A phased array radar transmit beam forming method and device based on a DDS array

Abstract

The application discloses a phased array radar transmitting beam forming method and device based on a DDS array. The method comprises the following steps: generating N parallel phase control words according to a desired beam direction; sending a starting signal to the N parallel direct digital frequency synthesizers at the same time, and each DDS starts working synchronously; N DDSs generate N transmitting waveforms with a preset phase difference according to the corresponding phase control words; and the transmitting waveforms are radiated to space by an antenna array element after power amplification to form a composite beam. The device comprises a reference clock source, a phase control word generation unit, a DDS array, a synchronous starting unit, a power amplification array and an antenna array. The application realizes high-precision, fast switching and waveform flexible digital generation of the phased array radar transmitting beam, and is suitable for application scenarios such as fast beam scanning, multi-target tracking and multi-functional radar.

Description

Technical Field

[0001] This invention belongs to the field of phased array radar technology, specifically relating to a method and apparatus for transmitting beamforming of phased array radar based on DDS array, which is particularly suitable for application scenarios such as fast beam scanning, multi-beam forming and waveform agility of phased array radar. Background Technology

[0002] Phased array radar achieves beam scanning by controlling the phase difference of the transmitted signals of each antenna element. Traditional transmit beamforming usually uses a phase shifter scheme: the radio frequency signal is distributed to each array element channel through a power divider network, each channel adjusts the signal phase through a phase shifter, and then amplified by a power amplifier before being radiated by the antenna element. However, traditional phase shifter solutions have the following problems: (a) Limited phase accuracy Traditional phase shifters typically use 5-bit or 6-bit quantization (in 11.25° or 5.625° steps), which limits beam pointing accuracy. For applications requiring high-precision angle measurement and low sidelobes, this level of accuracy is insufficient. (ii) High insertion loss Phase shifters operate at radio frequency and have relatively high insertion loss (typically 2-5dB), which directly reduces transmission efficiency and equivalent radiated power. (iii) Slow beam switching speed Each beam direction requires an independent phase shift setting, and beam switching is limited by the response speed of the phase shifter and the update rate of the control circuit. (iv) The analog power distribution network is complex. As the number of array elements increases, the complexity of the analog power divider network rises sharply, and the insertion loss and amplitude-phase inconsistency intensify, making it difficult to achieve large-scale arrays. (v) Limited waveform flexibility Traditional phase shifter solutions can only change the phase and cannot flexibly change the modulation method or frequency of the transmitted waveform, which limits the radar's multi-waveform operation capability. To address the aforementioned problems, this invention provides a method and apparatus for generating transmit beams of a phased array radar based on a DDS array. Summary of the Invention

[0003] This invention provides a method and apparatus for beamforming a phased array radar based on a DDS array, aiming to solve the technical problems of limited phase accuracy, high insertion loss, slow beam switching speed, and poor waveform flexibility in existing phase shifter schemes. The technical solution is as follows: This invention provides a method for beamforming a phased array radar based on a DDS array, comprising the following steps: generating N parallel phase control words according to the desired beam direction; simultaneously sending start signals to N parallel direct digital frequency synthesizers (DDS), with each DDS starting synchronously under a unified reference clock; the N DDS, according to their respective phase control words, preset initial phase values ​​in their phase accumulators, and synchronously generating N transmit waveforms with preset phase differences; amplifying the N transmit waveforms by N power amplifiers, and then radiating them simultaneously into space by N antenna elements to form a composite beam in the far field. The N DDS operate in parallel under the same reference clock, and the initial phase of each transmit waveform is independently set by its corresponding phase control word; the beam direction is switched by changing the phase control word. This invention also provides a phased array radar transmit beamforming device based on a DDS array, comprising a reference clock source, a phase control word generation unit, a DDS array, a synchronization start-up unit, a power amplifier array, and an antenna array. The DDS array includes N parallel direct digital frequency synthesizers (DDSs), each DDS generating a transmit waveform with a preset initial phase based on a reference clock signal and a corresponding phase control word. The synchronization start-up unit simultaneously sends start signals to the N DDSs, causing each DDS to synchronously begin waveform generation. Working principle: A reference clock source provides a unified reference clock signal to the DDS array. The phase control word generation unit calculates the required phase difference for each array element based on the desired beam direction, generating N parallel phase control words. The synchronization start unit simultaneously triggers all DDSs, each of which presets an initial phase value in its internal phase accumulator, and then synchronously generates a transmit waveform with a preset phase difference under the drive of the reference clock. The transmit waveforms of each channel are amplified and radiated into space by the antenna elements, coherently superimposed in the far field to form a composite beam pointing in the desired direction. Since each DDS shares the same reference clock and the same start signal, the phase consistency of the output waveform is guaranteed by digital circuitry and is unaffected by environmental factors such as temperature and frequency. Beam pointing can be switched between pulses by updating the phase control word. Beneficial effects: High phase accuracy: The phase accumulator of DDS is usually 16 bits or more (corresponding to 0.0055° steps), which is far superior to the 5-6 bit accuracy of traditional phase shifters; Zero insertion loss: DDS generates phase in the digital domain, eliminating the insertion loss of analog phase shifters and significantly improving transmission efficiency; Fast beam switching: The beam pointing is switched between pulses by updating the phase control word, and the switching time is less than 1μs; Flexible waveforms: DDS can simultaneously achieve phase control, frequency control and amplitude control, and supports various radar waveforms such as linear frequency modulation and phase coding; Good synchronization: Each DDS shares the same reference clock and start signal, and the phase consistency between channels is guaranteed by digital circuitry; Easy to expand: Digital domain distribution makes it easy to implement phase control of large-scale arrays, and no complex analog power divider network is needed when the number of array elements increases. Attached Figure Description

