Probe-fed strip-element microstrip phased arrays: E- and H-planescan resonances and broadbanding guidelines

A comprehensive investigation is presented of E- and H-plane scan-frequency characteristics of probe-fed microstrip strip-element phased arrays with a single probe per unit cell. A parametric study of the principal, large mismatch producing scan resonances is carried out utilizing Galerkin-type analysis and an associated computer code. While the E-plane scan characteristics confirm earlier findings, those of the H-plane exhibit a heretofore not reported array blindness condition which is traced to excitation of a strip-line mode of the periodic array structure. The largest element spacing is identified which, independently of substrate thickness, excludes the principal E- and H-plane scan resonances. Element broadbanding is then achieved via interplay between substrate thickness and strip width. For a fixed scan angle with an appropriately configured element geometry, the unmatched active impedance exhibits a double-tuned behavior. The form of the equivalent network in the neighborhood of the double-tuned resonance is established via computer-aided approach. Finally, an example of scan-frequency array performance (without using suppressor pins) for a ±15% frequency range and a 40-degree E- and H-plane scan coverage with voltage standing wave ratio (VSWR) ⩽2 is presented     

A flat-feed technique for phased arrays

A recently developed phased-array feed configuration offering significant advantages over the conventional space, corporate, and series feed techniques is described. This technique, referred to as the "flat feed," allows power division for monopulse sum and difference pattern illumination functions in a feed depth of less than a half-wavelength with low loss. The technique used to extract energy from the power divider, which consists in part of a radial transmission line, results, in its simplest configuration, in a circular grid of antenna elements. Relations governing the circular grid array geometry design are derived which relate the angular locations of attenuated grating lobes to the spacing between the rings of radiating elements. ExperimentalS-band hardware, built to prove the feed technique, is described. It includes a multimode launcher with measured coupling between circular wavegulde sum (TM_{01}) and difference (TE_{11}) modes of less than -37 dB; a seven-ring 1:195 radial power divider measured across a 10-percent band to have insertion loss of 0.1 dB and rms phase and amplitude deviations of less than3.5degand 0.47 dB; a 144-element array whose measured sum and difference beam radiation patterns are compared with calculated patterns for scan angles out to60degand whose sum port VSWR, measured across a 10-percent band, was under 1.8:1 with the array steered to broadside, and under 1.5:1 for other scan angles out to60deg.     

Optical techniques for reconfiguring microwave phased arrays

Very large phased array antennas, particularly in radar and adaptive receive applications as opposed to communications usages, require large amounts of digital data processing for beamsteering, null-formation, imaging, and signal correlation computations. Such processing requires a computational capability which is effectively proportional to the square of the antenna size, and can readily become one of the main design drivers. This processing bottleneck problem is addressed for large phased array antennas. An approach in terms of parallel processing in the optical domain is presented as a potential solution. The defining equations for a phased array antenna system are given, along with the transfer functions for an embedded optical spatial filter control element. Such a control element is shown to have the potential of rapidly reconfiguring a large phased array antenna without the speed penalties associated with conventional sequential addressing methods. A hypothetical phased array antenna, with optical spatial filter control elements, is simulated in a computer model and performance results are presented     

Constrained feed technique for subarrays of large phased arrays

A technique is presented which combines the subarraying qualities of constrained dual transform beamforming sections and partial overlapping networks to produce arrays of contiguous subarrays. This approach is shown to facilitate wideband scanning or limited field of view coverage with a minimum number of controls and low sidelobes     

一种实用的相控阵近场诊断新方法

提出了一种相控阵天线近场诊断的新方法.传统的方法要诊断出相控阵天线单元的激励,必须已知阵列单元的方向图和探头的方向图.文中基于相控阵天线的激励、单元方向图、探头方向图和近场测量数据之间的关系,得到了相控阵天线的激励和近场测量数据之间的耦合方程.利用多项式插值,在不必已知单元方向图和探头方向图的情况下,求解出相控阵天线的单元激励.     

A broadcast reference technique for self-calibrating of largeantenna phased arrays

A modified phase-multilateration technique is proposed for calibrating the element locations of a flexible phased array. The technique requires several auxiliary beacons. The calibrating system measures the phase, relative to a broadcast reference, of each beacon signal at each array element. Automatic calibration of the differential phase delay in each antenna element signal path is included in the self-survey process. Digital beamforming is used for array signal processing. The beacon locations can be accurately or loosely known. For the system with loosely known beacon locations, an additional baseline measurement is required, and the beacon locations are treated as unknown variables. It is shown that a simple variable transformation can transform the mathematical equations of this technique into a form identical to that of the corresponding equations of previous cabled reference systems. The mathematical properties of the algorithm and its associated tolerance analysis are therefore readily available. A combination of the versions of this technique with accurately known and loosely known beacon locations is shown to have better performance than the individual version     

Thinning and broadbanding antenna arrays by unequal spacings

This paper presents a theory for, and a method of designing a thinned or broad-band antenna array by means of unequal spacings. Using the theory of unequally spaced arrays developed by one of the authors, an antenna array can be designed to produce a desired beamwidth and sidelobe level with the average spacing many wavelengths apart. The patterns are expressed in a series of the Anger functions and its sidelobe level is shown to decrease approximately asN^{-0.5}simN^{-0.4}whereNis the total number of elements, and the gain is approximately equal toN. It is also shown that the sidelobe level can be improved by varying the amplitude distribution. Numerical examples are given to illustrate the method.     

