CN110830040A

CN110830040A - U-frequency-band microwave direct modulation system

Info

Publication number: CN110830040A
Application number: CN201911056691.6A
Authority: CN
Inventors: 贺一峰; 徐进; 王永塔; 张毅; 周超; 宫景丰; 赵妍; 李�杰
Original assignee: Xian Institute of Space Radio Technology
Current assignee: Xian Institute of Space Radio Technology
Priority date: 2019-10-31
Filing date: 2019-10-31
Publication date: 2020-02-21
Anticipated expiration: 2039-10-31
Also published as: CN110830040B

Abstract

A U-band microwave direct modulation system comprising: the device comprises a C-band local oscillation circuit, a C-band amplifying circuit, a U-band 8-frequency doubling circuit, a U-band QPSK microwave direct modulation circuit and a level conversion circuit; the C frequency band local oscillation circuit takes a high-stability reference source as input, performs sampling phase locking on the high-stability reference source and generates C frequency band carrier waves with extremely low phase noise; the C frequency band amplifying circuit is used for amplifying and isolating the power of the C frequency band carrier with extremely low phase noise; the 8 frequency doubling circuit of the U frequency band is used for carrying out multiple harmonic frequency doubling and isolation on the amplified and isolated C frequency band carrier with extremely low phase noise so as to generate the carrier of the U frequency band; the level conversion circuit carries out bipolar transformation on external data to obtain bipolar level data; the QPSK microwave direct modulation circuit of the U frequency band modulates the phase of a carrier wave of the U frequency band under the drive of data of a bipolar level to realize QPSK modulation, obtains a QPSK modulation signal and outputs the signal after isolation.

Description

U-frequency-band microwave direct modulation system

Technical Field

The invention relates to a U-band microwave direct modulation system, and belongs to the technical field of U-band microwave direct modulation.

Background

In the field of satellite high-speed data transmission, the traditional use frequency is an X frequency band, along with the increasing transmission rate, the occupied bandwidth is increasing, and the number of satellites transmitted by each country is increasing, so that the X frequency band is crowded. At present, the KA frequency band is increasingly used as a scheme for solving the frequency conflict of the X frequency band. However, in the face of more and more applications, especially mobile communication satellite constellations, the number of satellites increases geometrically, for example, the size of the swan constellation which is setting up terms is calculated by thousands, which causes a problem that the problem of frequency interference among thousands of satellites becomes more and more prominent.

In the prior art, only the microwave direct modulator of X, KA is widely applied, and the U-band is used as the potential frequency of the next-stage microwave data transmission, so that the current frequency is too high, which brings huge challenges in the design of various millimeter wave microstrip circuits, and the current domestic and foreign has no successful U-band microwave direct modulation product, and the modulation task of data transfer to the U-band carrier wave cannot be realized. The concrete expression is as follows:

(1) at home and abroad, a mature U-band microwave direct modulation system is not available, baseband data cannot be modulated onto a phase carrier wave of 40-60 GHz, and a U-band satellite-ground and inter-satellite wireless data transmission function cannot be realized.

(2) The phase noise of the carrier wave in the U frequency band is difficult to control, and the phase noise of the carrier wave is directly related to the modulation performance, which directly affects the bit error rate of the wireless link. In the traditional circuit, the phase noise of the C wave band is basically less than or equal to-60 dBc/Hz @100Hz, less than or equal to-70 dBc/Hz @1kHz, less than or equal to-80 dBc/Hz @10kHz, less than or equal to-90 dBc/Hz @100kHz, if frequency doubling is carried out on the basis, even if the phase noise of the U frequency band calculated only according to theory (not considering the noise introduced by circuit nonidealities) is deteriorated by-20 log (8) ≦ 20dB, the output phase noise corresponds to less than or equal to-40 dBc/Hz @100Hz, less than or equal to-50 dBc/Hz @1kHz, less than or equal to-60 dBc/Hz @10kHz, less than or equal to-70 dBc/Hz @100 kHz; a link loss of > 11.3dB would be directly introduced and would not be tolerable by the system.

(3) The millimeter wave QPSK direct modulation layout with extremely high frequency is difficult to realize, based on the influence of the traditional plate and circuit processing precision, the serious influence of the width and radian of a millimeter wave slot line on the imbalance of modulation phase, the problem of wireless crosstalk of millimeter waves, the millimeter wave QPSK direct modulation layout is difficult to realize, the performance of the layout after being reluctantly realized is very poor, the indexes of a bare plate are that the amplitude imbalance is less than or equal to 3dB, the phase imbalance is less than or equal to 15 degrees, and the millimeter wave QPSK direct modulation layout can not be basically applied to the transmission of the practical U frequency.

Disclosure of Invention

The technical problem solved by the invention is as follows: the defects in the prior art are overcome, the direct U-band microwave modulation system is provided, data are directly modulated in the U-band through QPSK, and therefore the system can transmit the data in the new frequency band U-band, and the bottleneck problem of U-band transmission is solved.

The technical scheme of the invention is as follows: a U-band microwave direct modulation system comprising: the device comprises a C-band local oscillation circuit, a C-band amplifying circuit, a U-band 8-frequency doubling circuit, a U-band QPSK microwave direct modulation circuit and a level conversion circuit;

the C-band local oscillation circuit takes a high-stability reference source as input, performs sampling phase locking on the high-stability reference source, generates a C-band carrier wave with extremely low phase noise (the preferred frequency range is 5-8 GHz), and sends the C-band carrier wave to the C-band amplifying circuit;

the C frequency band amplifying circuit is used for amplifying and isolating the power of the C frequency band carrier with extremely low phase noise and then transmitting the C frequency band carrier to the 8 frequency doubling circuit of the U frequency band;

the 8-order harmonic frequency multiplication and isolation circuit of the U frequency band is used for carrying out 8-order harmonic frequency multiplication and isolation on the amplified and isolated C frequency band carrier with extremely low phase noise so as to generate a U frequency band carrier, and the U frequency band carrier is sent to the QPSK microwave direct modulation circuit of the U frequency band; (preferred frequency range of carrier wave in U band 40 to 60GHz)

The level conversion circuit carries out bipolar transformation on external data to obtain bipolar level data, and the bipolar level data are sent to a QPSK microwave direct modulation circuit of a U frequency band;

the QPSK microwave direct modulation circuit of the U frequency band modulates the phase of a carrier wave of the U frequency band under the drive of data of a bipolar level to realize QPSK modulation, obtains a QPSK modulation signal and outputs the signal after isolation.

Preferably, the C-band local oscillation circuit includes: a sampling frequency division phase discrimination circuit and a C-band CRO;

the sampling frequency division phase discrimination circuit converts a reference sinusoidal signal sent by an external high-stability reference source (the preferred frequency is 100MHz) into a sampling reference narrow pulse, samples the sinusoidal wave input by the C-band CRO circuit by the reference narrow pulse, and keeps the voltage at the sampling moment, so that the sampling and frequency division phase discrimination circuit continuously performs to form an error voltage; the error voltage becomes a CRO oscillation control voltage after passing through a loop filter, and is output to a C-band CRO circuit.

And the C-band CRO receives the CRO oscillation control voltage, oscillates under the control of the CRO oscillation control voltage, outputs a C-band frequency signal to the C-band amplifying circuit, and simultaneously couples out 1-path signal to be reversely fed to the sampling frequency-division phase-demodulation circuit.

The sampling frequency division phase discrimination circuit and the C-band CRO circuit are combined to form a loop, and when the loop is locked, a C-band single carrier with low phase noise is generated and sent to the C-band amplifier.

Preferably, the C-band amplifying circuit includes: a C-band amplifier, a first isolator;

and the C-band amplifier receives the C-band single carrier signal with low phase noise, amplifies the power of the C-band single carrier signal (preferably to +23dBm) and sends the amplified power to the first isolator.

The first isolator receives a single carrier signal of medium power, and the signal is transmitted to the microwave 8 frequency doubling circuit after microwave isolation and reflection prevention.

Preferably, the frequency 8 multiplier circuit for the U band includes: a microwave 8 frequency multiplier, a band-pass filter and a second isolator;

and the microwave 8 frequency multiplier receives a single-carrier signal with low phase noise in the C wave band, loads the single-carrier signal on the step diode after passing through an internal impedance converter, generates higher harmonics of input frequency and sends the higher harmonics to the band-pass filter.

