the expanded open end, the protrusion having a tip that faces the second conductive pattern. According to the fourth aspect, adjustment work for matching can be easily performed, and capacitive coupling between the enlarged open end and a part of the second conductive pattern can be easily achieved.

[0063] (Aspect 5) Aspect 5 is an RF detector according to aspect 3 or 4, wherein the shapes of the enlarged open end, the input end of the detection element, the output end of the detection element, and the second conductive pattern are each symmetrical with respect to the line axis of the input signal line. According to the fifth aspect, the imbalance of the high-frequency current on the printed circuit board is eliminated, and matching can be achieved in a well-balanced manner.

[0064] (Aspect 6) A sixth aspect is an RF detector according to any one of the third, fourth or fifth aspects, in which a grounding short stub is formed at a predetermined portion of the input signal line, and an open stub extends parallel to the input signal line at a predetermined portion of the short stub, and the sizes of the short stub and the open stub form a filter in which the cutoff frequency on the low side of the RF signal input to the detection element is lower than the frequency band used. According to the sixth aspect, the open stub can be operated as a notch filter, so that a steep attenuation characteristic can be obtained on the low frequency side. Also, by providing a short stub, the occurrence of a match disturbance can be prevented, and a large attenuation can be obtained, and furthermore, the loss can be suppressed to a minimum. Furthermore, it is not necessary to provide a separate RF filter, which increases the cost due to the increase in size and the addition of parts, and which increases the insertion loss and sacrifices the conversion characteristic.

[0065] (Aspect 7) A seventh aspect is the RF detector according to the sixth aspect, in which an open stub having a length of approximately ¼ of the wavelength of a lower cutoff frequency is formed in a predetermined portion of the input signal line on the opposite side of the line axis of the input signal line from the portion where the short stub is formed. According to the seventh aspect, a narrow-band notch filter can be formed, and the conversion characteristics can be made steeper on the low-frequency side. In addition, because of the narrow band, even if there is a mismatch, the effect of the mismatch can be reduced.

[0066] (Aspect 8) An eighth aspect is an RF detector according to any one of the first to sixth aspects, wherein the second conductive pattern includes an output signal line extending from an output end of the detection element, and a reflection stub having a length of approximately 1 / 4 of the wavelength of a high-frequency cutoff frequency is formed at a predetermined position on the output signal line. According to the eighth aspect, the reflection stub reflects the set frequency on the high frequency side, so that the wide frequency part in the conversion characteristic is rapidly attenuated. Also, since the reflection point is away from the output end of the detection element, phase adjustment is easy, and cancellation of the input signal at the input end of the detection element and the reflected signal at the output end is not caused, so that the matching is less likely to be disturbed.

[0067] (Aspect 9) A ninth aspect is a high-frequency module including an RF detector located on the surface of a printed circuit board whose back surface is a ground conductor and which detects the signal level of an input RF signal, wherein the RF detector is an RF detector as defined in any one of claims 1 to 8. According to the ninth aspect, since the width of the usable frequency band can be expanded without causing matching between the detection element and the first and second conductive patterns, the detection element and the printed circuit board used in the microwave band can also be used in the quasi-millimeter wave band or higher. Therefore, it is possible to easily realize a high-frequency module that has sufficient mechanical properties and can also be cost-reduced.

Claims

1. a detection element for detecting a signal strength of an RF signal; a printed circuit board on which a first conductive pattern electrically connected to an input terminal of the detection element and a second conductive pattern electrically connected to an output terminal of the detection element are formed, the first conductive pattern and the second conductive pattern face each other with the detection element therebetween, thereby causing capacitive coupling between the conductive patterns; The first conductive pattern includes an input signal line having an enlarged open end whose line width increases toward an input end of the detection element. RF detector.

2. The detection element is a rectifier diode that directly converts an input RF signal. The RF detector of claim 1 .

3. The outer edge between the ends of the expanded open end is formed in a non-linear shape, The RF detector of claim 1 .

4. a projection having a tip directed toward the opposing second conductive pattern is formed on an outer edge between the ends of the expanded open end; The RF detector of claim 3 .

5. the enlarged open end, the input end of the detection element, the output end of the detection element, and the second conductive pattern are each symmetrical with respect to the line axis of the input signal line; The RF detector of claim 1 .

6. a short stub for grounding is formed at a predetermined portion of the input signal line, and an open stub extends in parallel to the input signal line at a predetermined portion of the short stub, and the sizes of the short stub and the open stub form a filter in which the cutoff frequency on the low side of the RF signal input to the detection element is lower than the frequency band used. The RF detector of claim 1 .

7. an open stub having a length of approximately 1 / 4 of the wavelength of a low-frequency cutoff frequency is formed at a predetermined portion of the input signal line opposite to the portion where the short stub is formed across the line axis of the input signal line; 7. The RF detector of claim 6.

8. the second conductive pattern includes an output signal line extending from an output end of the detection element, and a reflection stub having a length of approximately ¼ of a wavelength of a cutoff frequency on a high frequency side is formed at a predetermined position on the output signal line; The RF detector of claim 1 .

9. A high-frequency module including an RF detector that is provided on a surface of a printed circuit board whose back surface is a ground conductor and detects a signal level of an input RF signal, A high frequency module, wherein the RF detector is the RF detector according to claim 1 .

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