Design method of terahertz quasi-optical Schottky mixer based on frequency scanning

Abstract

The invention belongs to the technical field of terahertz wide-angle electric scanning and quasi-optical mixers, and particularly relates to a design method of a terahertz quasi-optical Schottky mixer based on frequency scanning, which comprises the following steps: firstly, determining a receiver scanning range and antenna gain requirements, designing a frequency scanning receiving antenna unit of radio frequency, verifying an antenna S11, and adjusting and optimizing the performance of the antenna unit; then, frequency scanning receiving antenna units form an array, the antenna performance is optimized again, and then the structure of the receiver is designed; and finally, substituting the optimized frequency impedance values corresponding to the local oscillator receiving antenna and the frequency scanning receiving antenna into the schematic circuit diagram, and optimizing the mixing performance of the receiver. And if the frequency conversion gain and the noise coefficient both reach target values, the simulation is ended. The wide-angle electric scanning function of the terahertz mixer is achieved, terahertz signals can be received at a large angle, impedance matching between mixer elements is good, the maximum frequency conversion gain is achieved, and the gap of the wide-angle electric scanning design of a quasi-optical terahertz Schottky mixer is made up.

Description

Technical Field

[0001] The invention belongs to the technical field of terahertz wide-angle electric scanning and quasi-optical mixers, and in particular relates to a design method of a terahertz quasi-optical Schottky mixer based on frequency scanning. Background Art

[0002] The Schottky mixer is a passive mixer based on the Schottky diode. It is widely used in high-frequency radio frequency systems, such as microwave communications, radar, and satellite communications. Compared with transistor mixers, Schottky mixers have the advantages of higher detection sensitivity and no need for external bias circuits when working. Compared with superconductor mixers, the Schottky mixer manufacturing process is simpler and cheaper, and has good application prospects as a front-end device for terahertz communication systems.

[0003] The terahertz Schottky mixers disclosed in the prior art can only receive signals from a specific single angle, and the receiving antenna beam angle is extremely narrow, and does not have a wide-angle beam scanning function; the terahertz Schottky mixers disclosed in the prior art mostly use waveguide technology, but the waveguide has radio frequency attenuation, poor thermal isolation, and low module integration. There are few quasi-optical Schottky mixers reported so far, and they can only achieve reception from a specific angle.

[0004] In view of the above situation, the present invention proposes a design method of a terahertz quasi-optical Schottky mixer based on frequency scanning. The present invention considers integrating a leaky wave antenna on the mixer to receive wide-angle radio frequency signals, and utilizes the characteristic that the beam angle of the leaky wave antenna changes with the signal frequency to achieve wide-angle reception of radio frequency signals, so that the terahertz quasi-optical Schottky mixer based on frequency scanning designed by the present invention can meet the wide-angle electric scanning function within the working frequency band. Summary of the invention

[0005] The purpose of the present invention is to provide a design method of a terahertz quasi-optical Schottky mixer based on frequency scanning.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A design method of a terahertz quasi-optical Schottky mixer based on frequency scanning comprises the following steps:

[0008] Step 1: Determine the receiver scanning range and frequency scanning antenna gain requirements, use 3D electromagnetic simulation software to design the RF frequency scanning receiving antenna unit, and verify the antenna S 11 And adjust and optimize the frequency scanning receiving antenna unit performance;

[0009] Step 2: Array the optimized frequency scanning receiving antenna units, optimize the frequency scanning receiving antenna performance again until its scanning range and gain reach the required values, and then design the local oscillator receiving antenna of the receiver;

[0010] Step 3: Use 3D electromagnetic simulation software to design the structure of the receiver, including the filtering network of each port and the 3D structure related to Schottky diodes; then combine with circuit simulation software, import the S-parameters corresponding to each structure into the circuit schematic diagram in the form of SnP, and design a matching network to conjugate-match each port with the Schottky diode;

[0011] Step 4: Substitute the corresponding frequency impedance values of the optimized local oscillator receiving antenna and frequency scanning receiving antenna into the circuit schematic diagram to optimize the mixing performance of the receiver; if both the conversion gain and the noise figure reach the target values, the simulation ends, otherwise continue to optimize the frequency scanning antenna and the circuit simultaneously in the target frequency band, and repeat the above steps until the mixing performance reaches the target.

[0012] Preferably, the frequency scanning receiving antenna uses a leaky wave antenna for frequency scanning and has a wide-angle electrical scanning function.

[0013] Preferably, combine the frequency scanning receiving antenna with a wide-angle electrical scanning function with the receiver circuit to enable the receiver to have a large-angle beam receiving range.