And the band-pass filter is used for receiving millimeter wave frequency signals containing various harmonic components generated by the step diode, preferably suppressing 7 th harmonic and 9 th harmonic, preferably generating a U-band single carrier signal of 8 th harmonic signals, wherein the typical frequency is 48GHz, and sending the signal to the second isolator.

And the second isolator receives the single carrier signal of the U waveband, and the millimeter wave is isolated to prevent reflection and then is sent to the U waveband QPSK microwave direct modulation circuit.

Preferably, the QPSK microwave direct modulation circuit of the U band includes: a QPSK modulator and a third isolator of a U frequency band;

the QPSK modulator of the U-band receives a U-band single carrier (for a single-frequency signal with low phase noise, the preferred frequency is 48GHz) sent by the U-band 8 frequency doubling circuit, performs millimeter wave 0-degree common division on the two signals, and respectively enters the I \ Q path; simultaneously receiving two paths of bipolar data levels of I \ Q input by the level conversion circuit, and respectively carrying out respective phase inversion on the millimeter wave signals of the two paths of I \ Q under the control of the bipolar levels so as to form two paths of independent BPSK signals; and finally, synthesizing the millimeter wave 90-degree broadband to obtain a QPSK modulation signal of the millimeter wave in the U waveband, and sending the QPSK modulation signal to a third isolator.

And the third isolator receives the QPSK modulation signal of the millimeter wave of the U waveband, and the millimeter wave is isolated to prevent reflection and then sent out of the single machine.

Preferably, the high-stability reference source preferably requires: the external input high-stability reference source needs extremely low phase noise, and is generally defined as less than or equal to-65 dBc/Hz @1Hz, less than or equal to-97 dBc/Hz @10Hz, less than or equal to-127 dBc/Hz @100Hz, less than or equal to-150 dBc/Hz @1kHz, less than or equal to-155 dBc/Hz @10kHz, less than or equal to-157 dBc/Hz @100kHz, so that the modulation precision is further improved.

Preferably, the C-band carrier with extremely low phase noise preferably requires: compared with the traditional PLL phase-locked loop technology, the sampling phase-locked technology is adopted, and the low-phase-noise dielectric resonator oscillator CRO is adopted as the oscillator, so that the far-end phase noise and the near-end phase noise of the carrier signal after frequency multiplication are both close to theoretical values, namely, the far-end phase noise and the near-end phase noise are only deteriorated by-20 log (N) (wherein N is the frequency multiplication times). The C-band phase noise is generally defined as ≦ -90dBc/Hz @100Hz, ≦ -110dBc/Hz @1kHz, ≦ -115dBc/Hz @10kHz, and ≦ -117dBc/Hz @100kHz, further improving the accuracy of the modulation.

Preferably, the U-band carrier with extremely high frequency preferably requires: the U-band carrier range is 40 GHz-60 GHz, typically 48GHz, and the traditional PLL cannot realize frequency division phase discrimination with high frequency. Therefore, the millimeter wave step diode 8 frequency doubling direct frequency doubling method is adopted to realize the production of the ultrahigh frequency carrier.

Preferably, the U-band carrier with lower phase noise preferably requires: planning and distributing the phase noise of the whole carrier link, inputting a 100MHz nominal reference signal of the ultra-low phase noise from the outside at the forefront end, then adopting sampling lock-multiple 60 frequency multiplication, adopting CRO to obtain the C-band carrier of the ultra-low phase noise, and then directly multiplying the frequency by a millimeter step diode to realize the ultra-high frequency U-band carrier. The phase noise of the U-band carrier is generally defined as: less than or equal to-60 dBc/Hz @100Hz, less than or equal to-70 dBc/Hz @1kHz, less than or equal to-80 dBc/Hz @10kHz, and less than or equal to-90 dBc/Hz @100 kHz; the accuracy of the modulation is further improved.

Preferably, the external data, preferably requirements are: the external data input level is LVDS signals, the input signals are I \ Q signals with 2 paths, and the single-path signal rate is 150 Mbps. The accuracy of the modulation is further improved.

The preferred bipolar level of data preferably requires: after receiving data, the data is converted into LVDS differential signals through LVDS31, the LVDS differential signals are current mode signals, the current mode signals flow through a precision resistor in the forward direction or the reverse direction and are converted into voltages, bipolar levels with positive and negative polarities are generated easily, the signals are amplified and driven through an operational amplifier and then are sent to a QPSK microwave direct modulation circuit in a U frequency band, and therefore modulation is achieved. The performance requirements for bipolar levels are typically: 0. 1, the unequal width is less than 5 percent; the jump delay of the I \ Q path is less than or equal to 2 ns; the level amplitude is +/-0.65V; the positive and negative level symmetry is less than or equal to 0.05V; the accuracy of the modulation is further improved.

Preferably, the millimeter wave QPSK direct layout of the extremely high frequency is preferably required to: the millimeter wave circuit principle form of the QPSK modulator is innovated (different from the conventional circuit principle, the form is that a Wilkinson synthesizer firstly carries out 0-degree power division, then a BPSK phase shifter of a Schottky diode is carried out, and finally 90-degree synthesis of a Lange bridge is carried out; the radian of the slot line in the millimeter wave state is subjected to circular curvature processing by the coincidence point; redesigning and simulating each part of circuit in a millimeter wave state; the wireless crosstalk of millimeter waves after the whole layout is combined is simulated, optimized and adjusted, so that the circuit principle after the layout circuit is combined is ensured to realize the correctness. Index requirements for bare ideal input states of extremely high-frequency millimeter wave QPSK direct layouts: the amplitude imbalance is less than or equal to 0.5dB, the phase imbalance is less than or equal to 2 degrees, and the modulation precision is further improved.

Preferably, the carrier frequency range, preferably requires: the carrier frequency range for wireless transmission is 40-60 GHz. Preferably, the transmission code rate range preferably requires: the code rate range for wireless transmission is 1 Mbps-2 Gbps; further improving the modulation precision

Compared with the prior art, the invention has the advantages that:

(1) the U-band microwave direct modulation system designed by the invention realizes the modulation of baseband data to 40-60 GHz carrier waves, thereby being capable of using the U-band to perform the satellite-ground and inter-satellite wireless data transmission function, solving the problem of no U-band transmitting equipment and filling the domestic blank

(2) The invention designs a U-band microwave direct modulation system, which is a cascaded U-band low-phase-noise carrier generation scheme, and finally generates phase noise of a U-band carrier, harmonic waves and clutter of the U-band carrier, so that the transmission requirement can be met, the modulation loss can not be caused under the E-7 bit error rate in actual measurement, and the U-band carrier index is good.

(3) The invention designs a U-band microwave direct modulation system, wherein a QPSK direct modulation circuit of a U-band is a BPSK phase shifter based on a Schottky diode, a microstrip-slot line-microstrip transition structure, a Lange bridge and a Wilkinson synthesizer are designed on a ceramic chip in a smart way, and after the layout is put into production, a QPSK modulation signal of the U-band can be generated after electric installation. The modulation performance meets the index requirements that the amplitude imbalance is less than or equal to 0.5dB and the phase imbalance is less than or equal to 2 degrees, the performance is excellent, and the domestic blank is filled.

(4) The invention provides a U-band microwave direct modulation system, which directly modulates data in a U-band by QPSK, thereby enabling the system to transmit data in a new band U-band, solving the bottleneck problem of U-band transmission, supporting the system demonstration of U-band transmission and filling the domestic blank. In the U-band microwave direct modulation system, a cascaded U-band low-phase-noise carrier generation scheme is also designed, so that the phase noise, harmonic waves and clutter of the finally generated U-band carrier can meet the emission requirement, the modulation loss cannot be caused under the E-7 bit error rate in actual measurement, and the U-band carrier index is good. In addition, in a modulation system, a QPSK direct modulation circuit of a U frequency band is invented, a BPSK phase shifter based on a Schottky diode, a microstrip-slot line-microstrip transition structure, a Lange bridge and a Wilkinson synthesizer are designed on a ceramic chip ingeniously, a QPSK modulation signal of the U frequency band can be generated after the electric mounting of a layout after production, the modulation performance is good, and the domestic blank is filled.

Drawings

FIG. 1 is a block diagram of a U-band microwave direct modulation method;

FIG. 2 is a block diagram of U-band carrier generation;

FIG. 3 is a schematic block diagram of 8 th harmonic frequency multiplication;

fig. 4 is a schematic block diagram of a U-band QPSK modulator;

fig. 5 is a QPSK modulator layout of the U band;

FIG. 6 is a schematic block diagram of a level shift circuit;

FIG. 7 is a schematic diagram of a DC/DC module topology;

fig. 8 is a block diagram of a scheme for implementing a 48GHz local oscillator by using sampling phase locking.

