High-frequency circuit board

Abstract

To provide a high-frequency circuit board and a light receiving device having a structure that does not require scaling for reducing an unnecessary propagation mode generated in a board.SOLUTION: A high-frequency circuit board according to the present invention comprises: a metal thin film layer 102 in which a band stop filter 102C is formed by a microstrip line (MSL) and which conducts in the MSL; a metal thin film layer 104 in which a planar circuit pattern is formed by the MSL and which conducts in the MSL; and an insulating layer 103 sandwiched between the metal thin film layer 102 and the metal thin film layer 104. The high-frequency circuit board is characterized in that a short stub line 110 is formed of the metal thin film layer 102 and the metal thin film layer 104; the short stub line 110 is disposed inside a planar circuit pattern of the band stop filter 102C when viewed from the metal thin film layer 104 side; and a capacitor 109 formed of the metal thin film layer 102, the metal thin film layer 104, and the insulating layer 103 is connected to one end of the short stub line 110.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to the structure of a device that handles high frequencies, such as millimeter waves or even terahertz (THz) waves, as carrier frequencies. [Background technology]

[0002] (1) THz wireless communication and photodiodes In the field of wireless communications, research and development is accelerating to expand carrier frequencies to millimeter waves and even terahertz (THz) waves in order to further increase transmission capacity. For example, NTT Docomo's white paper "5G Enhancements and 6G," published in 2022, states, "We are considering radio waves up to approximately 300 GHz as part of the 6G consideration range." Ultra-high-speed information data always takes the form of optical signals. During wireless communications, optical subcarriers are transmitted modulated by the data signal on the carrier. This requires optical-to-electrical conversion (OE conversion) using ultra-high-speed photodiodes (PDs), and typically electrical amplification of the PD output. When the required transmission power is low, such as in LAN systems, or when electrical amplifiers cannot be installed at frequencies above 200 GHz, direct OE conversion using only PDs is also possible.

[0003] The optical-to-electrical (OE) conversion by a PD must maintain sufficient characteristics at the wireless carrier frequency. For example, when using a 300 GHz THz carrier, the PD must be able to operate efficiently at 300 GHz (sufficient response speed and frequency bandwidth). NTT Innovative Devices already sells photodiode modules (waveguide-output THz photomixers) for various frequency bands up to the J-band (220-330 GHz), which are being used in various research and development projects. However, there is still room for improvement in these waveguide-output THz photomixers, including in terms of performance. In particular, there is a need for technologies to reduce characteristic variability, simplify implementation, and reduce cost.

[0004] (2) THz photomixer configuration 1 is a schematic diagram illustrating the internal structure of a typical waveguide-output THz photomixer. The waveguide-output THz photomixer includes a photomixer chip 402 and a waveguide coupler substrate 401 (see, for example, Non-Patent Document 1). The waveguide coupler substrate 401 is equipped with a waveguide coupler 409 that guides a signal from the photomixer chip 402 to a waveguide 410 and then converts the signal into a waveguide mode. The photomixer chip 402 includes a photodiode 403 that converts signal light 400 focused by a lens 413 into an electrical signal, a ground pad 408 that grounds the photodiode 403, a bias pad 407 that applies a bias to the photodiode 403, and a signal pad 406 that outputs the electrical signal from the photodiode 403.

[0005] Furthermore, since a waveguide output THz photomixer is not usually required to operate in the baseband, it is necessary to introduce a matching circuit for the photodiode 403 according to the frequency band. This matching circuit is composed of a short stub 404 and an MIM capacitor 405. Figure 2 is an equivalent circuit diagram of the waveguide output THz photomixer.

[0006] The photodiode 403 and matching circuit are formed on the same InP substrate as the photomixer chip 402. The waveguide coupler substrate 401 is typically made of quartz glass. Usually, the tip of the waveguide coupler substrate 401 has a dc open structure, which is advantageous in terms of bandwidth characteristics. For electrical signal connection, connection pads are arranged on both the photomixer chip 401 and the waveguide coupler substrate 402. Since it is essential that the photomixer chip 401 has a surface ground, the signal pad 406 and the ground pad 408 are connected to the waveguide coupler substrate 401 with Au wires 411, as shown in Figure 1.

