Terahertz IQ second harmonic mixer

Abstract

The invention provides a terahertz IQ second harmonic mixer, which is characterized in that the input ends of two terahertz sub-harmonic mixers are respectively connected with two output ends of a waveguide directional coupler and a local oscillator power distribution network, and the waveguide directional coupler respectively inputs radio frequency signals with a phase difference of 90 degrees into the radio frequency ends of the two terahertz sub-harmonic mixers; equal-amplitude local oscillation signals with the phase difference of 180 degrees output by the local oscillation power distribution network are respectively transmitted to local oscillation ends of the two terahertz sub-harmonic mixers; a Schottky diode pair is arranged between the radio frequency end and the local oscillator end, an intermediate-frequency low-pass filter is arranged between the Schottky diode pair and the local oscillator end, and two paths of intermediate-frequency signals which are generated after the Schottky diode pair carries out frequency mixing processing on input radio frequency signals and input local oscillator signals and have the phase difference of 90 degrees are output after passing through the intermediate-frequency low-pass filter. The I-path / Q-path frequency conversion loss is small, the amplitude unbalance degree and the phase unbalance degree are low, the intermediate frequency is wide, and the radio frequency, local oscillation and intermediate frequency port return loss is small.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz devices, and in particular to a terahertz IQ second harmonic mixer. Background Art

[0002] Terahertz (THz) waves refer to electromagnetic waves with a frequency in the spectrum range of 0.1THz-10THz. Terahertz waves and terahertz technology have broad application space in radar imaging, communication, meteorological monitoring, human security inspection, biomedicine and other fields. Terahertz communication is a technology that uses the terahertz frequency band as a carrier to achieve wireless communication. It is another important spectrum technology after microwave and optical communication and is considered to be the core of the next generation of communication technology. As one of the most core circuits in the terahertz communication system, the terahertz mixer mixes the lower frequency intermediate frequency signal with the local oscillator signal to produce a higher frequency radio frequency signal at the transmitting end, which is called up-conversion. At the receiving end, the higher frequency radio frequency signal is mixed with the local oscillator signal to produce a lower frequency intermediate frequency signal, which is called down-conversion.

[0003] In the patents and literatures that have been published, most of them focus on the research of traditional mixer circuits. This mixer only outputs one intermediate frequency signal and cannot suppress the image frequency. However, the image frequency is the main problem that cannot be ignored in the current terahertz superheterodyne structure. This is because in the incoherent demodulation communication system, the information contained in the two sidebands is complete and identical. When the two sidebands are received, they will cause the two sideband down-conversion signals to alias. There are two ways to suppress the image signal. The commonly used method is that in the communication system, the mixed signal passes through a filter to directly filter out the image frequency; the other method is to use the equal-amplitude orthogonal I and Q intermediate frequency signals generated by the orthogonal mixer to superimpose to offset the image frequency signal. Compared with the first method, the image suppression based on the orthogonal mixer has the following advantages: First, this method can simplify the system structure, without the need to design a multi-stage frequency conversion structure for the separation of the upper and lower sidebands, and reduce the design of filters; second, this method can improve the flexibility of the system, and the image frequency suppression is achieved through the filter. The change of the local oscillator frequency is limited. Once it exceeds the filter passband, the filter needs to be redesigned. The orthogonal mixing can adapt to a wider local oscillator operating frequency; third, this method can improve the bandwidth utilization without considering the problem of the protection band between the upper and lower sidebands; fourth, this method integrates two mixers, orthogonal couplers and other devices into a cavity to achieve a higher degree of integration.

[0004] In addition, in the continuous wave Doppler radar based on the zero intermediate frequency system, it is necessary to determine the motion trajectory of the object by observing the relative phase relationship between the two intermediate frequency signals I and Q of the orthogonal mixer; in the FMCW radar leakage cancellation system, the transmission sampling signal and the leakage signal are used as the local oscillator signal and the radio frequency signal of the orthogonal mixer respectively, and the two intermediate frequency signals output need to be processed to provide the control signal for the vector modulator to realize the function of signal cancellation. Therefore, the traditional mixer cannot be used in the above system. Summary of the invention