FIG. 9 is a first schematic diagram of a sampling phase-locked circuit;

FIG. 10 is a second schematic diagram of a sampling phase-locked circuit;

FIG. 11 is a third schematic diagram of a sampling phase-locked circuit;

FIG. 12 is a schematic block diagram of an 8-multiplier;

fig. 13 is a block diagram of a QPSK modulator;

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

The invention relates to a U-band microwave direct modulation system, which comprises: the device comprises a C-band local oscillation circuit, a C-band amplifying circuit, a U-band 8-frequency doubling circuit, a U-band QPSK microwave direct modulation circuit and a level conversion circuit; the C frequency band local oscillation circuit takes a high-stability reference source as input, performs sampling phase locking on the high-stability reference source and generates C frequency band carrier waves with extremely low phase noise; the C frequency band amplifying circuit is used for amplifying and isolating the power of the C frequency band carrier with extremely low phase noise; the 8 frequency doubling circuit of the U frequency band is used for carrying out multiple harmonic frequency doubling and isolation on the amplified and isolated C frequency band carrier with extremely low phase noise so as to generate the carrier of the U frequency band; the level conversion circuit carries out bipolar transformation on external data to obtain bipolar level data; the QPSK microwave direct modulation circuit of the U frequency band modulates the phase of a carrier wave of the U frequency band under the drive of data of a bipolar level to realize QPSK modulation, obtains a QPSK modulation signal and outputs the signal after isolation. FIG. 1 is a block diagram of a U-band microwave direct modulation method; CRO in fig. 1: (Coaxial-resonator oscillator) Coaxial dielectric oscillator; QPSK (QuadriPhase Shift Keying) QuadriPhase Shift Keying; fig. 2 is a block diagram of U-band carrier generation, and SPD in fig. 2: (Sample Phase Detector) sampling Phase Detector; LOOP AMP: loop filter

In the field of satellite high-speed data transmission, the traditional use frequency is increasingly used in an X frequency band and a KA frequency band, and the completion of a space mission is influenced. Therefore, it is necessary to perform advanced pre-research on potential frequencies except X, KA, and the U-band, which is the next frequency band of X, KA frequency band, has the advantages of less pollution, wider frequency range and greater technical implementation possibility, so that the development of a microwave direct modulator of the U-band has great prospective significance.

Compared with the prior art, the microwave direct modulator is obviously different, in the prior art, only the microwave direct modulator of X, KA is widely applied, the U frequency band is used as the potential frequency of the next-stage microwave data transmission, the current frequency is too high, great challenges are brought in the design aspects of various millimeter wave microstrip circuits, the current domestic and foreign successful U frequency band microwave direct modulation products are not available, and the modulation task of data transfer to the U frequency band carrier wave cannot be realized.

The invention designs a U-band microwave direct modulation system, which directly modulates data in a U-band by QPSK, thereby enabling the system to transmit data in a new band U-band, solving the bottleneck problem of U-band transmission, supporting the system demonstration of U-band transmission and filling the domestic blank. In the U-band microwave direct modulation system, a cascaded U-band low-phase-noise carrier generation scheme is also designed, so that the phase noise, harmonic waves and clutter of the finally generated U-band carrier can meet the emission requirement, the modulation loss cannot be caused under the E-7 bit error rate in actual measurement, and the U-band carrier index is good. In addition, in a modulation system, a QPSK direct modulation circuit of a U frequency band is invented, a BPSK phase shifter based on a Schottky diode, a microstrip-slot line-microstrip transition structure, a Lange bridge and a Wilkinson synthesizer are designed on a ceramic chip ingeniously, a QPSK modulation signal of the U frequency band can be generated after the electric mounting of a layout after production, the modulation performance is good, and the domestic blank is filled.

As shown in fig. 1, the system of the present invention comprises: the device comprises a C-band local oscillation circuit, a C-band amplifying circuit, a U-band 8-frequency doubling circuit, a U-band QPSK microwave direct modulation circuit and a level conversion circuit. The C-band local oscillator circuit takes a high-stability reference source as input, performs sampling phase locking on the high-stability reference source, generates a C-band carrier wave (the frequency range is preferably 5-8 GHz) with extremely low phase noise, and sends the C-band carrier wave to the C-band amplifying circuit; the C frequency band amplifying circuit is used for amplifying and isolating the power of the C frequency band carrier with extremely low phase noise and then transmitting the C frequency band carrier to the 8 frequency doubling circuit of the U frequency band; the 8-order harmonic frequency multiplication and isolation circuit of the U frequency band is used for carrying out 8-order harmonic frequency multiplication and isolation on the amplified and isolated C frequency band carrier with extremely low phase noise so as to generate a U frequency band carrier, and the U frequency band carrier is sent to the QPSK microwave direct modulation circuit of the U frequency band; (the frequency range of the carrier wave in the U frequency band is preferably 40-60 GHz); the level conversion circuit carries out bipolar transformation on external data to obtain bipolar level data, and the bipolar level data are sent to a QPSK microwave direct modulation circuit of a U frequency band; (ii) a The QPSK microwave direct modulation circuit of the U frequency band modulates the phase of a carrier wave of the U frequency band under the drive of data of a bipolar level to realize QPSK modulation, obtains a QPSK modulation signal and outputs the signal after isolation.

As shown in fig. 2, the C-band local oscillation circuit preferably includes: a sampling frequency division phase discrimination circuit and a C-band CRO;

the sampling frequency division phase discrimination circuit converts a reference sinusoidal signal sent by an external 100MHz high-stability reference source into a sampling reference narrow pulse, samples a sinusoidal wave input by the C-band CRO circuit by the reference narrow pulse, and keeps the voltage at the sampling moment, so that an error voltage is formed continuously; the error voltage becomes a CRO oscillation control voltage after passing through a loop filter, and is output to a C-band CRO circuit.

As shown in fig. 2, the C-band amplifying circuit preferably includes: a C-band amplifier, a first isolator;

and the C-band amplifier receives the C-band single carrier signal with low phase noise, amplifies the power of the C-band single carrier signal to +23dBm and then sends the power to the first isolator.

As shown in fig. 3, the frequency-8 multiplier circuit for the U band preferably includes: a microwave 8 frequency multiplier, a band-pass filter and a second isolator;

As shown in fig. 4, the QPSK microwave direct modulation circuit of the U band preferably includes: a QPSK modulator and a third isolator of a U frequency band;

the QPSK modulator of the U band receives a U band single carrier (a single frequency signal with low phase noise, and a typical frequency is 48GHz) sent by the U band 8 frequency doubling circuit, and performs millimeter wave 0 degree power division on two signals, as shown in fig. 5, and enters I \ Q two paths respectively; simultaneously receiving two paths of bipolar data levels of I \ Q input by the level conversion circuit, and respectively carrying out respective phase inversion on the millimeter wave signals of the two paths of I \ Q under the control of the bipolar levels so as to form two paths of independent BPSK signals; finally, millimeter wave 90-degree broadband synthesis is preferably performed, so that a QPSK modulation signal of the millimeter wave in the U waveband is obtained and is sent to the third isolator.

The invention has the following preferable requirements on an external high-stability reference source: an externally input highly stable reference source requires very low phase noise, typically defined as ≦ -65dBc/Hz @1Hz, ≦ -97dBc/Hz @10Hz, ≦ -127dBc/Hz @100Hz, ≦ -150dBc/Hz @1kHz, ≦ -155dBc/Hz @10kHz, ≦ -157dBc/Hz @100 kHz.

As shown in fig. 2, the preferred scheme of the C-band carrier with very low phase noise is as follows: compared with the traditional PLL phase-locked loop technology, the sampling phase-locked technology is adopted, and the low-phase-noise dielectric resonator oscillator CRO is adopted as the oscillator, so that the far-end phase noise and the near-end phase noise of the carrier signal after frequency multiplication are both close to theoretical values, namely, the far-end phase noise and the near-end phase noise are only deteriorated by-20 log (N) (wherein N is the frequency multiplication times). C-band phase noise is typically defined as ≦ -90dBc/Hz @100Hz, ≦ -110dBc/Hz @1kHz, ≦ -115dBc/Hz @10kHz, and ≦ -117dBc/Hz @100 kHz.

