Frequency source synthesis system and method based on frequency agility radar

Abstract

The invention discloses a frequency source synthesis system and method based on a frequency agility radar, and belongs to the technical field of microwave radio frequency, and the method specifically comprises the steps: generating a target clock signal, carrying out the frequency processing of the target clock signal to generate a frequency multiplication signal, and dividing the frequency multiplication signal into two clock signals through a power divider; performing frequency multiplication processing on one path of clock signal, taking 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 path of clock signal, and taking the processed clock signal as a local oscillation signal of the frequency mixer; performing frequency conversion processing to obtain a frequency mixing signal, performing quadruplicated frequency processing on the frequency mixing signal, and calibrating the processed frequency mixing signal as a final output signal; according to the invention, the frequency source has the characteristics of low phase noise, rapid agility, fine resolution and miniaturization at the same time.

Description

Technical Field

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

[0002] Frequency agile radar is a radar system that can quickly change its operating frequency to deal with enemy electronic interference or make it difficult for the enemy to find the radar 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, agility time and frequency resolution. Phase noise will mask the Doppler signal and reduce the resolution and sensitivity of the radar; the agility time affects the radar's anti-interference ability; and the frequency resolution directly affects the radar's frequency resolution. The frequency source of the frequency agile radar has a high frequency and is in the microwave band. It is generally generated by frequency synthesis.

[0003] At present, the frequency synthesis methods of frequency sources are as follows: 1) Direct frequency synthesis technology is used. Direct frequency synthesis has excellent phase noise, spurious performance and frequency conversion time, but the frequency resolution is insufficient; 2) Indirect frequency synthesis (phase-locked loop) technology is used to achieve a higher frequency step resolution, but the phase noise is high and the loop locking time is long, which makes it difficult to meet the higher phase noise and agility time requirements of the frequency source; 3) Ping-pong loop (dual phase-locked loop) technology is used to lock the phase-locked loop in advance by presetting the frequency, which can greatly shorten the frequency conversion time to within 1 microsecond, but the problem of high phase noise still exists; 4) Direct digital synthesis technology is used. Direct digital synthesis has a very high frequency conversion speed and very fine resolution, but its output frequency is not high and the spurious performance is poor. Their respective technical principles lead to different advantages and disadvantages, which makes the phase noise, agility time, frequency resolution and volume of the frequency source form a mutually opposing and restrictive relationship, making it difficult to achieve excellent levels for 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 frequency agile radar to solve the following technical problems:

[0005] At present, the frequency synthesis methods of frequency sources are as follows: 1) Direct frequency synthesis technology is used. Direct frequency synthesis has excellent phase noise, spurious performance and frequency conversion time, but the frequency resolution is insufficient; 2) Indirect frequency synthesis (phase-locked loop) technology is used to achieve a higher frequency step resolution, but the phase noise is high and the loop locking time is long, which makes it difficult to meet the higher phase noise and agility time requirements of the frequency source; 3) Ping-pong loop (dual phase-locked loop) technology is used to lock the phase-locked loop in advance by presetting the frequency, which can greatly shorten the frequency conversion time to within 1 microsecond, but the problem of high phase noise still exists; 4) Direct digital synthesis technology is used. Direct digital synthesis has a very high frequency conversion speed and very fine resolution, but its output frequency is not high and the spurious performance is poor. Their respective technical principles lead to different advantages and disadvantages, which makes the phase noise, agility time, frequency resolution and volume of the frequency source form a mutually opposing and restrictive relationship, making it difficult to achieve excellent levels for all indicators.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A frequency source synthesis method based on frequency agile radar, characterized in that it includes 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 4-frequency multiplier to generate a frequency multiplied signal, and dividing the frequency multiplied signal into two clock signals through a power divider;

[0009] S2, processing one of the clock signals by five times the frequency, using the processed clock signal as the clock reference signal of the direct digital synthesizer, performing phase accumulation according to the preset frequency control word and the reference clock signal to generate a corresponding phase value, looking up the 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; processing the other clock signal by seven times the frequency, and using the processed clock signal as the local oscillator signal of the mixer;

[0010] S3, input the output signal to the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed signal, perform 4-times frequency processing on the mixed signal, calibrate the processed mixed signal as the final output signal and output it.

[0011] As a further solution of the present invention: the S1 uses a constant temperature crystal oscillator with a frequency of 120 MHz.

[0012] As a further solution of the present invention: the frequency multiplication process is to achieve frequency multiplication through a frequency multiplier, and the frequency multiplier adopts step recovery diode technology to perform frequency multiplication.

