Wideband Phased Array Research Articles

Compact Spiral Element for Wideband Beam-Steering Arrays

In this letter, a compact spiral element is proposed for wideband beam-steering arrays. The extremely limited element spacing and size to prevent the occurrence of grating lobes at high frequency range are the most critical issues in designing wideband phased arrays. Two miniaturization techniques are simultaneously applied to an Archimedean spiral radiator to reduce the area of the proposed spiral. This spiral radiator is designed with a reflector plane instead of an absorber and cavity to realize low-profile characteristics and achieve unidirectional pattern without power loss. A wideband balun that operates simultaneously as a wideband impedance transformer is also miniaturized to be integrated between the radiator and reflector plane. The proposed element consists of these three components, and its size is 0.25 λ $_{L}$ × 0.25 λ $_{L}$ × 0.13 λ $_{L}$ , where λ $_{L}$ is the wavelength at 2 GHz, the lowest frequency of interest. This compact spiral element with a simple structure and design procedure can achieve wideband beam steering without grating lobes and be employed in numerous applications, such as conformal arrays.

A 2–15-GHz Accurate Built-in-Self-Test System for Wideband Phased Arrays Using Self-Correcting Eight-State $I/Q$ Mixers

A built-in-self-test (BIST) system for wideband phase arrays channels is presented. The BIST is implemented using an on-chip in-phase/quadrature ( $I/Q$ ) receiver with an integrated ring oscillator that provides both the channel test signal and the mixer local oscillator (LO). The BIST achieves wideband accuracy for relative phase and gain measurements at 2–15 GHz with a one-time self-correction algorithm with eight LO phases. The sequential algorithm determines the $I/Q$ errors, such as dc offset, gain and phase imbalances from the $I/Q$ outputs resulting from different LO phase states. An rms power detector network is also implemented for absolute gain measurements. The BIST can operate at rates >1 MHz (less than 1- $\mu \text{s}$ sampling time) with signal-to-noise ratio greater than 50 dB and provides measurements that agree well with the vector network analyzer S-parameter data over a wide frequency range. To the best of our knowledge, this is the first implementation of high accuracy wideband BIST system for phased-array channels.

A 2-15 GHz VCO With Harmonic Cancellation for Wide-Band Systems

A 2-15 GHz SiGe VCO (voltage controlled oscillator) has been developed with a very low harmonic content. The design is based on the harmonic cancellation concept and uses a multiple-phase ring oscillator together with a wide-band active-weighted summer. The VCO results in an output power of −8 to −6 dBm and $3^{rd}$ and $5^{th}$ harmonic level at 2-15 GHz. The active area of the chip is very small ( $0.67 \times 0.25$ mm2) due to the lack of inductors, and the power consumption is 88-120 mW from a 2.5 V supply. To our knowledge, this is the first demonstration of a wide-band VCO showing a near-perfect sinewave output over a wide frequency range. The application areas are in built-in-self-test sources for wide-band radios and phased arrays.

A Broadband Digital Step Attenuator with Low Phase Error and Low Insertion Loss in 0.18-μ#x3BC;m SOI CMOS Technology

This paper presents a 5-bit digital step attenuator (DSA) using a commercial 0.18-μm silicon-on-insulator (SOI) process for the wideband phased array antenna. Both low insertion loss and low root mean square (RMS) phase error and amplitude error are achieved employing two attenuation topologies of the switched path attenuator and the switched T-type attenuator. The attenuation coverage of 31 dB with a least significant bit of 1 dB is achieved at DC to 20 GHz. The RMS phase error and amplitude error are less than 2.5° and less than 0.5 dB, respectively. The measured insertion loss of the reference state is less than 5.5 dB at 10 GHz. The input return loss and output return loss are each less than 12 dB at DC to 20 GHz. The current consumption is nearly zero with a voltage supply of 1.8 V. The chip size is , including pads. To the best of the authors' knowledge, this is the first demonstration of a low phase error DC-to-20-GHz SOI DSA.

An Active Bi-Directional SiGe DPDT Switch With Multi-Octave Bandwidth

This letter proposes a wideband active double-pole double-throw (DPDT) switch for wideband phased array antennas, which realizes multi-octave bandwidth with positive gain and 4-way switching operation using a bi-directional distributed amplifier technique. The measured gain is 2.0–6.0 dB and the input and output return losses are better than 9 dB from 2–22 GHz. The isolation is over 15 dB and the measured input P1dB is greater than $-$ 9.1 dBm and the output P1dB is greater than $-$ 7.8 dBm from 2–22 GHz. The chip size is $1.07 \times 0.98 \text{mm}^{2}$ , including pads. The switch consumes 10 mA from a 2.5 V supply. Almost identical RF performance is achieved in each of the 4-way switching operations due to a symmetric circuit topology and careful layout. To the authors' knowledge, this is the first demonstration of the active DPDT switch configuration.