[0004] Figure 1 This is a structural block diagram of a phased array radar transmit beamforming device based on a DDS array, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of a single DDS channel provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the phase control word generation unit provided in an embodiment of the present invention. Figure 4 This is a timing diagram for rapid beam switching provided in an embodiment of the present invention. Figure 5 This is a structural block diagram of a multi-beam transmitting beamforming apparatus provided in an embodiment of the present invention. Detailed Implementation

[0005] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Example 1: FPGA-based 64-channel DDS transmit beamforming device Step 1: Refer to the clock source configuration. A 100MHz temperature-compensated crystal oscillator (TCXO) was selected as the reference clock source to provide a reference clock signal for the DDS array. The clock signal was distributed to the 64 DDS channels via a fan-out buffer to ensure clock synchronization among the channels. Step 2: Phase control word generation. The phase control word generation unit generates the word based on the desired beam direction (e.g., azimuth angle). ), calculate the phase difference required for each array element: in The element spacing is half a wavelength. For array element index ( The calculation result is converted into a 16-bit phase control word (0). 65535对应0° (360°), parallel output to 64 DDS channels. Step 3: Start the DDS array synchronously. The synchronous startup unit simultaneously sends a startup signal to 64 DDSs. Upon receiving the startup signal, each DDS writes its corresponding phase control word into the initial value register of the phase accumulator, and then synchronously begins waveform generation under the drive of the reference clock. The 64 DDSs share the same reference clock and the same startup signal, ensuring that the initial phase accuracy of the output waveform is better than 0.0055°. Step 4: Parallel waveform generation. Sixty-four digital signal processing units (DDSs) operate in parallel. Each DDS's phase accumulator starts accumulating from a preset initial phase, outputs a sine wave digital sequence via a waveform lookup table, and then converts it into an analog intermediate frequency signal via a digital-to-analog converter. The output signal of each channel has a precise phase difference. Step 5: Up-conversion and power amplification. The intermediate frequency signal output from each channel of the DDS is converted to radio frequency (such as X-band 9.5GHz) by an upconverter, and then amplified to the required transmission power by a power amplifier. Step 6: Antenna radiation. The amplified radio frequency signal is radiated into space by 64 antenna elements. The radiated signals from the 64 elements coherently superimpose in the far field to form a transmission beam pointing in the desired direction. The advantages of this embodiment are as follows: The DDS array is implemented as an IP core within the FPGA, with 64 channels generating transmit signals with precise phase differences in parallel, replacing traditional phase shifters and power dividers. The phase accuracy is 0.0055°, the beam switching time is less than 1μs, and the transmit efficiency is improved by approximately 30% compared to the phase shifter solution. Example 2: Rapid Beam Switching and Multi-Beam Scanning Step 1: Pre-store multiple sets of phase control words. Multiple beam direction corresponding phase control word groups are pre-stored in the lookup table of the phase control word generation unit (e.g., direction 1: azimuth -45°; direction 2: azimuth -30°; direction 3: azimuth 0°; direction 4: azimuth 30°; direction 5: azimuth 45°). Step 2: Pulse switching. According to the timing signal, the radar controller reads the phase control word group corresponding to the next beam direction from the lookup table during the switching period between adjacent pulses and loads it into the phase accumulator of each DDS. Step 3: Synchronize and update. Each DDS synchronously updates the initial phase of the output waveform at the start of the next pulse cycle, achieving inter-pulse switching of beam pointing. The switching time is less than 1μs, which is far superior to traditional phase shifter solutions. The beneficial effects of this embodiment are: rapid multi-beam switching is suitable for rapid airspace scanning and multi-target tracking applications of phased array radar, with a frame rate of over 10kHz. Example 3: Waveform Agile Transmit Beamforming Step 1: Configure DDS parameters. In addition to the initial phase control word, each DDS is also configured with a frequency control word (which determines the transmission frequency) and a waveform mode control word (which determines the modulation method). Step 2: Synchronization waveform generation. Each DDS, triggered by a unified start signal, synchronously generates a transmit waveform with a preset initial phase, frequency, and modulation scheme according to its own control word. It supports various radar waveforms, including linear frequency modulation (LFM), phase coding (such as Barker code and P4 code), and frequency stepping. Step 3: Beam-waveform combined agility. By simultaneously switching beam pointing and transmitted waveform parameters between pulses, beam-waveform joint agility is achieved, enhancing the radar's anti-jamming capability and target recognition capability. The beneficial effect of this embodiment is that the waveform flexibility of DDS allows the transmitter to quickly switch between multiple waveforms without the need for additional waveform generation hardware. Example 4: Multi-beam simultaneous formation device Step 1: Configure the multibeam synthesizer unit. In the phase control word generation unit, multi-beam synthesis logic is configured to calculate the superposition value of phase control words in multiple beam directions for each antenna element. Step 2: Generate the composite phase control word. Each DDS receives a composite phase control word and generates a transmit waveform that simultaneously contains phase information of multiple beam directions. Step 3: Multi-beam radiation. The electromagnetic waves radiated by the antenna array simultaneously form multiple beams pointing in different directions in space. The beneficial effects of this embodiment are: simultaneous multi-beam formation is suitable for simultaneous multi-target tracking and multi-functional radar applications.

