A frequency source synthesis system and method based on a frequency agile radar

Abstract

The present invention discloses a frequency source synthesis system and method based on a frequency-agile radar, belonging to the technical field of microwave radio frequency, and specifically including: generating a target clock signal and performing frequency processing on the target clock signal to generate a frequency-multiplied signal, and dividing the frequency-multiplied signal into two clock signals through a power divider; performing frequency multiplication processing on one of the clock signals and using the processed signal as a clock reference signal of a direct digital synthesizer, generating an analog signal according to the clock reference signal, and calibrating the analog signal as an output signal; performing frequency multiplication processing on the other clock signal and using the processed clock signal as a local oscillator signal of a mixer; performing frequency conversion processing to obtain a mixed-frequency signal, performing 4-fold frequency multiplication processing on the mixed-frequency signal, and calibrating the processed mixed-frequency signal as a final output signal; the present invention realizes that the frequency source simultaneously has the characteristics of low phase noise, fast frequency agility, fine resolution and miniaturization.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave radio frequency, and particularly relates to a frequency source synthesis system and method based on a frequency agile radar. Background Art

[0002] A frequency agile radar is a radar system that can quickly change its operating frequency to cope with enemy electronic interference or make it difficult for the enemy to find the radar emission source through radio direction finding. The frequency source is an important component in the frequency agile radar system, and its key indicators include phase noise, frequency agility time, and frequency resolution, etc. Phase noise will mask the Doppler signal and reduce the resolution and sensitivity of the radar; the frequency agility time affects the anti-jamming ability of the radar; the frequency resolution directly affects the frequency resolution of the radar. The frequency of the frequency source of the frequency agile radar is relatively high, in the microwave band, and generally uses the method of frequency synthesis to generate.

[0003] At present, the frequency synthesis methods of the frequency source are as follows: 1) Using direct frequency synthesis technology, direct frequency synthesis has excellent phase noise, spurious performance, and frequency conversion time, but the frequency resolution is insufficient; 2) Using indirect frequency synthesis (phase-locked loop) technology, a relatively high frequency step resolution can be achieved, but the phase noise is high and the loop lock time is long, making it difficult to meet the requirements of the frequency source for high phase noise and frequency agility time; 3) Using the ping-pong loop (dual phase-locked loop) technology, the phase-locked loop can be pre-locked by presetting the frequency, and the frequency conversion time can be greatly shortened to within 1 microsecond, but there is still the problem of high phase noise; 4) Using direct digital synthesis technology, direct digital synthesis has a very high frequency conversion speed and very fine fractional resolution, but its output frequency is not high and the spurious performance is poor. The respective technical principles lead to different advantages and disadvantages, making the indicators such as phase noise, frequency agility time, frequency resolution, and volume of the frequency source form an opposing and restrictive relationship, and it is difficult to achieve excellent levels in all indicators. Summary of the Invention

[0004] The purpose of the present invention is to provide a frequency source synthesis system and method based on a frequency agile radar to solve the following technical problems:

[0005] Currently, the frequency synthesis methods of frequency sources are as follows: 1) Using direct frequency synthesis technology, direct frequency synthesis has excellent phase noise, spurious performance and frequency conversion time, but the frequency resolution is insufficient; 2) Using indirect frequency synthesis (phase-locked loop) technology, a relatively high frequency step resolution can be achieved, but the phase noise is high and the loop lock time is long, making it difficult to meet the requirements of high phase noise and fast frequency agility of the frequency source; 3) Using ping-pong loop (dual phase-locked loop) technology, the phase-locked loop can be pre-locked by presetting the frequency, and the frequency conversion time can be greatly shortened to within 1 microsecond, but there is still the problem of high phase noise; 4) Using direct digital synthesis technology, direct digital synthesis has a very high frequency conversion speed and very fine fractional resolution, but its output frequency is not high and the spurious performance is poor. The respective technical principles lead to different advantages and disadvantages, making the indicators such as phase noise, frequency agility time, frequency resolution and volume of the frequency source form an opposing and restrictive relationship, and it is difficult to achieve excellent levels in all indicators.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A frequency source synthesis method based on a frequency agile radar, characterized by comprising the following steps:

[0008] S1, controlling a crystal oscillator to generate a target clock signal, and performing frequency multiplication processing on the target clock signal through a frequency multiplier to generate a frequency-multiplied signal, and dividing the frequency-multiplied signal into two clock signals through a power divider;

[0009] S2, performing 5-fold frequency multiplication processing on one of the clock signals, using the processed clock signal as the clock reference signal of a direct digital synthesizer, performing phase accumulation according to a preset frequency control word and the reference clock signal to generate a corresponding phase value, looking up a table according to the phase value to obtain a signal amplitude value, converting the amplitude value into an analog signal through digital-to-analog conversion, and calibrating the analog signal as an output signal; performing 7-fold frequency multiplication processing on the other clock signal, and using the processed clock signal as the local oscillator signal of a mixer;

[0010] S3, inputting the output signal into a mixer and performing frequency conversion processing with the local oscillator signal to obtain a mixed signal, performing 4-fold frequency multiplication processing on the mixed signal, calibrating the processed mixed signal as a final output signal and outputting it.