[0014] Preferably, the working principle of the terahertz quasi-optical Schottky mixer: The local oscillator signal and the RF signal are respectively coupled to the Schottky diode through the corresponding antennas for heterodyne frequency down-conversion; in order to achieve wide-angle reception of the RF signal, it is necessary to satisfy the condition that the distance between the RF source and the RF leaky wave antenna remains unchanged, and the RF source can move within a large-angle range; the RF signal is emitted from the RF source horn antenna and reaches the RF leaky wave antenna of the mixer; the local oscillator signal is emitted from the local oscillator source horn antenna, collimated and focused through a pair of polytetrafluoroethylene lenses and then reaches the local oscillator antenna; after the RF and local oscillator signals pass through the corresponding filters respectively, they are effectively coupled to the Schottky diode, and the down-converted intermediate frequency signal is generated by heterodyne mixing, and finally output from the output port of the mixer through a low-pass filter.

[0015] Preferably, the terahertz quasi-optical Schottky mixer includes a local oscillator monopole lens antenna, an RF leaky wave antenna array, filters for each port, a pair of Schottky diodes, and a matching microstrip line for compensating the parasitic impedance of the diodes.

[0016] The technical effects achieved by the present invention are:

[0017] The present invention uses a leaky wave antenna to receive RF signals and utilizes the frequency scanning characteristics of the leaky wave antenna to achieve the wide-angle electrical scanning function of the RF beam.

[0018] The present invention makes up for the gap in the system design method of the wide-angle electrical scanning quasi-optical terahertz Schottky mixer, and lays a design and application foundation for the development and use of the quasi-optical terahertz Schottky mixer. Description of the Drawings

[0019] Figure 1 is a schematic diagram of the working principle of the terahertz quasi-optical Schottky mixer based on frequency scanning in the present invention;

[0020] Figure 2 is a flowchart of the design method of the terahertz quasi-optical Schottky mixer based on frequency scanning in the present invention;

[0021] Figure 3 is a circuit design diagram of the terahertz quasi-optical Schottky mixer based on frequency scanning in the present invention;

[0022] Figure 4 is a micrograph of the mixer device chip fabricated in the present invention;

[0023] Figure 5 are the transmission coefficient S21, achievable gain, and standing wave ratio of the simulated radio frequency leaky wave antenna in the present invention;

[0024] Figure 6 are the transmission coefficient S21, achievable gain, and standing wave ratio of the simulated local oscillator antenna in the present invention;

[0025] Figure 7 is the relationship between the SSB noise parameters NFmix and mixing gain Gmix measured and simulated at room temperature in the present invention and the radio frequency operating frequency fRF at room temperature;

[0026] Figure 8 is the radiation pattern of the mixer measured and simulated at room temperature in the present invention. Detailed implementation manners

[0027] In order to make the objectives and advantages of the present invention more clear, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific implementation manners of the present invention, and does not strictly limit the scope of protection specifically claimed by the present invention.

[0028] As Figure 1-8 shown, a design method of a terahertz quasi-optical Schottky mixer based on frequency scanning can utilize the characteristic that the beam angle of the leaky wave antenna changes with the signal frequency to achieve wide-angle electrical scanning of the radio frequency signal; and achieve impedance matching between the receiving antenna and the Schottky diode to achieve the maximum mixing gain.

[0029] Figure 1 shows the working principle of the terahertz quasi-optical Schottky mixer based on frequency scanning. The local oscillator signal and the radio frequency signal are respectively coupled to the Schottky diode through the corresponding antennas for heterodyne frequency down-conversion. In order to achieve wide-angle reception of the radio frequency signal, it is necessary to satisfy the condition that the distance between the radio frequency source and the radio frequency leaky wave antenna remains unchanged, and the radio frequency source can move within a large angular range.

[0030] First, a 220 GHz frequency-scanning quasi-optical terahertz mixer was fabricated and encapsulated. Figure 4 The micrograph of the fabricated mixer chip is shown, which includes a local oscillator monopole lens antenna, a radio frequency leaky wave antenna array, filters for each port, Schottky diode pairs, and matching microstrip lines for compensating the parasitic impedance of the diodes.

[0031] The 220 GHz frequency-scanning quasi-optical terahertz mixer was designed according to the terahertz quasi-optical Schottky mixer design method based on frequency scanning mentioned in the invention content, as Figure 2 shown, and specifically includes the following steps:

[0032] Step 1: Determine the receiver scanning range and antenna gain requirements, and use the three-dimensional electromagnetic simulation software ANSYS HFSS to design the radio frequency frequency-scanning receiving antenna unit, and verify the antenna S 11 and adjust the distance between antenna units, the distance between antenna sub-arrays, and the radiation frequency of the antenna unit to optimize the pattern and reflection parameter performance of the frequency-scanning receiving antenna unit;

