FDA Radar Ambiguity Function Characteristics Analysis and Optimization

Frequency diverse array (FDA) radar provides new application capabilities and potentials due to its range-dependent transmit array beampattern, but the FDA using linearly increasing frequency increments produces a range and angle coupled beampattern. This paper proposes a uniform linear array (ULA) FDA using Costas sequence modulated frequency increments to produce random-like energy distribution in the transmit beampattern to decouple the range-angle-dependent of targets. In doing so, the range and angle of targets can be solely estimated through matched filtering and subspace decomposition algorithms in the receiver signal processor. Numerical results show that the proposed scheme outperforms the standard FDA in focusing the transmit energy, especially in the range dimension.

In recent years, frequency diverse array (FDA) radar with uniform interelement frequency offset has been proposed and investigated. It has been shown that the beampattern of this form of radar is range-angle-dependent, and it exhibits maxima at multiple range values. Due to the multiple maxima, a number of reflectors located at any of the maxima can interfere the target-return, thus deteriorating signal-to-interference-plus-noise ratio (SINR). In this letter, we have proposed FDA with logarithmically increasing frequency offset to achieve a beampattern with a single maximum at the target location. A transmitter for the proposed radar system has been described and analyzed mathematically. Furthermore, the transmit beampattern has been derived and plotted and compared to that of phased-array radar (PAR) and the existing forms of FDA employing uniform frequency offset.

Different from phased array providing only angle‐dependent transmit beampattern, frequency diverse array (FDA) employs a small frequency increment across its array elements to provide range–angle‐dependent transmit beampattern. This enables the array beam to scan without the need of phase shifters or mechanical steering. Since FDA has received much attention in antenna and radar signal processing societies, it is necessary to make an overview on this interesting topic. This study introduces what FDA is and why it could be exploited for radar and navigation applications from a top‐level system description and appeal to the radar signal processing and system engineering communities for more investigations on this promising array technique. The status of FDA studies is overviewed and the most recent advances of FDA radar are discussed. The basic FDA system architectures are introduced, along with performance compared to a conventional phased‐array. Next, guidelines for choosing good system parameters and typical implementation schemes are provided. Finally, potential applications in range and angle estimation of targets, cognitive FDA radar and low probability of identification FDA radar are discussed, along with several technical challenges.

To meet the urgent demand of low-observable moving target detection in complex environments, a novel method of Frequency Diverse Array (FDA) radar signal processing method based on Space-Rang-Doppler Focusing (SRDF) is proposed in this paper. The current development status of the FDA radar, the design of the array structure, beamforming, and joint estimation of distance and angle are systematically reviewed. The extra degrees of freedom provided by FDA radar are fully utilizsed, which include the Degrees Of Freedom (DOFs) of the transmitted waveform, the location of array elements, correlation of beam azimuth and distance, and the long dwell time, which are also the DOFs in joint spatial (angle), distance, and frequency (Doppler) dimensions. Simulation results show that the proposed method has the potential of improving target detection and parameter estimation for weak moving targets in complex environments and has broad application prospects in clutter and interference suppression, moving target refinement, etc..

Coherent receiver design and aperture expansion beamforming for frequency diverse array radar

Frequency diverse array (FDA) radar with non-uniform frequency increasing offset is the most potent method to decouple the range-angle dependent beampattern and form a dot-shaped beampattern. However, little known empirical research has focused on the joint range-angle estimation of FDA radar with non-uniform frequency offset. The aim of this letter is to investigate a decoupling model and propose a range-angle estimation algorithm of FDA radar with uniform or non-uniform frequency offset. First, the blind source separation algorithm is performed to process the observation signal and obtain the separation matrix. Then, the array manifold matrix of observation signal is estimated by separation matrix correction. Next, a decoupling model is formulated to separate the range and angle component from the estimated array manifold matrix. Finally, an independent range and angle estimation algorithm via pulse-pair technique is developed. The numerical simulations are performed to indicate the effectiveness and superior performance.

Different from conventional phased-array, which provides only angle-dependent beampattern, frequency diverse array (FDA) employs a small frequency increment across the antenna elements and results in a range-angle-dependent beampattern. This beampattern offers a potential to localize the targets in two dimensions in terms of slant ranges and azimuth angles. However, it is difficult to obtain the target location information from a standard FDA radar due to the couplings in range and angle responses. In this paper, we propose a transmit subaperturing scheme on the FDA radar for range and angle estimation of targets. The essence is to divide the FDA elements into multiple subarrays and optimize the transmit beamspace matrix with the use of convex optimization. We also discuss several practical issues for designing the FDA radar system parameters. Since the subarrays offer decoupled range and angle responses, the targets can be located using the beamspace-based multiple signal classification algorithm. The range and angle estimation performance is evaluated by comparing with the Cramer-Rao lower bound.

