Range-angle Dependent Beampattern Research Articles

Transmit beampattern design for FDA-MIMO radar using complex manifold optimization

Frequency diverse array multiple-input multiple-output (FDA-MIMO) radar can produce time-stationary range-angle dependent beampattern. The problem with these beampatterns is the repeating lobes in the angle-range domain. Different methods are proposed to obtain better beampattern in terms of grating lobe and sidelobe suppression by using frequency offsets. However, these methods mostly choose the frequency offsets using an analytic expression and do not offer a control on the resulting range beampattern. In this paper, a new method for transmit beampattern design in range is presented. This method transfers the design problem into a tangential space and solves the problem using complex manifolds through an optimization procedure. The proposed approach considers amplitude tapering in the transmitter antenna elements and the practical instrumented range of the radar. Range beampattern constraints can be defined conveniently leading to an effective design process. Several simulations are done to show that the proposed method can significantly improve the beamwidth and sidelobe level in range patterns.

Time-Invariant and Localized Secure Reception With Sequential Multicarrier Receive-FDA

Secure communication in the physical layer (PHY) using frequency diverse array (FDA) antennas has become a prominent research topic in recent years due to the unique range-angle dependent beam pattern exhibited by FDAs. However, the time-varying and periodic nature of the FDA beam pattern prevents the achievement of a time-invariant range-angle focused beam pattern. Consequently, a range-angle focused beam is only achieved at a specific time instant. Therefore, it is not yet possible to focus a beam to a specific point or area in space permanently in a time-invariant manner, due to both natural propagation mechanisms and the independent time parameter. Once a wave is transmitted, time variation cannot be altered. Thus, for the FDA beam pattern, it continues to propagate over time indefinitely. However, in the case of receiving, the time parameter is under the control of the receiver. The receiver can set the time at which the incoming wave is sampled or acquired. In this study, a cross-linear array structure called the Sequential Multi-Carrier Receiver FDA (SMCR-FDA) and a relevant methodology are proposed to obtain a three-dimensionally localized time-invariant range-angle focused receive beam pattern. Additionally, several novel concepts, including the cross-linear array structure, the secure reception concept, and the Positional Modulation Technique are introduced.

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

Frequency diverse array (FDA) radar has attracted considerable attention in interference suppression due to its range-angle dependent beampattern property. However, the full-band coherent receiver design is sophisticated and expensive. Furthermore, prior research on FDA radar adaptive beamforming failed to suppress adjacent-target interference because of insufficient beam resolution. This paper aims to develop a receiver architecture based on fractional domain signal separation and to investigate aperture expansion adaptive beamforming based on interference-noise covariance matrix reconstruction and signal of interest steering vector estimation. The proposed receiver design not only simplifies the structure and saves resources, but it can also effectively separate the received signals, particularly for the FDA radar's overlapping linear frequency modulated baseband emission waveforms. The proposed aperture expansion beamforming approach improves beam resolution of beamforming and effectiveness in adjacent-target interference suppression.

Range-Angle Dependent Beampattern Synthesis Method for OFDM-Based Passive Radar

Frequency diverse array (FDA) radar applies a tiny frequency offset across its adjacent transmitting array elements to generate a range-angle-dependent beampattern. The increased degrees-of-freedom (DOFs) in range domain can help improve the performance of radar in target detection, localization, and clutter suppression. Passive radar utilizes uncontrollable external signal as illuminator, which makes it difficult to apply traditional frequency diverse process method. However, the third-party illuminator such as Orthogonal Frequency Division Multiplexing (OFDM) signal usually consists of several closely spaced modulated carriers, and it has been widely selected as the illuminator for passive radar in recent years. Considering the orthogonality between even separated subcarriers, we propose a new frequency diverse process method by extracting and processing each subcarrier of received data independently and attempt to provide a range-angle dependent beampattern for OFDM passive radar. Numerical results and real data analyses verify the superiority of frequency diversity process on the received data of OFDM passive radar.

