CN104660171B - A kind of sub-harmonic mixer of modified based on coplanar waveguide transmission line - Google Patents

Abstract

The invention discloses an improved subharmonic mixer based on coplanar waveguide transmission lines. The inner bottom surface of the main air cavity is provided with a dielectric substrate, and the dielectric substrate is provided with coupling probes, coplanar waveguide transmission lines, and local oscillator matching lines. , Microstrip line structure, the coplanar waveguide transmission line includes a matching line connected in sequence from left to right, the first transverse transmission line, and a local oscillator low-pass filter matching line, and the microstrip line structure includes a second transverse transmission line connected in sequence from left to right , a third transverse transmission line, a fourth transverse transmission line, and an intermediate frequency low-pass filter matching line; the coplanar waveguide transmission line also includes two grounding lines located on both sides of the matching line, and both grounding lines are connected to the inner wall of the main air cavity; It includes planar Schottky anti-parallel frequency mixing diodes, wherein the ohmic contact layer of one mixing diode is connected to the front surface away from the dielectric substrate from the matching line, and the ohmic contact layer of the other frequency mixing diode is connected to the front surface far away from the dielectric substrate from the grounding line.

Description

An Improved Subharmonic Mixer Based on Coplanar Waveguide Transmission Line

technical field

The invention relates to the technical field of terahertz, and specifically refers to an improved subharmonic mixer based on a coplanar waveguide transmission line.

Background technique

In almost all terahertz technology application systems, the terahertz receiving front-end is the core technology in the system, which completes the frequency conversion of terahertz signals. The terahertz subharmonic mixer is a key component of the terahertz receiving front end. At present, among the few types of mixers that can work in the terahertz frequency band, only terahertz subharmonic mixers based on planar Schottky diodes can work at room temperature, so subharmonic mixers are used as frequency Conversion devices play an important role in the field of terahertz applications. In the prior art, the subharmonic mixer realizes the grounding of RF and DC through the microstrip line and the upper cavity at the RF transition end, which not only increases the difficulty of assembly and reduces the accuracy of the circuit, but also the intermediate frequency and local oscillator signals only A virtual ground can be achieved. Therefore, an improved subharmonic mixer based on coplanar waveguide transmission lines can effectively solve the above problems.

Terahertz (THz) science and technology is an emerging interdisciplinary subject and research hotspot that has developed rapidly in the past two decades, involving electromagnetics, optoelectronics, optics, semiconductor physics, materials science, biology, medicine and other sciences. The terahertz frequency band covers the 0.1THz~10THz frequency range of the electromagnetic spectrum, and is a wide-band electromagnetic radiation area with rich physical connotations. It is an important member of the electromagnetic spectrum family, between infrared light waves and microwaves, long-wave bands coincide with millimeter waves and submillimeter waves, and short-wave bands coincide with infrared rays. The two disciplines are connected and compatible with each other, and they are a comprehensive branch of disciplines that developed rapidly at the end of the last century and the beginning of this century.

THz waves can be widely used in many fields, mainly including: radar detection, remote sensing and atmospheric and environmental monitoring, security monitoring and anti-terrorism, high-speed real-time high-security data communication and transmission, biotechnology and medical diagnosis, etc. Terahertz science and technology has become a very active frontier subject that has an important impact on modern science and technology, national economy, national defense and military affairs, and provides a very attractive opportunity for technological innovation, national economic development and national security. At present, governments, social organizations, enterprises, universities and research institutions in the United States, Europe, Asia, Australia and other countries and regions have invested considerable manpower, material and financial resources in the basic theoretical research and engineering application technology development of terahertz science and technology. .

In recent years, terahertz technology, as an important research field, has received more and more attention at home and abroad. No matter which aspect and which frequency band the terahertz wave is applied to, it is inseparable from the reception of the terahertz wave. For the most commonly used receivers based on the superheterodyne system, the mixer for frequency down-conversion is one of them. a key component. In systems such as solid-state terahertz radar and communication, due to the lack of low-noise amplifiers, the mixer becomes the first stage of the receiving end, and its specifications directly affect the performance of the overall system. Since it is difficult to realize high-performance local oscillators in the same frequency band, the use of sub-harmonic mixing technology is an effective way to solve this problem. Among the few types of mixers that can work in the terahertz frequency band, only terahertz subharmonic mixers based on planar Schottky diodes can work at room temperature without providing such as liquid helium to achieve harsh low temperatures environment.