[0007] When the operating frequency is low (for example, below 100 GHz), connections using Au wires do not cause any major problems, but at higher frequencies (millimeter waves, THz waves), the characteristics vary depending on the Au wire connection, which makes it difficult to simplify the implementation and reduce the cost, as mentioned above.

[0008] (3) THz photomixer chip If the photodiode and waveguide coupler were all made out of InP to avoid connections using Au wires, the following difficulties would arise: For example, if a photomixer chip operating at 300 GHz were to be made out of InP, the substrate thickness would need to be approximately 30 μm or less, and as the frequency increases, the required substrate thickness would become even thinner. Strength issues arise due to the mechanical fragility of InP and the mismatch in thermal expansion coefficients between the waveguide and InP.

[0009] Regarding THz receiving diode technology rather than photomixer technology, a chip has recently been reported in which only the junction of the receiving diode is locally mounted on a mechanically strong host substrate (see, for example, Non-Patent Document 2). This is an integrated chip that also includes a waveguide coupler, so there is no need to wire the path of the 300 GHz electrical signal. By applying this technology, it is basically possible to fabricate a photomixer chip with a single chip configuration. In other words, it is possible to create an integrated THz photomixer in which the waveguide coupler and PD element parts are integrated on a single substrate.

[0010] The challenge in creating an integrated THz photomixer is that the photodiode, matching circuit based on short stubs, bias pads, and ground pads must all be mounted on a narrow host substrate. This imposes constraints on the host substrate's dimensions (width × length). To enable flexible photomixer pattern placement with a backside ground and a stable frontside ground, the general theory of microwave propagation requires that the substrate width be less than half the operating wavelength, which is determined by the dielectric constant of the substrate material. For example, if the host substrate is made of SiC, the substrate width must be less than 130–140 μm for the J-band. This host substrate width constraint becomes even more pronounced as the operating frequency increases.

[0011] If a microstrip line (MSL) structure without a surface ground is adopted as the host substrate, the substrate width can be increased by approximately two times. However, even with an MSL structure, unwanted propagation modes are still likely to occur inside the substrate, which may adversely affect the output characteristics of the photomixer. Furthermore, since an MSL structure typically does not have a surface ground, it is often difficult to arrange various circuit patterns on the substrate surface and to connect ground wires to pads on the substrate.

[0012] As mentioned above, THz photomixer chip technology can be said to be a structural design that requires a substrate width of at least a certain level to accommodate the matching circuit and that can suppress the occurrence of unwanted propagation modes within the substrate. In other words, as the operating frequency increases, this circuit configuration and substrate structure allows for the design of photomixer circuits without following the conventional design structure with general top and bottom grounds. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] Hiroshi Ito et al., “High-Speed ​​and High-Output InP-InGaAs Unitraveling-Carrier Photodiodes”, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 10, NO. 4, JULY / AUGUST 2004 (pp. 709-727) [Non-patent document 2] Hiroshi Ito et al., “Terahertz-wave detector on silicon carbide platform”, Applied Physics Express 15, 2022 (pp. 026501-1~4) Summary of the Invention [Problem to be solved by the invention]

[0014] As mentioned above, THz photomixers mounted on waveguides consist of two main components: an InP-substrate photomixer chip and a quartz waveguide coupler. However, variations in characteristics related to the wiring during mounting have been an issue. This issue is being resolved by integrated THz photomixer chips, which combine these components on a host substrate. However, integrated THz photomixer chips have the constraint of requiring scaling (size adjustment according to the operating frequency) to reduce unwanted propagation modes generated within the substrate due to the ground on the substrate surface.