[0011] As a further scheme of the present invention: the constant temperature crystal oscillator with a frequency of 120 MHz is used in S1.

[0012] As a further scheme of the present invention: the frequency multiplication processing is to achieve frequency multiplication through a frequency multiplier, and the frequency multiplier uses step recovery diode technology for frequency multiplication.

[0013] As a further solution of the present invention: in the step S2, it further includes setting the reference clock frequency to 2.4 GHz.

[0014] As a further solution of the present invention: in the step S2, the preset frequency control word is 32 bits.

[0015] As a further solution of the present invention: in the step S3, it further includes inputting the output signal into a preset digital tuning filter for signal denoising processing, and inputting the denoised output signal into a mixer.

[0016] As a further solution of the present invention: the preset digital tuning filter is a narrowband digital tuning filter.

[0017] A frequency source synthesis system based on a frequency agile radar, characterized by comprising:

[0018] A signal generation module, configured to control a crystal oscillator to generate a target clock signal, perform frequency multiplication processing on the target clock signal through a quadrupler to generate a frequency-multiplied signal, and divide the frequency-multiplied signal into two clock signals through a power divider;

[0019] A signal processing module, configured to perform 5-fold frequency multiplication processing on one of the clock signals, use the processed clock signal as a clock reference signal of a direct digital synthesizer, perform phase accumulation according to a preset frequency control word and a reference clock signal to generate a corresponding phase value, look up a table according to the phase value to obtain a signal amplitude value, convert the amplitude value into an analog signal through digital-to-analog conversion, and calibrate the analog signal as an output signal; perform 7-fold frequency multiplication processing on the other clock signal, and use the processed clock signal as a local oscillator signal of a mixer;

[0020] A signal synthesis module, configured to input the output signal into a mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed signal, perform 4-fold frequency multiplication processing on the mixed signal, and calibrate the processed mixed signal as a final output signal and output it.

[0021] The beneficial effects of the present invention:

[0022] The present invention first uses a crystal oscillator to generate a target signal, multiplies the frequency of the target clock signal to generate a frequency-multiplied signal, divides the frequency-multiplied signal into two clock signals through a power divider, uses direct digital frequency synthesis technology for one of the signals to generate a first output signal as the DDS reference signal, uses direct frequency synthesis for the other signal to generate a second output signal as the local oscillator signal of the mixer. The DDS reference signal and the local oscillator signal of the mixer share a 4x frequency multiplication link. After 4x frequency multiplication, it is divided into two paths through a power divider and then each is frequency-multiplied to the required signal frequency. Sharing the frequency multiplication link reduces the number of components used in the design, and can better control the volume, power consumption, and cost of the frequency source. And the function of the mixer is to achieve frequency addition. The phase noise performance of the signal at the RF end of the mixer depends on the phase noise of the local oscillator signal. Therefore, the reference crystal oscillator signal is directly frequency-multiplied to the required frequency as the local oscillator signal, that is, the second output signal is used as the local oscillator signal, to minimize the phase noise of the local oscillator. The output signal is input to the mixer and undergoes frequency conversion processing with the local oscillator signal to obtain a mixed signal. The mixed signal is subjected to 4x frequency multiplication processing. It can be understood that when the DDS output frequency is relatively high, a large DAC (digital-to-analog converter) image spurious component will be generated. This spurious component is close to the main signal and is difficult to filter out by conventional filters. Therefore, in the present invention, a 4x frequency multiplier is used after the mixer to perform frequency multiplication processing on the mixed signal, and the processed mixed signal is designated as the final output signal and output, so that the output frequency range of the DDS is reduced, thereby increasing the frequency gap between the spurious component and the main signal, reducing the interference degree of these spurious components on the main signal, and thus effectively reducing the influence of DAC image spurs. The present invention combines direct frequency synthesis and direct digital frequency synthesis technologies, integrating the technical advantages of both, and realizes the characteristics of low phase noise, fast frequency agility, fine resolution, and miniaturization of the output signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following further describes the present invention with reference to the accompanying drawings.