At present, the terahertz subharmonic mixer based on GaAs Schottky diode in planar package mainly adopts the mainstream circuit structure of suspended microstrip, and the passive circuit consists of RF port transition, local oscillator low-pass filter, local oscillator IF duplex The device (including local oscillator port transition and intermediate frequency low-pass filter) consists of two parts. At the radio frequency transition end, the grounding of radio frequency and DC is realized through full contact between the microstrip line and the upper cavity. The RF and LO signals are respectively fed from their respective ports, passed through the suspension microstrip and loaded onto the mixing diode after passing through the corresponding matching network. Since the frequency of the LO signal is lower than the waveguide cut-off frequency of the RF port, the LO signal does not It will leak from the RF port, and the RF signal will not leak from the local oscillator port due to the existence of the local oscillator low-pass filter (passing the local oscillator frequency, blocking the RF frequency), so as to achieve isolation between the two ports; frequency mixing The generated intermediate frequency signal is output from the local oscillator through a microstrip low-pass filter.

In the existing technology, the subharmonic mixer realizes the grounding of RF and DC through the microstrip line and the upper cavity at the RF transition end, which not only increases the difficulty of assembly and reduces the accuracy of the circuit, but also the intermediate frequency and local oscillator signals only A virtual ground can be achieved.

Contents of the invention

The purpose of the present invention is to provide an improved subharmonic mixer based on a coplanar waveguide transmission line. The present invention adopts a coplanar waveguide transmission line, and the diode is directly placed on one side of the cavity wall, thereby realizing signal grounding, and the circuit structure is simple Easy to assemble.

The implementation scheme of the present invention is as follows: an improved subharmonic mixer based on a coplanar waveguide transmission line, including a main air cavity, the inner bottom surface of the main air cavity is provided with a dielectric substrate, and the dielectric substrate is provided with a coupling probe, Coplanar waveguide transmission line, local oscillator matching line, microstrip line structure, coplanar waveguide transmission line includes matching line connected in sequence from left to right, the first transverse transmission line, local oscillator low-pass filter matching line, the right end of the coupling probe and the matching The left end of the line is connected, the right end of the local oscillator low-pass filter matching line is connected to the left end of the local oscillator matching line, and the microstrip line structure includes the second horizontal transmission line, the third horizontal transmission line, the fourth horizontal transmission line, An intermediate frequency low-pass filter matching line, the left end of the second horizontal transmission line is connected to the right end of the local oscillator matching line; it also includes two first vertical transmission lines, one first vertical transmission line is connected between the first horizontal transmission line and the matching line, and the other The first longitudinal transmission line is connected between the first transverse transmission line and the local oscillator low-pass filter matching line, and the two sides of the first transverse transmission line are respectively provided with first branch transverse transmission lines. The horizontal transmission lines are arranged symmetrically to the left and right axes, and the two first branch horizontal transmission lines are connected to the first horizontal transmission line through the first branch longitudinal transmission line, and the left and right ends of the two first branch horizontal transmission lines are bent and point to the first branch. A horizontal transmission line, the length direction of the first horizontal transmission line is perpendicular to the length direction of the first longitudinal transmission line; it also includes 2 "I"-shaped transmission lines, and the "I"-shaped transmission line includes 2 parallel horizontal branch transmission lines and connecting The longitudinal branch transmission line between the two transverse branch transmission lines is composed of one "I"-shaped transmission line, the longitudinal branch transmission line is connected between the second transverse transmission line and the third transverse transmission line, and the other "I"-shaped The longitudinal branch transmission line of the transmission line is connected between the third horizontal transmission line and the fourth horizontal transmission line; the coplanar waveguide transmission line also includes two grounding lines located on both sides of the matching line, and the two grounding lines are connected to the inner wall of the main air cavity ; Also includes planar Schottky anti-parallel mixing diodes, the planar Schottky anti-parallel mixing diodes are a combined structure of 2 parallel mixing diodes, the fronts of the 2 mixing diodes are ohmic contact layers, one of which The ohmic contact layer of the mixing diode is connected to the front side of the matching line away from the dielectric substrate, and the ohmic contact layer of the other mixing diode is connected to the front side of the grounding line away from the dielectric substrate; it also includes a radio frequency input transition waveguide cross-connected with the main air cavity and The local oscillator port transition waveguide cross-connected with the main air cavity, the overlapping area of the radio frequency input transition waveguide and the main air cavity is area M, the coupling probe extends through the radio frequency input transition waveguide to extend into area M, the local oscillator port transition waveguide and The overlapping area of the main air cavity is area N, and the local oscillator port matching line is located in area N; the first transverse transmission line and the first longitudinal transmission line, the first branch longitudinal transmission line, and the first branch transverse transmission line form a local oscillator low-pass filter , the third horizontal transmission line and the "I"-shaped transmission line, the fourth horizontal transmission line, and the second horizontal transmission line constitute an intermediate frequency low-pass filter.