[0015] Therefore, an object of the present invention is to provide a high-frequency circuit board having a structure free from the above-mentioned constraints, and a light-receiving device including the same. [Means for solving the problem]

[0016] In order to achieve the above object, a high-frequency circuit board according to the present invention is a circuit board arranged on a host substrate, and a matching circuit for a photodiode is formed within the region of a band-stop filter formed of a microstrip line.

[0017] Specifically, the high-frequency circuit board according to the present invention comprises: a first metal thin film layer in which a planar circuit pattern of the band-stop filter is formed by microstrip lines and which is electrically connected to the microstrip lines; a second metal thin film layer having a planar circuit pattern formed by microstrip lines and electrically connected to the microstrip lines; a planar insulating layer sandwiched between the first metal thin film and the second metal thin film; A high-frequency circuit board comprising: a short stub line is formed by the first metal thin film layer and the second metal thin film layer; the short stub line is disposed inside the planar circuit pattern of the band-elimination filter when viewed from the second metal thin film layer side; and a capacitor formed by the first metal thin film layer, the second metal thin film layer, and the insulating layer is connected to one end of the short stub line; It is characterized by:

[0018] In the high-frequency circuit board according to the present invention, a band-stop filter is formed using a microstrip line, and a short stub line that serves as a matching circuit is formed within the band-stop filter. As a result, the matching circuit does not have a surface ground, and is not directly subject to the scaling constraints of the board width. Therefore, the present invention can provide a high-frequency circuit board with a structure that is not subject to scaling constraints.

[0019] the planar circuit pattern of the band-elimination filter of the high-frequency circuit board according to the present invention has a cutout portion in which a metal film is removed with a width wider than that of the microstrip line of the second metal film layer; and The short stub line is arranged so that the microstrip line of the second metal film layer passes through the center of the cutout portion when viewed from the second metal thin film side, and the first metal film layer and the second metal film layer form a coplanar line. The short stub line is formed in the band-stop filter.

[0020] The band rejection filter of the high-frequency circuit board according to the present invention may have a planar circuit pattern in which two types of microstrip lines with different impedances are connected in series.

[0021] The band-elimination filter of the high-frequency circuit board according to the present invention may be a planar circuit pattern including a pair of radial lines.

[0022] The light-receiving device according to the present invention is a light-receiving device in which the high-frequency circuit board is mounted on one surface of a rectangular host substrate, the high-frequency circuit board further includes a photodiode, an optical input port, and a high-frequency electrical output port; the photodiode is disposed at the other end of the short stub line such that its cathode is connected to the second metal thin film layer and its anode is connected to the first metal thin film layer; the high frequency electrical output port is a metal waveguide coupler formed in the second metal thin film layer; and The optical input port is a light introduction window provided in a ground metal film layer disposed on the other surface of the host substrate. It is characterized by:

[0023] The photodetector device of the present invention is an integrated THz photomixer chip that uses a host substrate, eliminating the need for wiring as a high-frequency signal path, preventing the characteristic variations that arise from the conventional two-chip configuration and enabling the fabrication of a photomixer with stable performance that is less susceptible to the effects of mounting. Furthermore, because the high-frequency circuit board does not have a surface ground, circuit pattern layout is simplified without being directly restricted by the scaling of the board width, enabling pattern design with good performance.

[0024] The above inventions can be combined as much as possible. [Effects of the Invention]

[0025] The present invention can provide a high-frequency circuit board having a structure that does not require adjustment of the board size according to the operating frequency, and can provide a light-receiving device that prevents variations in characteristics, facilitates circuit pattern layout, and enables high-performance pattern design.