As shown in fig. 2, the preferable scheme of the U-band carrier with extremely high frequency is as follows: the U-band carrier range is 40 GHz-60 GHz, typically 48GHz, and the traditional PLL cannot realize frequency division phase discrimination with high frequency. Therefore, the millimeter wave step diode 8 frequency doubling direct frequency doubling method is adopted to realize the production of the ultrahigh frequency carrier.

The preferred scheme of the U-band carrier with lower phase noise is as follows: planning and distributing the phase noise of the whole carrier link, inputting a 100MHz nominal reference signal of the ultra-low phase noise from the outside at the forefront end, then adopting sampling lock-multiple 60 frequency multiplication, adopting CRO to obtain the C-band carrier of the ultra-low phase noise, and then directly multiplying the frequency by a millimeter step diode to realize the ultra-high frequency U-band carrier. The phase noise of the U-band carrier is generally defined as: less than or equal to-60 dBc/Hz @100Hz, less than or equal to-70 dBc/Hz @1kHz, less than or equal to-80 dBc/Hz @10kHz, and less than or equal to-90 dBc/Hz @100 kHz.

The external data of the invention preferably comprises: the external data input level is LVDS signals, the input signals are I \ Q signals with 2 paths, and the single-path signal rate is 150 Mbps.

As shown in fig. 6, the data of the bipolar level preferably includes: after receiving data, the data is converted into LVDS differential signals through LVDS31, the LVDS differential signals are current mode signals, the current mode signals flow through a precision resistor in the forward direction or the reverse direction and are converted into voltages, bipolar levels with positive and negative polarities are generated easily, the signals are amplified and driven through an operational amplifier and then are sent to a QPSK microwave direct modulation circuit in a U frequency band, and therefore modulation is achieved. The preferred performance requirements for bipolar levels in general are: 0. 1, the unequal width is less than 5 percent; the jump delay of the I \ Q path is less than or equal to 2 ns; the level amplitude is +/-0.65V; the positive and negative level symmetry is less than or equal to 0.05V; the modulation accuracy is further improved.

As shown in fig. 5, the millimeter wave QPSK direct layout of the extremely high frequency is preferably: the millimeter wave circuit principle form of the QPSK modulator is innovated (different from the conventional circuit principle, the form is that a Wilkinson synthesizer firstly carries out 0-degree power division, then a BPSK phase shifter of a Schottky diode is carried out, and finally 90-degree synthesis of a Lange bridge is carried out; the radian of the slot line in the millimeter wave state is subjected to circular curvature processing by the coincidence point; redesigning and simulating each part of circuit in a millimeter wave state; the wireless crosstalk of millimeter waves after the whole layout is combined is simulated, optimized and adjusted, so that the circuit principle after the layout circuit is combined is ensured to realize the correctness. Index requirements for bare ideal input states of extremely high-frequency millimeter wave QPSK direct layouts: the amplitude imbalance is less than or equal to 0.5dB, and the phase imbalance is less than or equal to 2 degrees.

The carrier frequency range of the invention is preferably as follows: the carrier frequency range for wireless transmission is 40-60 GHz.

The transmission code rate range of the present invention preferably includes: the code rate range for wireless transmission is 1Mbps to 2 Gbps.

Further preferred embodiments of the present invention are as follows:

the C-band local oscillation circuit preferably takes a 100MHz high-stability reference source as input, generates a C-band carrier wave with extremely low phase noise by adopting sampling phase locking, and preferably has a frequency range of 5-8 GHz;

the C frequency band amplifying circuit amplifies the optimized 5-8 GHz carrier power to an optimized 23dBm or other enough power value;

the 8-order harmonic frequency multiplication is carried out on the 8-order frequency multiplication circuit of the U frequency band by using a step diode, so that an optimal carrier wave of 40-60 GHz is generated;

the U-band-pass filter suppresses other harmonic waves generated by the 8-order frequency multiplier, and further preferably suppresses 7-order and 9-order harmonic waves by more than 25 dB;

the QPSK direct modulation circuit of the U frequency band preferably consists of two BPSK modulators, an in-phase power divider and a quadrature power synthesizer, and realizes QPSK modulation of the U frequency band on data;

the level switching circuit realizes bipolar conversion of data level and meets the requirement of the modulation diode on the data level.

The U-band microwave direct modulation method preferably comprises the design of a C-band local oscillator circuit, a C-band amplifying circuit, an 8-frequency doubling circuit of a U-band, a U-band-pass filter, a QPSK microwave direct modulation circuit of the U-band and a level conversion circuit, and comprises the following steps:

c frequency channel local oscillator circuit, the preferred scheme is:

the sampling phase locking scheme design is used. The sampling phase-locked loop consists of a sampling phase discriminator, a loop filter and a capturing circuit. The sampling phase discriminator converts the reference signal into a narrow pulse with the same repetition frequency as the reference signal, the reference pulse samples the sine wave of the CRO, and the holding circuit holds the sampled voltage to the next period. When CRO is integral multiple of reference frequency and keeps strict phase synchronization, the sampling phase discriminator outputs a stable direct current voltage, and the loop is locked; otherwise, the discrete sample voltage will be a continuous stepped beat voltage through the holding circuit, pulling the CRO frequency until locked. The sampling phase-locked loop belongs to an analog phase-locked loop, and a phase discriminator of the sampling phase-locked loop does not have a frequency discrimination function, so that the difference between the CRO frequency and the reference frequency is large when the phase-locked loop is started, the loop cannot be locked by depending on the self-capturing capability of the loop, an auxiliary capturing circuit needs to be introduced to carry out frequency traction on the CRO, and when the CRO frequency scans the quick-capture zone of the loop, the loop locking is realized by depending on the self-capturing capability of the loop.

In order to effectively isolate the low frequency and the radio frequency in space, the frequency doubling circuit consists of two mutually independent single boards, namely a sampling phase locking circuit, a CRO (cross reference point) and an amplifying circuit, and each single board is provided with an independent cover plate.

The sampling phase-locked circuit preferably consists of 100MHz reference amplification, a sampling phase discriminator, a loop filter and a voltage stabilizing circuit. The preferred 100MHz reference amplifier selects rubidium clock input, the sampling phase discriminator is MSPD-xxxx, and the loop filter and the spread-capture circuit mainly comprise a preferred operational amplifier OP470 and peripheral resistance-capacitance components.

The CRO and amplifying circuit mainly comprises a voltage-controlled oscillator CRO, a power amplifier in an S frequency band and a directional coupler. The CRO preferably achieves low phase noise using coaxial dielectric resonator frequency stabilization.

The preferred scheme of the C-band amplifying circuit is as follows: :

since the 8-multiplier requires a large (≧ 20dBm) input drive level, a medium power amplifier is preferred to accomplish the amplification of the CRO output signal. The amplifier is preferably selected taking into account the following points as preferred solutions:

p-1 of the output is more than or equal to 23dBm

Gain is more than or equal to 15dB

Gain stability is better than +/-1 dB

Through the preferred scheme, the modulation precision of the whole system is improved, and an amplifier with low power consumption is further preferably selected.

The preferred scheme of the 8-frequency multiplier circuit of the U frequency band is as follows:

the microwave frequency multiplier preferably consists of an input impedance transformer, an output filter, a step diode, etc., as shown in fig. 3. The frequency multiplier works in a self-bias mode, input power is added to a step diode after passing through an input isolator and an input impedance converter to generate higher harmonics of input frequency, desired 8 harmonics are selected through an output filter and then output from the output isolator, and meanwhile, direct-current working points of the diodes can be maintained in a better range by adding direct-current voltage generated by the diodes to a self-bias resistor R1, so that the efficiency is improved, inconvenience of external power supply is avoided, and the design is simplified.

The step diode is preferably a microwave step diode WY46 manufactured by information industry sector 55, which is already used in models XX-5, HY-1, etc., and can be used in the U band through communication with 55 designers. The input-output filter and the diode self-bias circuit are fabricated on a ceramic die.

The preferred scheme of the U-band-pass filter is as follows:

since the filter in the frequency multiplier cannot meet the requirement of other harmonic suppression, a band-pass filter is required to be added behind the frequency multiplier to suppress other harmonics generated by the frequency multiplier, and the suppression on 7 th order and 9 th order harmonics is preferably more than 25 dB. The circuit form is the same as the filter in the frequency multiplier, and adopts the form of parallel coupling lines.