[0005] In view of the technical problems of large I / Q conversion loss and large return loss in existing IQ mixers, the present invention proposes a terahertz IQ second harmonic mixer with small I / Q conversion loss and small return loss of RF, local oscillator and intermediate frequency ports.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the present invention is implemented as follows: a terahertz IQ second harmonic mixer comprises two terahertz subharmonic mixers, one input end of the two terahertz subharmonic mixers is respectively connected to the two output ends of the waveguide directional coupler, the waveguide directional coupler inputs the equal-amplitude radio frequency signals with a phase difference of 90° into the radio frequency ends of the two terahertz subharmonic mixers, the other input ends of the two terahertz subharmonic mixers are respectively connected to the two output ends of the local oscillator power distribution network, and the two equal-amplitude local oscillator signals with a phase difference of 180° output by the local oscillator power distribution network are respectively transmitted to the local oscillator ends of the two terahertz subharmonic mixers; a Schottky diode pair is provided between the radio frequency end and the local oscillator end of the two terahertz subharmonic mixers, an intermediate frequency low-pass filter is provided between the Schottky diode pair and the local oscillator end, and two intermediate frequency signals with a phase difference of 90° generated by the Schottky diode pair after mixing the input radio frequency signal and the local oscillator signal are output after passing through the intermediate frequency low-pass filter.

[0007] Preferably, a first air cavity is provided between the RF end and the local oscillator end of the two terahertz subharmonic mixers, a suspended microstrip line is provided in the first air cavity, a first matching circuit, a Schottky diode pair and a second matching circuit are provided in sequence on the suspended microstrip line from the RF end and the local oscillator end, a second air cavity is provided between the second matching circuit and the local oscillator end, and an intermediate frequency low-pass filter is provided on the suspended microstrip line in the second air cavity.

[0008] Preferably, one end of the suspended microstrip line of the first air cavity is connected to an output end of the waveguide directional coupler through a radio frequency probe transition structure, and the other end of the suspended microstrip line of the first air cavity is connected to an output end of a local oscillator power distribution network through a local oscillator probe transition structure.

[0009] Preferably, the two output ends of the waveguide directional coupler are connected to the RF probe transition structure through the RF reduction waveguide, and the two output ends of the local oscillator power distribution network are connected to the local oscillator probe transition structures of two terahertz subharmonic mixers through the local oscillator reduction waveguide.

[0010] Preferably, a local oscillator low-pass filter is provided between the second matching circuit and the intermediate frequency low-pass filter.

[0011] Preferably, the RF signal is input through a standard waveguide, and is transmitted to the Schottky diode pair through a waveguide directional coupler, a RF height reduction waveguide, a RF probe transition structure and a first matching circuit; the local oscillator signal is input through a standard waveguide, and is transmitted to the Schottky diode through a local oscillator power distribution network, a local oscillator height reduction waveguide, a local oscillator probe transition structure, a local oscillator low-pass filter and a second matching circuit. The Schottky diode pair mixes the input RF signal and the local oscillator signal, and the two intermediate frequency signals with a phase difference of 90° generated by the mixing pass through the second matching circuit, the local oscillator low-pass filter and the intermediate frequency low-pass filter, and are output through a 2.4mm connector.

[0012] Preferably, the waveguide directional coupler is a seven-branch waveguide coupler with a four-port network, the first port of the waveguide directional coupler is connected to the radio frequency signal, the second port of the waveguide directional coupler is a straight-through end, the third port of the waveguide directional coupler is a coupling end, and the radio frequency signals output by the second port and the third port have equal amplitudes and a phase difference of 90°; the fourth port of the waveguide directional coupler is an isolation end, an absorbing material is placed on the isolation end, and the isolation end adopts a curved waveguide design;

[0013] The local oscillator power distribution network adopts a T-junction waveguide power divider, the local oscillator signal is input from the input port, and after being equally divided, two equal-amplitude and anti-phase local oscillator signals are output from two ports;

[0014] Both the RF height reduction waveguide and the LO height reduction waveguide adopt a waveguide gradient structure;

[0015] The radio frequency probe transition structure and the local oscillator probe transition structure both adopt a waveguide-suspended microstrip probe transition structure, and the waveguide-suspended microstrip probe transition structure adopts an E-plane probe transition structure;

[0016] The first matching circuit and the second matching circuit both adopt high and low impedance line forms;

[0017] The local oscillator low-pass filter and the intermediate frequency low-pass filter both adopt CMRC filters.