GA-Based Optimization of Irregular Subarray Layouts for Wideband Phased Arrays Design

The design of phased arrays generating low sidelobes and grating-lobes-free patterns over wide frequency bandwidths is addressed. The array structure is decomposed in subarrays with irregular polyomino tiles whose locations and orientations are optimized by means of a genetic algorithms-based approach. A set of representative results is reported and discussed to give some insights on the performance of the proposed approach also in comparison to state-of-the-art solutions.

Wideband Planar Array With Integrated Feed and Matching Network for Wide-Angle Scanning

It is traditionally known that wideband apertures lose bandwidth when placed over a ground plane. To overcome this issue, this paper introduces a new non-symmetric tightly coupled dipole element for wideband phased arrays. The proposed array antenna incorporates additional degrees of freedom to control capacitance and cancel the ground plane inductance. Specifically, each arm on the dipole is different than the other (or non-symmetric). The arms are identical near the center feed section but dissimilar towards the ends, forming a ball-and-cup. It is demonstrated that the non-symmetric qualities achieve wideband performance. Concurrently, a design example for planar installation with balun and matching network is presented to cover X-band. The balun avoids extraneous radiation, maintains the array's low-profile height and is printed on top of the ground plane connecting to the array aperture with 180° out of phase vertical twin-wire transmission lines. To demonstrate the concept, a 64-element array with integrated feed and matching network is designed, fabricated and verified experimentally. The array aperture is placed λ/7 (at 8 GHz) above the ground plane and shown to maintain a active VSWR less than 2 from 8-12.5 GHz while scanning up to 70° and 60° in E- and H-plane, respectively. The array's simulated diagonal plane cross-polarization is approximately 10 dB below the co-polarized component during 60° diagonal scan and follows the theoretical limit for an infinite current sheet.

Multi-Beam Spatio-Spectral Beamforming Receiver for Wideband Phased Arrays

This paper reports the first analog integrated spatio-spectral beamforming front-end. The proposed front-end allows for accurate beam steering of signals with large fractional bandwidths, thus minimizing beam squinting, and simultaneous and independent steering of multi-carrier signals. Different spatio-spectral beamforming strategies are discussed and compared. As a proof of concept, an 8 GHz 2-channel, 4-frequency phased-array beamformer is designed and implemented in 65 nm CMOS. The IF signal on each channel is frequency split using an all passive 4-point analog FFT. The orthogonal frequency outputs are then beam-steered using an all passive I-Q vector-combiner. The RF circuit draws 22.8 mA from a 1.2 V supply while the analog baseband consumes 135 μW at 120 MS/s (9 pJ/conv.).

Analysis and Design of Wide-Scan Angle Wide-Band Phased Arrays of Substrate-Integrated Cavity-Backed Patches

A class of wide-scan angle wide-band microstrip patch phased arrays is proposed. The proposed phased arrays are composed of probe-fed microstrip patches backed by substrate-integrated cavities. First, a simplified 2-D numerical analysis based on Floquet's theorem is presented to qualitatively demonstrate the E-plane scan performance of the cavity-backed structure compared to that of the conventional microstrip patch phased array. Second, the 3-D scan performance of the proposed phased arrays is thoroughly investigated varying both the substrate thickness and dielectric constant using commercially available EM simulation tools, which is followed by presenting simple design guidelines for the cavity, patch and substrate. A 7 × 7 prototype phased array of the proposed SIW cavity-backed patch structure was fabricated and its measured results agree well with our theoretical prediction and indicate a relatively wide-scan performance when compared to the corresponding microstrip patch phased array without cavities.

Status of the ITER Ion Cyclotron H&CD system

The ongoing design of the ITER Ion Cyclotron Heating and Current Drive system (20MW, 40–55MHz) is rendered challenging by the wide spectrum of requirements and interface constraints to which it is subject, several of which are conflicting and/or still in a high state of flux. These requirements include operation over a broad range of plasma scenarios and magnetic fields (which prompts usage of wide-band phased antenna arrays), high radio-frequency (RF) power density at the first wall (and associated operation close to voltage and current limits), resilience to ELM-induced load variations, intense thermal and mechanical loads, long pulse operation, high system availability, efficient nuclear shielding, high density of antenna services, remote-handling ability, tight installation tolerances, and nuclear safety function as tritium confinement barrier. R&D activities are ongoing or in preparation to validate critical antenna components (plasma-facing Faraday screen, RF sliding contacts, RF vacuum windows), as well as to qualify the RF power sources and the transmission and matching components. Intensive numerical modeling and experimental studies on antenna mock-ups have been conducted to validate and optimize the RF design. The paper highlights progress and outstanding issues for the various system components.