[0033] Step 2: Combine the optimized frequency-scanning receiving antenna units into an array, and optimize the performance of the frequency-scanning receiving antenna again until its scanning range and gain reach the required values, and then design the local oscillator receiving antenna of the receiver; specifically in Step 2: Combine the optimized frequency-scanning receiving antenna units into an array, further optimize the performance of the frequency-scanning receiving antenna until its scanning range and gain reach the required values, and then use the computer simulation technology (CST) Microwave Studio software to design the local oscillator receiving antenna. At this time, the total bilateral scanning angle range of the radio frequency leaky wave antenna is 80°;

[0034] Step 3: Use the three-dimensional electromagnetic simulation software ANSYS HFSS to design the structure of the receiver, including the filtering network for each port and the three-dimensional structure related to the Schottky diode; then combine with the circuit simulation software ADS (Advanced Design system), import the S parameters corresponding to each structure into the circuit schematic diagram in the form of SnP, and design a matching network to conjugate match each port with the Schottky diode;

[0035] Step 4: Substitute the optimized local oscillator receiving antenna and the corresponding frequency impedance values of the frequency-scanning receiving antenna into the circuit schematic diagram to optimize the mixing performance of the receiver; if both the conversion gain and the noise figure reach the target values, the simulation ends, otherwise continue to optimize the antenna and the circuit simultaneously in the target frequency band, and repeat the above steps until the mixing performance reaches the expected target; at this time, the input real impedances of the local oscillator receiving antenna and the frequency-scanning receiving antenna are 80 Ω and 50 Ω respectively, and the reactance values of the radio frequency and the local oscillator source always remain zero during the optimization process.

[0036] Figure 5 shows the performance of the optimized frequency-scanning receiving antenna, whose gain is greater than 17 dBi in the range of 200 - 235 GHz, and the standing wave ratio in the whole frequency band is less than 2.5, and S 21 is less than -15 dB. Figure 6 is the performance of the optimized local oscillator receiving antenna, whose average gain is 14 dBi, the radiation efficiency is about 83.5%, and in the frequency band of 99.5 - 114.5 GHz, the VSWR is less than 2.2.

[0037] Preferably, the frequency-scanning receiving antenna uses a leaky-wave antenna for frequency scanning and has a wide-angle electrical scanning function.

[0038] Preferably, the frequency-scanning receiving antenna with a wide-angle electrical scanning function is combined with the receiver circuit to enable the receiver to have a large-angle beam receiving range.

[0039] Preferably, the working principle of the terahertz quasi-optical Schottky mixer is as Figure 3 shown: The local oscillator signal and the radio frequency signal are respectively coupled to the Schottky diode through the corresponding antennas for heterodyne frequency down-conversion; in order to achieve wide-angle reception of the radio frequency signal, it is necessary to satisfy the condition that the distance between the radio frequency source and the radio frequency leaky-wave antenna remains unchanged, and the radio frequency source can move within a large-angle range; the radio frequency signal is emitted from the radio frequency source horn antenna and reaches the radio frequency leaky-wave antenna of the mixer; the local oscillator signal is emitted from the local oscillator source horn antenna, collimated and focused through a pair of polytetrafluoroethylene lenses and then reaches the local oscillator antenna; after the radio frequency and local oscillator signals respectively pass through the corresponding filters, they are effectively coupled to the Schottky diode, and the down-converted intermediate frequency signal is generated by heterodyne mixing, and finally output from the output port of the mixer through a low-pass filter.

[0040] According to the working principle of the invention content, the physical object of the previously designed terahertz quasi-optical Schottky mixer based on frequency scanning is experimentally verified. The packaged terahertz mixer module is fixed on an iron stand, and the RF source is fixed on a semi-circular slide rail with an adjustable angle of 0 - 180°. The local oscillator signal is generated by a ×6 frequency multiplier driven by an HP 83732B signal generator, with a frequency ranging from 99.5 GHz to 114.5 GHz. After being amplified by a W-band power amplifier, the multiplied local oscillator signal is emitted from the local oscillator horn antenna, collimated and focused by a pair of Teflon lenses, and then received by the on-chip local oscillator lens antenna. The Ceyear 1431 signal generator generates an RF signal in the frequency band of 200 - 235 GHz. After passing through a ×18 frequency multiplier, it is emitted from the RF horn antenna and received by the RF leaky antenna array and then enters the mixer module to be measured. It should be noted that the distance between the RF source and the module is maintained at 21.5 cm, and the angle between them can be adjusted by sliding the RF module on the semi-circular track. After the local oscillator and RF signals are heterodyne mixed by the mixer, the down-converted intermediate frequency signal is amplified by a low-noise amplifier (LNA) with a frequency range of 1 - 20 GHz and then connected to a spectrum analyzer to observe the relationship between the signal power and frequency. Finally, through link budget, the conversion gain of the terahertz quasi-optical Schottky mixer based on frequency scanning is calculated.