[0024] Figure 1 It is a schematic flow diagram of a frequency source synthesis method based on a frequency-agile radar according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] Please refer to Figure 1As shown in the figure, the present invention is a frequency source synthesis method based on a frequency agile radar, comprising the following steps:

[0027] S1, controlling a crystal oscillator to generate a target clock signal, doubling the frequency of the target clock signal through a quadrupler to generate a doubled frequency signal, and dividing the doubled frequency signal into two clock signals through a power divider;

[0028] S2, performing a quintupling frequency process on one of the clock signals, using the processed clock signal as a clock reference signal of a direct digital synthesizer, performing phase accumulation according to a preset frequency control word and the reference clock signal to generate a corresponding phase value, looking up a table according to the phase value to obtain a signal amplitude value, converting the amplitude value into an analog signal through digital-to-analog conversion, and calibrating the analog signal as an output signal; performing a septupling frequency process on the other clock signal, and using the processed clock signal as a local oscillator signal of a mixer;

[0029] S3, inputting the output signal into a mixer and performing frequency conversion processing with the local oscillator signal to obtain a mixed frequency signal, performing a quadrupling frequency process on the mixed frequency signal, calibrating the processed mixed frequency signal as a final output signal and outputting it.

[0030] The present invention first uses a crystal oscillator to generate a target signal, multiplies the frequency of the target clock signal to generate a multiplied signal, divides the multiplied signal into two clock signals through a power divider, uses direct digital frequency synthesis technology for one of the signals to generate a first output signal and use it as the DDS reference signal, uses direct frequency synthesis for the other signal to generate a second output signal and use it as the local oscillator signal of the mixer. The DDS reference signal and the local oscillator signal of the mixer share a quadrupled frequency link. After quadrupling the frequency, it is divided into two paths through a power divider, and then each path is multiplied to the required signal frequency. Sharing the multiplied frequency link reduces the number of components used in the design and can better control the volume, power consumption, and cost of the frequency source. And the function of the mixer is to realize the addition of frequencies. The phase noise performance of the signal at the RF end of the mixer depends on the phase noise of the local oscillator signal. Therefore, the reference crystal oscillator signal is directly multiplied to the required frequency as the local oscillator signal, that is, the second output signal is used as the local oscillator signal, to minimize the phase noise of the local oscillator. The output signal is input to the mixer and frequency conversion processing is performed with the local oscillator signal to obtain a mixed signal. The mixed signal is multiplied by 4 times. It can be understood that when the DDS output frequency is high, a large DAC (Digital-to-Analog Converter) image spurious component will be generated. This spurious component is close to the main signal and is difficult to filter out by conventional filters. Therefore, in the present invention, a quadrupler is used after the mixer to multiply the mixed signal, and the processed mixed signal is calibrated as the final output signal and output, so that the output frequency range of the DDS is reduced, thereby increasing the frequency gap between the spurious component and the main signal and reducing the interference degree of these spurious components on the main signal, effectively reducing the influence of DAC image spurs. The present invention combines direct frequency synthesis and direct digital frequency synthesis technologies, integrates the technical advantages of both, and realizes that the output signal has the characteristics of low phase noise, fast frequency agility, fine resolution, and miniaturization at the same time.

[0031] It should be noted that the present invention proposes a design method for a Ku-band frequency source. The Ku band refers to the electromagnetic wave frequency band between 12 GHz and 18 GHz. In the present invention, a high-performance temperature-controlled crystal oscillator is adopted. At present, the phase noise performance of the top temperature-controlled crystal oscillator with a frequency of 120 MHz is -130 dBc / Hz@100 Hz, -160 dBc / Hz@1 KHz, -165 dBc / Hz@10 KHz. According to the calculation of the phase noise deterioration degree 20lgN (N is the N-times frequency multiplication factor), assuming that the additional phase noise of the circuit is zero, the phase noise of the frequency source outputting 15.15 GHz using this temperature-controlled crystal oscillator can reach -160 + 20lg(15.15 / 0.12) = -118 dBc / Hz@1 KHz; at the same time, the frequency multiplier uses a step diode to achieve lower phase noise. The additional phase noise of the step diode is about 1 dB. After passing through 3 frequency multipliers, the phase noise of the signal with a frequency of 15.15 GHz output by the frequency source is -160 + 20lg(15.15 / 0.12) + 3 = 115 dBc / Hz@1 KHz; the frequency agility time of the frequency source depends on the worse of the DDS and the digital tuning filter hopping times. The frequency conversion time of the DDS is less than 200 ns. In the case of small signals, the hopping time of the digital tuning filter is several hundred nanoseconds to 1 microsecond. Therefore, the frequency agility time of the frequency source is less than 1 us; optionally, if the frequency source needs to achieve a lower frequency agility time, a switched filter bank can be used at the output end of the DDS, and the switching time can reach 50 ns or even lower. At this time, the frequency agility time of the frequency source depends on the hopping time of the DDS; in the present invention, the DDS reference clock frequency is 2.4 GHz and the number of bits is 32. After 4-fold frequency broadening, the resolution of the frequency source is 2.4 GHz * 2^(1 / 32) * 4 = 2.235 Hz, providing a finer resolution.