[0018] Preferably, the Schottky diode pair is mounted on a metal pad of a suspended microstrip line by means of conductive adhesive, and a radio frequency grounding structure is provided on the first air cavity, the radio frequency grounding structure is a grounding gold mesh, and the grounding gold mesh is fixedly connected to the metal cavity by means of gold wire bonding.

[0019] Preferably, the metal cavity is divided into an upper cavity and a lower cavity along the center of the waveguide E surface, the upper cavity and the lower cavity are positioned by positioning pins, and the upper cavity and the lower cavity are fixedly connected; a circuit substrate is fixed in the circuit groove of the lower cavity by conductive glue.

[0020] Preferably, the circuit substrate comprises a first quartz substrate, a second quartz substrate and a Rogers 5880 substrate, the first quartz substrate and the second quartz substrate are connected by a gold wire bond; the microstrip line in the radio frequency probe transition structure, the first matching circuit, the Schottky diode pair, the second matching circuit, the local oscillator low-pass filter, and the microstrip line in the local oscillator probe transition structure are arranged on the first quartz substrate, and the Schottky diode pair is installed on the first quartz substrate in an anti-parallel manner through a conductive adhesive; the intermediate frequency low-pass filter is arranged on the second quartz substrate; the output end of the intermediate frequency low-pass filter is connected to one end of the Rogers 5880 substrate by a gold wire bond, and the other end of the Rogers 5880 substrate is fixedly connected to a 2.4mm connector joint, and the 2.4mm connector is fixed on the lower cavity.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention realizes good port isolation of radio frequency, local oscillator and intermediate frequency. Since the frequency of the local oscillator signal is lower than the cutoff frequency of the radio frequency waveguide port, the local oscillator signal will not leak from the radio frequency port; since the local oscillator low-pass filter can allow the local oscillator signal to pass through and suppress the radio frequency signal, the radio frequency signal will not leak at the local oscillator port, thereby realizing signal isolation between the radio frequency and the local oscillator port. The frequency of the intermediate frequency signal generated by the mixing is lower than the cutoff frequency of the radio frequency waveguide and the local oscillator waveguide port, so the intermediate frequency signal will not leak from the radio frequency and the local oscillator port, while the intermediate frequency low-pass filter can only allow the intermediate frequency signal to pass through, and the radio frequency and local oscillator signals will not leak at the intermediate frequency port, thereby realizing signal isolation between the radio frequency-intermediate frequency and the local oscillator-intermediate frequency ports.

[0023] The RF port of the present invention selects an orthogonal coupler, which is conducive to improving the isolation between the mixing units and effectively improving the echo of the RF port. In addition, the isolation port of the orthogonal coupler adopts the method of placing an absorbing material to achieve port isolation, rather than the traditional external matching load, which is conducive to the miniaturization of the overall structure of the mixer.

[0024] The terahertz IQ second harmonic mixer realized by the present invention has small I-channel / Q-channel frequency conversion loss, low amplitude imbalance and phase imbalance, and small intermediate frequency bandwidth, radio frequency, local oscillator and intermediate frequency port return loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the HFSS (High Frequency Structure Simulator) model structure of the terahertz IQ second harmonic mixer of the present invention.

[0027] Figure 2 It is a two-dimensional structural diagram of the lower shell of the terahertz IQ second harmonic mixer of the present invention.

[0028] Figure 3 This is an exploded diagram of the terahertz IQ second harmonic mixer of the present invention.

[0029] Figure 4 This is a design principle diagram of the terahertz IQ second harmonic mixer of the present invention.

