Agile Array Research Articles

A Geometric Phase Presetting Technique for CP Agile and Beam-Steering Reconfigurable Array With Enhanced AR Bandwidth

A Geometric Phase Presetting Technique for CP Agile and Beam-Steering Reconfigurable Array With Enhanced AR Bandwidth

A phase shift keying modulator integrated single‐feed circular polarization agile array antenna

AbstractThis paper proposes a novel design of a circular polarization agile array antenna using two phase shift keying (PSK) modulators. The proposed antenna includes four dual linear polarization microstrip patch antenna elements, two PSK modulators, two quarter‐wavelength slot transmission lines, microstrip‐slot line transitions, and a single feed network. The PSK modulator generates phase switching of either 180° or 0° of the vertical signals of each antenna element with the aid of the four diodes. The quarter‐wavelength slot transmission lines are added to adjust the 90° phase difference between orthogonal signals of the array antenna. By controlling the PSK modulators, the proposed antenna can achieve dual circular polarization switching capabilities. A prototype antenna is used to demonstrate the antenna concept. The measured results confirm the concept with a good agreement between the simulated and measured performances. The proposed antenna has no complex circuits for RF and DC signals, and it provides a compact structure.

Multi-layer approach of polarization agile oscillating-type active integrated array antennas for RFtransmitter front-end

AbstractThis paper presents a polarization switchable self-oscillating active integrated array antenna (AIAA) using a multi-layer approach. The antenna comprises two antenna elements, four PIN diodes, and a Gunn oscillator employing a microstrip line resonator. Reconfiguring the feed network of the array antenna realizes slant polarization (± 45°) switching. The multi-layer structure allows the patch spacing to be adjusted, thereby helping to minimize the antenna's sidelobe level. The Gunn oscillator, which employs a λ/2 microstrip–line resonator, is placed at the bottom layer. The proposed AIAA has an effective isotopic radiated power (EIRP) of + 18.25 dBm at the oscillation frequency of 9.47 GHz. EIRP is improved by better than 8.45 dB compared to the single-layer structure. The proposed AIAA features a transmitted power of + 8.45 dBm, DC-to-RF efficiency of 1.0%, and a low phase noise of −101.8 dBc/Hz at 1-MHz offset frequency with better than 12-dB cross-polarization suppression.

Circular Polarization-Agile and Continuous Beam-Steerable Array Antenna Using a Hybrid Design Approach

A circular polarization (CP)-agile and continuous beam-steerable array antenna is presented using a hybrid design approach. It is accomplished by combining digital reconfigurable antenna elements with analog continuously tunable phase shifters. To realize both polarization reconfiguration and initial phase generation for beam-scanning simultaneously, the designed antenna element enables eight states that corresponds to two CP modes with four quantized phases. The phase shifters further provide additional variable phases of -90° to 0° for antenna element excitation. Superposition of the initial and additional phases helps to satisfy a full and continuous 360° phase coverage for a beam-steerable array. Meanwhile, the phase decomposition also facilitates the design of phase shifters without complex or cascaded structures. By altering the bias states of the electronic components loaded in the array antenna, CP switching and beam scanning can be independently controlled. For verification, prototypes of the antenna element, phase shifter, and a four-element array are all fabricated and tested. Reasonable agreement is obtained between simulation and measurement. The resultant array could scan up to nearly ±40° off the boresight, along with stable radiation patterns and good CP performance.