[0032] It should be noted that the amplifier is ignored in the present invention. During the implementation process, an appropriate amplifier can be selected and inserted into the circuit according to the actual required signal amplitude, and a low-phase-noise amplifier should be used for the amplifier selection.

[0033] In a preferred embodiment of the present invention, the temperature-controlled crystal oscillator with a frequency of 120 MHz is used in S1.

[0034] In the present invention, a high-performance temperature-controlled crystal oscillator is adopted. Currently, the phase noise performance of the top temperature-controlled crystal oscillator with a frequency of 120 MHz is -130 dBc / Hz @ 100 Hz, -160 dBc / Hz @ 1 KHz, -165 dBc / Hz @ 10 KHz. According to the calculation of the phase noise deterioration degree 20lgN (N is the N-times frequency multiplication factor), assuming that the additional phase noise of the circuit is zero, when using this temperature-controlled crystal oscillator frequency source to output a signal with a frequency of 15.15 GHz, the phase noise can reach -160 + 20lg(15.15 / 0.12) = -118 dBc / Hz @ 1 KHz, ensuring that it can still maintain a low phase noise level under high-frequency multiplication.

[0035] In another preferred embodiment of the present invention, the frequency multiplication process is to achieve frequency multiplication through a frequency multiplier, and the frequency multiplier uses step recovery diode technology for frequency multiplication.

[0036] The use of step diodes in the frequency multiplier can achieve lower phase noise. The additional phase noise of step diodes is usually about 1 dB. In the present invention, even after passing through three frequency multipliers, the phase noise of the signal with a frequency of 15.15 GHz output by the frequency source is still approximately -160 + 20lg(15.15 / 0.12) + 3 = -115 dBc / Hz @ 1 KHz, greatly reducing the phase noise.

[0037] In another preferred embodiment of the present invention, in S2, it further includes setting the reference clock frequency to 2.4 GHz.

[0038] In the present invention, the DDS reference clock frequency is 2.4 GHz and the number of bits is 32. After four-fold frequency broadening, the resolution of the frequency source reaches 2.4 GHz * 2 ^ (1 / 32) * 4 = 2.235 Hz. It can be understood that fine frequency control enables the radar system to quickly switch between multiple frequency bands, thereby significantly improving the detection accuracy and sensitivity.

[0039] In another preferred embodiment of the present invention, in S2, the preset frequency control word is 32 bits.

[0040] In the present invention, the DDS reference clock frequency is 2.4 GHz and the number of bits is 32. After four-fold frequency broadening, the resolution of the frequency source reaches 2.4 GHz * 2 ^ (1 / 32) * 4 = 2.235 Hz. It can be understood that fine frequency control enables the radar system to quickly switch between multiple frequency bands, thereby significantly improving the detection accuracy and sensitivity.

[0041] In another preferred embodiment of the present invention, in S3, it further includes inputting the output signal into a preset digital tuning filter for signal denoising processing, and inputting the output signal after denoising processing into a mixer.

[0042] The frequency multiplier will generate rich high-order harmonic components. It is necessary to select the required frequency through a suitable narrow-band filter. If the frequency multiplication factor is large, a filter with an extremely narrow relative bandwidth needs to be used. Limited by technology and process, such a filter is very difficult to implement. Therefore, in the present invention, the single-stage frequency multiplication factor is reduced through two-stage frequency multiplication, and there is a larger selection space for the filter, and better performance indicators can be achieved and the cost can be reduced.

[0043] In another preferred embodiment of the present invention, the preset digital tuning filter is a narrow-band digital tuning filter.

[0044] The signal frequency generated by the DDS is 52.5 MHz to 427.5 MHz. Although the DAC image spurious components are large, they are hundreds of MHz away from the main signal and can be easily filtered out by a filter. The narrow-band spurious of the DDS is relatively good, about -90 dBc, while the wide-band spurious is relatively poor, about -60 dBc. Therefore, in the present invention, a narrow-band digital tuning filter is used for the filter at the DDS output. The center frequency of the filter can follow the DDS output frequency switch. The out-of-band rejection ability of the filter can make the spurious level of the DDS output signal -85 dBc. Even after the subsequent 4x frequency multiplier, the spurious level of the frequency source output signal only reaches -73 dBc, greatly improving the spurious level of the frequency source output signal.