Accurate Theoretical Models for Frequency Diverse Array Based Wireless Power Transmission

Wireless power transfer (WPT) is a well-known problem, and has received wide attention in the next generation industrial applications and consumer electronics. On the other hand, frequency diverse array (FDA) is a new concept with the ability to generate a range-angle dependent beampattern. Therefore, some researchers are engaged in designing WPT systems based on the FDA framework (FDA-WPT) instead of phased arrays. Unlike phased arrays, the FDA beampattern is time-variant. Therefore, existing beam collection efficiency models based on the phased array are not suitable for the FDA-WPT system. More importantly, the time-variant property of FDAs is usually ignored in the literature, and the system configuration of the target area where the power-harvesting end is located does not conform to the actual WPT scenario. In this paper, we derive and present accurate models of the FDA-WPT system. The power transfer performance of the corrected FDA-WPT system is then compared with the phased array based WPT system. Simulation results demonstrate that time-variant consideration in the FDA-WPT model causes difficulty in controlling the main beam direction to focus the power. The accurate FDA-WPT is theoretically investigated, and numerical simulations are implemented to validate the theoretical analysis.

Frequency diverse array radar with non-uniform array spacing based on sigmoid function

Abstract As a widely recognized electronic beam steering concept, frequency diverse array (FDA) radar is an effective and feasible solution to provide beam scanning ability in both angle as well as range dimension as a function of time. However, the conventional FDA radar employing progressive incremental frequency offsets across the array elements generates an S-shaped and range-angle coupled beampattern. As such, the FDA beampattern can be decoupled into range-angle dimensions by employing non-linear frequency offsets or using non-uniform arrays. Frequency offsets design has been extensively researched in recent years, whereas non-uniform arrays were given little attention so far. In this paper, we propose a novel FDA radar with a unified configuration of non-uniform linear array, and non-linear frequency offsets to achieve a high-resolution dot-shaped range-angle dependent beampattern. More specifically, the non-uniform inter-element spacing is calculated using the sigmoid function, and non-linear frequency offsets are generated by logistic map, and triangular window function. Simulation results clearly demonstrate the performance advantages of the proposed FDA radar in terms of beam width and side lobe levels.

Focused tracking beamforming of frequency diversity array with multiple repeated subpulses

A range-angle–dependent beam pattern can be produced by frequency diversity array (FDA) due to the small frequency offsets between the array elements. The beam pattern can be used to automatically scan an area in its entirety and estimate the distance and angle to a target. However, for constant tracking of the target after recognition, energy is wasted in the scanning mode because of periodic scanning of the main lobe of the beam. To eliminate this energy waste, we propose multiple repeated subpulses of FDA. This scheme achieves stable tracking without range–angle coupling. This special transmission method considerably improves the transmission energy and signal-to-noise ratio, while ensuring accurate range detection and high resolution. The results of a feasibility analysis and simulation experiments verify the superiority of the proposed method.

Range-Angle Decoupling and Estimation for FDA Radar With Non-Uniform Frequency Offset

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.

Joint Transmit and Receive Beamforming for Cognitive FDA-MIMO Radar With Moving Target

Cognitive radars can possess intelligent active sensing ability and adapt complex variable environment. Inspired by this technology, a cognitive frequency diverse array multiple-input multiple-output (FDA-MIMO) radar is proposed to apply for surveillance and detect the moving target timely. FDA-MIMO radar is a novel array structure which employs the small frequency offset across the transmit waveform to produce the range-angle dependent beampattern. The range-angle dependent beampatterns have ability to suppress the jammers when they are located at the same angle of the target. To obtain the maximum signal-to-interference-plus-noise-ratio (SINR) and suppress the jammers effectively, we consider the transmit and receive beamforming filters design and proposed an iterating optimization algorithm to obtain optimal beamforming filters. For the moving target, the Extended Kalman filter (EKF) method is utilized to update the position of the target and the new position information is applied for the filters design to obtain optimal performance of SINR timely. In addition, expressions for the detection probability and SINR are deduced for the FDA-MIMO radar target detection. Finally, numerical results show that the proposed cognitive FDA-MIMO radar can effectively suppress the jammers and detect the moving target.