The QPSK microwave direct modulation circuit of U frequency band, the preferred scheme is:

the QPSK microwave direct modulator scheme is composed of two BPSK modulators, an in-phase power divider, a quadrature power combiner, and two baseband low-pass filters, and the principle is as shown in fig. 4. The input carrier is divided into two paths by a 3dB in-phase power divider, then the two paths of carriers are subjected to 0/pi modulation by I, Q two paths of BPSK modulators, and finally synthesized into a QPSK modulation signal by a 90-degree phase-shift synthesizer for output. Ideally, the output signal is an error-free four-phase modulated signal. However, the actual power divider and the mixer have certain amplitude and phase errors, and the BPSK modulators of the two branches cannot be completely consistent. These factors all affect the modulation accuracy of the modulator. This also puts higher demands on the choice of circuit form and the machining accuracy.

In the aspect of components, only one component, namely a Schottky diode in a BPSK modulator, is used in the circuit, the model is 4E2037(MACOM), and the device can be screened and upgraded to an aerospace-grade product by a third party.

The preferred scheme of the level conversion circuit is as follows:

the received LVDS signal I, Q signals are as follows:

the code rate is preferably: 150Mbps

The level is preferably: LVDS level

The data processor directly sends I, Q two paths of preferred 150Mbps data, the data is converted into TTL level after being received by LVDS32, the TTL level is converted into differential level through LVDS31, the differential level is sent to LMH6702, the bipolar level signal is converted, and the bipolar level signal is sent to the modulation circuit for modulation. See figure 6 for details.

The invention discloses a U-band microwave direct modulation method, which comprises the following steps: c frequency range local oscillator circuit, C frequency range amplifier circuit, the 8 frequency doubling circuit of U frequency range, U frequency range band pass filter, the QPSK microwave direct modulation circuit of U frequency range, level conversion circuit design, preferred working method is:

(1) the input data is converted to the bipolar levels required by the BPSK modulator diodes by level shifting circuitry.

(2) And the C-band local oscillator circuit takes the preferred 100MHz of an externally input rubidium clock as a reference signal and multiplies the frequency to the C-band 6GHz by adopting a sampling phase-locking mode.

(3) The C-band amplifying circuit amplifies the power of a single-frequency-point signal of 6GHz to a preferable 23 dBm. And the C frequency band amplifying circuit inherits the capture amplifying circuit of the sampling phase lock.

(4) 8 times of the U frequency band use 8 times of harmonic frequency to obtain the preferred carrier signal of 48 GHz.

(5) The U-band bandpass filter re-filters the preferred 7 th or 9 th harmonic of the preferred 48GHz carrier signal, ensuring that the far-end frequency of the carrier signal is relatively clean.

(6) The bipolar level of data is input to a data port of a QPSK microwave direct modulation circuit of a U-band, then the level can cause a Schottky diode to be switched on or switched off, so that the impedance of a signal on a slot line is influenced to be in a switched-on or switched-off state, a carrier signal is influenced to be transmitted through an upper branch or a lower branch, the signal path difference transmitted by 2 branches causes 180-degree phase shift of the signal, and the BPSK modulation is realized based on the phase shift. And then, orthogonal 2-path BPSK vector synthesis is realized based on a 0-degree power divider and a 90-degree synthesizer, so that QPSK modulation is realized.

The parameter decomposition of the invention preferably comprises the following steps:

based on the realization of a microwave direct modulation system of a U frequency band, key indexes of the system need to be decomposed. The main index determining the modulation performance is the modulation loss in the radio link, i.e. the modulation loss can ultimately characterize the performance of the modulation system.

To improve modulation system performance, the following factors are preferably determined:

the phase noise of the carrier wave is preferably as follows: when the carrier phase noise is better than less than or equal to-60 dBc/Hz @100Hz, less than or equal to-70 dBc/Hz @1kHz, less than or equal to-80 dBc/Hz @10kHz, and less than or equal to-90 dBc/Hz @100kHz, the further improvement of the phase noise has no obvious effect on reducing the modulation loss in the wireless link. And when the phase position gradually deteriorates and deteriorates by 20dB, namely the indexes are inferior to more than or equal to-40 dBc/Hz @100Hz, more than or equal to-50 dBc/Hz @1kHz, more than or equal to-60 dBc/Hz @10kHz, more than or equal to-70 dBc/Hz @100kHz, the demodulator cannot lock the carrier wave, and the whole wireless link fails. Therefore, to ensure good modulation performance and ensure modulation function and performance, the carrier phase noise should satisfy the following criteria: less than or equal to-60 dBc/Hz @100Hz, less than or equal to-70 dBc/Hz @1kHz, less than or equal to-80 dBc/Hz @10kHz, and less than or equal to-90 dBc/Hz. Therefore, the phase noise of the whole carrier link must be uniformly budgeted, and table 1 below is a phase noise budget table of the system.

TABLE 1 Link budget Table for phase noise

The bipolar level waveform quality is preferably as follows: the bipolar level is directly applied to the millimeter wave Schottky diode, and is controlled to be switched on or switched off, so that the signal impedance on the slot line is influenced to be in a switched-on or switched-off state, the carrier signal is influenced to be transmitted through the upper branch or the lower branch, and the signal path difference transmitted by the 2 branches causes 180-degree phase shift of the signal. Therefore, the bipolar level waveform quality directly influences the modulation performance, and particularly influences the indexes of I \ Q amplitude imbalance and phase imbalance of the modulation system. The waveform quality of the bipolar level is specifically determined by several factors: 0. 1, the unequal width is less than 5 percent; the jump delay of the I \ Q path is less than or equal to 2 ns; the level amplitude is +/-0.65V; the symmetry of the positive and negative levels is less than or equal to 0.05V. Specific IQ amplitude imbalance and phase imbalance index decomposition budget tables, i.e. table 2, are as follows:

TABLE 2 Link budget TABLE with unbalanced amplitude and unbalanced phase

The engineering of the millimeter wave circuit realizes the optimal design requirement on the structure: due to the complexity of the U-band microwave direct modulation system and the designed frequency of 48GHz, the circuit is designed at such a high frequency, the electrical performance and the whole machine adaptation are ensured, and the design of structural matching with the electrical performance is important. The following structural design measures are taken to finally ensure the functions and performances of each key millimeter wave circuit and other circuits.

Since the signal in the U-band modulator covers various frequencies from 100M reference to 48G rf output and also has low-frequency signals such as digital signals, power supply, etc., in order to prevent mutual interference, it is preferable to design a plurality of cavities in the modulator to be isolated from space, and to design a small cover plate for each cavity.

For the radio frequency link, it is preferable that each ceramic chip is designed with a small cavity with a cover plate to enhance its EMC performance.

The further preferable scheme of the invention is as follows: the data interface used by the invention is I, Q-path LVDS signal input in total, and the modulation of 300Mbps code rate can be realized; if the interface is changed to be a CML level interface, the CML level is directly used for driving the operational amplifier so as to generate a bipolar level, and the transmission code rate can be further improved to 2 Gbps;

the system of the invention preferably uses a primary power supply, converts the primary power supply into secondary voltage for each circuit, has the function of doubling the frequency of an externally supplied 100MHz reference source to a U wave band, has the function of receiving I, Q paths of 150Mbps LVDS data, performs level conversion on the received data to form the function of I, Q paths of data, directly modulates the data onto a U carrier, and adopts QPSK modulation; the function of executing relevant instructions and providing corresponding telemetry is provided; double-machine cold backup

Among the performance index requirements of the system of the present invention, the requirements for the interface are preferably: the data input interface adopts a DEM9P1B7N high-contact plug-in module of ITT company. Preferred parameters are as follows:

a) data level: LVDS;

b) number of data signal paths: I. q is 1 path;

c) i, Q each 150Mbps per lane;

input interface with 100MHz reference source

The reference source input interface adopts an SMA connector.