[0030] Among them, 1 is a waveguide directional coupler, 2 is an RF height reduction waveguide, 3 is an RF probe transition structure, 4 is an RF grounding structure, 5 is a first matching circuit, 6 is a Schottky diode pair, 7 is a second matching circuit, 8 is a local oscillator low-pass filter, 9 is an intermediate frequency low-pass filter, 10 is a local oscillator probe transition structure, 11 is a first quartz substrate, 12 is a second quartz substrate, 13 is a local oscillator height reduction waveguide, 14 is a local oscillator power distribution network, 15 is an absorbing material, 16 is a Rogers 5880 substrate circuit, 17 is a 2.4mm connector, 18 is an upper cavity, 19 is a lower cavity, 20 is a positioning pin, and 21 is a screw. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A terahertz IQ second harmonic mixer includes two terahertz subharmonic mixers, one input end of the two terahertz subharmonic mixers is respectively connected to the two output ends of a waveguide directional coupler 1, the waveguide directional coupler 1 respectively inputs equal-amplitude radio frequency signals with a phase difference of 90° into the radio frequency ends of the two terahertz subharmonic mixers, the other input ends of the two terahertz subharmonic mixers are respectively connected to the two output ends of a local oscillator power distribution network 14, and the two equal-amplitude local oscillator signals with a phase difference of 180° output by the local oscillator power distribution network 14 are respectively transmitted to the local oscillator ends of the two terahertz subharmonic mixers. A Schottky diode pair 6 is provided between the radio frequency ends and the local oscillator ends of the two terahertz subharmonic mixers, an intermediate frequency low-pass filter 9 is provided between the Schottky diode pair 6 and the local oscillator end, and two intermediate frequency signals with a phase difference of 90° generated by the Schottky diode pair 6 after mixing the input radio frequency signal and the local oscillator signal are output after passing through the intermediate frequency low-pass filter 9.

[0034] Example 2

[0035] A terahertz IQ second harmonic mixer, wherein a first air cavity is provided between the radio frequency end and the local oscillator end of two terahertz subharmonic mixers, a suspended microstrip line is provided in the first air cavity, a first matching circuit 5, a Schottky diode pair 6, and a second matching circuit 7 are provided on the suspended microstrip lines from the radio frequency end and the local oscillator end in sequence, a second air cavity is provided between the second matching circuit 7 and the local oscillator end, and an intermediate frequency low-pass filter 9 is provided on the suspended microstrip line in the second air cavity. A local oscillator low-pass filter is provided between the second matching circuit and the intermediate frequency low-pass filter, and a second air cavity is provided between the local oscillator low-pass filter 8 and the local oscillator end.

[0036] One end of the suspended microstrip line of the first air cavity is connected to an output end of the waveguide directional coupler 1 through the RF probe transition structure 3, and the other end of the suspended microstrip line of the first air cavity is connected to an output end of the local oscillator power distribution network 14 through the local oscillator probe transition structure 10.

[0037] The two output ends of the waveguide directional coupler 1 are connected to the RF probe transition structure 3 through the RF reduction waveguide 2, and the two output ends of the local oscillator power distribution network 14 are connected to the local oscillator probe transition structures 10 of two terahertz subharmonic mixers through the local oscillator reduction waveguide 13.

[0038] The RF signal (210-230 GHz) is input through the WR-4.3 standard waveguide, and is transmitted to the Schottky diode pair 6 through the 220 GHz waveguide directional coupler 1, the RF height reduction waveguide 2, the RF probe transition structure 3 and the first matching circuit 5. The local oscillator signal (105-115 GHz) is input through the WR-8 standard waveguide, and is transmitted to the Schottky diode pair 6 through the local oscillator power distribution network 14, the local oscillator height reduction waveguide 13, the local oscillator probe transition structure 10, the local oscillator low-pass filter 8 and the second matching circuit 7. The Schottky diode pair 6 performs mixing processing on the input RF signal and the local oscillator signal, and the two intermediate frequency signals (DC-20 GHz) with a phase difference of 90° generated by the mixing are output through the 2.4 mm connector 17 after passing through the second matching circuit 7, the local oscillator low-pass filter 8, and the intermediate frequency low-pass filter 9.

[0039] The waveguide directional coupler 1 is a four-port network, which is implemented by a seven-branch waveguide coupler. Port 1 is the RF signal input port, port 2 is the through port, port 3 is the coupling port, and port 4 is the isolation port. The RF signal is input from port 1 and output from port 2 and port 3. The two output signals have equal amplitudes and a phase difference of 90°. The absorbing material 15 is placed at the isolation port to absorb the combined reflection of the two mixers, reduce the standing wave ratio of the RF input port, and is conducive to the miniaturization of the overall structure of the mixer. In addition, in order to prevent the signal at the isolation end from being reflected back to the main circuit, affecting the unevenness of the IQ amplitudes, and achieving the effect of impedance matching, the isolation end adopts a curved waveguide design.

[0040] The local oscillator power distribution network 14 is implemented by a T-junction waveguide power divider. The local oscillator signal is input from port 1 and is output from port 2 and port 3 after being equally divided. The two output signals have equal amplitude and opposite phases.