[0026] The present invention can provide a high-frequency device that has the structure of an RF (alternating current operation) photodiode used for generating electromagnetic waves using optical signals, particularly terahertz waves, and converting optical subcarriers to THz carriers in wireless communications, and that advantageously realizes high-frequency operation. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 2 is a schematic diagram illustrating the internal structure of a waveguide output THz photomixer. [Figure 2] FIG. 1 is an equivalent circuit diagram of a waveguide output THz photomixer. [Figure 3] 1A and 1B are diagrams illustrating a light receiving device according to the present invention. [Figure 4] 1A and 1B are diagrams illustrating a high-frequency circuit board according to the present invention. [Figure 5] 1A and 1B are diagrams illustrating a light receiving device according to the present invention. [Figure 6] 1A and 1B are diagrams illustrating a high-frequency circuit board according to the present invention. [Figure 7] FIG. 1 is a diagram illustrating a model for performing a simulation. [Figure 8] FIG. 10 is a diagram illustrating the evaluation results. DETAILED DESCRIPTION OF THE INVENTION

[0028] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0029] (Embodiment 1) FIG. 3 is a diagram illustrating the light-receiving device of this embodiment. This light-receiving device is a waveguide output THz photomixer. FIG. 4 is an enlarged diagram illustrating a matching circuit 116 formed in this light-receiving device. This waveguide output THz photomixer is a light-receiving device in which a high-frequency circuit board is mounted on one surface of a rectangular host substrate 101.

[0030] The high-frequency circuit board comprises: A planar circuit pattern of the band-stop filter 102C is formed by a microstrip line, and a first metal thin film layer 102 is electrically connected to the microstrip line; a second metal thin film layer 104 having a planar circuit pattern formed by microstrip lines and electrically connected to the microstrip lines; a planar insulating layer 103 sandwiched between a first metal thin film 102 and the second metal thin film 104; The high-frequency circuit board comprises: a short stub line 110 is formed by the first metal thin film layer 102 and the second metal thin film layer 104; When viewed from the second metal thin film layer 104 side, the short stub line 110 is disposed inside the planar circuit pattern of the band-stop filter 102C; and A capacitor 109 composed of a first metal thin film layer 102, a second metal thin film layer 104, and an insulating layer 103 is connected to one end of the short stub line 110. It is characterized by:

[0031] the high-frequency circuit board further comprises a photodiode 105, an optical input port 103A, and a high-frequency electrical output port; The photodiode 105 is disposed at the other end of the short stub line 110 so that the cathode is connected to the second metal thin film layer 104 and the anode is connected to the first metal thin film layer 102; the high frequency electrical output port is a metal waveguide coupler 112 formed in the second metal thin film layer 104; and The optical input port 103A is a light introduction window provided in the ground metal film layer 113 disposed on the other surface of the host substrate 101. It is characterized by:

[0032] A first metal film layer 102 as a lower layer, a dielectric film as an insulating layer 103, and a second metal film layer 104 as an upper layer are arranged on a host substrate 101. The first metal film layer 102 forms an MSL-based planar circuit (electrically connected ground pad 114 and band-stop filter 102). The second metal film layer 104 also forms an MSL-based planar circuit (electrically connected bias pad 115, matching circuit 116, output MSL 111, and waveguide coupler 112). In addition, a cathode 106 of a photodiode 105 is connected to the first metal film layer 102, and an anode 107 of the photodiode 105 is connected to the second metal film layer 104.

[0033] A voltage is applied to the photodiode 105 from a ground pad 114 also provided in part of the first metal film layer 102 and a bias pad 115 also provided in part of the second metal film layer 104. When an optical signal is incident on the photodiode 105 from a light introducing window 113A provided in part of the ground metal film layer 113 arranged on the underside of the host substrate 101, the high-frequency component of the output current propagates through the output MSL 111 and reaches the waveguide coupler 112. Power is coupled from the waveguide coupler 112 to a waveguide (not shown), and a THz output is obtained.

[0034] In this embodiment, the band-stop filter 102C is a planar circuit pattern in which two types of microstrip lines with different impedances are connected in series. Specifically, the band-stop filter 102C has a multi-stage structure consisting of an MSL low-impedance portion 102A and an MSL high-impedance portion 102B, from the photodiode 105 side. In Fig. 3, the band-stop filter 102C has a two-stage structure in which two sets of an MSL low-impedance portion 102A and an MSL high-impedance portion 102B are connected.