Frequency 100MHz

Signal level: 3 + -1 dBm

Output impedance of 50 omega

Phase noise: less than or equal to-65 dBc/Hz @1Hz

≤-97dBc/Hz@10Hz

≤-127dBc/Hz@100Hz

≤-150dBc/Hz@1kHz

≤-155dBc/Hz@10kHz

≤-157dBc/Hz@100kHz

≤-157dBc/Hz@1MHz

In the performance index requirements of the system of the present invention, the preferred scheme for performance is as follows

The QPSK modulator specification requirement is preferably:

a) modulation scheme QPSK

b) Amplitude imbalance of better than 1dB

c) Phase imbalance better than + -3 °

d) Channel code rate: 300Mbps

The U carrier index requirement is preferably:

a) frequency 48GHz

b) And (3) inhibiting clutter inside and outside the band:

in-band: better than 60dBc (48GHz +/-200 MHz);

out of band: 60dBc, rear end connected with U output filter 4(QSXB117-3) and tested

a) Harmonic suppression: better than 30dBc

b) Single sideband phase noise power spectral density is preferred

L(100Hz)≤-60dBc/Hz

L(1kHz)≤-70dBc/Hz

L(10kHz)≤-80dBc/Hz

L(100kHz)≤-90dBc/Hz

The preferred scheme of the functional module in the invention is as follows:

the U-modulator should preferably have the following functions:

the power interface is preferably a +100V primary power supply, the power supply of the internal circuit of the equipment adopts a secondary power supply, and the on-off is controlled

Receiving LVDS data signals

Has the function of realizing the level conversion of the I and Q two paths of 150MHzbps data

Providing output state telemetry

QPSK modulated signal capable of outputting ≧ 22dBm

Satisfying phase noise of modulated carrier

According to the above main functions, and considering the modulator back end with a linearized traveling wave tube amplifier, the apparatus should have the following components: the system comprises a DC/DC power supply module, a startup and shutdown instruction execution module, a data receiving and processing module, a telemetering level generation module, a QPSK modulation module, a carrier generation module for ensuring the modulation of carrier phase noise and a carrier frequency doubling module.

The preferred implementation scheme of each module is as follows:

the DC/DC power supply module adopts a PCB single-board type DC/DC module developed by the institute of microwave technology of the Western institute of Security, and by adopting the design scheme, the input of a +100V bus can be adapted, the reliability is improved, and the functions of on-off control, on-off remote measurement, voltage remote measurement and the like are designed on one PCB.

The startup and shutdown instruction execution module adopts a photoelectric coupler GH302, receives the driving control of a startup and shutdown instruction, and performs on-off control on the circuit power supply of the whole machine, thereby realizing the remote control function of startup and shutdown.

The telemetering level generating module adopts a method of direct current limiting resistance voltage division.

The QPSK modulation module selects direct modulation in the U wave band, and compared with the method of performing up-conversion after modulation, the QPSK modulation module has the advantages that a frequency converter and a frequency conversion local oscillator signal generation circuit are reduced, the complexity of the whole machine is reduced, and the reliability is improved.

And the modulation carrier generation module adopts a sampling phase-locked circuit according to the analysis of the phase noise, supplies a 100MHz reference source externally, directly discriminates the phase to 6000MHz through a sampling phase discriminator, thus obtaining good phase noise, and adds an amplifier at the back end of the 6000MHz local oscillator output to boost the power of the 6000MHz local oscillator output to saturation so that the local oscillator output power is stabilized to 20 dBm.

And the carrier frequency doubling module adopts a passive 8-frequency doubling circuit according to the overall reliability requirement, obtains higher harmonics by exciting a step diode, and isolates and outputs a 48GHz carrier signal. However, the passive 8-frequency multiplier circuit has large power change under temperature, and an ALC + traveling wave tube amplifier is generally used at the rear end of the modulator, so that the power of the system is stable.

The data receiving and processing module is used for transmitting 150MHz LVDS data of I and Q paths to the modulator through the data processor, has high transmission rate and cannot be processed by using an FPGA (field programmable gate array), so that the LVDS data is realized by level conversion through a CMOS (complementary metal oxide semiconductor) device, but has high requirements on phase difference of the I and Q paths output to the modulator by the data processor because resampling comparison of data is not carried out in the modulator.

The preferred scheme of the U-band QPSK modulator is as follows:

ITT, AIRBORN Low frequency connector, 853 Mill, Radiallel radio frequency connector was used. The single machine consists of two box bodies, wherein one box body is a power management unit and is used for completing the sending and the collection of primary electric input, DC/DC conversion, secondary electric output and remote control and remote measurement, and the other box body is respectively a modulator and is used for completing the functions of level conversion, carrier generation, amplification, frequency doubling, filtering, microwave modulation and the like.

The U-band QPSK modulator stand-alone product comprises an XX-X satellite signal forwarding and data transmission subsystem U modulator module and a power management module.

The power management module mainly completes the conversion from primary electricity to secondary electricity of the modulator, and the functions of startup and shutdown, remote control and remote measurement.

The modulator module internally comprises: the device comprises a secondary electric conversion module, a level conversion module, a QPSK microwave modulation module, a C-band carrier generation and amplification module and a microwave 8 frequency doubling and filtering module. Wherein, 100MHz reference frequency is sent out, and then the C wave band carrier signal is generated through sampling and locking times, and then the C wave band carrier signal is amplified and sent to microwave 8 for frequency doubling, and finally the C wave band carrier signal is sent to a modulator module through a semi-rigid cable for band-pass filtering. The input interface circuit completes the receiving of LVDS data, level conversion, and data conversion to the level required for driving the modulator. The XX-X satellite signal forwarding and data transmission subsystem U modulator directly modulates data on a U carrier, and QPSK modulation signals formed after modulation are finally isolated and output.

The power management module and the modulator module are bridged by a bridge circuit board.

Index decomposition is performed on each functional module of the U-band QPSK modulator, and table 3 lists the specific corresponding relation between each preferable index and the design position.

TABLE 3 index decomposing chart for whole machine

The power management circuit preferably has the following scheme:

the modulator power supply circuit unit receives the control of the instruction signal, converts the 100V voltage input by the bus into 3 paths of output voltage +5V, -5V and +12V isolated from the bus and supplies power to other single boards of the modulator.

The scheme is that a DC/DC module developed by the institute of microwave technology of the Siam institute is used, the module is a PCB single-board type DC/DC module, functions of on-off control, on-off remote measurement, voltage remote measurement and the like can be designed on one PCB by adopting the design scheme, two connectors are designed on the PCB, the connector 1 is used for connecting a whole satellite power distribution controller, and the connector 2 is used for connecting the box body 2.

The design scheme adopts a step-down + push-pull topological structure. The power conversion part in the switching power supply has various topological structures, and commonly used structures comprise a voltage reduction type, a push-pull type, a half bridge type, a single-end flyback type, a single-end forward type, a full bridge type and the like. Wherein, the step-down type does not have an isolation function.

Most of the power supplies developed by microwaves in the past adopt a push-pull structure. The structure has the advantages that:

the magnetic core of the power transformer works in quadrants 1 and 3 of a hysteresis curve, and the utilization rate of the magnetic core is higher

Simple design, no need of demagnetizing circuit

The transformer is simple to process, and the homonymous ends of the windings are easy to distinguish.

The modulator power supply preferably employs a push-pull topology. But has one disadvantage: when the input voltage of the power supply varies within a relatively large range, the voltage of the primary and secondary windings of the transformer is relatively high. This means that the voltage stress of the power switching devices of the power supply is high.

Preferably, a step-down structure is connected in series to the input end of the push-pull structure to reduce the voltage stress of the device, as shown in fig. 7, which is a schematic diagram of a DC/DC module topology.

When the input voltage of the power supply changes between 93V and 110V, the output of the buck converter is stabilized at about 60V under the control of the control circuit. In this way, the input voltage of the push-pull converter is no longer a range but a point, thereby reducing the voltage stress of the switching device.

It should be noted that the scheme of the present invention is greatly different from the existing simple serial connection of 2 power supplies: the two converters share an input filter circuit, an output rectifying filter circuit and a control circuit. So that much power consumption is not increased. But the efficiency can be remarkably improved by adopting a switching device with low voltage resistance.

The use of a buck + push-pull topology also has other advantages:

has good universality for different input voltages

The output end does not need to be connected with an energy storage inductor, and the method is particularly favorable for multi-path output

Is convenient for the output end to adopt the synchronous rectification technology

Selection of devices and calculation of magnetic elements is relatively easy

The correlation of each part of circuit is small, the debugging can be respectively carried out, and the debugging work is simple

The preferred scheme of the C-band local oscillator circuit is as follows:

the C-band carrier circuit uses a sampling phase locking scheme, preferably as follows.