MAJoRCom: A Dual-Function Radar Communication System Using Index Modulation

Dual-function radar communication (DFRC) systems implement both sensing and communication using the same hardware. Such schemes are often more efficient in terms of size, power, and cost, over using distinct radar and communication systems. Since these functionalities share resources such as spectrum, power, and antennas, DFRC methods typically entail some degradation in both radar and communication performance. In this work we propose a DFRC scheme based on the carrier agile phased array radar (CAESAR), which combines frequency and spatial agility. The proposed DFRC system, referred to as multi-carrier agile joint radar communication (MAJoRCom), exploits the inherent spatial and spectral randomness of CAESAR to convey digital messages in the form of index modulation. The resulting communication scheme naturally coexists with the radar functionality, and thus does not come at the cost of reduced radar performance. We analyze the performance of MAJoRCom, quantifying its achievable bit rate. In addition, we develop a low complexity decoder and a codebook design approach, which simplify the recovery of the communicated bits. Our numerical results demonstrate that MAJoRCom is capable of achieving a bit rate which is comparable to utilizing independent communication modules without affecting the radar performance, and that our proposed low-complexity decoder allows the receiver to reliably recover the transmitted symbols with an affordable computational burden.

DOA Estimation Method in Multipath Environment for Passive Bistatic Radar

Direction-of-arrival (DOA) estimation in multipath environment is an important issue for passive bistatic radar (PBR) using frequency agile phased array VHF radar as illuminator of opportunity. Under such scenario, the main focus of this paper is to cope with the closely spaced uncorrelated and coherent signals in low signal-to-noise ratio and limited snapshots. Making full use of the characteristics of moduli of eigenvalues, the DOAs of the uncorrelated signals are firstly estimated. Afterwards, their contributions are eliminated by means of spatial difference technique. Finally, in order to improve resolution and accuracy DOA estimation of remaining coherent signals while avoiding the cross-terms effect, a new beamforming solution based iterative adaptive approach (IAA) is proposed to deal with a reconstructed covariance matrix. The proposed method combines the advantages of both spatial difference method and the IAA algorithm while avoiding their shortcomings. Simulation results validate its effectiveness; meanwhile, the good performances of the proposed method in terms of resolution probability, detection probability, and estimation accuracy are demonstrated by comparison with the existing methods.

Multi-Carrier Agile Phased Array Radar

Modern radar systems are expected to operate reliably in congested environments. A candidate technology for meeting these demands is frequency agile radar (FAR), which randomly changes its carrier frequencies. FAR is known to improve the electronic counter-countermeasures (ECCM) performance while facilitating operation in congested setups. To enhance the target recovery performance of FAR in complex electromagnetic environments, we propose two radar schemes extending FAR to multi-carrier waveforms. The first is Wideband Multi-carrier Agile Radar (WMAR), which transmits/receives wideband waveforms simultaneously with every antenna. To mitigate the demanding hardware requirements associated with wideband waveforms used by WMAR, we next propose multi-Carrier AgilE phaSed Array Radar (CAESAR). CAESAR uses narrowband monotone waveforms, thus facilitating ease of implementation of the system, while introducing {\em spatial agility}. We characterize the transmitted and received signals of the proposed schemes, and develop an algorithm for recovering the targets, based on concepts from compressed sensing to estimate the range-Doppler parameters of the targets. We then derive conditions which guarantee their accurate reconstruction. Our numerical study demonstrates that both multi-carrier schemes improve performance compared to FAR while maintaining its practical benefits. We also demonstrate that the performance of CAESAR, which uses monotone waveforms, is within a small gap from the wideband radar.

Target Detection and Localization Using Non-Cooperative Frequency Agile Phased Array Radar Illuminator

Recently, passive bistatic radar (PBR) has become an emerging technology because it allows target detection and localization with advantages of low cost, covert detection, low vulnerability to electronic jamming and high valuable counter to stealth technology. However, these researchers mainly focus on the illuminators of opportunity such as FM radio, television broadcast, mobile network basestation, wireless fidelity, long term evolution, global navigation satellite, etc. Different from the aforementioned illuminators, this paper introduces a new PBR using a non-cooperative frequency agile phased array radar illuminator. The types of illuminator of opportunity are enriched, whereas the difficulties in PBR signal processing also come along. On one hand, since PBR works in a non-cooperative mode, there is a problem that the instantaneous parameters of transmitting signal are unknown at the receiver. On the other hand, the frequency agility technology destroys the coherency between pulses and the ability of rapidly changing beam scanning makes it difficult for PBR to realize space synchronization. Under such scenarios, conventional radar signal processing methods cannot be conducted effectively. To address these problems, this paper then proposes a feasible target detection and localization method, which is tested by field experiments. Preliminary results validate the proposed method can be applied to PBR system successfully.