[0035] Furthermore, the planar circuit pattern of the band-stop filter 102C has a cutout portion 117 that removes the first metal film layer 102 with a width wider than the microstrip line of the second metal film layer 104; The short stub line 110 is arranged so that the microstrip line of the second metal film layer 104 passes through the center of the cutout portion 117 when viewed from the second metal thin film 104 side, and the first metal film layer 102 and the second metal film layer 104 form a coplanar waveguide (CPW). It is characterized by:

[0036] That is, when viewed from above, short stub line 110 is a coplanar line (a 3D-like coplanar line) in which first metal film layer 102 is sandwiched between second metal film layer 104 with a gap therebetween. At one end of this coplanar line, metal / insulating layer / metal (MIM) capacitor 109 consisting of first metal film layer 102, insulating layer 103, and second metal film layer 104 is connected, and high-frequency signals are short-circuited.

[0037] A feature of this waveguide output THz photomixer is that it contains, within the area of ​​the band element filter 102C, a short stub line that is an element of the photomixer's matching circuit 116 and a short function for high-frequency signals. This waveguide output THz photomixer does not have a physical surface ground, but the two metal film layers stacked above and below act as capacitors that effectively function as grounds for high-frequency signals.

[0038] As mentioned in the technical background section, to enable flexible photomixer pattern placement with a stable surface ground, the general theory of microwave propagation is that the substrate width must be less than half the operating wavelength, which is determined by the substrate's dielectric constant. On the other hand, if a microstrip line (MSL) structure with no surface ground is used as the host substrate, the substrate width can be increased by approximately two times. However, this still leaves the possibility of unwanted propagation modes occurring inside the substrate, which can adversely affect the output characteristics of the photomixer.

[0039] However, MSL-based bandstop filters are exceptional in that, even if the metal pattern surface is relatively large, the inherent nature of their function prevents unwanted propagation modes from occurring in the operating band. Specifically, the size of the low-impedance section 102A of the bandstop filter 102C can be expanded up to λ / 4 in the signal propagation direction (the MSL longitudinal direction) and up to approximately λ / 2 in the MSL width direction.

[0040] Further, by increasing the size of the low impedance portion 102A of the band-stop filter 102C, the following structure becomes possible. The short stub line of the photomixer is typically about λ / 8. By making the dielectric constants of the insulating layer 103 and the host substrate 101 equal, a structure can be achieved in which the stub is housed in the low-impedance portion 102A of the band-stop filter 102C. Furthermore, by utilizing the capacitance formed by the first metal film layer 102, the insulating layer 103, and the second metal film layer 104, it is possible to create a structure in which a capacitor with sufficient capacitance to serve as the shorting surface of the stub is also housed in the low impedance portion 102A of the band rejection filter 102C.

[0041] By configuring the integrated THz photomixer chip in this manner, the matching circuit 116 of the photomixer can be designed to fit the width of the host substrate 101, which corresponds to the size of the waveguide coupler 112, and can be mounted on the host substrate 101. In other words, since the light-receiving device of the present invention does not have a surface ground, the matching circuit of the photomixer can be easily arranged without being directly restricted by the width of the host substrate, making it possible to design a pattern that improves the performance of the photomixer.

[0042] (Embodiment 2) FIG. 5 is a diagram illustrating a light-receiving device of this embodiment. This light-receiving device is also a waveguide output THz photomixer. FIG. 6 is a diagram illustrating an enlarged view of a matching circuit 116R formed in this light-receiving device. The light-receiving device of this embodiment has a structure in which the matching circuit 116 of the light-receiving device of embodiment 1 is replaced with a matching circuit 116B. Therefore, in this embodiment, only the matching circuit 116B, which is different from the light-receiving device of embodiment 1, will be described.