In the phase-locked loop design, the invention leads the crystal oscillator reference signal to excite the step recovery diode so as to convert the crystal oscillator reference signal into sampling pulse. The pulse repetition frequency is identical to the product oscillation and is sent directly to the gate switch circuit of the sampling phase detector, the 'switch' is periodically turned on, when the 'switch' is turned on, the signal from the VCO is sent to the holding circuit (this is called sampling), the voltage is held until the 'switch' is turned on again, and so on, and an error voltage is formed. The error voltage is amplified and then sent to a loop filter for filtering and re-amplifying, and then the bias voltage of the varactor is changed to control the output frequency of the oscillator, so that the purpose of frequency stabilization is achieved.

The sampling phase-locked loop consists of a sampling phase discriminator, a loop filter and a capturing circuit. The sampling phase discriminator converts the reference signal into a narrow pulse with the same repetition frequency as the reference signal, the reference pulse samples the sine wave of the CRO, and the holding circuit holds the sampled voltage to the next period. When CRO is integral multiple of reference frequency and keeps strict phase synchronization, the sampling phase discriminator outputs a stable direct current voltage, and the loop is locked; otherwise, the discrete sample voltage will be a continuous stepped beat voltage through the holding circuit, pulling the CRO frequency until locked. The sampling phase-locked loop belongs to an analog phase-locked loop, and a phase discriminator of the sampling phase-locked loop does not have a frequency discrimination function, so that the difference between the CRO frequency and the reference frequency is large when the phase-locked loop is started, the loop cannot be locked by depending on the self-capturing capability of the loop, an auxiliary capturing circuit needs to be introduced to carry out frequency traction on the CRO, and when the CRO frequency scans the quick-capture zone of the loop, the loop locking is realized by depending on the self-capturing capability of the loop.

The sampling phase-locked circuit mainly comprises a 100MHz reference amplifier, a sampling phase discriminator, a loop filter and a voltage stabilizing circuit. The 100MHz reference amplifier, the sampling phase discriminator, the loop filter and the spread-capture circuit are mainly composed of an operational amplifier OP470 and peripheral resistance-capacitance components.

The CRO and amplifying circuit mainly comprises a voltage-controlled oscillator CRO, a power amplifier in a C wave band and a directional coupler. The CRO is preferably CROXXXS as X, which is based on the principle of achieving low phase noise using coaxial dielectric resonator for frequency stabilization, and the preferred electrical properties are shown in table 4 below.

TABLE 4CROXXXS Electrical Properties

According to the above principle, firstly, a sampling phase locking method is adopted to lock 6000MHz CRO on 100MHz reference signal, and 48GHz carrier signal is generated after 8 times frequency multiplication, as shown in FIG. 8

Phase noise: with sample phase locking, the phase noise budget for a 48GHz modulated carrier is shown in table 5 below.

TABLE 5 modulated Carrier phase noise budget with sampled CRO, 48GHz

The preferred scheme of the C-band amplifying circuit is as follows:

since the 8-multiplier needs a large input drive level (more than or equal to 20dBm), a medium power amplifier is selected to amplify the signal output by the CRO. The amplifier is preferably selected taking into account the following:

p-1 of the output is more than or equal to 23dBm

Gain is more than or equal to 15dB

Gain stability is better than +/-1 dB

The power consumption can be small

Based on the above four requirements, while considering the on-track experience, the preferred amplifier criteria are given in table 7 below:

TABLE 7 preferred Amplifier Electrical Performance Table

And finally selecting XXXX-6 according to the requirement of minimizing power consumption. In order to ensure good heat dissipation, the amplifier is directly fixed on the casing.

In a sample phase locked loop, the 100MHz external reference source is first passed through a high pass filter and amplifier XXXX-4 as shown in FIG. 9.

The amplified signal is passed through a transformer and into a sampling phase detector xxxxxxxx-H50, shown in fig. 10.

Since the difference between the CRO frequency and the reference frequency is too large during startup, the loop cannot be locked due to the self-capture capability, and an auxiliary capture circuit is introduced to perform frequency pulling on the CRO, as shown in fig. 11:

the PCB of the sample phase lock circuit is preferably a 28mm 102mm FR-4 substrate PCB.

The amplifier XXXXX-4 is preferably soldered to the ground of the PCB by a large area solder, the 100M reference input is a SMA-KFD90 type connector and the mounting is by a lap solder.

In the CRO and amplification circuit board, the control voltage is input into CROXXXS, and the output of the CRO is input into amplifier XXXX-6 for amplification.

The output end of the amplifier is preferably designed with a coupling circuit for coupling the signal and outputting the signal to the sampling phase-locked circuit

Because amplifier XXXX consumption is great, in order to solve its heat dissipation, adopt its mode of directly installing on the casing to install. For this purpose, a boss is designed on the casing, which has the same size as the bottom of the amplifier and the same height as the thickness of the PCB

The square opening with the same size as the amplifier is arranged on the PCB, the amplifier is arranged on the lug boss by using a screw, and the pin is directly led out outwards and is lap-welded on the PCB.

8 frequency doubling circuit, the preferred scheme is:

the microwave frequency multiplier preferably consists of an input impedance transformer, an output filter, a step diode, etc., as shown in fig. 12. The frequency multiplier works in a self-bias mode, input power is added to a step diode after passing through an input isolator and an input impedance converter to generate higher harmonics of input frequency, desired 8 harmonics are selected through an output filter and then output from the output isolator, and meanwhile, direct-current working points of the diodes can be maintained in a better range by adding direct-current voltage generated by the diodes to a self-bias resistor R1, so that the efficiency is improved, inconvenience of external power supply is avoided, and the design is simplified.

The step diode is a microwave step diode XXX46 produced by information industry department X, which is already used in models XX-5, HY-1, etc., and can be used in U frequency band through communication with X design personnel. The input-output filter and the diode self-bias circuit are fabricated on a ceramic die.

The preferred scheme of the U band-pass filter circuit is as follows:

because the filter in the frequency multiplier can not meet the requirements for inhibiting other harmonics, a band-pass filter is required to be added behind the frequency multiplier to inhibit other harmonics generated by the frequency multiplier, and the inhibition on 7 th harmonic and 9 th harmonic is more than 25 dB. The circuit form is the same as the filter in the frequency multiplier, and adopts the form of parallel coupling lines.

The U-band QPSK modulator preferably adopts the following scheme:

the U-band QPSK modulator is preferably composed of two BPSK modulators, an in-phase power splitter, a quadrature power combiner, and two baseband low pass filters. The input carrier is divided into two paths by a 3dB in-phase power divider, then the two paths of carriers are subjected to 0/pi modulation by I, Q two paths of BPSK modulators, and finally synthesized into a QPSK modulation signal by a 90-degree phase-shift synthesizer for output. Ideally, the output signal is an error-free four-phase modulated signal. However, the actual power divider and the mixer have certain amplitude and phase errors, and the BPSK modulators of the two branches cannot be completely consistent. These factors all affect the modulation accuracy of the modulator. This also puts higher demands on the choice of circuit form and the machining accuracy.

In terms of components, only one component, namely a Schottky diode in a BPSK modulator, is used in the circuit, the model is XXXXX7(MACOM), the diode is not used by other models, and high-grade products are not available. Through communication with the material department, the aerospace-grade product can be screened and upgraded by a third party. This type of diode is therefore considered for use.

A schematic diagram of a preferred scheme of a U-band QPSK modulator is shown in fig. 13:

the secondary power supply circuit preferably has the following configuration:

the function of the power supply processing circuit is to filter the secondary power of +12V, +5V, -5V from the DC/DC module and convert +5V into 3.3V for the interface chip to use.

The low dropout regulator preferably uses a MSK5232-3.3HG type regulator produced by MSK company in America, the grade of the regulator is H grade, and the regulator has the experience of successful on-rail flight of a plurality of types and has stable and reliable performance. The only devices in the modulator using 3.3V power supply are LVDS interface devices, and MSK5232-3.3HG can meet the power use requirement.

The inductor used in the filter circuit is a self-made inductor, preferably an enameled wire with the diameter of 0.33 is wound on a MAGNETIC ring, and the MAGNETIC ring is model 55035-A2 produced by MAGNETIC company. The home-made inductor is also used in FY-2, XX-6, XX-7 and the like, and has experience in successful on-track flight.

All capacitors in the circuit are designed in series, so that single machine faults caused by short circuit of the capacitors are avoided, and the reliability of the whole machine is improved.

The preferred scheme of the level conversion circuit is as follows:

the level conversion circuit is used for receiving data sent by the data processor.