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

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

[0015] As a further solution of the present invention: S3 further includes inputting the output signal into a preset digital tuning filter to perform signal denoising, 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 frequency agile radar, characterized by comprising:

[0018] A signal generation module, used for controlling a crystal oscillator to generate a target clock signal, performing frequency multiplication processing on the target clock signal through a 4-frequency multiplier to generate a frequency multiplied signal, and dividing the frequency multiplied signal into two clock signals through a power divider;

[0019] A signal processing module, used to perform 5-fold frequency processing 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 a preset frequency control word and a reference clock signal, generate a corresponding phase value, perform a table lookup according to the phase value, 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 processing on the other clock signal, and use the processed clock signal as the local oscillator signal of the mixer;

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

[0021] Beneficial effects of the present invention:

[0022] The present invention firstly adopts a constant temperature crystal oscillator to generate a target signal, performs frequency multiplication processing on the target clock signal to generate a frequency multiplication signal, divides the frequency multiplication signal into two clock signals through a power divider, adopts direct digital frequency synthesis technology for one of the signals to generate a first output signal as a DDS reference signal, adopts direct frequency synthesis for the other signal to generate a second output signal as a local oscillator signal of a mixer, the DDS reference signal and the local oscillator signal of the mixer multiplex a 4-fold frequency multiplication link, after 4-fold frequency multiplication, they are divided into two paths through a power divider, and then each is frequency multiplied to the required signal frequency, the multiplexing 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 realize 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 into the mixer and frequency conversion is performed with the local oscillator signal to obtain a mixed signal, and the mixed signal is subjected to 4 times frequency processing. It can be understood that when the DDS output frequency is high, a larger DAC (digital-to-analog converter) image spurious component will be generated. The spurious component is close to the main signal and is difficult to filter out by conventional filters. Therefore, in the present invention, a 4-time frequency multiplier is used after the mixer to perform frequency multiplication processing on 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, reducing the interference degree of these spurious components on the main signal, thereby effectively reducing the influence of DAC image spurious. The present invention combines direct frequency synthesis and direct digital frequency synthesis technology, integrates the technical advantages of both, and realizes that the output signal has low phase noise, fast agility, fine resolution and miniaturization characteristics at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 It is a flow chart of a frequency source synthesis method based on frequency agile radar of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] See also Figure 1As shown, the present invention is a frequency source synthesis method based on frequency agile radar, comprising the following steps:

[0027] S1, controlling a crystal oscillator to generate a target clock signal, and performing frequency multiplication processing on the target clock signal through a 4-frequency multiplier to generate a frequency multiplied signal, and dividing the frequency multiplied signal into two clock signals through a power divider;

[0028] S2, processing one of the clock signals by five times the frequency, using the processed clock signal as the clock reference signal of the direct digital synthesizer, performing phase accumulation according to the preset frequency control word and the reference clock signal to generate a corresponding phase value, looking up the 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; processing the other clock signal by seven times the frequency, and using the processed clock signal as the local oscillator signal of the mixer;

[0029] S3, input the output signal to the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed signal, perform 4-times frequency processing on the mixed signal, calibrate the processed mixed signal as the final output signal and output it.

[0030] The present invention firstly adopts a constant temperature crystal oscillator to generate a target signal, performs frequency multiplication processing on the target clock signal to generate a frequency multiplication signal, divides the frequency multiplication signal into two clock signals through a power divider, adopts direct digital frequency synthesis technology for one of the signals to generate a first output signal as a DDS reference signal, adopts direct frequency synthesis for the other signal to generate a second output signal as a local oscillator signal of a mixer, the DDS reference signal and the local oscillator signal of the mixer multiplex a 4-fold frequency multiplication link, after 4-fold frequency multiplication, they are divided into two paths through a power divider, and then each is frequency multiplied to the required signal frequency, the multiplexing 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 realize 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 into the mixer and frequency conversion is performed with the local oscillator signal to obtain a mixed signal, and the mixed signal is subjected to 4 times frequency processing. It can be understood that when the DDS output frequency is high, a larger DAC (digital-to-analog converter) image spurious component will be generated. The spurious component is close to the main signal and is difficult to filter out by conventional filters. Therefore, in the present invention, a 4-time frequency multiplier is used after the mixer to perform frequency multiplication processing on 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, reducing the interference degree of these spurious components on the main signal, thereby effectively reducing the influence of DAC image spurious. The present invention combines direct frequency synthesis and direct digital frequency synthesis technology, integrates the technical advantages of both, and realizes that the output signal has low phase noise, fast agility, fine resolution and miniaturization characteristics at the same time.

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

[0032] It is worth noting that the amplifier is ignored in the present invention. During implementation, a suitable amplifier can be selected and inserted into the circuit according to the actual required signal amplitude, and the amplifier should be a low phase noise amplifier.

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

[0034] In the present invention, a high-performance constant-temperature crystal oscillator is used. The phase noise performance of the current top constant-temperature crystal oscillator with a frequency of 120MHz is -130dBc / Hz@100Hz, -160dBc / Hz@1KHz, and -165dBc / Hz@10KHz. According to the calculation of the phase noise deterioration degree 20lgN (N is the N-frequency multiplication multiple), assuming that the additional phase noise of the circuit is zero, the constant-temperature crystal oscillator frequency source outputs a 15.15GHz phase noise of -160+20lg(15.15 / 0.12)=-118dBc / Hz@1KHz, ensuring that it can still maintain a low phase noise level at high frequency multiplication.