[0041] The function of the RF height reduction waveguide 2 is to reduce discontinuity, adopt a waveguide gradient structure, and expand the bandwidth. The function of the local oscillator height reduction waveguide 13 is the same, but the frequency is different.

[0042] The function of the RF probe transition structure 3 is to transmit the RF signal to the suspended microstrip line with low loss, so that it can be well fed into the Schottky diode pair 6 to achieve the function of mixing. The function of the local oscillator probe transition structure 10 is to transmit the local oscillator signal to the suspended microstrip line with low loss, so that it can be well fed into the Schottky diode pair to achieve the function of mixing. The RF probe transition structure 3 and the local oscillator probe transition structure 10 in the present invention both adopt a waveguide-suspended microstrip probe transition structure. In the terahertz frequency band, the relatively mature transition structures currently used mainly include a waveguide-suspended microstrip probe transition structure, a waveguide-microstrip fin line transition structure, and a waveguide-microstrip ridge waveguide transition structure. Due to the thin substrate and narrow conductor width, the waveguide-microstrip ridge waveguide transition structure has high processing precision requirements, complex process, high implementation difficulty, and poor reliability; the waveguide-microstrip fin line transition structure is close to the edge of the medium, and the fin line structure is easily damaged during processing, and the yield rate is low; the waveguide-suspended microstrip probe transition structure has the advantages of low loss, wide bandwidth, simple structure and easy processing and assembly. The present invention finally selects the waveguide-suspended microstrip probe transition structure. The waveguide-suspended microstrip probe transition structure generally has two transition forms, E-plane probe transition and H-plane probe transition. The H-plane probe opens a hole in the direction parallel to the magnetic field component of the waveguide's conductive magnetic field, and passes the dielectric substrate through the waveguide parallel to the magnetic field direction, that is, perpendicular to the narrow side; the E-plane probe opens a hole in the direction parallel to the conductive magnetic field component of the waveguide, and the direction of the dielectric substrate is parallel to the direction of the electric field component in the rectangular waveguide, that is, perpendicular to the wide side; both transition forms are theoretically feasible. If the H-plane transition is used, the suspended microstrip line will inevitably form cut electric field lines when the upper and lower cavities are divided, and the electric field direction cannot form a loop, which will lead to increased losses. The narrow side of the waveguide is relatively small, which is not conducive to design and assembly, so the E-plane probe transition structure is adopted.

[0043] The first matching circuit 5 and the second matching circuit 7 are both in the form of high and low impedance lines on both sides of the Schottky diode pair 6, and their function is to achieve good impedance matching, reduce signal reflection, and ensure low-loss transmission.

[0044] The Schottky diode pair 6 is mounted upside down on the metal pad of the suspended microstrip line through conductive glue. In order to eliminate the influence of the DC bias generated by the inconsistency of the Schottky diode pair 6 on the mixing circuit, a grounding gold mesh connected to the metal cavity is led out from the microstrip circuit, that is, the RF grounding structure 4, and the gold mesh is welded to the metal cavity by gold wire bonding.

[0045] In order to achieve better isolation between ports, the present invention adds a low-pass filter between the radio frequency and the local oscillator and between the local oscillator and the intermediate frequency. The local oscillator low-pass filter 8 is located between the local oscillator probe transition structure 10 and the Schottky diode pair 6, and plays the role of "isolating the radio frequency and passing the local oscillator and the intermediate frequency", allowing the local oscillator signal to be well transmitted, preventing the radio frequency signal from leaking, and allowing it to be well reflected back to the Schottky diode pair 6 to participate in the mixing, thereby improving the isolation from the radio frequency to the local oscillator port, and the intermediate frequency generated by the mixing can also pass through this filter well. The intermediate frequency low-pass filter 9 is located between the local oscillator probe transition structure 10 and the local oscillator low-pass filter 8, and plays the role of "isolating the local oscillator and passing the intermediate frequency". The filter can prevent the leakage of the local oscillator and radio frequency signals, and allow the intermediate frequency signal generated by the mixing to pass through the filter smoothly and then be output through the 2.4mm connector 17.

[0046] In the present invention, a quartz substrate is selected as the dielectric substrate of the mixer to provide a medium for signal transmission and support the circuit. The selection of the dielectric substrate needs to take into account the cost, manufacturing difficulty, dielectric loss and smoothness. RT / duroid@5880 has large dielectric loss and low processing accuracy in the terahertz frequency band, and is not suitable for the design of terahertz mixers; ceramics and sapphire are complex to manufacture and costly, and do not meet the cost requirements of the mixer; quartz substrates have small high-frequency dielectric loss, high processing accuracy, and a moderate price. The present invention finally selects a quartz substrate with a dielectric constant of 3.78 and a thickness of 50μm and 127μm as the dielectric substrate of the mixer.

