CN112332780A

CN112332780A - Broadband low-frequency conversion loss terahertz frequency mixer

Info

Publication number: CN112332780A
Application number: CN202011190645.8A
Authority: CN
Inventors: 熊阳; 裴乃昌; 何毅龙; 李凯
Original assignee: Southwest Electronic Technology Institute No 10 Institute of Cetc
Current assignee: Southwest Electronic Technology Institute No 10 Institute of Cetc
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2021-02-05
Anticipated expiration: 2040-10-30
Also published as: CN112332780B

Abstract

The invention discloses a broadband low-frequency conversion loss terahertz frequency mixer, and aims to achieve high isolation, simple structure, high working frequency, low frequency conversion loss and wide working bandwidth. The invention is realized by the following technical scheme: the quartz circuit cavity penetrates through the radio frequency height reducing waveguide and the local oscillator height reducing waveguide, the reverse parallel terahertz Schottky diode is arranged between a radio frequency direct current ground microstrip line and a radio frequency matching branch on the upper surface of the quartz substrate, the microstrip line is suspended through radio frequency transition in sequence, the local oscillator low-pass filter and the local oscillator matching network are connected in series, the local oscillator transition microstrip penetrates through the local oscillator height reducing waveguide, the intermediate frequency low-pass filter is connected in series, and finally the mixing frequency signal is output through the intermediate frequency port.

Description

Broadband low-frequency conversion loss terahertz frequency mixer

Technical Field

The invention relates to a solid terahertz device applied to the technical field of terahertz, in particular to a broadband low-frequency conversion loss terahertz frequency mixer.

Background

With the development of terahertz technology, terahertz solid-state devices exhibit unprecedented huge application potential in the fields of radio astronomy, nondestructive testing, object imaging, safety inspection, high-speed communication and the like. For a super heterodyne receiver of a terahertz frequency band, a mixer is an indispensable key device at a receiving front end, and can realize a frequency spectrum shifting function. However, due to the lack of a mature terahertz low-noise amplifier chip, the first stage of the terahertz receiving front end is usually a terahertz mixer, and therefore, the overall performance of the receiving system is greatly affected by the index of the mixer. For example, the magnitude of the conversion loss of the mixer directly determines the quality of the noise figure of the receiving front end. At present, solid terahertz down-conversion is mainly realized by using a GaAs Schottky diode. As a typical circuit design model, passive circuits of the terahertz subharmonic mixer based on the Schottky diode comprise a radio frequency transition circuit, a local oscillator low-pass filter and a local oscillator intermediate frequency duplexer. In order to pursue a higher suppression degree, the order of the filter of the conventional high-low impedance structure is often higher, and the size is larger, which obviously increases the transmission loss of signals on the transmission line. In order to obtain greater bandwidth benefits, radio frequency and local oscillator matching circuits are often relatively complex and bulky. In many published documents and patents, the rf ground loop is handled with almost the same design concept, i.e. the anti-parallel diode is located at the right side of the rf transition and grounded through the quarter-wave line, so that its bandwidth has a certain narrow-band characteristic.

The terahertz subharmonic mixer in the prior art has the following defects and shortcomings: in the traditional terahertz mixer design, a radio frequency signal is loaded on an anti-parallel diode, and the radio frequency ground loop design almost adopts a quarter-wave line for grounding treatment; the frequency mixer has low working frequency and narrow bandwidth. Generally, the manual assembly of the schottky diode inevitably has assembly errors and introduces parasitic capacitance inductance, so that the frequency shift and the low operating frequency are caused. Because the reverse parallel diode depends on a quarter-wave line for radio frequency grounding, the bandwidth of the reverse parallel diode has certain narrow-band characteristics; the mixer has a complex structure and large frequency conversion loss. The traditional terahertz frequency mixer is designed to separate a local oscillator radio frequency probe from matching, so that the final frequency mixer is easily overlong in structure. Too long of the quartz substrate would make the quartz substrate more easily broken, increasing the difficulty in processing and assembling the substrate, and would increase the transmission loss of the terahertz signal. In order to obtain greater bandwidth benefits, radio frequency and local oscillator matching circuits are often relatively complex and bulky. An excessively complex matching circuit not only increases or decreases the circuit size, but also increases the circuit loss, resulting in an increase in the frequency conversion loss.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the terahertz frequency mixer which is simple in structure, high in isolation, wide in working frequency band and low in frequency conversion loss.