[0043] In this embodiment, the band-stop filter 102C is a planar circuit pattern including a pair of radial lines 202. That is, the light-receiving device of this embodiment has a structure in which the pattern of the low-impedance section 102A near the photodiode 105 in the band-stop filter 102C of the light-receiving device of embodiment 1 is replaced with a pattern of a pair of radial lines 202.

[0044] In this embodiment, the short stub line 110 is formed from the position of the photodiode 105 in a direction perpendicular to the longitudinal direction of the microstrip line of the second metal film layer 104. In other words, the short stub line 110 is formed inside one of the radial lines 202. The structure of the short stub line 110 is the same as that of the first embodiment, and when viewed from the second thin metal film 104 side, the microstrip line of the second metal film layer 104 is arranged to pass through the center of the cutout portion 117 of the first metal film layer 102 (radial line 202), and the first metal film layer 102 and the second metal film layer 104 form a coplanar waveguide (CPW).

[0045] Also, a metal / insulating layer / metal (MIM) capacitor 209 consisting of a first metal film layer 102, an insulating layer 103, and a second metal film layer 104 is connected to one end of this coplanar line (the side opposite to the photodiode 105 side), and high-frequency signals are short-circuited, as in embodiment 1. Although the area of ​​the MIM capacitor 209 tends to be narrow depending on the size of the radial line 202, by adjusting the thickness of the first dielectric film 103, it is possible to ensure sufficient capacitance and obtain characteristics that are the same as those of the structure in embodiment 1.

[0046] In this embodiment, the band-stop filter 102C is composed of a pair of radial lines 202, a high-impedance line 102B, a low-impedance line 102A, and a high-impedance line 102B, and the length of the band-stop filter portion 102C is shortened by λ / 4, allowing the optical receiving device (waveguide output THz photomixer) to be miniaturized.

[0047] (Embodiment 3) In this embodiment, it will be explained that even if there is a portion (cutout portion 117) where the metal surface of the bandstop filter 102C described in embodiments 1 and 2 has been locally removed, the original bandstop characteristics (characteristics when there is no cutout portion) are maintained. Here, in the example of FIG. 3, a simulation is performed to verify that the electrical signal propagating from the cathode 106 of the photodiode 105 in the direction of the first metal film layer 102 is not affected by the presence of the cutout portion 117 of the short stub line 110.

[0048] The following describes the results of a simulation performed using the model shown in Fig. 7. The model in Fig. 7 is a model of the light-receiving device in Fig. 3, in which an MSL pattern of a first metal film layer 302 and a second metal film layer 304 is formed on one surface of a host substrate 301. The first metal film layer 302 is an MSL pattern of a band-stop filter 302C with a multistage structure consisting of a low-impedance portion 302A and a high-impedance portion 302B.

[0049] Inside one low-impedance portion 302A of first metal film layer 302, a cutout portion 317 of a size equivalent to cutout portion 117 was formed in the portion where short stub line 110 described in embodiments 1 and 2 was arranged. In this simulation, to simplify the structure, a photodiode was not used, and signal source port P1 was placed at the position of the photodiode. How the electrical signal from signal source port 305 propagates to THz output side port P2 and bias side port P3 was evaluated using S parameters (the amount of signal leakage (attenuation) from each of ports P1 and P2 to port P3).

[0050] FIG. 8 is a diagram illustrating the evaluation results. The S parameter of the signal from port P1 to port P3 is indicated by S31, and the S parameter of the signal from port P2 to port P3 is indicated by S32. Both S parameters (S31 and S32) are low at -35 dB in the J-band (220 to 330 GHz). From this result, it can be seen that even with cutout portion 317 in the metal film layer, leakage of electrical signals from ports P1 and P2 to band-stop filter 302C is extremely small.