[0047] The quartz substrate is fixed by conductive glue and suspended in the air cavity to form a suspended microstrip line structure. The suspended microstrip line has a high Q value, low transmission loss, low dispersion, flexible circuit design, low cost, and is easy to assemble the diode. The shielded cavity design can ensure single-mode transmission within a wider bandwidth, with good high-order mode suppression, and low loss when the waveguide is coupled to the suspended microstrip. It is a more common transmission line form in terahertz circuit design.

[0048] The local oscillator low-pass filter 8 and the intermediate frequency low-pass filter 9 in the present invention are both implemented by CMRC filters. In the terahertz frequency band, there are two main structures of common low-pass filters, namely, compact microstrip resonant unit (CMRC) filter and high-low impedance filter. The high-low impedance filter is composed of high-impedance microstrip lines and low-impedance microstrip lines alternately, and has the advantage of simple structure, but the designed low-pass filter is easy to cause the dielectric substrate to have too large physical length, and considering that the quartz substrate used in the mixer design has the characteristics of being fragile, the excessive physical substrate size will cause its physical structure to be unstable, thereby increasing the difficulty of processing and assembly. Compared with the high-low impedance filter, the CMRC filter is more compact in structure, smaller in size, saves area, helps to reduce the length of the entire dielectric substrate, is convenient for processing, and the CMRC filter can also achieve a higher rectangular coefficient, better flatness and wider stopband. Compared with the high-low impedance filter, when achieving the same filtering performance, the size of the CMRC filter is much smaller than the former.

[0049] like Figure 3 As shown, the metal cavity of the terahertz IQ second harmonic mixer of the present invention is processed according to computer numerical control technology, and the cavity is divided into an upper cavity 18 and a lower cavity 19 along the center of the waveguide E surface. The principle is not to cut off the power line. The upper cavity 18 and the lower cavity 19 are positioned by positioning pins 20 and fixed with screws 21. At the same time, the standard waveguide ports of the radio frequency and the local oscillator (the ports of the WR-4.3 standard waveguide and the WR-8 standard waveguide) are also fixed with screws 21 to reduce the waveguide radiation loss. The entire cavity material is brass. After the processing is completed, the surface is gold-plated to prevent oxidation. After the circuit substrate (the first quartz substrate 11, the second quartz substrate 12 and the Rogers 5880 substrate 16) are manufactured, they are fixed in the circuit slot of the lower cavity 19 of the mixer by conductive glue.

[0050] The microstrip line in the RF probe transition structure 3, the first matching circuit 5, the Schottky diode pair 6, the second matching circuit 7, the local oscillator low-pass filter 8, and the microstrip line in the local oscillator probe transition structure 10 are located on a first quartz substrate 11 with a thickness of 0.05 mm, wherein the Schottky diode pair 6 is mounted on the first quartz substrate 11 in an anti-parallel manner through a conductive adhesive. The intermediate frequency low-pass filter 9 is located on a second quartz substrate 12 with a thickness of 0.127 mm. The first quartz substrate 11 is connected to the second quartz substrate by a gold wire bond, and the output end of the intermediate frequency low-pass filter 8 is connected to a 50 ohm transmission line on a Rogers 5880 substrate 16 (thickness 0.127 mm) by a gold wire bond, as shown in FIG. Figure 2 As shown, the 2.4 mm connector 17 is welded to the other end of the Rogers 5880 substrate 16 to output the intermediate frequency signal, and is fixed to the lower cavity 19 by screws 21 to achieve connection with external devices.