The working principle of the above structure is: the transitional waveguide at the local oscillator port and the intermediate frequency low-pass filter constitute a local oscillator intermediate frequency duplexer, the transitional waveguide at the local oscillator port is the standard waveguide WR-4, and the transitional waveguide at the local oscillator port is used as the input terminal of the local oscillator The local oscillator signal, the RF input transition waveguide is the standard waveguide WR-2.2, and the RF input transition waveguide is used as the RF input terminal to input the RF signal. When the local oscillator signal and the RF signal pass through the planar Schottky antiparallel mixing diode, it will generate rich Harmonic signals, intermediate frequency signals are output after filtering through local oscillator low-pass filters and intermediate frequency low-pass filters; RF signals and local oscillator signals are respectively fed from their respective ports, transitioned to coplanar waveguide transmission lines and loaded after corresponding matching networks To the planar Schottky anti-parallel mixing diode, since the local oscillator signal frequency is lower than the RF port waveguide cut-off frequency, the local oscillator signal will not leak from the RF port, and the RF signal is due to the local oscillator low-pass filter (pass LO frequency, blocking RF frequency) without leakage from the LO port, thereby achieving isolation between these two ports; the RF signal and the LO signal are recycled at the planar Schottky antiparallel mixer diode for use The energy of the required intermediate frequency signal is large enough, and the intermediate frequency signal generated by the mixing is output from the local oscillator through an intermediate frequency low-pass filter. The matching circuit is used to match the impedance of the mixing diode to make the signal better transmitted. Among them, the planar Schottky anti-parallel frequency mixing diode is pasted with conductive glue after high temperature baking in the form of reverse buckle.

The transition process of the RF signal from the RF input transition waveguide to the coplanar waveguide transmission line is as follows: use the coupling probe to penetrate the side wall of the RF input transition waveguide into the inside of the RF input transition waveguide, and through the coupling effect of the coupling probe, the RF input The signal energy in the transition waveguide is coupled to the coplanar waveguide transmission line, and the dimensions are optimized to avoid the occurrence of high-order modes and transmission zeros.

The local oscillator low-pass filter adopts a compact resonant unit structure as described above. The compact resonant unit is a special circuit structure with a specific pattern formed in a standard 50 ohm transmission line by photolithography and etching technology. Since a part of the metal is etched away on the normal 50 ohm transmission line, the formed narrow transmission line connected up and down will increase its equivalent series inductance. On the contrary, the two etched gaps increase its equivalent parallel capacitance. The above structure can be equivalent to an RLC resonant circuit, which exhibits a band-stop characteristic. By adjusting the length of the compact resonant unit structure and the structure of the corrosion pattern, the band-stop effect in different frequency bands can be obtained. The role of the local oscillator low-pass filter is to make the local oscillator signal reach the diode pair with a small loss to drive the mixer tube, and suppress the radio frequency signal, prevent the radio frequency signal from leaking from the local oscillator port, improve the port isolation, and at the same time prevent the radio frequency from leaking. The signal is lost due to leakage and energy can be concentrated on the diode pair for mixing.

The setting principle of the planar Schottky antiparallel mixing diode is as follows: in the microwave and millimeter wave bands, since the package size of the planar Schottky antiparallel mixing diode is much smaller than the wavelength, its package will hardly affect the field distribution, so The SPICE parametric linear equivalent circuit model extracted by planar Schottky antiparallel mixing diodes at different operating frequencies can be considered accurate. However, as the frequency rises to the terahertz frequency band, the size of the shielding cavity decreases sharply due to the sharp increase in frequency, and the limitation of the manufacturing process of the planar Schottky antiparallel mixing diode makes the planar Schottky antiparallel mixing Diode package size reductions are limited, well below the increase in operating frequency. Therefore, the equivalent model of the traditional planar Schottky antiparallel mixing diode in ADS has defects in the terahertz frequency band, and it is necessary to re-establish the equivalent model. In the present invention, the planar Schottky anti-parallel frequency mixing diode is arranged in the way of sticking upside down, that is to say, sticking with conductive glue after high temperature baking in the form of turning upside down.

The intermediate frequency low-pass filter adopts the "I" shape structure. It is very simple to design the I-shaped filter. The upper and lower wide transmission lines of "I" are equivalent to capacitors, and the thin transmission lines in the middle are equivalent to inductors, and the capacitors and inductors are connected to the ground in parallel. Adjusting the size of the capacitor and inductor creates a transmission zero outside the band of the filter. The function of the intermediate frequency low-pass filter is to extract the intermediate frequency signal generated by the mixing from the circuit, and to suppress the signal of useless frequency, mainly to suppress the local oscillator signal with strong energy, so as to prevent it from outputting from the intermediate frequency port to cause local oscillation. The loss of signal energy and the impurity of the IF output spectrum. The IF filter needs to reduce the insertion loss in the passband as much as possible, so that the IF signal can be output with less loss, and improve the suppression of unwanted frequencies, especially the suppression of the local oscillator frequency.

