Basic Frequency Diverse Array Research Articles

Dot-shaped beamforming analysis based on OSB log-FDA

The range and angle information of the frequency diverse array (FDA) cannot be exclusively determined at the output of the array because of the range-angle coupled transmit beampattern. The best decoupling approach is to form a dot-shaped beam-pattern rather than the S-shaped beampattern of the basic FDA. Considering the degradation of the output signal-to-interference-plus-noise ratio (SINR) caused by the coupled beampattern, we propose a dot-shaped beamforming method based on the analyzed overlapping subarray-based using a logarithmic offset and a subarray-based planar FDA using a logarithmically increasing frequency offset, with elements transmitting at multiple frequencies. Several simulation results demonstrate the effectiveness of the proposed method in transmit energy focusing, sidelobe suppression and array resolution.

Beamforming analysis based on CSB sin-FDA

This paper studies the adaptive beamforming algorithm based on the frequency diverse array (FDA) array where the interference is located at the same angle (but different range) with the target. We take the cross subarray-based FDA with sinusoidal frequency offset (CSB sin-FDA) as the receiving array instead of the basic FDA. The sampling covariance matrix under insufficient snapshot can be corrected by the automatic diagonal loading method. On the basis of decomposing the mismatched steering vector error into a vertical component and a parallel one, this paper searches the vertical component of the error by the quadratic constraint method. The numerical simulation verifies that the beamformer based on the CSB sin-FDA can effectively hold the mainlobe at the target position when the snapshot is insufficient or the steering vector is mismatched.

A Novel Transmit–Receive System of Frequency Diverse Array Radar for Multitarget Localization

The frequency diverse array (FDA) has drawn substantial attention because it provides a new degree of freedom. However, the multitarget localization is fundamentally limited by the range-angle-coupled and range-periodic beampattern of the basic FDA. It has been suggested to design a special FDA configuration to localize targets, but seldom of the existing works consider the design both in transmitting and receiving. In this paper, a transmit–receive system of FDA radar is proposed for the multitarget localization. In order to decouple the beampattern in the range and angle domains, the configurations of subarray-based FDA (SB-FDA) and full-band FDA (FB-FDA) are chosen as transmitter and receiver, respectively. In such a system framework, the receive beamwidth in range domain is only a quarter of the transmission. Then, two typical multitarget scenarios, sparse targets and unresolved targets, are both considered in the multitarget localization. For sparse targets, a proper frequency increment is selected to control the range-periodic transmit and receive mainlobes to focus on a single target, besides being staggered with others. In this way, multitarget localization is achieved in different pulses with monopulse processing. For unresolved targets, a method of intra-pulse beam scanning is proposed to localize each target with little interference from others. We also analyze the system performance in Cramér-Rao lower bound (CRLB) of localization and output signal to interference-plus-noise ratio (SINR). Several simulation results demonstrate the effectiveness of the proposed transmit–receive system in multitarget localization.

Time-Invariant Joint Transmit and Receive Beampattern Optimization for Polarization-Subarray Based Frequency Diverse Array Radar

We propose a polarization-subarray based frequency diverse array (FDA) radar with the subarray-based FDA as the transmit (Tx) array and the polarization-sensitive subarray-based FDA (PSFDA) as the receive (Rx) array. The subarray-based FDA has the capability to achieve a single maximum beampattern at the target location, while the PSFDA can provide an extra degree of freedom to further suppress the interference and, thus, to improve the radar's signal-to-interference-plus-noise ratio (SINR). The time-dependent frequency offsets are designed for the proposed radar to realize the time-invariant beampattern at the desired target location over the whole pulse duration. To further improve the target detection performance, the time-invariant joint Tx–Rx beampattern design is considered based on the output SINR maximization. To effectively solve the nonconvex output SINR maximization problem, a suboptimal alternating optimization algorithm is proposed to iteratively optimize the FDA Tx beamforming, the PSFDA spatial pointings, and the PSFDA Rx beamforming. Numerical experiments illustrate that the time-invariant and single-maximum joint Tx–Rx beampattern at the target location is achieved. Moreover, compared to the basic FDA and logarithmic frequency offset FDA as well as conventional phased array radars, the proposed polarization-subarray based FDA radar achieves a significant SINR improvement, particularly when the desired target and the interferences are spatially indistinguishable.

Beampattern Synthesis for Frequency Diverse Array Based on Time-Modulated Double Parameters Approach

Abstract The basic frequency diverse array (FDA) using linearly increasing frequency increments generates a range-angle dependent beampattern. However, it is coupled in range and angle dimensions and is also periodic in range and time, making its applications limited. In this paper, a novel FDA beampattern synthesis approach is proposed utilizing the time-modulated double parameters based on the chaos sequence. The chirp signal mechanism is used instead of the single-frequency signal mechanism. Meanwhile, the multi-carrier architecture is used for range-angle decoupling. Satisfactory time-invariant range-angle beampattern can be synthesized for both single and multiple targets locations. Simulation results show the effectiveness of the proposed FDA scheme. Furthermore, comparative study with the existing technology indicates that the proposed approach can provide better performance in spatial focusing and side-lobe suppressing.