The above object of the present invention can be achieved by the following technical solutions: a broadband low conversion loss terahertz mixer comprises: radio frequency subtracts high waveguide, and the local oscillator subtracts high waveguide, quartz circuit cavity and quartz circuit to silver thick liquid connection quartz circuit cavity, its characterized in that are paintd to quartz substrate bottom: the quartz circuit cavity penetrates through the radio frequency height reducing waveguide and the local oscillator height reducing waveguide, the reverse parallel terahertz Schottky diode 2 is arranged between a radio frequency direct current ground microstrip line 1 and a radio frequency matching branch 3 on the upper surface of the quartz substrate, the microstrip line 4 is suspended through radio frequency transition in sequence, the local oscillator low-pass filter 6, the local oscillator matching branch 7 and the local oscillator matching branch 8 are connected in series, the local oscillator transition microstrip 9 penetrates through the local oscillator height reducing waveguide 12, the intermediate frequency low-pass filter 10 is connected in series, and finally the mixing frequency signal is output through the intermediate frequency port 11.

Compared with the prior art, the invention has the following beneficial effects:

simple structure and low frequency conversion loss. Firstly, the radio frequency transition and radio frequency matching circuit in the invention are considered as a whole, so that the secondary design of the radio frequency matching circuit and the radio frequency transition circuit is avoided, and the radio frequency matching circuit is prevented from excessively using redundant circuits such as step impedance conversion and the like, thereby simplifying and simplifying the circuit size and reducing the frequency conversion loss. Secondly, the CMRC filter structure is shorter than the traditional stepped impedance filter structure, the length of a transmission line of the mixer is reduced, and therefore the transmission loss of signals is reduced.

The frequency mixer has high working frequency and wide bandwidth. The passive circuit of the frequency mixer and the reverse parallel diode can be integrated in a heterogeneous mode, so that parasitic capacitance and inductance and manual assembly errors caused by reverse adhesion and bonding of the diodes are avoided, and the working frequency and the stability of the diodes are greatly improved. The processing method of direct grounding of radio frequency can realize larger working bandwidth. The defect of narrow-band characteristics caused by the fact that a quarter-wave line is adopted for grounding in the traditional radio frequency ground loop design is overcome.

The isolation is high. The invention adopts the CMRC low-pass filter with high out-of-band rejection and the cut-off characteristic of the waveguide, thereby realizing high isolation of local oscillation, radio frequency and intermediate frequency signals. Due to the existence of the local oscillator low-pass filter, the radio frequency signal cannot leak to the local oscillator port and the intermediate frequency port. Similarly, the local oscillation signal is fed in through the standard waveguide, is coupled to the microstrip line through the local oscillation height reducing waveguide and the local oscillation transition microstrip, and can be loaded to the inverse parallel diode to the maximum extent after passing through the local oscillation matching network. Due to the existence of the intermediate frequency low pass filter, the local oscillation signal cannot leak to the intermediate frequency port. And due to the cut-off characteristic of the waveguide, the local oscillator signal cannot be leaked to the radio frequency port. Therefore, the local oscillator and the radio frequency have good isolation.

Drawings

FIG. 1 is a schematic structural diagram of a broadband low-conversion-loss terahertz frequency mixer according to the present invention;

in the figure, 1 radio frequency direct current ground microstrip, 2 reverse parallel terahertz Schottky diodes, 3 radio frequency matching branch nodes, 4 radio frequency transition suspension microstrip, 5 radio frequency height reducing waveguide, 6CMRC local oscillator low-pass filter, 7 local oscillator matching branch nodes, 8 local oscillator matching branch nodes, 9 local oscillator transition microstrip, 10CMRC intermediate frequency low-pass filter, 11 intermediate frequency output and 12 local oscillator height reducing waveguide.

The invention will be further explained with reference to the drawings.

Detailed Description

See fig. 1. In a preferred embodiment described below, a broadband low conversion loss terahertz mixer comprises: radio frequency subtracts high waveguide, and the local oscillator subtracts high waveguide, quartz circuit cavity and quartz circuit to silver thick liquid connection quartz circuit cavity, its characterized in that are paintd to quartz substrate bottom: the quartz circuit cavity penetrates through the radio frequency height reducing waveguide and the local oscillator height reducing waveguide, the reverse parallel terahertz Schottky diode 2 is arranged between a radio frequency direct current ground microstrip line 1 and a radio frequency matching branch 3 on the upper surface of the quartz substrate, the microstrip line 4 is suspended through radio frequency transition in sequence, the local oscillator low-pass filter 6, the local oscillator matching branch 7 and the local oscillator matching branch 8 are connected in series, the local oscillator transition microstrip 9 penetrates through the local oscillator height reducing waveguide 12, the intermediate frequency low-pass filter 10 is connected in series, and finally a mixing signal is output through the intermediate frequency output end 11.

The circuit sequence of the upper surface of the quartz substrate is sequentially a radio frequency direct current ground microstrip line 1, a reverse parallel Schottky diode 2, a radio frequency matching branch 3, a radio frequency transition suspension microstrip 4, a local oscillator low-pass filter 6, a local oscillator matching branch 7, a local oscillator matching branch 8, a local oscillator transition microstrip 9, a medium-frequency low-pass filter 10 and a medium-frequency output 11.

