CN111987997B

CN111987997B - Terahertz frequency mixer without local oscillator filter structure

Info

Publication number: CN111987997B
Application number: CN202010912907.0A
Authority: CN
Inventors: 张勇; 李宇; 张博; 延波
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2020-09-03
Filing date: 2020-09-03
Publication date: 2022-04-08
Anticipated expiration: 2040-09-03
Also published as: CN111987997A

Abstract

The invention discloses a terahertz frequency mixer without a local oscillator filter structure, which comprises an RF input waveguide, an LO input waveguide, a height reduction waveguide, a mixing circuit substrate and a suspension microstrip probe section, wherein the suspension microstrip probe section is provided with an RF probe and an LO probe; this terahertz mixer is based on whole circuit method, through adjusting whole circuit matching, convert circuit energy to intermediate frequency as far as possible, thereby accomplish the isolation naturally, no longer design local oscillator filter, very big simplification mixer's structure has reduced the whole size of mixer, the length of quartz substrate has been shortened, thereby transmission loss has been reduced, the bandwidth of mixer has been widened, the frequency mixing wholeness can has been promoted, and this terahertz mixer still has simple structure, processing is convenient, the advantage of easily realizing, good application prospect has.

Description

Terahertz frequency mixer without local oscillator filter structure

Technical Field

The invention relates to the technical field of terahertz frequency mixers, in particular to a terahertz frequency mixer without a local oscillator filter structure.

Background

The electromagnetic wave with the wavelength of 3 mm-30 um is called terahertz wave, the long wave band of the terahertz wave is close to millimeter waves, the short wave band is close to infrared rays, and the terahertz wave is located in the crossing region of electronics and photonics. Compared with the microwave of a lower frequency band, the characteristics of the microwave are as follows: 1. the used frequency spectrum range is wide, and the information capacity is large. 2. The antenna with narrow beam and high gain is easy to realize, thus the resolution is high and the anti-interference performance is good. 3. The plasma penetration ability is strong. 4. The Doppler frequency shift is large, and the speed measurement sensitivity is high. Terahertz waves have great significance in the aspects of communication, radar, guidance, remote sensing technology, radio astronomy and wave spectroscopy. The mixer is a three-port network, different frequencies are generated through the nonlinearity of diodes, and the frequency selection circuit selects the required frequency. The terahertz transceiving front end is widely applied to nearly all millimeter wave and terahertz application systems such as communication and radar, solves the problem of frequency conversion of signals, is a core component of the system, and mainly comprises key devices such as a frequency mixer, a filter, an amplifier and the like. The millimeter wave and terahertz frequency mixer is a core device at the transmitting and receiving front end, and has the function of carrying the frequency spectrum downwards by down-converting millimeter wave or terahertz radio frequency signals to intermediate frequency signals or carrying the frequency spectrum upwards by up-converting intermediate frequency signals to millimeter wave or terahertz radio frequency signals, and the quality of the technical indexes of the mixer greatly influences the overall performance of the millimeter wave and terahertz system. Therefore, the development of high-performance millimeter wave and terahertz frequency mixers is one of the key research directions of millimeter wave and terahertz technology.

In the terahertz frequency band, when the frequency is low, the size of the shielding cavity is relatively wide, the length-width ratio of the quartz substrate which is properly long cannot be too high, and when the frequency is high to a certain degree, the shielding cavity is generally designed to be narrow, and the intermediate frequency filter, the local oscillator filter and the matching structure between the intermediate frequency filter and the local oscillator filter are relatively long, so that the length-width ratio of the frequency mixer designed by the traditional method and the structure is generally too high. In the terahertz mixer, quartz is used as a substrate, so that the loss is small, the high-frequency performance is good, but the quartz is fragile and easy to break, if the middle of the quartz with the too high length-width ratio is warped, a circuit is uneven, the assembly difficulty is increased, the quartz is not a planar circuit after being assembled, but is an arc, the performance of the mixer is affected, the loss is increased, the size of the mixer is large, and the stability of the circuit is relatively poor.

Disclosure of Invention

The invention aims to provide a terahertz frequency mixer without a local oscillator filter structure, which simplifies a circuit, reduces the length-width ratio of quartz, improves the overall performance of the frequency mixer by sacrificing a certain isolation degree, has the advantages of small structure size, easiness in implementation and the like, and has a good application prospect in the terahertz frequency mixer.

The embodiment of the invention is realized by the following steps:

the utility model provides a no terahertz of local oscillator filter structure mixes ware, it includes RF input waveguide, LO input waveguide, subtract high waveguide, mixing circuit substrate and suspension microstrip probe section, mixing circuit substrate's one end is IF microstrip output, mixing circuit substrate's the other end is shielding cavity structures, RF input waveguide and LO input waveguide connect two different subtract high waveguides respectively, two subtract high waveguide conduction and pass through suspension microstrip probe section and connect on mixing circuit substrate mutually at an interval, be provided with the schottky diode between two suspension microstrip probe sections, be provided with RF probe and LO probe on two suspension microstrip probe sections respectively, the schottky diode respectively with be connected with the high impedance line between RF probe and the LO probe, be provided with the mixer circuit on the mixing circuit substrate, the mixer circuit is located above-mentioned cavity structures.