Different from traditional phased array radar, frequency diverse array (FDA) radar uses a small frequency increment across the array elements; thus, the beampattern of FDA can be performed in both range and angle domains. Nevertheless, the transmit beampattern of conventional FDA is coupled in range and angle domains, which is not suitable for target detection. In this paper, we propose a multi-carrier FDA framework to generate the range-angle-decoupled beampattern. To focus the transmit energy at the desired position and suppress the interference at the undesired position, we then propose a beampattern synthesis approach based on Lagrange programming neural network, which can be implemented by hardware easily. Numerical simulation results demonstrate the effectiveness of the proposed method.

The range-angle coupling in Frequency Diverse Array (FDA) radar is uniquely solved. The array operates as a linear pulsed FDA in the transmission (TX) mode while it operates as a pulsed phased array (PA) in the receiving (RX) mode. The duration of FDA TX pulse is chosen as minimum. A novel radar concept is proposed. It is shown that FDA waveform can be further compressed by matched filtering (MF).

In this article, a novel technique is applied to achieve time-invariant spatial focusing performance for static and moving target by applying an irregular frequency modulation method to a frequency diverse array (FDA) waveform transmission system. The FDA radar can improve the anti-noise ability of the system by the means of concentrating the waveform energy on the required range or angle sector. However, the synthesized waveform has high sidelobes and is time-varying during the transmission waveform. In view of the above problems, a new waveform synthesis model of rang compensation frequency diverse array (TMRC-FDA) is established and the effect of parameter $$\varsigma$$ on the waveform synthesis is analyzed. A new accelerated particle swarm optimization algorithm is used to optimize the distribution of parameter $$\varsigma$$. The numerical simulation results show that the proposed TMRC-FDA waveform synthesis method achieves the goal of time invariance and reduces the waveform sidelobes. At the same time, it has better performance in terms of waveform focus compared to log-frequency offset FDA based on time-modulated and fixed parameters $$\varsigma$$.

Different classic phased-array that generates only angle-dependent transmit beampattern, frequency diverse array (FDA) offers both angle-dependent and range-dependent transmit beampattern. This paper adopts the information geometry theory to study the fundamental information resolution for a general FDA radar system. The information resolution, associated with the waveform, measurement and noise model and characterized by the Fisher information metric, provides a statistical measure for the FDA radar system. Numerical results show that FDA radar indeed outperforms conventional phased-array radar in information geometry resolution capability.

This paper studies the optimal detection performance of the standard frequency diverse array (FDA) radar and FDA multi-input multioutput (FDA-MIMO) radar in Gaussian clutter and noise. Array signal processing scheme at the receiver is firstly designed to obtain the array steering vector containing range, azimuth, and frequency increment. For the two array configurations, namely, collocated transmit-receive and collocated transmit distributed receive, the likelihood ratio test statistics and the test statistic distributions are derived in the Neyman–Pearson sense. It is then investigated how the number of array elements influences the detection performance of various radar systems at low signal-to-noise ratio (SNR). Several numerical simulations are carried out to demonstrate that the performance improvement is hard for MIMO and FDA-MIMO by only increasing the number of transmit elements, while it is achievable for the FDA. The paper finally makes a comparative analysis for detection performances of five radar configurations under different SNRs.

Frequency diverse array (FDA) can provide a range-angle-dependent beam that can be controlled by using a frequency increment between adjacent elements, but the frequency increment is fixed in a basic FDA, which restraints the performance improvement in different environments significantly. In this letter, we propose an adaptive frequency offset selection scheme to control the transmit beam direction by choosing the frequency offset adaptively. In doing so, we design the frequency increment of transmit signal in each step by maximizing the output signal-to-interference-plus-noise ratio (SINR) criteria. Our proposal can adaptively adjust the beam direction to match the current target angle and range sector. The effectiveness of the proposed scheme is verified by simulation results.

In the last few years, valuable research in frequency diverse arrays (FDAs) has been conducted. However, emphasis had mainly been on uniform linear arrays (ULAs) and uniform rectangular arrays (URAs). Not much attention has been devoted to other configurations. Circular symmetry of uniform circular arrays (UCAs) has been an attraction to researchers for several reasons such as the ability to scan azimuthally through 360° and better spatial resolutions. Motivated by the potential advantages of UCA, this letter presents an in-depth investigation of circular geometries in FDA radars. In this letter theory, analysis and basic beam steering in uniform circular frequency diverse arrays (UCFDAs) is presented along with comparison with linear and rectangular counterparts.

Waveform optimization with SINR criteria for FDA radar in the presence of signal-dependent mainlobe interference