The transitional waveguide at the local oscillator port and the intermediate frequency low-pass filter constitute a local oscillator intermediate frequency duplexer. The local oscillator signal is input from the standard waveguide WR-4 through the coplanar waveguide transmission line and enters the mixing diode to mix with the RF signal. The intermediate frequency signal generated is passed through Local oscillator low-pass filter, because the cut-off frequency of the input waveguide of the local oscillator is much higher than the frequency of the intermediate frequency, it is impossible for the intermediate frequency signal to enter the waveguide of the local oscillator. Output from the IF port.

The specific structure of the mixing diode is as follows: the mixing diode includes a buffer layer, an ohmic contact layer and an epitaxial layer are arranged on the buffer layer, a silicon dioxide layer is arranged on the epitaxial layer, a metal anode bridge is connected to the ohmic contact layer, two mixing The metal anode bridge of one mixing diode in the diode penetrates the silicon dioxide layer of the other mixing diode, and the buffer layers of the two mixing diodes are installed on the substrate layer at the same time.

The ohmic contact layer is baked with conductive glue at a high temperature to paste the grounding wire and the matching wire.

The side of all structures included in the coplanar waveguide transmission line away from the dielectric substrate is flush with the upper surface of the dielectric substrate.

Coupling probe, matching line, grounding line, first transverse transmission line, local oscillator low-pass filter matching line, local oscillator matching line, second transverse transmission line, third transverse transmission line, fourth transverse transmission line, intermediate frequency low-pass filter matching line, The first longitudinal transmission lines are all rectangular transmission lines.

The main air cavity is a rectangular tube.

The transitional waveguide at the local oscillator port is a variable-diameter waveguide.

The RF input transition waveguide is a rectangular tube.

The long side of the ground wire is parallel to the long side of the matching wire, and the length of the long side of the ground wire is equal to the distance from the transition waveguide of the local oscillator port to the transition waveguide of the radio frequency input.

Due to the large size of the planar Schottky anti-parallel mixing diode, the mixing diode connected to the ground line extends through the wall of the main air cavity to the outside of the main air cavity, where a The arc-shaped air cavity connected to the outer wall of the cavity, and the frequency mixing diode extends into the arc-shaped air cavity.

The invention has the advantages that: the invention adopts the coplanar waveguide transmission line, does not need radio frequency grounding, reduces the assembly difficulty and increases the circuit precision by manual errors.

Description of drawings

Figure 1 is a schematic diagram of the overall structure of the present invention.

FIG. 2 is a schematic diagram of the front structure of a planar Schottky antiparallel frequency mixing diode.

FIG. 3 is a schematic diagram of a side-section structure of a planar Schottky antiparallel frequency mixing diode.

Figure 4 is a schematic diagram of the enlarged structure of the local oscillator low-pass filter

FIG. 5 is a schematic diagram of simulation parameters of a local oscillator low-pass filter.

FIG. 6 is a schematic diagram of simulation parameters of an intermediate frequency low-pass filter.

FIG. 7 is a schematic diagram of simulation parameters of the local oscillator frequency band of the intermediate frequency duplexer of the local oscillator.

FIG. 8 is a schematic diagram of simulation parameters of the intermediate frequency band of the local oscillator intermediate frequency duplexer.

Fig. 9 is a schematic diagram of simulation parameters of a radio frequency input transitional waveguide.

Figure 10 shows the results of the overall simulation optimization in the ADS software.

The labels in the figure are respectively represented as: 1. Main air cavity; 2. Dielectric substrate; 3. Radio frequency input transition waveguide; 4. Coupling probe; 5. Matching line; 6. Grounding line; 7. First transverse transmission line; 71 , the first longitudinal transmission line; 72, the first branch longitudinal transmission line; 73, the first branch transverse transmission line; 8, the local oscillator port transition waveguide; 9, the second transverse transmission line; 91, "I" shaped transmission line; 93, The third transverse transmission line; 94, the fourth transverse transmission line; 92, the intermediate frequency low-pass filter matching line; 10, the local oscillator port matching line; 11, the planar Schottky antiparallel mixing diode; 12, the arc-shaped air cavity; 13 , local oscillator low-pass filter matching line; 21, ohmic contact layer; 22, silicon dioxide layer; 23, epitaxial layer; 24, metal anode bridge; 25, buffer layer; 26, substrate layer.

detailed description

Embodiment one

As shown in Figure 1 to Figure 9.