Optical beam former for phased arrays with independent control of radiated frequency and phase

A new beam forming technique for use in optically controlled phased arrays is presented. The system, which is the optical equivalent of the microwave Huggins phase shifter, uses two optical fibre networks to produce a beam having independently specified frequency and aperture phase slope. The theory of the system is presented together with experimental results for a system implemented at the L-band.<>     

Optimum tilt for elevation-scanned phased arrays

It is shown that, subject to certain restrictions, the optimum tilt angle can be calculated as a function of only the highest beam elevation angle. The term optimum means the condition that the antenna gain at the horizon is maximum. The restrictions are that the antenna be operated outside the grating-lobe regime for all required scan angles and that scan angles greater than 60° off broadside by avoided to allow useful operation of the radar system (considering antenna impedance match, sidelobes, gain, and beam width). It is assumed that the antenna, in principle, can be impedance matched to any elevation angle, leaving the match at broadside as a special case, without particular advantages. The results indicate that for most practical requirements (high-beam elevation between 45° and 70 °) the optimum tilt angle should be around 20° to 30°     

Beamwidth of phased arrays

A formula is developed for estimating the far-field beamwidth of an arbitrary narrow-beam phased array of identical isotropic elements at a single frequency. Equations are developed for the effects of errors in the estimated positions of the array elements.     

Active phased arrays for multi-beam earth coverage

The anticipated density of satellite communications traffic with mobiles will require multi-beam earth coverage. Multiple beams can be generated from reflector antennas with multiple feeds or from a phased array aperture. The constraints on each system are discussed, and it is concluded that for more than about seven beams the best system involves a phased array antenna, particularly if reconfigurability of the beams may be required. Active phased arrays, with a power amplifier at each radiating element offer advantages in reliability and may indeed be the only way of handling the large total radiated power of future systems at acceptable levels of intermodulation.     

平面相控阵宽角扫描技术

平面相控阵天线的宽带、宽角扫描理论与技术是当前天线电波传播领域的核心课题与关键技术,对高性能雷达、通信、导航等信息系统起到重要支撑作用. 研究表明,制约平面相控阵天线宽角扫描的瓶颈主要有：单元的波束形状、阵列排布方式以及扫描阵列中的耦合关系. 据此,本文将从以上三方面回顾平面相控阵宽角扫描理论与技术的发展历程,并对其研究发展做出展望.

     

Design of thinned phased arrays

A new method for determining the element position in a phased array is presented, only one array factor being calculated in each step. It is thereby possible to design larger arrays than can be designed using other methods.     

Voltage-controlled ferroelectric lens phased arrays

A new concept for phased arrays is proposed using a voltage-controlled ferroelectric lens. The ferroelectric lens concept uniquely incorporates bulk phase shifting-the array does not contain individual phase shifters-using ferroelectric material. This will reduce the number of phase shifters from (n×m) to (n+m), where n is the number of columns and m is the number of rows in a phased array. The number of phase shifter drivers and phase shifter controls is also significantly reduced by using row-column beam steering. Thus, the ferroelectric lens concept can potentially lead to low-cost phased arrays. This paper presents the ferroelectric lens concept, theoretical analysis and design, and experimental results. The results indicate that the ferroelectric lens concept is viable and sound. Various phased-array configurations using ferroelectric lens are included. A discussion on ferroelectric materials is included along with information on a US Department of Defense program to improve ferroelectric materials     

A method for removing blindness in phased arrays

In periodic phased arrays, due to the mutual coupling effect, there is a sharp dip in radiation at a certain scan angle, thus causing the so-called blindness phenomenon. It is shown that by using random (or other aperiodic) arrays, this adverse effect can be almost completely removed.     

Microoptical phased arrays for spatial and spectral switching

This article describes two optical devices based on linear arrays of micromirrors. The first is a phased array of micromirrors that can be rotated as well as translated vertically to maintain coherence across the array. We demonstrate experimentally that such micromirrors are capable of high-diffraction-efficiency phased-array scanning of laser beams. The second device is a Gires-Tournois (1969) interferometer with a micromirror array that provides tunable phase modulation for the multitude of partially reflected beams within the interferometer. We demonstrate experimentally that the MEMS-GT interferometer can operate as a tunable deinterleaver for dense wavelength-division multiplexed fiber optic communication.     

Analysis of interinjection-locked oscillators for integrated phased arrays

The behavior of a system of coupled oscillators is shown to have potential applications in the generation of power for integrated phased antenna arrays. Nonlinear differential equations are derived to describe a system of oscillators coupled by an arbitrary frequency-dependent network. State-variable analysis of the linearized equations leads to closed-form solutions for one- and two-dimensional phased array systems. Experimental data for a VHF prototype system is presented, and practical considerations in system design are discussed.