In a preferred embodiment of the present invention, the terahertz frequency mixer integrally adjusts the frequency mixing circuit through the schottky diode, improves the frequency conversion efficiency, and converts energy to an intermediate frequency as much as possible, thereby achieving natural isolation between the local oscillator and the radio frequency.

In a preferred embodiment of the present invention, the RF input waveguide and the LO input waveguide respectively form cavity structures on two sides of the mixer circuit substrate, the cavity structures of the RF input waveguide and the LO input waveguide are symmetrical and form a closed waveguide, and the shielding cavity structure of the mixer circuit is also a closed waveguide.

In a preferred embodiment of the present invention, the dimensions of the closed waveguide structure vary with the operating frequency.

In a preferred embodiment of the present invention, the mixer circuit is a microwave planar integrated circuit, and is implemented by using a suspended microstrip line.

In a preferred embodiment of the present invention, the integrated circuit includes a mixing diode and is impedance matched.

In a preferred embodiment of the present invention, the mixer circuit is a suspended microstrip structure designed based on a global circuit method.

In a preferred embodiment of the present invention, a high impedance line is disposed between the mixing diode and the RF probe and between the mixing diode and the LO probe, and the high impedance line is connected to the mixing circuit.

The invention has the beneficial effects that:

the invention utilizes the cut-off frequency of the waveguide and the natural isolation generated when the frequency conversion efficiency is improved, compared with the terahertz frequency mixer with the local oscillator filter, the isolation degree is slightly poor, but the overall performance of the circuit is better, the processing difficulty is lower, through proper design, the input suspension microstrip probe segment can be directly matched with the suspension microstrip at the Schottky diode, and the design of a matching circuit among the input probe, the CMRC low-pass filter (or a high-low impedance filter) and the diode is not needed like the design of the traditional frequency mixer, thereby greatly reducing the design size of the circuit.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, and it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope.

FIG. 1 is a schematic diagram of a terahertz mixer according to the present invention;

FIG. 2 is a diagram showing simulation results of a mixer with a center frequency of 500GHz according to the present invention;

FIG. 3 is a schematic diagram showing the length comparison between the terahertz frequency mixer of the present invention and a conventional terahertz frequency mixer;

icon: 1-an RF input waveguide; a 2-LO input waveguide; 3-a height-reducing waveguide; 4-a mixer circuit substrate; 5-an RF probe; a 6-LO probe; 7-Schottky diode.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

First embodiment

Referring to fig. 1, fig. 2 and fig. 3, the present embodiment provides a terahertz frequency mixer without a local oscillator filter structure, which includes an RF input waveguide 1, an LO input waveguide 2, a height reduction waveguide 3, a mixer circuit substrate 4 and a suspended microstrip probe segment, where the suspended microstrip probe segment is provided with an RF probe 5 and an LO probe 6; the invention innovatively provides the terahertz frequency mixer without the local oscillator filter structure, the final simulation result is shown in FIG. 2, the frequency conversion loss is less than 10dB at 475-525GHz, the return loss is better than 10dB, and the bandwidth is 50 GHz; the terahertz frequency mixer is improved on the basis of the traditional terahertz frequency mixer, and has the advantages of simple circuit, small circuit size, high circuit stability and the like, and because the specific microwave circuit has different index requirements according to frequency and different specific sizes of the frequency mixer circuit, the terahertz frequency mixer has no specific circuit size, and according to the comparison of the physical sizes of the terahertz frequency mixer in the embodiment in the figure 3 and the traditional frequency mixer in the same frequency band, the traditional frequency mixer is arranged on the left, the frequency mixer in the embodiment is arranged on the right, so that the terahertz frequency mixer without the local oscillator filter structure is simpler in structure, and the quartz substrate is shortened by more than half.

The mixer of the embodiment is designed based on an integral circuit method, a planar circuit is only composed of high and low impedance lines, in order to verify the feasibility of the structure and the design method, a mixer with the center frequency of 500GHz and the bandwidth of 50GHz is designed by using the structure, wherein a quartz substrate is adopted as a mixer circuit substrate 4, one end of the mixer circuit substrate 4 is an IF microstrip output end, the other end of the mixer circuit substrate 4 is a shielding cavity structure, an RF input waveguide 1 and an LO input waveguide 2 respectively form cavity structures on two sides of the mixer circuit substrate 4, the cavity structures of the RF input waveguide 1 and the LO input waveguide 2 are symmetrical and form a closed waveguide, the shielding cavity structure of the mixer circuit is also a closed waveguide, and the size of the closed waveguide structure is changed along with the change of the working frequency.