Radio frequency signals are fed in through a standard waveguide, coupled to a microstrip line through a radio frequency height reducing waveguide 5 and a radio frequency transition suspension microstrip 4, and loaded to the inverse parallel diode 2 after passing through the radio frequency matching stub 3. Due to the existence of the local oscillator low pass filter 6, the radio frequency signal cannot leak to the local oscillator port and the intermediate frequency port. Similarly, the local oscillation signal is fed in through the standard waveguide, coupled to the microstrip line through the local oscillation decreasing waveguide 12 and the local oscillation transition microstrip, and loaded onto the antiparallel diode 2 after passing through the local oscillation matching network and the local oscillation low pass filter. Due to the presence of the intermediate frequency low pass filter 10, the local oscillator signal cannot leak to the intermediate frequency port. And due to the cut-off characteristic of the waveguide, the local oscillator signal cannot be leaked to the radio frequency port. Therefore, the local oscillator and the radio frequency have good isolation.

The reverse parallel Schottky diode is positioned on the left side of the radio frequency transition and is directly grounded through a radio frequency direct current ground microstrip 1.

Particularly, the thickness of the quartz substrate may be 30 to 70 μm.

In particular, the radio frequency feed waveguide is a standard waveguide WR-5;

particularly, the local oscillator feed-in waveguide is a standard waveguide WR-10;

particularly, the radio frequency direct current ground microstrip 1 can be grounded by silver paste coating, substrate side wall metallization, gold wire bonding and other modes.

In particular, the local oscillator low-pass filter 6 is a third order CMRC low-pass filter.

In particular, the intermediate frequency low-pass filter 10 is a third order CMRC low-pass filter.

The above is a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions made by those skilled in the art based on the innovative concept of the present invention are within the scope of the present invention.

Claims

1. A broadband low conversion loss terahertz mixer comprises: radio frequency subtracts high waveguide, and the local oscillator subtracts high waveguide, quartz circuit cavity and quartz circuit to silver thick liquid connection quartz circuit cavity, its characterized in that are paintd to quartz substrate bottom: the quartz circuit cavity runs through the radio frequency height reducing waveguide and the local oscillator height reducing waveguide, the reverse parallel terahertz Schottky diode (2) is arranged between the radio frequency direct current ground microstrip line (1) and the radio frequency matching branch (3) on the upper surface of the quartz substrate, the suspended microstrip line (4) is suspended through radio frequency transition in sequence, the local oscillator low-pass filter (6) is connected in series, the local oscillator matching branch (7) and the local oscillator matching branch (8) are connected in series, the local oscillator height reducing waveguide (12) is run through the local oscillator transition microstrip (9), the intermediate frequency low-pass filter (10) is connected in series, and finally, a mixing signal is output through the intermediate frequency.

2. The broadband low conversion loss terahertz mixer of claim 1, wherein the antiparallel schottky diode is located on the left side of the radio frequency transition.

3. The broadband low conversion loss terahertz mixer according to claim 2, wherein the antiparallel Schottky diode is grounded through a radio frequency direct current ground microstrip line (1) or directly grounded.

4. The broadband low-conversion-loss terahertz frequency mixer as claimed in claim 1, wherein the radio frequency direct current ground microstrip line (1) is coated with silver paste, the substrate sidewall is metallized, and the grounding is realized by gold wire bonding.

5. The broadband low conversion loss terahertz frequency mixer according to claim 1, wherein the local oscillator low-pass filter (6) and the intermediate frequency low-pass filter (10) are third-order compact microstrip resonance unit (CMRC) low-pass filters.

6. The broadband low-conversion-loss terahertz frequency mixer according to claim 1, wherein the circuit on the upper surface of the quartz substrate is sequentially a radio frequency direct current ground microstrip line (1), an inverse parallel Schottky diode (2), a radio frequency matching branch (3), a radio frequency transition suspension microstrip (4), a local oscillator low-pass filter (6), a local oscillator matching branch (7), a local oscillator matching branch (8), a local oscillator transition microstrip (9), an intermediate frequency low-pass filter (10) and an intermediate frequency output (11).

7. The broadband low-conversion-loss terahertz frequency mixer according to claim 1, wherein a radio frequency signal is fed in through a standard waveguide, is coupled to a microstrip line through a radio frequency height-reducing waveguide (5) and a radio frequency transition suspension microstrip (4), and is loaded to the antiparallel diode (2) after passing through a radio frequency matching stub (3) on the left side of a transition structure.

8. The broadband low conversion loss terahertz mixer of claim 1, wherein the radio frequency feed waveguide is a standard waveguide WR-5.

9. The broadband low conversion loss terahertz frequency mixer according to claim 1, wherein the local oscillator feed-in waveguide is a standard waveguide WR-10.