Claims

1. A method for beamforming the transmitted beam of a phased array radar based on a DDS array, characterized in that, Includes the following steps: Phase control word generation steps: Calculate the required phase difference for each array element according to the desired beam direction, and generate N parallel phase control words, each phase control word containing initial phase information; DDS array synchronous startup steps: Start signals are sent simultaneously to N parallel direct digital synthesizers (DDS), and each DDS starts working synchronously under the drive of a unified reference clock; Waveform parallel generation steps: N DDSs, according to their respective phase control words, preset the initial phase value in the phase accumulator and synchronously generate N transmit waveforms with preset phase differences. Power amplification and radiation steps: The N transmitted waveforms are amplified by N power amplifiers and then radiated into space simultaneously by N antenna elements to form a composite beam in the far field; In this system, N DDSs operate in parallel under the same reference clock, and the initial phase of each transmitted waveform is independently set by the corresponding phase control word. The beam pointing is switched by changing the phase control word.

2. The method according to claim 1, characterized in that: In the phase control word generation step, the phase difference required for the i-th array element is determined by the following formula:

3. Among them For the operating wavelength, For the spacing between array elements, For array element index ( ), The desired beam pointing angle.

4. The method according to claim 1, characterized in that: It also includes a beam switching step: during the inter-pulse switching cycle, a new phase control word is loaded into each DDS, and at the beginning of the next pulse cycle, each DDS synchronously updates the initial phase of the output waveform to achieve inter-pulse switching of beam pointing.

5. The method according to claim 1, characterized in that: It also includes a waveform agility step: while keeping the phase difference between each channel constant, the frequency or modulation method of the transmitted waveform is changed synchronously by adjusting the frequency control word or waveform mode control word of each DDS.

6. The method according to claim 1, characterized in that: The N parallel direct digital frequency synthesizers are implemented as IP cores within a single field-programmable gate array (FPGA) chip, with each DDS sharing the same reference clock and the same reset signal. A phased array radar transmit beamforming device based on a DDS array, characterized in that it comprises: A reference clock source, configured to provide a reference clock signal; A phase control word generation unit is connected to the reference clock source and configured to generate N parallel phase control words according to the desired beam direction. A DDS array contains N parallel direct digital frequency synthesizers. The input of each direct digital frequency synthesizer is connected to the corresponding output of the reference clock source and the phase control word generation unit. It is configured to generate a transmit waveform with a preset initial phase after presetting an initial phase value in the phase accumulator according to the reference clock signal and the corresponding phase control word. A synchronous start unit is connected to the start terminal of each DDS in the DDS array and is configured to send start signals to N DDS simultaneously, so that each DDS starts waveform generation synchronously. A power amplifier array comprising N parallel power amplifiers, the input of each power amplifier being connected to the output of the corresponding direct digital frequency synthesizer, configured to amplify the power of the transmitted waveform; An antenna array contains N antenna elements, the input of each antenna element is connected to the output of the corresponding power amplifier, and is configured to radiate the transmitted waveform after power amplification.

7. The apparatus according to claim 6, characterized in that: The direct digital frequency synthesizer includes a phase accumulator, a waveform lookup table, and a digital-to-analog converter. The phase accumulator generates a phase sequence based on the phase control word and the reference clock signal. The waveform lookup table outputs a digital waveform based on the phase sequence. The digital-to-analog converter converts the digital waveform into an analog waveform.

8. The apparatus according to claim 6, characterized in that: The phase control word generation unit includes a lookup table, which pre-stores N phase control word groups corresponding to multiple desired beam directions. The phase control word generation unit selects the target phase control word group according to the radar timing signal and outputs it to the DDS array.

9. The apparatus according to claim 6, characterized in that: It also includes an upconversion array containing N parallel upconverters, each of which is disposed between the corresponding direct digital frequency synthesizer and the corresponding power amplifier, and is configured to upconvert the transmitted waveform to radio frequency.

10. The apparatus according to claim 6, characterized in that: The device is integrated on a single chip, which is a field-programmable gate array (FPGA) chip or an application-specific integrated circuit (ASIC) chip, and the value of N ranges from 4 to 3072.

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