The positions, spaced from each other, of the mixer circuit substrate 4 are respectively provided with suspension microstrip probe segments, the two suspension microstrip probe segments are respectively provided with an RF probe 5 and an LO probe 6, an RF input waveguide 1 and an LO input waveguide 2 are respectively connected with two different height reducing waveguides 3, the height reducing waveguides 3 and the mixer circuit substrate 4 form waveguide-suspension microstrip line transition through the RF probe 5 and the LO probe 6, the two height reducing waveguides 3 are connected on the mixer circuit substrate 4 through the suspension microstrip probe segments at intervals, and thus the transition conversion is realized between the RF input waveguide 1 and the LO input waveguide 2 and the suspension microstrip lines on the mixer circuit substrate 4; the frequency mixing circuit is a microwave planar integrated circuit and is realized by adopting suspended microstrip lines, the integrated circuit comprises a frequency mixing diode, the impedance matching is realized, the frequency mixing diode of the embodiment is a Schottky diode 7, the Schottky diode 7 is arranged on a frequency mixing circuit substrate 4 between two suspended microstrip probe segments, high-impedance lines are respectively connected between the Schottky diode 7 and an RF probe 5 and an LO probe 6, the high-impedance lines are connected with the frequency mixing circuit, the frequency mixing circuit is a suspended microstrip structure designed based on an integral circuit method, the frequency mixing circuit substrate 4 is provided with the frequency mixing circuit, the frequency mixing circuit is positioned in the cavity structure, the terahertz frequency mixer integrally adjusts the frequency mixing circuit through the Schottky diode 7, the frequency conversion efficiency is improved, the energy is converted into the intermediate frequency as much as possible, and the natural isolation from the radio frequency is realized.

In summary, the embodiment of the present invention utilizes the cut-off frequency of the waveguide and the natural isolation generated when the frequency conversion efficiency is improved, and compared with the terahertz frequency mixer with the local oscillator filter, the isolation is slightly poor, but the overall performance of the circuit is better, the processing difficulty is lower, and through proper design, the input suspended microstrip probe segment can be directly matched with the suspended microstrip at the schottky diode, and the design of matching circuits among the input probe, the CMRC low-pass filter (or high-low impedance filter) and the diode is not needed as in the design of the traditional frequency mixer, so that the design size of the circuit is greatly reduced.

This description describes examples of embodiments of the invention, and is not intended to illustrate and describe all possible forms of the invention. It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. A terahertz frequency mixer without a local oscillator filter structure is characterized by comprising an RF input waveguide, an LO input waveguide, a height reduction waveguide, a frequency mixing circuit substrate and a suspended microstrip probe segment, one end of the mixing circuit substrate is an IF microstrip output end, the other end of the mixing circuit substrate is a shielding cavity structure, the RF input waveguide and the LO input waveguide are respectively connected with two different height reducing waveguides, the two height reducing waveguides are connected on the mixing circuit substrate at intervals through the suspended microstrip probe segments, a Schottky diode is arranged between the two suspended microstrip probe segments, an RF probe and an LO probe are respectively arranged on the two suspended microstrip probe segments, high-impedance lines are connected between the Schottky diodes and the RF probe and between the Schottky diodes and the LO probe respectively, a mixing circuit is arranged on the mixing circuit substrate, and the mixing circuit is located in the cavity structure.

2. The terahertz frequency mixer without the local oscillator filter structure as claimed in claim 1, wherein the terahertz frequency mixer integrally adjusts a frequency mixing circuit through a schottky diode, improves frequency conversion efficiency, and enables energy to be converted into an intermediate frequency as much as possible, thereby realizing natural isolation of a local oscillator from a radio frequency.

3. The terahertz frequency mixer without the local oscillator filter structure as claimed in claim 2, wherein the RF input waveguide and the LO input waveguide respectively form cavity structures on two sides of the mixing circuit substrate, the cavity structures of the RF input waveguide and the LO input waveguide are symmetrical and form a closed waveguide, and the shielding cavity structure of the mixing circuit is also a closed waveguide.

4. The terahertz mixer without the local oscillator filter structure as claimed in claim 3, wherein the size of the closed waveguide structure changes with the change of the operating frequency.

5. The terahertz frequency mixer without the local oscillator filter structure as claimed in claim 2, wherein the frequency mixing circuit is a microwave planar integrated circuit implemented by using a suspended microstrip line.

6. The terahertz frequency mixer without the local oscillator filter structure of claim 4, wherein the frequency mixer comprises a mixing diode and is impedance matched.

7. The terahertz frequency mixer without the local oscillator filter structure as claimed in claim 5, wherein the mixing circuit is a suspended microstrip structure designed based on an overall circuit method.

8. The terahertz frequency mixer without the local oscillator filter structure as claimed in claim 6, wherein a section of high impedance line is arranged between the mixing diode and the RF probe and between the mixing diode and the LO probe, and the high impedance line is connected to the mixing circuit.