[0051] This result that the degree of leakage signal is extremely small confirms the following hypothesis: In the light-receiving devices of the first and second embodiments, the reflection of the electrical signal propagating from the cathode 106 of the photodiode 105 toward the band-stop filter 102C is not affected by the recess 117 inside the first metal film layer 102, as long as its size is small. [Industrial Applicability]

[0052] In the field of wireless communications, research and development is underway to increase communication capacity and reduce power consumption by increasing carrier frequencies. In the useful 300 GHz frequency band, there are no suitable electrical amplifiers, so direct optical-to-electrical conversion using only a photodiode is often used. For this type of application, as well as for applications such as spectroscopic imaging that require stable THz signals, the present invention can provide a fabrication technology for integrated THz photomixers with stable performance and lower cost. [Explanation of symbols]

[0053] 101: Host board 102: First metal film layer (connected) 102A: Low impedance section of band-stop filter 102B: High impedance section of band-stop filter 103: Insulating layer (first dielectric film) 104: Second metal film layer 105: Photodiode 106: Cathode of the photodiode (bottom) connected to the first metal film layer 107: Anode of the photodiode (top) connected to the second metal film layer 109: MIM capacitor (overlapping portion of first metal film layer and second metal film layer) 110: Short stub part (CPW line) 111: Output MSL 112: Waveguide coupler 113: Bottom ground metal film layer arranged on the back surface 113A: Light introduction window 114: Ground pad section 115: Bias pad section 116: Matching circuit part 202: Radial Line 209: MIM capacitor (overlapping portion of first metal film layer and second metal film layer) 301: Host board 302: First metal film layer 302A: Low impedance section of band-stop filter 302B: High impedance section of band-stop filter 302C: Band-stop filter 304: Second metal film layer 305: Signal source port (P1) 306: Output port (P2) 307: Bias side port (P3) 317: Hollowed out section 401: Waveguide coupler substrate (quartz) 402: Photomixer chip 403: Photodiode 404: Short stub 405: MIM capacitor 406: Signal Pad 407: Bias pad 408: Ground pad 409: Waveguide coupler 410: Rectangular waveguide 411: Au wire 412: High frequency output 413: Lens focusing system 415: Back short side

Claims

1. a first metal thin film layer in which a planar circuit pattern of the band-stop filter is formed by microstrip lines and which is electrically connected to the microstrip lines; a second metal thin film layer having a planar circuit pattern formed by microstrip lines and electrically connected to the microstrip lines; a planar insulating layer sandwiched between the first metal thin film layer and the second metal thin film layer; A high-frequency circuit board comprising: a short stub line is formed by the first metal thin film layer and the second metal thin film layer; the short stub line is disposed inside the planar circuit pattern of the band-elimination filter when viewed from the second metal thin film layer side; and a capacitor formed by the first metal thin film layer, the second metal thin film layer, and the insulating layer is connected to one end of the short stub line; A high frequency circuit board characterized by:

2. the planar circuit pattern of the band-elimination filter has a cutout portion in which a metal film is removed with a width wider than that of the microstrip line of the second metal film layer; and The short stub line is arranged so that the microstrip line of the second metal film layer passes through the center of the cutout portion when viewed from the second metal thin film layer side, and the first metal film layer and the second metal film layer form a coplanar line.

2. The high frequency circuit board according to claim 1,

3. 2. The high-frequency circuit board according to claim 1, wherein the band-elimination filter is a planar circuit pattern in which two types of microstrip lines with different impedances are connected in series.

4. 2. The high-frequency circuit board according to claim 1, wherein the band-elimination filter is a planar circuit pattern including a pair of radial lines.

5. A light-receiving device in which the high-frequency circuit board according to any one of claims 1 to 4 is mounted on one surface of a rectangular host substrate, the high-frequency circuit board further includes a photodiode, an optical input port, and a high-frequency electrical output port; the photodiode is disposed at the other end of the short stub line such that its cathode is connected to the second metal thin film layer and its anode is connected to the first metal thin film layer; the high frequency electrical output port is a metal waveguide coupler formed in the second metal thin film layer; and The optical input port is a light introduction window provided in a ground metal film layer disposed on the other surface of the host substrate. A light receiving device comprising:

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