An improved subharmonic mixer based on a coplanar waveguide transmission line, comprising a main air cavity 1, the inner bottom surface of the main air cavity 1 is provided with a dielectric substrate 2, and the dielectric substrate 2 is provided with a coupling probe 4, coplanar Waveguide transmission line, local oscillator matching line 10, microstrip line structure, coplanar waveguide transmission line includes matching line 5, first transverse transmission line 7, local oscillator low-pass filter matching line 13, and coupling probe 4 connected in sequence from left to right The right end is connected to the left end of the matching line 5, the right end of the local oscillator low-pass filter matching line 13 is connected to the left end of the local oscillator matching line 10, and the microstrip line structure includes the second transverse transmission line 9 and the third transverse transmission line connected sequentially from left to right. Transmission line 93, fourth horizontal transmission line 94, intermediate frequency low-pass filter matching line 92, the left end of the second horizontal transmission line 9 is connected to the right end of the local oscillator matching line 10; two first vertical transmission lines 71 and one first vertical transmission line 71 are also included Connected between the first horizontal transmission line 7 and the matching line 5, another first vertical transmission line 71 is connected between the first horizontal transmission line 7 and the local oscillator low-pass filter matching line 13, and the two sides of the first horizontal transmission line 7 are also respectively A first branch transverse transmission line 73 is provided, and the two first branch transverse transmission lines 73 are arranged symmetrically to the left and right axis of the first transverse transmission line 7 , and the two first branch transverse transmission lines 73 pass through the first branch longitudinal transmission line 72 Connected to the first transverse transmission line 7, the left and right ends of the two first branch transverse transmission lines 73 are bent to point to the first transverse transmission line 7, and the length direction of the first transverse transmission line 7 is perpendicular to the length direction of the first longitudinal transmission line 71 ; Also include 2 "I"-shaped transmission lines 91, "I"-shaped transmission lines 91 include 2 parallel transverse branch transmission lines and vertical branch transmission lines connected between the 2 transverse branch transmission lines, one of them The longitudinal branch transmission line of "I" shaped transmission line 91 is connected between the second transverse transmission line 9 and the third transverse transmission line 93, and the longitudinal branch transmission line of another "I" shaped transmission line 91 is connected between the third transverse transmission line 93 and the third transverse transmission line 93. Between the fourth transverse transmission line 94; the coplanar waveguide transmission line also includes two grounding lines 6 respectively located on both sides of the matching line 5, and the two grounding lines 6 are connected to the inner wall of the main air cavity; Parallel connection mixing diode 11, planar Schottky anti-parallel connection mixing diode 11 is a combined structure of 2 parallel connection mixing diodes, the fronts of the 2 mixing diodes are ohmic contact layers 21, and the ohmic contact layer 21 of one of the mixing diodes Layer 21 is connected to the front side of the matching line 5 away from the dielectric substrate 2, and the ohmic contact layer 21 of the other mixing diode is connected to the front side of the grounding line 6 away from the dielectric substrate 2, and the ohmic contact layer (21) of one of the mixing diodes is connected to the matching The front side of the matching line (5) is connected to the front side of the matching line (5). 6) The front side is away from the dielectric substrate (2); it also includes the radio frequency input transition waveguide 3 cross-connected with the main air cavity and the main air cavity cross-connected Oscillator port transition waveguide 8, the overlapping area of radio frequency input transition waveguide 3 and the main air cavity is area M, the coupling probe extends through the radio frequency input transition waveguide 3 to extend into area M, the local oscillator port transition waveguide 8 and the main air cavity The overlapping area is area N, and the local oscillator port matching line is located in area N; the first transverse transmission line 7 and the first longitudinal transmission line 71, the first branch longitudinal transmission line 72, and the first branch transverse transmission line 73 form a local oscillator low-pass filter , the third transverse transmission line 93 and the "I"-shaped transmission line 91, the fourth transverse transmission line 94, and the second transverse transmission line 9 form an intermediate frequency low-pass filter.

The working principle of the above structure is: the transitional waveguide 8 at the local oscillator port and the intermediate frequency low-pass filter form a local oscillator intermediate frequency duplexer, the transitional waveguide 8 at the local oscillator port is the standard waveguide WR-4, and the transitional waveguide 8 at the local oscillator port is used as the local oscillator The input terminal inputs the local oscillator signal, the RF input transition waveguide 3 is a standard waveguide WR-2.2, and the RF input transition waveguide 3 is used as the RF input terminal to input the RF signal, and the local oscillator signal and the RF signal pass through the planar Schottky antiparallel mixing diode 11 , will generate rich harmonic signals, and the intermediate frequency signal will be output after being screened by the local oscillator low-pass filter and the intermediate frequency low-pass filter; Loaded on the planar Schottky anti-parallel mixing diode 11 after the corresponding matching network, since the local oscillator signal frequency is lower than the RF port waveguide cut-off frequency, the local oscillator signal will not leak from the RF port, and the RF signal will not leak due to the local The vibration low-pass filter passes the local oscillator frequency and blocks the existence of the RF frequency without leaking from the local oscillator port, so as to realize the isolation between the two ports; the RF signal and the local oscillator signal are mixed in the plane Schottky anti-parallel Diode 11 is recycled so that the energy of the required intermediate frequency signal is large enough, and the intermediate frequency signal generated by mixing is output from the local oscillator terminal through an intermediate frequency low-pass filter. The matching circuit is used to match the impedance of the mixing diode to make the signal better transmitted. Wherein the planar Schottky anti-parallel frequency mixing diode 11 is pasted with conductive glue after high temperature baking in the form of reverse buckling.