[0045] A frequency source synthesis system based on a frequency-agile radar, characterized by comprising:

[0046] A signal generation module, configured to control a crystal oscillator to generate a target clock signal, perform frequency multiplication processing on the target clock signal through a 4x frequency multiplier to generate a frequency-multiplied signal, and divide the frequency-multiplied signal into two clock signals through a power divider;

[0047] A signal processing module, configured to perform 5x frequency multiplication processing on one of the clock signals, use the processed clock signal as the clock reference signal of a direct digital synthesizer, perform phase accumulation according to a preset frequency control word and the reference clock signal to generate a corresponding phase value, look up a table according to the phase value to obtain a signal amplitude value, convert the amplitude value into an analog signal through digital-to-analog conversion, and calibrate the analog signal as an output signal; perform 7x frequency multiplication processing on the other clock signal, and use the processed clock signal as the local oscillator signal of a mixer;

[0048] A signal synthesis module is configured to input an output signal into a mixer and perform frequency conversion processing with a local oscillator signal to obtain a mixed-frequency signal, perform quadruple frequency processing on the mixed-frequency signal, calibrate the processed mixed-frequency signal as a final output signal and output it.

[0049] The above has described in detail an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A frequency source synthesis method based on a frequency agile radar, characterized in that It includes the following steps: S1, control the crystal oscillator to generate a target clock signal, perform quadruple frequency multiplication on the target clock signal to generate a frequency-multiplied signal, and divide the frequency-multiplied signal into two clock signals through a power divider; S2, perform quintuple frequency multiplication on one of the clock signals, use the processed clock signal as the clock reference signal of the direct digital synthesizer, perform phase accumulation according to the preset frequency control word and the reference clock signal to generate a corresponding phase value, look up the table according to the phase value to obtain a signal amplitude value, convert the amplitude value into an analog signal through digital-to-analog conversion, and calibrate the analog signal as the output signal; perform septuple frequency multiplication on the other clock signal, and use the processed clock signal as the local oscillator signal of the mixer; S3, input the output signal into the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed-frequency signal, perform quadruple frequency multiplication on the mixed-frequency signal, and calibrate the processed mixed-frequency signal as the final output signal and output it.

2. A frequency source synthesis method based on a frequency agile radar according to claim 1, characterized in that, In S1, a temperature-controlled crystal oscillator with a frequency of 120 MHz is used.

3. A frequency source synthesis method based on a frequency agile radar according to claim 1, characterized in that The frequency multiplication processing is to achieve frequency multiplication through a frequency multiplier, and the frequency multiplier uses step recovery diode technology for frequency multiplication.

4. A frequency source synthesis method based on a frequency agile radar according to claim 1, characterized in that, In S2, it also includes setting the reference clock frequency to 2.4 GHz.

5. A frequency source synthesis method based on a frequency agile radar according to claim 1, characterized in that, In S2, the preset frequency control word is 32 bits.

6. A frequency source synthesis method based on a frequency agile radar according to claim 1, characterized in that In S3, it also includes inputting the output signal into a preset digital tuning filter for signal denoising processing, and inputting the output signal after denoising processing into the mixer.

7. A frequency source synthesis method based on a frequency agile radar according to claim 6, characterized in that, The preset digital tuning filter is a narrowband digital tuning filter.

8. A frequency source synthesis system based on a frequency agile radar, characterized in that, It includes: A signal generation module, which is used to control the crystal oscillator to generate a target clock signal, perform quadruple frequency multiplication on the target clock signal to generate a frequency-multiplied signal, and divide the frequency-multiplied signal into two clock signals through a power divider; A signal processing module, which is used to perform quintuple frequency multiplication on one of the clock signals, use the processed clock signal as the clock reference signal of the direct digital synthesizer, perform phase accumulation according to the preset frequency control word and the reference clock signal to generate a corresponding phase value, look up the table according to the phase value to obtain a signal amplitude value, convert the amplitude value into an analog signal through digital-to-analog conversion, and calibrate the analog signal as the output signal; perform septuple frequency multiplication on the other clock signal, and use the processed clock signal as the local oscillator signal of the mixer; A signal synthesis module, which is used to input the output signal into the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed-frequency signal, perform quadruple frequency multiplication on the mixed-frequency signal, and calibrate the processed mixed-frequency signal as the final output signal and output it.

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