[0041] Compare the simulation results and the measured curves to verify the effectiveness of the design method of the terahertz quasi-optical Schottky mixer based on frequency scanning involved in the present invention. Figure 7 The single-sideband (SSB) noise figure NF mix and the mixer conversion gain G mix versus the RF operating frequency f RF variation relationship diagram. Generally, NF mix and G mix The performance first improves and then deteriorates with the operating frequency, showing the characteristics of a convex function. Generally speaking, except for small differences caused by measurement calibration errors and environmental changes, the measured values of the conversion gain and noise figure are in good agreement with the simulation results. The SSB noise figure of the terahertz quasi-optical Schottky mixer based on frequency scanning fabricated in this design is approximately 8.75 dB at room temperature, and the conversion gain is approximately -10.5 dB. Figure 8 What is shown is the radiation pattern of the terahertz quasi-optical Schottky mixer based on frequency scanning involved in the present invention. It can be seen that the 3 dB angle ranges of the mixer are 44° - 84° and 95° - 135° respectively, and a total wide-angle electrical scan of 80° can be achieved.

[0042] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. The structures, devices, and operation methods not specifically described and explained in the present invention are implemented according to the conventional means in the art without special explanation and limitation.

Claims

1. A design method of a terahertz quasi-optical Schottky mixer based on frequency scanning, characterized in that: It includes the following steps: Step 1: Determine the receiver scanning range and the frequency scanning antenna gain requirement, design the radio frequency frequency scanning receiving antenna unit by using three-dimensional electromagnetic simulation software, and verify the antenna S 11 and adjust and optimize the performance of the frequency scanning receiving antenna unit; Step 2: Form an array with the optimized frequency-scanning receiving antenna units, and optimize the performance of the frequency-scanning receiving antenna again until its scanning range and gain reach the required values, and then design the local oscillator receiving antenna of the receiver; Step 3: Use 3D electromagnetic simulation software to design the structure of the receiver, including the filtering network of each port and the 3D structure related to the Schottky diode; Then, in combination with circuit simulation software, import the S-parameters corresponding to each structure into the circuit schematic diagram in the form of SnP, and design a matching network to conjugate-match each port with the Schottky diode; Step 4: Substitute the corresponding frequency impedance values of the optimized local oscillator receiving antenna and the frequency-scanning receiving antenna into the circuit schematic diagram to optimize the mixing performance of the receiver; if both the conversion gain and the noise figure reach the target values, the simulation ends, otherwise continue to optimize the frequency-scanning antenna and the circuit simultaneously in the target frequency band, and repeat the above steps until the mixing performance reaches the target.

2. The design method of a terahertz quasi-optical Schottky mixer based on frequency scanning according to claim 1, wherein: The frequency-scanning receiving antenna uses a leaky-wave antenna for frequency scanning and has a wide-angle electrical scanning function.

3. The design method of a terahertz quasi-optical Schottky mixer based on frequency scanning according to claim 2, characterized in that: Combine the frequency-scanning receiving antenna with a wide-angle electrical scanning function with the receiver circuit to enable the receiver to have a large-angle beam receiving range.

4. The design method of a terahertz quasi-optical Schottky mixer based on frequency scanning according to claim 3, characterized in that: The working principle of the terahertz quasi-optical Schottky mixer is as follows: The local oscillator signal and the radio frequency signal are respectively coupled to the Schottky diode through the corresponding antennas for heterodyne frequency down-conversion; in order to achieve wide-angle reception of the radio frequency signal, it is necessary to satisfy the condition that the distance between the radio frequency source and the radio frequency leaky-wave antenna remains unchanged, and the radio frequency source can move in a large-angle range; the radio frequency signal is emitted from the radio frequency source horn antenna and reaches the radio frequency leaky-wave antenna of the mixer; the local oscillator signal is emitted from the local oscillator source horn antenna, and after being collimated and focused by a pair of polytetrafluoroethylene lenses, it reaches the local oscillator antenna; the radio frequency and local oscillator signals respectively pass through the corresponding filters and are effectively coupled to the Schottky diode, and the down-converted intermediate frequency signal is generated by heterodyne mixing, and finally passes through the low-pass filter and is output from the output port of the mixer.

5. A design method of a terahertz quasi-optical Schottky mixer based on frequency scanning according to any one of claims 1-4, characterized in that: The terahertz quasi-optical Schottky mixer based on frequency scanning includes a local oscillator antenna, a radio frequency leaky-wave antenna, filters for each port, a pair of Schottky diodes, and a matching microstrip line for compensating the parasitic impedance of the diodes.

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