Subarray-Based Frequency Diverse Array for Target Range-Angle Localization With Monopulse Processing

Frequency diverse array (FDA) can offer new degrees-of-freedom, but the target localization of basic FDA is fundamentally limited by the range-angle-coupled and range-periodic peaks of beampattern. In this paper, we propose a localization system with the combination of subarray-based FDA and full-band FDA, as the transmitter and the receiver, respectively. The transmit and receive beampatterns are both decoupled in range and angle domains. Target range-angle localization is achieved by two steps. First, using the outputs of subarrays, we solve the range ambiguity and obtain a coarse location. Second, the monopulse processing of range-angle localization is developed for the proposed system by taking the coarse location as the receiving beam pointing. The localization performance is also analyzed in Cramer-Rao lower bound, computational complexity, and output signal to interference-plus-noise ratio. Several simulation results demonstrate that unambiguous target range-angle localization can be achieved with a low computational cost by the proposed method.

Transmit Beampattern Design in Range and Angle Domains for MIMO Frequency Diverse Array Radar

The frequency diverse array (FDA) has a range-angle-dependent transmit beampattern, which can provide the potential capability for novel radar application. However, the basic FDA's beampattern is periodic in range and coupled in range and angle dimensions, which limits the application of FDA in radar field. In this letter, we propose a novel FDA model with nonmonotone increasing frequency offset to form a narrow pencil beam, which eliminates the range periodicity and coupling of range and angle domains. Combining this new FDA with multiple-input–multiple-output radar, not only can multiple narrow pencil beams be formed to track multiple targets simultaneously, but also a flat-top transmit beampattern for targets searching can be synthesized. Simulation results show the effectiveness and outperformance of the proposed scheme compared to the existing Log-FDA, which uses the logarithmically increasing frequency offset.

Time-Invariant Range-Angle-Dependent Beampattern Synthesis for FDA Radar Targets Tracking

The frequency-diverse array (FDA) radar has drawn substantial attention in recent years because of its particular range-angle-dependent beampattern. However, with the linear incremental frequency offset, the basic FDA radar's beampattern is time-variant, range-periodic, and coupled in range and angle dimensions, which limits FDA radar's practical application seriously. In this letter, we propose a novel transmit beampattern synthesis method using the multicarrier FDA architecture and nonlinear time-dependent frequency offset. As a result, a pencil-shaped time-invariant and range-angle-dependent beampattern can be synthesized for target tracking. Furthermore, a time division method is utilized to form multiple narrow pencil-shaped beampatterns for tracking multiple targets within one pulse duration. Simulation results show the effectiveness of the proposed scheme and demonstrate its outperformance via comparison to other existing methods.

Subarray-based FDA radar to counteract deceptive ECM signals

In recent years, the frequency diverse array (FDA) radar concept has attracted extensive attention, as it may benefit from a small frequency increment, compared to the carrier frequency across the array elements and thereby achieve an array factor that is a function of the angle, the time, and the range which is superior to the conventional phase array radar (PAR). However, limited effort on the subject of FDA in electronic countermeasure scenarios, especially in the presence of mainbeam deceptive jamming, has been published. Basic FDA is not desirable for anti-jamming applications, due to the range-angle coupling response of targets. In this paper, a novel method based on subarrayed FDA signal processing is proposed to counteract deceptive ECM signals. We divide the FDA array into multiple subarrays, each of which employs a distinct frequency increment. As a result, in the subarray-based FDA, the desired target can be distinguished at subarray level in joint range-angle-Doppler domain by utilizing the fact that the jammer generates false targets with the same ranges to each subarray without reparations. The performance assessment shows that the proposed solution is effective for deceptive ECM targets suppression. The effectiveness is verified by simulation results.

Overview of frequency diverse array in radar and navigation applications

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.

Cognitive frequency diverse array radar with situational awareness

By jointly utilising the advantages of cognitive radar with situational awareness due to closed-loop control and frequency diverse array (FDA) with range-angle-dependent beampattern, this study proposes a cognitive FDA radar with situational awareness. Different from conventional phased-array, FDA offers a range-dependent beampattern. The proposed cognitive FDA radar can avoid undesired strong interferences and focus to the desired targets through the presented closed-loop control algorithm. This algorithm aims to maximise the receiver output signal-to-interference-plus-noise ratio (SINR) performance by iteratively optimising the frequency increment in a closed-loop manner. That is, the cognitive FDA radar can adaptively change its frequency increment according to the environment and thus better performance can be obtained. The cognitive FDA radar performance is evaluated by examining the SINR and direction-of-arrival (DOA) estimation mean square errors. How the performance depends on the FDA frequency increment is also investigated. Simulation results show that the cognitive FDA radar yields much better SINR performance and thus higher DOA estimation precision than basic FDA and conventional phased-array radars.

Adaptive Frequency Offset Selection in Frequency Diverse Array Radar

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.