The transition process of the radio frequency signal of the radio frequency input transition waveguide 3 to the coplanar waveguide transmission line is as follows: the coupling probe is used to pass through the side wall of the radio frequency input transition waveguide 3 and extend into the interior of the radio frequency input transition waveguide 3, and through the coupling effect of the coupling probe, The signal energy in the radio frequency input transition waveguide 3 is coupled to the coplanar waveguide transmission line, and the size is optimized to avoid the occurrence of high-order modes and transmission zero points.

The local oscillator low-pass filter adopts a compact resonant unit structure as described above. The compact resonant unit is a special circuit structure with a specific pattern formed in a standard 50 ohm transmission line by photolithography and etching technology. Since a part of the metal is etched away on the normal 50 ohm transmission line, the formed narrow transmission line connected up and down will increase its equivalent series inductance. On the contrary, the two etched gaps increase its equivalent parallel capacitance. The above structure can be equivalent to an RLC resonant circuit, which exhibits a band-stop characteristic. By adjusting the length of the compact resonant unit structure and the structure of the corrosion pattern, the band-stop effect in different frequency bands can be obtained. The role of the local oscillator low-pass filter is to make the local oscillator signal reach the diode pair with a small loss to drive the mixer tube, and suppress the radio frequency signal, prevent the radio frequency signal from leaking from the local oscillator port, improve the port isolation, and at the same time prevent the radio frequency from leaking. The signal is lost due to leakage and energy can be concentrated on the diode pair for mixing.

The setting principle of the planar Schottky antiparallel mixing diode is as follows: in the microwave and millimeter wave bands, since the package size of the planar Schottky antiparallel mixing diode is much smaller than the wavelength, its package will hardly affect the field distribution, so The SPICE parametric linear equivalent circuit model extracted by planar Schottky antiparallel mixing diodes at different operating frequencies can be considered accurate. However, as the frequency rises to the terahertz frequency band, the size of the shielding cavity decreases sharply due to the sharp increase in frequency, and the limitation of the manufacturing process of the planar Schottky antiparallel mixing diode makes the planar Schottky antiparallel mixing Diode package size reductions are limited, well below the increase in operating frequency. Therefore, the equivalent model of the traditional planar Schottky antiparallel mixing diode in ADS has defects in the terahertz frequency band, and it is necessary to re-establish the equivalent model. In the present invention, the planar Schottky anti-parallel frequency mixing diode is arranged in the way of sticking upside down, that is to say, sticking with conductive glue after high temperature baking in the form of turning upside down.

The intermediate frequency low-pass filter adopts the "I" shape structure. It is very simple to design the I-shaped filter. The upper and lower wide transmission lines of "I" are equivalent to capacitors, and the thin transmission lines in the middle are equivalent to inductors, and the capacitors and inductors are connected to the ground in parallel. Adjusting the size of the capacitor and inductor creates a transmission zero outside the band of the filter. The function of the intermediate frequency low-pass filter is to extract the intermediate frequency signal generated by the mixing from the circuit, and to suppress the signal of useless frequency, mainly to suppress the local oscillator signal with strong energy, so as to prevent it from outputting from the intermediate frequency port to cause local oscillation. The loss of signal energy and the impurity of the IF output spectrum. The IF filter needs to reduce the insertion loss in the passband as much as possible, so that the IF signal can be output with less loss, and improve the suppression of unwanted frequencies, especially the suppression of the local oscillator frequency.

The local oscillator port transition waveguide 8 and the intermediate frequency low-pass filter constitute a local oscillator intermediate frequency duplexer. The local oscillator signal is input from the standard waveguide WR-4 through the coplanar waveguide transmission line and enters the mixing diode and mixes the RF signal to generate an intermediate frequency signal. Through the local oscillator low-pass filter, since the cut-off frequency of the input waveguide of the local oscillator is much higher than the frequency of the intermediate frequency, it is impossible for the intermediate frequency signal to enter the waveguide of the local oscillator. It cannot be output by the IF port.

The specific structure of the mixing diode is: the mixing diode includes a buffer layer 25, an ohmic contact layer 21 and an epitaxial layer 23 are arranged on the buffer layer 25, a silicon dioxide layer 22 is arranged on the epitaxial layer, and a metal anode is connected to the ohmic contact layer 21 The bridge 24, the metal anode bridge of one of the two mixing diodes penetrates the silicon dioxide layer 22 of the other mixing diode, and the buffer layer 25 of the two mixing diodes is installed on the substrate layer 26 at the same time.

The ohmic contact layer 21 is pasted on the ground wire and the matching wire 5 with conductive glue after high-temperature baking.

The side of all structures included in the coplanar waveguide transmission line away from the dielectric substrate 2 is flush with the upper surface of the dielectric substrate 2 .