[0051] Example 3

[0052] A terahertz IQ second harmonic mixer, wherein a radio frequency (RF) signal is coupled into two signals with a phase difference of 90° by a waveguide directional coupler 1, and then enters two terahertz subharmonic mixers respectively; a local oscillator (LO) signal is divided into two equal-amplitude signals with a phase difference of 180° by a local oscillator power distribution network, and then enters two terahertz subharmonic mixers respectively. The core of the terahertz IQ second harmonic mixer is a Schottky diode pair 6. If the parameters of the two reverse-parallel Schottky diodes are exactly the same, theoretically, only the combined frequency components related to the even harmonics of the local oscillator signal and the radio frequency signal are generated, and other combined frequency components will be suppressed and reused, thereby improving the mixing efficiency. The Schottky diode pair mixes the input radio frequency signal and the local oscillator signal, and the mixing generates two intermediate frequency (IF) signals (I channel / Q channel) with a phase difference of 90°, which are output through the corresponding intermediate frequency low-pass filter. Figure 4 As shown, the specific signal processing process is:

[0053] Using the small signal analysis approximation, the input RF signal is expressed as

[0054] v RF (t) = V 1 cosω RF t

[0055] Among them, V 1 Represents the amplitude of the RF signal, ω RF represents the frequency of the RF signal, and t represents the time.

[0056] According to the S matrix of waveguide directional coupler

[0057]

[0058] Here, j represents the imaginary part.

[0059] Two RF signals with a phase difference of 90° can be obtained:

[0060]

[0061] The input local oscillator signal is expressed as

[0062] v LO (t) = V 2 cosω LO t

[0063] Among them, V 2Represents the amplitude of the local oscillator signal, ω LO Indicates the frequency of the local oscillator signal.

[0064] The local oscillator signals with a phase difference of 180° obtained through the local oscillator power distribution network are:

[0065]

[0066] After mixing and intermediate frequency low-pass filter 9, the intermediate frequency signals output from the I port and Q port are respectively

[0067]

[0068]

[0069] Where K is a constant coefficient.

[0070] From the intermediate frequency signal v IFI (t) and v IFQ (t) It can be seen that the amplitudes of the two intermediate frequency signal outputs are equal, but there is a 90° phase difference.

[0071] The other structures are the same as those in Example 2.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A terahertz IQ second harmonic mixer, characterized in that: The invention comprises two terahertz subharmonic mixers, one input end of the two terahertz subharmonic mixers is respectively connected to the two output ends of a waveguide directional coupler (1), the waveguide directional coupler (1) inputs equal-amplitude radio frequency signals with a phase difference of 90° into the radio frequency ends of the two terahertz subharmonic mixers, the other input ends of the two terahertz subharmonic mixers are respectively connected to the two output ends of a local oscillator power distribution network (14), and two equal-amplitude local oscillator signals with a phase difference of 180° output by the local oscillator power distribution network (14) are respectively transmitted to the local oscillator ends of the two terahertz subharmonic mixers; a Schottky diode pair (6) is provided between the radio frequency ends and the local oscillator ends of the two terahertz subharmonic mixers, an intermediate frequency low-pass filter (9) is provided between the Schottky diode pair (6) and the local oscillator end, and two intermediate frequency signals with a phase difference of 90° generated by mixing the input radio frequency signal and the local oscillator signal by the Schottky diode pair (6) are output after passing through the intermediate frequency low-pass filter (9).

2. The terahertz IQ second harmonic mixer according to claim 1, characterized in that: A first air cavity is provided between the radio frequency end and the local oscillator end of the two terahertz subharmonic mixers, a suspended microstrip line is provided in the first air cavity, a first matching circuit (5), a Schottky diode pair (6) and a second matching circuit (7) are provided in sequence on the suspended microstrip lines from the radio frequency end and the local oscillator end, a second air cavity is provided between the second matching circuit (7) and the local oscillator end, and an intermediate frequency low-pass filter (9) is provided on the suspended microstrip line in the second air cavity.

3. The terahertz IQ second harmonic mixer according to claim 2, characterized in that: One end of the suspended microstrip line of the first air cavity is connected to an output end of the waveguide directional coupler (1) via a radio frequency probe transition structure (3), and the other end of the suspended microstrip line of the first air cavity is connected to an output end of a local oscillator power distribution network (14) via a local oscillator probe transition structure (10).

4. The terahertz IQ second harmonic mixer according to claim 3, characterized in that: The two output ends of the waveguide directional coupler (1) are respectively connected to the radio frequency probe transition structure (3) via the radio frequency reduction waveguide (2), and the two output ends of the local oscillator power distribution network (14) are respectively connected to the local oscillator probe transition structures (10) of two terahertz subharmonic mixers via the local oscillator reduction waveguide (13).