USING SPHERICAL SHELLS FOR GAIN ENHANCEMENT OF COMPACT WIDEBAND PHASED ARRAYS

Spherical shells are proposed and presented to improve the gain of a class of wideband phased array systems. This kind of phased arrays is composed of compact elements, which allow for a small distance between elements that is much less than half wavelength at lower operating frequencies. This small distance, as a function of wavelength, results in a small gain. Therefore, shells confronting the array are proposed to improve the gain. The formulations required to deflne the geometry and material properties of the shell are developed. Two and four element arrays are designed and simulated with and without shells to test the technique, and promising results are obtained at lower frequencies for the array with shells.

Overlapped Subarray Architecture of an Wideband Phased Array Antenna with Interference Suppression Capability

This paper presents a novel architecture of combining the linear array of antenna elements, where each antenna element has digitally selectable true time-delays as weights. Use of time-delays for beam-formation inherently makes the phased array network a wideband system. In particular, this technique envisage a new method of sharing antenna elements, by fixed overlapped sub-array architecture, which is able to maintain permissible element spacing to avoid grating lobe in antenna pattern. Moreover, this scheme additionally offers an easier null steering capability to the subarray architecture. This method essentially eliminates the need for intensive computation of complex weight vectors attached to each antenna element.

ENHANCEMENT OF PHASED ARRAY SIZE AND RADIATION PROPERTIES USING STAGGERED ARRAY CONFIGURATIONS

In this paper, two staggered array conflgurations are presented for enhancing size and radiation properties of wideband phased array systems. The proposed arrays are obtained either by rotating each element 45 - or by inserting additional rows in the middle which are shifted by half the distance between elements. These two conflgurations allow for a smaller distance between array elements (29% less), while the actual distance between elements in the diagonal direction is kept the same. Reducing the distance between elements results in eliminating/reducing the grating lobes in a wider frequency range, which improves the array usable bandwidth. In addition, this proposed array produces better gain and maximum steering angle.

Aperture Effect Influence and Analysis of Wideband Phased Array Radar

Wideband phased array becomes a research focus with the development of modern radar technology.Wideband phased array radar is one of the advanced radar technology. However, the aperture fill time results in the beam pointing offset, limits the instantaneous bandwidth and effects of the 1-D target range profile. This paper analyses the scheme of sub-array compensation for aperture fill time. For LFM signals system, we analyze the compensation using filters for aperture fill time, and for stepping frequency signal system, we analyze the scheme of interveinal phase matching, then simulate by Matlab. The simulation results show that the sub array division technology can compensate the aperture effect and increase the instantaneous bandwidth effectively. Both the filter and the interveinal phase matching methods can solve the main lobe expansion and targets range migration; lastly get the high resolution range profile.

A NOVEL WIDEBAND ANTENNA ARRAY WITH TIGHTLY COUPLED OCTAGONAL RING ELEMENTS

A novel phased array antenna with wide bandwidth and wide scan angle is presented. The radiating aperture of the phased array consists of periodically and closely spaced octagonal ring elements. Tight capacitive coupling between adjacent elements is realized by interdigitating the end portions of the ring elements. To improve the impedance matching of the individual antenna elements over wide frequency band, a novel impedance matching layer consists of periodic octagonal ring element is subtly designed and placed over the radiating aperture. Both of the radiating elements and impedance matching layer are printed on a flexible membrane substrate with a thickness of 0.04mm. Measured results of a 16-element linear array demonstrate that good impedance matching over a 4.4 : 1 bandwidth can be obtained for beam scan angles within ±45◦ from broadside. As compared to conventional wideband phased array such as tapered slot antenna array, the proposed phased array has the features such as low cost, low profile, light weight, and ease of fabrication.

Edge-Born Waves in Connected Arrays: A Finite$\,\times\,$Infinite Analytical Representation

Connected arrays constitute one of the most promising options for wideband phased arrays. Like most phased arrays, they are designed using infinite array theory. However, when finiteness is included, edge effects perturb their behavior. These effects are more severe when the arrays are designed to operate over very broad frequency ranges, since the mutual coupling between the elements facilitates the propagation of edge-born waves that can become dominant over large portions of the arrays. Finite array simulations, which would predict these behaviors, are computationally unwieldy. In this paper we present a Green's function based procedure to assess edge effects in finite connected arrays. First the electric current distribution on the array is rigorously derived. Later on, the introduction of a few simplifying assumptions allows the derivation of an analytical approximation for the current distribution. This latter provides meaningful insights in the induced dominant edge-wave mechanism. The efficiency of connected arrays as a function of their dimension in terms of the wavelength and of the loading feed impedances is investigated.