The data input mode is preferably as follows: I. the Q data are relatively independent, and the data rate of each path is 150 Mbps. I. After the Q data is subjected to level conversion, the Q data is input to a modulator to perform QPSK modulation on a carrier.

The received LVDS signal I, Q signals are as follows:

code rate: 150Mbps

Level: LVDS level

The data processor directly sends I, Q two paths of 150Mbps data, the data is converted into TTL level after being received by LVDS32, the TTL level is converted into differential level through LVDS31, the differential level is sent to LMH6702, the bipolar level signal is converted, and the bipolar level signal is sent to the modulation circuit for modulation.

The level conversion circuit preferably employs the LVDS32 of TI. LVDS32 fully meets the requirements for a one-way 150Mbps rate.

The U-shaped modulator is designed into a completely sealed box body on the structural design so as to prevent electromagnetic leakage, and the proposal of the satellite on the engineering prototype is adopted to encrypt the screws of the outer cover plate.

For the top cover part, a boss is designed on the casing to be inserted into the cover to reduce the gap. The periphery of the housing is compressed by 8 screws for 4 circles to enhance EMC performance.

After testing, the modulation system of the invention is subjected to preliminary study of a preliminary core component, and then a test piece of an engineering prototype is produced.

From the test data, the following three points can be seen:

(1) the test result of the error return-to-zero test is error-free, which indicates that the microwave direct modulation system of the U frequency band has normal function and can be used for downloading wireless data in space missions, and the transmission code rate is 300Mbps in one step, so that the requirement of a conventional medium-rate wireless channel on the U-band microwave direct modulator system can be met. The problem of the direct U-band microwave modulation system is solved, and the method has great significance.

(2) The actual system test data for phase noise is:

less than or equal to-78.83 dBc/Hz @100Hz, and meets the requirement of less than-60 dBc/Hz;

less than or equal to-92.21 dBc/Hz @1kHz, and meets the requirement of less than-70 dBc/Hz;

less than or equal to-101.92 dBc/Hz @10kHz, and meets the requirement that the index is less than-80 dBc/Hz;

less than or equal to-100.35 dBc/Hz @100kHz, and meets the requirement of less than-90 dBc/Hz;

therefore, the practical data show that the low-phase-noise circuit of the U wave band solves the technical problem that the traditional PLL circuit cannot achieve low phase noise, and provides a carrier generation scheme with extremely high frequency and low phase noise of the U wave band. Since the phase noise is related to the modulation performance of the U-band microwave direct modulation system and directly influences the bit error rate of a wireless link, the circuit is successfully developed to solve the bottleneck of the U-band direct modulation system, and the circuit has great engineering value.

(3) The actual data of the system with unbalanced amplitude and phase are respectively: 0.38dB/2.8 degrees (A machine) and 0.24dB/0.72 degrees (B machine), and meets the requirement of 1dB/4 degrees of the system. And under the condition that the indexes of the amplitude and the phase are 1dB/4 degrees, the introduced modulation loss can be basically less than 1 dB. Therefore, the practical test data indicates that the U-band direct modulation system has good modulation performance. Meanwhile, the success of the electromechanical integrated design of the millimeter wave QPSK direct layout with extremely high frequency is also demonstrated. The bipolar data level is also shown to work normally; the results of the test of the imbalance between the amplitude and the phase of the U-band modulator are shown in Table 8

The direct U-band microwave modulation system provided by the invention realizes the modulation of baseband data onto a carrier wave of 40-60 GHz, so that the U-band can be used for performing a satellite-to-ground and inter-satellite wireless data transmission function, and the problem of no U-band transmitting equipment is solved.

The invention relates to a U-band microwave direct modulation system, wherein a QPSK direct modulation circuit of a U-band is a BPSK phase shifter based on a Schottky diode, a microstrip-slot line-microstrip transition structure, a Lange bridge and a Wilkinson synthesizer are designed on a ceramic chip in a smart way, and after the layout is put into production, a QPSK modulation signal of the U-band can be generated after electric installation. The modulation performance meets the index requirements that the amplitude imbalance is less than or equal to 0.5dB and the phase imbalance is less than or equal to 2 degrees, the performance is excellent, and the domestic blank is filled.

Claims

1. A U-band microwave direct modulation system is characterized by comprising: the device comprises a C-band local oscillation circuit, a C-band amplifying circuit, a U-band 8-frequency doubling circuit, a U-band QPSK microwave direct modulation circuit and a level conversion circuit;

the C frequency band local oscillation circuit takes a high-stability reference source as input, performs sampling phase locking on the high-stability reference source, generates C frequency band carrier waves with extremely low phase noise and sends the C frequency band carrier waves to the C frequency band amplifying circuit;

the 8-order harmonic frequency multiplication and isolation circuit of the U frequency band is used for carrying out 8-order harmonic frequency multiplication and isolation on the amplified and isolated C frequency band carrier with extremely low phase noise so as to generate a U frequency band carrier, and the U frequency band carrier is sent to the QPSK microwave direct modulation circuit of the U frequency band;

2. The U-band microwave direct modulation system according to claim 1, characterized in that: c frequency channel local oscillator circuit includes: a sampling frequency division phase discrimination circuit and a C-band CRO;

the sampling frequency-division phase-demodulation circuit converts a reference sinusoidal signal sent by an external high-stability reference source into a sampling reference narrow pulse, the reference narrow pulse samples a sinusoidal wave input by the C-band CRO circuit, and keeps the voltage at the sampling moment, and the sampling reference narrow pulse continuously samples the sinusoidal wave and keeps the voltage at the sampling moment to form an error voltage; the error voltage becomes a CRO oscillation control voltage after passing through a loop filter and is output to a C-band CRO circuit;

the C-band CRO receives the CRO oscillation control voltage, oscillates under the control of the CRO oscillation control voltage, outputs a C-band frequency signal to the C-band amplifying circuit, and simultaneously couples out 1-path signal to be reversely sent to the sampling frequency-division phase-demodulation circuit;

3. The U-band microwave direct modulation system according to claim 1, characterized in that: c frequency channel amplifier circuit includes: a C-band amplifier, a first isolator;

the C-band amplifier receives a C-band single carrier signal with low phase noise, amplifies the power of the C-band single carrier signal and sends the amplified power to the first isolator;

4. The U-band microwave direct modulation system according to claim 1, characterized in that: u frequency range's 8 frequency multiplier circuits include: a microwave 8 frequency multiplier, a band-pass filter and a second isolator;

the microwave 8 frequency multiplier receives a single carrier signal with low phase noise in a C wave band, loads the single carrier signal on a step diode after passing through an internal impedance converter, generates higher harmonics of input frequency and sends the higher harmonics to the band-pass filter;

the band-pass filter is used for receiving millimeter wave frequency signals containing various harmonic components generated by the step diode, suppressing multiple harmonics, generating U-band single carrier signals of the multiple harmonic signals and sending the U-band single carrier signals to the second isolator;

5. The U-band microwave direct modulation system according to claim 1, characterized in that: QPSK microwave direct modulation circuit of U frequency channel includes: a QPSK modulator and a third isolator of a U frequency band;

the QPSK modulator of the U band receives a U band single carrier wave sent by the U band 8 frequency doubling circuit, performs millimeter wave 0-degree power division on the two signals, and respectively enters the I \ Q path; simultaneously receiving two paths of bipolar data levels of I \ Q input by the level conversion circuit, and respectively carrying out respective phase inversion on the millimeter wave signals of the two paths of I \ Q under the control of the bipolar levels so as to form two paths of independent BPSK signals; finally, through millimeter wave 90-degree broadband synthesis, a QPSK modulation signal of the millimeter wave in the U waveband is obtained and sent to a third isolator;

6. The U-band microwave direct modulation system according to claim 1, characterized in that: the high-stability reference source is as follows: an externally input highly stable reference source requires very low phase noise.

7. The U-band microwave direct modulation system according to claim 1, characterized in that: the extremely high-frequency U-band carrier wave is: the U-band carrier ranges from 40GHz to 60 GHz.

8. The U-band microwave direct modulation system according to claim 1, characterized in that: external data, are: the external data input level is LVDS signal, and the input signal is I \ Q2-path signal.

9. The U-band microwave direct modulation system according to claim 1, characterized in that: the carrier frequency range is: the carrier frequency range for wireless transmission is 40-60 GHz.

10. The U-band microwave direct modulation system according to claim 1, characterized in that: the range of transmission code rates is: the code rate range for wireless transmission is 1Mbps to 2 Gbps.