Filtering Performance of Digital Alternate Array on Target Tracking

For target tracking of agile digital array, we propose a novel model called alternate array. The model means that total array is divided into vertical subarray at the present moment, and vertical subarray is transformed into horizontal subarray at the next moment, then the subarray comes to the first subarray divisions, and so on. Alternate array gives rise to differences of statistical characters of measurement error. Filtering performance is influenced by the feature of measurement data. In the paper, we come up with a new method based on Kalman filter (KF) to solve the difficulty. The new method merges pre-processing and data fusion thought together. Simulation results demonstrate the validity of the proposed algorithm.

Terahertz tomography using quantum-cascade lasers

The interfaces of a dielectric sample are resolved in reflection geometry using light from a frequency agile array of terahertz quantum-cascade lasers. The terahertz source is a 10-element linear array of third-order distributed-feedback QCLs emitting at discrete frequencies from 2.08 to 2.4 THz. Emission from the array is collimated and sent through a Michelson interferometer, with the sample placed in one of the arms. Interference signals collected at each frequency are used to reconstruct an interferogram and detect the interfaces in the sample. Because of the long coherence length of the source, the interferometer arms need not be adjusted to the zero-path delay. A depth resolution of 360 µm in the dielectric is achieved with further potential improvement through improved frequency coverage of the array. The entire experiment footprint is <1 m × 1 m with the source operated in a compact, closed-cycle cryocooler.

Weather radar equation correction for frequency agile and phased array radars

This paper presents the derivation of a correction to the Probert-Jones weather radar equation for use with advanced frequency agile, phased array radars. It is shown that two additional terms are required to account for frequency hopping and electronic beam pointing. The corrected weather radar equation provides a basis for accurate and efficient computation of a reflectivity estimate from the weather signal data samples. Lastly, an understanding of calibration requirements for these advanced weather radars is shown to follow naturally from the theoretical framework.

Active integrated photonic true time delay device

A photonic true time delay cell with two waveguide couplers and five semiconductor optical amplifiers is demonstrated. The five semiconductor optical amplifiers provide gain in the 1550-nm region and port selection to determine the time delay. With the amplifiers off the signal are blocked with extinction ratios of more than 10 dB. In the experiments reported here, the delay of 20 ns was provided by an optical fiber. Because of the potential for nanosecond switching times, the device has application in very agile phased array antenna applications, in optical switching and routing, and in optical filtering.

Reduction of sidelobe self-interference in an agile beam radar

In an agile beam phased array radar, the beam is often multiplexed over several angular positions, and "listens" in each position only over an instrumented range that may be a fraction of the unambiguous range as determined by the pulse repetition period in each position. After transmitting a pulse in a given direction, the beam is switched, essentially instantaneously, to another position, after the instrumented range delay. In this second position, echoes from the first position, from multiple trips of the instrumented range, enter the one-way angular sidelobes of the first position. This interference is compounded if there are several beam positions in a pulse repetition period. The author proposes a method of phase coding the pulses in such a way that the pulse-to-pulse phase variation in each direction is orthogonal to every other phase code in the other directions. The codes are Walsh functions. These are sets of binary valued (+1 or -1) functions such that all of the functions in the set are mutually orthogonal. Not every possible number N of pulses in each direction and number K of beam positions can be accommodated, but a large variety of such combinations can be accommodated. Several examples are given. The combination of low one-way sidelobes and orthogonality (or near orthogonality) of the phase codes should provide for very stringent sidelobe self interference rejection.