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

[0036] The frequency multiplier uses a step diode to achieve lower phase noise. The additional phase noise of the step diode is usually about 1dB. In the present invention, even after passing through three frequency multipliers, the phase noise of the frequency source outputting a 15.15GHz signal is still approximately -160+20lg(15.15 / 0.12)+3=115dBc / Hz@1KHz, which greatly reduces the phase noise.

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

[0038] In the present invention, a DDS reference clock frequency of 2.4 GHz and a bit number of 32 bits are used. After a 4-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 can enable the radar system to quickly switch between multiple frequency bands, thereby significantly improving 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, a DDS reference clock frequency of 2.4 GHz and a bit number of 32 bits are used. After a 4-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 can enable the radar system to quickly switch between multiple frequency bands, thereby significantly improving detection accuracy and sensitivity.

[0041] In another preferred embodiment of the present invention, the step S3 further includes inputting the output signal into a preset digital tuning filter to perform signal denoising, and inputting the denoised output signal into a mixer.

[0042] The frequency doubler will produce abundant high-order harmonic components, and the required frequency needs to be selected through a suitable narrowband filter. If the frequency multiplication factor is large, a filter with a relatively narrow bandwidth must be used. Due to technical and process limitations, such a filter is very difficult to implement. Therefore, in the present invention, the single frequency multiplication factor is reduced by two-stage frequency multiplication, the filter selection space is large, and better performance indicators can be achieved and costs can be reduced.

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

[0044] The signal frequency generated by DDS is 52.5MHz~427.5MHz. Although the DAC image spurious component is large, it is more than hundreds of MHz away from the main signal and can be easily filtered out by the filter. The narrowband spurious of DDS is good, about -90dBc, while the broadband spurious is poor, about -60dBc. Therefore, the filter at the output end of DDS of the present invention adopts a narrowband digital tuning filter, and the center frequency of the filter can switch with the DDS output frequency. The out-of-band suppression ability of the filter can make the DDS output signal spurious level -85dBc. Even after the 4-frequency multiplier of the subsequent stage, the spurious level of the frequency source output signal is only -73dBc, which greatly improves the spurious level of the frequency source output signal.

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

[0046] A signal generation module, used for controlling a crystal oscillator to generate a target clock signal, performing frequency multiplication processing on the target clock signal through a 4-frequency multiplier to generate a frequency multiplied signal, and dividing the frequency multiplied signal into two clock signals through a power divider;

[0047] A signal processing module, used to perform 5-fold frequency processing 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 a preset frequency control word and a reference clock signal, generate a corresponding phase value, perform a table lookup according to the phase value, 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 processing on the other clock signal, and use the processed clock signal as the local oscillator signal of the mixer;

[0048] The signal synthesis module is used to input the output signal into the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed signal, perform 4-times frequency processing on the mixed signal, calibrate the processed mixed signal as the final output signal and output it.

[0049] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A frequency source synthesis method based on frequency agile radar, characterized in that: The following steps are involved: S1, controlling a crystal oscillator to generate a target clock signal, performing a 4-fold frequency multiplication process 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; S2, processing one of the clock signals by five times the frequency, using the processed clock signal as the clock reference signal of the direct digital synthesizer, performing phase accumulation according to the preset frequency control word and the reference clock signal to generate a corresponding phase value, looking up the 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; processing the other clock signal by seven times the frequency, and using the processed clock signal as the local oscillator signal of the mixer; S3, input the output signal to the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed signal, perform 4-times frequency processing on the mixed signal, calibrate the processed mixed signal as the final output signal and output it.

2. The frequency source synthesis method based on frequency agile radar according to claim 1, characterized in that: The S1 uses a constant temperature crystal oscillator with a frequency of 120 MHz.

3. The frequency source synthesis method based on frequency agile radar according to claim 1, characterized in that: The frequency multiplication process is to realize frequency multiplication through a frequency multiplier, and the frequency multiplier adopts step recovery diode technology to perform frequency multiplication.

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

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

6. The frequency source synthesis method based on frequency agile radar according to claim 1, characterized in that: The step S3 further includes inputting the output signal into a preset digital tuning filter to perform signal denoising, and inputting the denoised output signal into a mixer.

7. The frequency source synthesis method based on 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 frequency agile radar, characterized in that: include: A signal generation module, used for controlling a crystal oscillator to generate a target clock signal, performing a 4-fold frequency multiplication process 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; A signal processing module, used to perform 5-fold frequency processing 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 a preset frequency control word and a reference clock signal, generate a corresponding phase value, perform a table lookup according to the phase value, 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 processing on the other clock signal, and use the processed clock signal as the local oscillator signal of the mixer; The signal synthesis module is used to input the output signal into the mixer and perform frequency conversion processing with the local oscillator signal to obtain a mixed signal, perform 4-times frequency processing on the mixed signal, calibrate the processed mixed signal as the final output signal and output it.

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