Ultra-Long Compact Optical Polymeric Array Waveguide True-Time-Delay Line Devices

New types of UV curable polymeric ultra-long array waveguide true-time-delay (TTD) lines for wideband phased array antennas (PAA) are designed and fabricated using direct UV photolithography process. The unique feature of the approach consists of different 1 × N waveguide splitters, low-loss S-bend cosine waveguide connectors, and 180° array bend waveguides with a constant spacing difference ¿R between adjacent waveguides. The delay time increments are measured from 1.4 ns to 6.6 ps. 1 × 2, 1 × 4, 1 × 8 polymeric star coupler devices are also successfully prepared. The bend loss of different curved waveguides is calculated and analyzed by the 3-D semivectorial beam propagation method (BPM). The optimized structural properties of the UV curable polymeric waveguides and fabrication procedures are demonstrated. The near-infrared field guided-mode patterns of the devices are obtained. The new technique can be well suited for realizing absence of "beam squint" in the antenna pattern as its frequency is switched from L(1-2.6 GHz) to X(8-12 GHz) band.

Ultra-Wideband Tapered Slot Antenna Arrays with Parallel-Plate Waveguides

Owing to their ultra-wideband characteristics, tapered slot antennas (TSAs) are used as element antennas in wideband phased arrays. However, when the size of a TSA is reduced in order to prevent the generation of a grating lobe during wide-angle beam scanning, the original ultra-wideband characteristics are degraded because of increased reflections from the ends of the tapered slot aperture. To overcome this difficulty, we propose a new antenna structure in which parallel-plate waveguides are added to the TSA. The advantage of this new structure is that the reflection characteristics of individual antenna elements are not degraded even if the width of the antenna aperture is very small, i.e., approximately one-half the wavelength of the highest operating frequency. In this study, we propose a procedure for designing the new antenna through numerical simulations by using the FDTD method. In addition, we verify the performance of the antenna array by experiments.

광대역 위상 배열 안테나의 빔 편이(Beam-Squint) 현상 제거를 위한 4-Bit 시간 지연기 설계

본 논문에서는 전기적으로 크기가 큰 능동 위상 배열 안테나에서 발생하는 빔-편이(beam-squint)현상을 해결할 수 있는 시간 지연기를 설계 및 제작하고, 측정 결과를 고찰한다. 시간 지연기는 4-bit 스위치로 제어되는 마이크로스트립 라인으로 설계되었으며, 시간 지연 구조의 손실을 보상해 주기 위해 송수신 경로에 MMIC 증폭기 모듈을 추가하였다. 시간 지연기의 측정을 통해 지연 상태별 이득 및 위상, P1dB, 수신 잡음 지수 등의 전기적 성능 규격을 만족함을 확인하였다. 또한, 제작된 시간 지연기의 성능 검증을 위해 측정 결과를 광대역 능동위상 배열 안테나에 적용하여 빔 패턴 보정 효과를 확인하였다. X 밴드 대역에서 800 MHz 대역차를 갖는 675.8 mm 크기의 안테나에 대해 빔 편이 현상을 보정해 본 결과 <TEX>${\pm}0.1^{\circ}$</TEX>이던 주파수에 따른 조향각 오차가 <TEX>${\pm}0.1^{\circ}$</TEX> 이내로 줄어드는 효과를 확인하였으며, 향후 광대역 능동 위상 배열 안테나 시스템에 적용 가능성을 확인하였다. In this paper, we have designed TDL(True-time Delay Line) for eliminating beam-squint occurring in active phased array antenna with large electrical size operated in wide bandwidth, and have tested its electrical performance. The proposed TDL device is composed of 4-bit microstrip delay line structure and MMIC amplifier for compensation of the delay-line loss. The measured results of gain and phase versus delay state satisfy the electrical requirements, also P1dB output power and noise figure meet the requirement. To verify the performance of fabricated TDL, we have simulated the beam patterns of wide-band active phased array antenna using the measured results and have certified the beam pattern compensation performance. As a result of simulated beam pattern compensation with respect to the 675.8 mm size antenna which is operated in X-band, 800 MHz bandwidth, we have reduced the beam squint error of <TEX>${\pm}1^{\circ}$</TEX> with <TEX>${\pm}0.1^{\circ}$</TEX>. So this TDL module is able to be applied to active phase array antenna system.

Segmented analysis of a finite planar ridged tapered slot antenna array for wideband phased array

AbstractThe segmented analysis method of a finite planar ridged tapered slot antenna (RTSA) array is presented to develop a wideband phased array with a triangular lattice. The RTSA array is segmented into two‐parts with a feeder and the arrays of tapered slot antenna (TSA) and these scattering parameters are analyzed respectively. This proposed method gives the merit of a great reduction of computational cost. To verify the advantage of this method, we build the numerical model of only one feeder and dual polarized arrays of TSA with 10 × 12 elements. The measured results of the fabricated array meet the design goals of 3:1 bandwidth, scan volume of ±45°, active VSWR (AVSWR) below 3:1. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1140–1143, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23314