Three-Dimensional Parameter Estimation of Uniform Circular Frequency Diverse Array Radar With Two-Stage Estimator

Frequency diverse array (FDA) radar has been studied by many researchers due to the range-angle dependent beampattern which is different from the conventional phased array radar. However, the contribution of previous studies has received little attention within the circular frequency diverse array radar and no known empirical research has focused on investigating the three-dimensional (3D) parameter estimation (azimuth, elevation, and range). In this paper, we proposed a two-stage estimation algorithm for 3D parameter estimation of uniform circular frequency diverse array (UC-FDA) radar and firstly demonstrate the capability and performance of 3D parameter estimation. The first step of the two-stage estimation is the estimation of azimuth and elevation from the beamspace which is transformed from the element space by the beamformer. The second step is to substitute the angle obtained in the first step into the transmitting steering matrix for the range estimation. Cramér-Rao bound (CRB) that is used to evaluate the 3D parameter estimation performance is derived to compare. Theoretical analysis and numerical simulation demonstrate that the UC-FDA radar has superior 3D parameter estimation performance and the effectiveness of the proposed two-stage estimation algorithm. The research findings can contribute to a better 3D localization method and represent an additional step towards developing multi-dimensional localization and interference suppression for UC-FDA radar.

A waveform design method for frequency diverse array systems based on diversity linear chirp waveforms

AbstractA frequency diverse array (FDA) radar has attracted wide attention, due to its capability to provide a range-angle dependent beampattern and to scan the spatial without phase shifters or rotating arrays. However, FDA systems will suffer from low echo signal energy or high sidelobe peaks when detecting targets by beamforming based on existing receivers. To reduce the sidelobe peak of detection results while increasing the echo signal energy, in this paper, we propose an FDA radar system based on diversity linear frequency modulation waveforms. Correspondingly, we propose a receiver architecture with a time-variant beamforming chain. The proposed system retains the ability of the FDA system to automatically spatial beam scanning, owing to the frequency increment across elements. By increasing the pulse duration of transmitted signals, we enhance the echo signal energy. By applying the artificial bee colony algorithm to design the bandwidth of each chirp signal, the proposed system reduces the sidelobe level of detection results while increasing pulse width. Numerical simulation results are presented to demonstrate the effectiveness of the proposed system.

Analysis of beampattern dwell time for planar frequency diverse array

Frequency diverse array (FDA) has received much attention due to its both range–angle-dependent beampattern. However, most of the existing works focus on the linear FDA, and time-varying characteristics of its beampattern only give a rough qualitative analysis. To further study the spatial beampattern dwell time issues, the pulsed-planar FDA measurement model is first given, and then, the quantitative analysis of beam dwell time which can be affected by observation point location (azimuth, elevation, and range) and array antenna frequency offset coding method for a given pulse transmitting signal is presented. Finally, the theoretical analysis is proved to be consistent with the simulations.

Frequency Diverse Array with Cubic Sinusoidal Frequency Offset

Frequency diversity array radar (FDA) has range-angle dependent beampattern, providing enormous potential for the application of this new type of radar. However, the beampattern of conventional FDA (CFDA) has two problems: range-angle coupling and range periodicity, limiting the application of FDA. How to solve the problems is the premise of realizing beam accurate control and target accurate positioning. In this paper, we propose a new FDA transmitter structure with cubic sinusoidal frequency offset (Cubic sin-FDA). Simulation results show that this FDA beampattern eliminates coupling and forms a spot-shaped beampattern. Compared with the existing nonlinear frequency offset FDA beampattern, this method has a narrower half power bandwidth and lower side lobe level.