Coupling probe 4, matching line 5, grounding line 6, first transverse transmission line 7, local oscillator low-pass filter matching line 13, local oscillator matching line 10, second transverse transmission line 9, third transverse transmission line 93, fourth transverse transmission line 94. The intermediate frequency low-pass filter matching line 92 and the first longitudinal transmission line 71 are both rectangular transmission lines.

The main air cavity is a rectangular tube.

The transitional waveguide at the local oscillator port is a variable-diameter waveguide.

The RF input transition waveguide is a rectangular tube.

The long side of the ground wire is parallel to the long side of the matching wire, and the length of the long side of the ground wire is equal to the distance from the transition waveguide of the local oscillator port to the transition waveguide of the radio frequency input. The long side of the ground line and the long side of the matching line refer to the axial side of the coplanar waveguide transmission line from left to right

The frequency mixing diode connected with the ground wire extends to the outside of the main air cavity through the wall of the main air cavity, and an arc-shaped air cavity 12 connected with the outer wall of the main air cavity is arranged at the frequency mixing diode, and the frequency mixing diode extends to the arc In the air cavity 12.

Figure 5: The parameters in this figure show that the simulation results of the local oscillator low-pass filter are shown in Figure 5, the insertion loss is less than 0.2dB in the 0-250GHz passband, the return loss is better than 10dB, and the frequency above 350GHz The suppression is greater than 20dB, which meets the requirements for radio frequency suppression. The insertion loss is small in the passband range of 0-250GHz, which can make the local oscillator signal be effectively used, which is particularly important in the terahertz frequency band where it is difficult to obtain a large local oscillator power source. At the same time, the wide passband is also realized for the local oscillator signal. A good match over a wide range provides the necessary assurance. .

Figure 6: The parameters in this figure show that the simulation results of the intermediate frequency low-pass filter are shown in Figure 6, and the insertion loss in the passband in the range of 0-40GHz is less than 0.2dB, and the return loss is better than 20dB. The suppression at the local oscillator frequency of 210GHz is greater than 20dB. It can pass the intermediate frequency signal well and suppress the local oscillator signal.

Figure 7.8: The parameters in this figure indicate that the simulation results of the intermediate frequency duplex of the local oscillator are shown in Figure 7.8. In Figure 7, in the range of local oscillator frequency 140-200GHz, the insertion loss from the input waveguide of the local oscillator to the output port of the low-pass filter of the local oscillator is less than 0.5dB, and the return loss, namely S11, is basically better than 10dB. In Fig. 8, in the range of intermediate frequency 0-25GHz, the return loss of the output port of the intermediate frequency is better than 10dB, and the insertion loss of the output port of the local oscillator low-pass filter is less than 0.5dB.

As shown in Figure 9: The parameters in this figure indicate that: Figure 9 is the simulation result of the radio frequency waveguide transition. The return loss of the RF input port, namely S11, is basically better than 20dB within 390GHz-450GHz, and the insertion loss S21 is less than 0.2dB, which lays a good foundation for the mixer to achieve a small conversion loss in a wide frequency range.

As shown in Figure 10: Import the S parameters of each part of the passive circuit optimized by the above simulation into the ADS simulation software as an SNP file, connect the ideal diode model built by ADS, and use the harmonic balance method to perform nonlinear optimization simulation to obtain the best frequency conversion loss. ADS simulation results show that in the range of 400-445GHz, the frequency conversion loss is less than 8dB. Frequency conversion loss is the ratio of input RF signal power to output IF signal power, expressed in dB. Simulation results prove that the mixer works well.

As described above, the present invention can be well realized.

Claims (10)