5. The terahertz IQ second harmonic mixer according to any one of claims 2 to 4, characterized in that: A local oscillator low-pass filter (8) is provided between the second matching circuit (7) and the intermediate frequency low-pass filter (9).

6. The terahertz IQ second harmonic mixer according to claim 5, characterized in that: The radio frequency signal is input through a standard waveguide, and is transmitted to the Schottky diode pair (6) through a waveguide directional coupler (1), a radio frequency height reduction waveguide (2), a radio frequency probe transition structure (3) and a first matching circuit (5); the local oscillator signal is input through a standard waveguide, and is transmitted to the Schottky diode pair (6) through a local oscillator power distribution network (14), a local oscillator height reduction waveguide (13), a local oscillator probe transition structure (10), a local oscillator low-pass filter (8) and a second matching circuit (7); the Schottky diode pair (6) performs mixing processing on the input radio frequency signal and the local oscillator signal; two intermediate frequency signals with a phase difference of 90° generated by the mixing are output through a 2.4 mm connector (17) after passing through a second matching circuit (7), a local oscillator low-pass filter (8) and an intermediate frequency low-pass filter (9).

7. The terahertz IQ second harmonic mixer according to claim 6, characterized in that: The waveguide directional coupler (1) is a seven-branch waveguide coupler with a four-port network, the first port of the waveguide directional coupler (1) is connected to a radio frequency signal, the second port of the waveguide directional coupler (1) is a through port, the third port of the waveguide directional coupler (1) is a coupling port, the radio frequency signals output from the second port and the third port have equal amplitudes and a phase difference of 90°; the fourth port of the waveguide directional coupler (1) is an isolation port, an absorbing material (15) is placed on the isolation port, and the isolation port adopts a curved waveguide design; The local oscillator power distribution network (14) adopts a T-junction waveguide power divider, wherein a local oscillator signal is input from an input port and is equally divided and then outputs two local oscillator signals of equal amplitude and opposite phase from two ports; The radio frequency height reduction waveguide (2) and the local oscillator height reduction waveguide (13) both adopt a waveguide gradient structure; The radio frequency probe transition structure (3) and the local oscillator probe transition structure (10) both adopt a waveguide-suspended microstrip probe transition structure, and the waveguide-suspended microstrip probe transition structure adopts an E-plane probe transition structure; The first matching circuit (5) and the second matching circuit (7) both adopt a high-low impedance line form; The local oscillator low-pass filter (8) and the intermediate frequency low-pass filter (9) both adopt CMRC filters.

8. The terahertz IQ second harmonic mixer according to any one of claims 2-4, 6 and 7, characterized in that: The Schottky diode pair (6) is mounted on a metal pad of a suspended microstrip line by means of conductive adhesive, and a radio frequency grounding structure (4) is provided on the first air cavity, the radio frequency grounding structure (4) being a grounding gold mesh, and the grounding gold mesh is fixedly connected to the metal cavity by means of gold wire bonding.

9. The terahertz IQ second harmonic mixer according to claim 8, characterized in that: The metal cavity is divided into an upper cavity (18) and a lower cavity (19) along the center of the waveguide E surface; the upper cavity (18) and the lower cavity (19) are positioned by means of positioning pins (20); the upper cavity (18) and the lower cavity (19) are fixedly connected; and a circuit substrate is fixed in the circuit groove of the lower cavity (19) by means of conductive adhesive.

10. The terahertz IQ second harmonic mixer according to claim 9, characterized in that: The circuit substrate comprises a first quartz substrate (11), a second quartz substrate (12) and a Rogers 5880 substrate (16); the first quartz substrate (11) and the second quartz substrate (12) are connected by means of gold wire bonding; the microstrip line in the radio frequency probe transition structure (3), the first matching circuit (5), the Schottky diode pair (6), the second matching circuit (7), the local oscillator low-pass filter (8), and the microstrip line in the local oscillator probe transition structure (10) are arranged on the first quartz substrate (11); the Schottky diode pair (6) is mounted on the first quartz substrate (11) in an anti-parallel manner through conductive adhesive; the intermediate frequency low-pass filter (9) is arranged on the second quartz substrate (12); the output end of the intermediate frequency low-pass filter (9) is connected to one end of the Rogers 5880 substrate (16) by means of gold wire bonding; The other end of the 5880 substrate (16) is fixedly connected to a 2.4 mm connector (17), and the 2.4 mm connector (17) is fixed on the lower cavity (19).

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