Time‐variant focused range‐angle dependent beampattern synthesis by frequency diverse array radar

The frequency diverse array (FDA) radar has been extensively studied due to its unique range-angle dependent beampattern. Time-invariant spatial patterns have been reported for FDAs proposed so far. However, some recent studies indicate that the patterns obtained by using these methodologies neglect the time-range or frequency-phase relationship, and the definition of time in some equations are misinterpreted which results in erroneous conclusions. Taking the time-variant property of FDA beampatterns into consideration, in this study, the authors propose a short range FDA radar to generate a time-variant focused range-angle dependent transmit beampattern, where chirp waveform with multi-carrier FDA architecture is used. Both the fixed and time-modulated frequency offsets are considered to analyse the proposed FDA radar. The frequency offset employed across each element is generated by chaos sequence and sine function. By compensating the propagation delays of signals, the transmitted signals sum up constructively to focus on the desired range-angle sector only at a specific instant of time. Numerical results are implemented to verify the validity of the proposed schemes.

Cognitive FDA-MIMO With Channel Uncertainty Information for Target Tracking

In this paper, we propose a cognitive frequency diverse array multiple input multiple output (FDA-MIMO) design by utilizing channel uncertainty information. Time-variant non-uniform frequency offsets are utilized to decouple frequency diverse array (FDA) range-angle dependent beampattern and a design strategy is proposed to maximize the transmit energy toward the desired range-angle region by steering the beam to match the channel uncertainty for enhanced target detect and tracking performance. To unambiguously estimate target parameters, we divide the FDA elements into multiple fully overlapped subarrays using orthogonal waveforms. Furthermore, we adaptively update the transmit beamspace matrix with two optimization criterions, namely, signal-to-noise ratio maximization and Cramer–Rao bound minimization. All proposed approaches are verified by numerical results.

A circular planar frequency diverse array for monostatic radar applications

ABSTRACTFrequency diverse arrays (FDAs) with scanning features have recently been of interest to radar researchers. Different frequencies with different patterns applied to the properly arranged array elements lead to the range-angle dependent beampattern. In this paper, a monostatic radar system in which the transmitter is an FDA and the receiver is a phased array is proposed, with both of which being arranged in circular planar arrays. The elements of the FDA transmitter are located at several concentric rings. The elements frequency in each ring is the same and the frequency difference between the two adjacent rings is constant. The radius of each ring is proportional to the half-wavelength of the same ring. The presented structure produces a periodic range-angle dependent beampattern. By applying a non-uniform inter-ring frequency offset, a non-periodic beampattern is radiated. In the transmitter and receiver mode, the transmitted signal to the target is reflected back to the phased array receiver. Similar to the transmitter, the receiver is composed of several concentric rings located after the last ring of the transmitter and the radius of each ring is proportional to the half-wavelength of central frequency.

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.

Impacts of frequency increment errors on frequency diverse array beampattern

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 thus results in a range angle-dependent beampattern. However, due to imperfect electronic devices, it is difficult to ensure accurate frequency increments, and consequently, the array performance will be degraded by unavoidable frequency increment errors. In this paper, we investigate the impacts of frequency increment errors on FDA beampattern. We derive the beampattern errors caused by deterministic frequency increment errors. For stochastic frequency increment errors, the corresponding upper and lower bounds of FDA beampattern error are derived. They are verified by numerical results. Furthermore, the statistical characteristics of FDA beampattern with random frequency increment errors, which obey Gaussian distribution and uniform distribution, are also investigated.

Range-Angle Dependent Transmit Beampattern Synthesis for Linear Frequency Diverse Arrays

Phased-array is widely used in communication and radar systems, but the beam steering is fixed in an angle for all the ranges. In this paper, we propose a range-angle dependent beampattern synthesis scheme for linear frequency diverse array (FDA) using the discrete spheroidal sequence, with an aim to focus the transmit energy in a desired two-dimensional spatial section. Different from conventional phased-arrays, FDA employs a small frequency increment, compared to the carrier frequency across the array elements. The range-angle dependent beampattern synthesis method allows the FDA to transmit energy over a desired range or angle sector. This provides a potential to suppress range-dependent clutter and interference, which is not accessible for conventional phased-arrays. The system performance of the proposed FDA is evaluated by the output signal-to-interference-plus-noise ratio (SINR). The effectiveness is verified by comprehensive numerical simulation results.