1. A kind of 1. sub-harmonic mixer of modified based on coplanar waveguide transmission line, it is characterised in that：Including a primary air chamber （1）, primary air chamber（1）Inner bottom surface be provided with medium substrate（2）, medium substrate（2）On be provided with coupling probe（4）, it is coplanar Waveguide transmission line, local oscillator matched line（10）, microstrip line construction, coplanar waveguide transmission line includes the matching that is from left to right sequentially connected Line（5）, the first lateral transport line（7）, local oscillator LPF matched line（13）, coupling probe（4）Right-hand member and matched line（5）'s Left end connects, local oscillator LPF matched line（13）Right-hand member and local oscillator matched line（10）Left end connection, microstrip line construction bag Include the second lateral transport line being from left to right sequentially connected（9）, the 3rd lateral transport line（93）, the 4th lateral transport line（94）、 Mid-frequency low-pass filters matched line（92）, the second lateral transport line（9）Left end and local oscillator matched line（10）Right-hand member connection；Also wrap Include 2 first longitudinal direction transmission lines（71）, a first longitudinal direction transmission line（71）It is connected to the first lateral transport line（7）With matched line （5）Between, another first longitudinal direction transmission line（71）It is connected to the first lateral transport line（7）With local oscillator LPF matched line （13）Between, the first lateral transport line（7）Both sides be also each provided with tie point lateral transport line（73）, 2 first Road lateral transport line（73）With the first lateral transport line（7）Left and right to axisymmetrical set, 2 tie point lateral transport lines （73）All pass through tie point longitudinal direction transmission line（72）With the first lateral transport line（7）Connection, 2 tie point lateral transport lines （73）Left and right to both ends all bend point to the first lateral transport line（7）, the first lateral transport line（7）Length direction and One longitudinal transmission line（71）Length direction it is vertical；Also include 2 " work " font transmission lines（91）, " work " font transmission line （91）Passed including 2 transverse legs transmission lines parallel to each other and the longitudinal branch road being connected between 2 transverse legs transmission lines Defeated line is formed, one of them " work " font transmission line（91）Longitudinal branch transmission line be connected to the second lateral transport line（9）With 3rd lateral transport line（93）Between, another " work " font transmission line（91）Longitudinal branch transmission line be connected to the 3rd laterally Transmission line（93）With the 4th lateral transport line（94）Between；Coplanar waveguide transmission line is also located at matched line respectively including 2（5）Two The ground wire of side（6）, 2 ground wires（6）Inwall all with primary air chamber is connected；Also include planar Schottky reverse parallel connection to be mixed Diode（11）, planar Schottky reverse parallel connection mixer diode（11）For the combining structure of 2 mixer diodes in parallel, 2 The front of individual mixer diode is ohmic contact layer（21）, the ohmic contact layer of one of mixer diode（21）With matched line （5）Front connection, matched line（5）Front be away from medium substrate（2）Face, ohm of another mixer diode connects Contact layer（21）With ground wire（6）Front connection, ground wire（6）Front be away from medium substrate（2）Face；Also include and master The radio frequency input transition waveguide of air chamber interconnection（3）With the local oscillator port transition waceguide with primary air chamber interconnection（8）, Radio frequency input transition waveguide（3）Overlapping region with primary air chamber is region M, and coupling probe prolongs through radio frequency input transition waveguide （3）Extend in the M of region, local oscillator port transition waceguide（8）Overlapping region with primary air chamber is region N, local oscillator port match Line is located in the N of region；First lateral transport line（7）With first longitudinal direction transmission line（71）, tie point longitudinal direction transmission line（72）, One branch road lateral transport line（73）Form local oscillator low pass filter, the 3rd lateral transport line（93）" work " font transmission line （91）, the 4th lateral transport line（94）, the second lateral transport line（9）Form mid-frequency low-pass wave filter.
2. 2. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：Mixer diode includes cushion（25）, cushion（25）On be provided with ohmic contact layer（21）And epitaxial layer（23）, extension Silicon dioxide layer is provided with layer（22）, ohmic contact layer（21）It is connected with metal anode bridge（24）, in 2 mixer diodes The metal anode bridge of one mixer diode penetrates the silicon dioxide layer of another mixer diode（22）, 2 two poles of mixing The cushion of pipe（25）It is arranged on substrate layer simultaneously（26）.
3. 3. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：Ohmic contact layer（21）With conducting resinl ground wire and matched line are pasted by high-temperature baking（5）On.
4. 4. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：All structures that coplanar waveguide transmission line is included are away from medium substrate（2）One side all with medium substrate（2）Upper surface Flush.
5. 5. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：Coupling probe（4）, matched line（5）, ground wire（6）, the first lateral transport line（7）, local oscillator LPF matched line（13）、 Local oscillator matched line（10）, the second lateral transport line（9）, the 3rd lateral transport line（93）, the 4th lateral transport line（94）, intermediate frequency it is low Pass filter matched line（92）, first longitudinal direction transmission line（71）All it is the transmission line of rectangle.
6. 6. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：Primary air chamber is rectangular tube.
7. 7. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：Local oscillator port transition waceguide is reducing waveguide.
8. 8. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 1, its feature exist In：The waveguide of radio frequency input transition is rectangular tube.
9. 9. sub-harmonic mixer of a kind of modified based on coplanar waveguide transmission line according to claim 5, its feature exist In：The long side of ground wire is parallel with the long side of matched line, while the long edge lengths being grounded are equal to local oscillator port transition waceguide extremely The distance of radio frequency input transition waveguide, the long side of ground wire and the long side of matched line refer to coplanar waveguide transmission line from left to right Axial side.
10. 10. subharmonic of a kind of modified based on coplanar waveguide transmission line according to any one in claim 1-9 mixes Frequency device, it is characterised in that：Extended to the wall of mixer diode through the primary air chamber of ground wire connection outside primary air chamber, The arc air chamber being connected with primary air cavity outer wall is provided with the mixer diode（12）, the mixer diode extends to arc Air chamber（12）It is interior.