Mode stability of radiation-coupled interinjection-lockedoscillators for integrated phased arrays

An analysis is presented of a two-element, 10-GHz array consisting of two oscillators coupled solely by means of the free-space interaction between their respective antenna elements. The oscillators are modeled as energy-storing L-C tank circuits in parallel with voltage-dependent negative conductances. A simplified far-field slot antenna model is used to derive the mutual admittance of the two antennas. Even-odd mode analysis yields the normal modes of the system, and a theorem from averaged potential theory is used to determine which mode is stable. Two microstrip Gunn diode oscillators were built to verify the essential features of the model. Oscillator frequencies, relative phases, and radiation patterns were measured as functions of the interantenna distance, and the periodic alternation of modes with distance predicted by theory was confirmed quite well     

MM-Wave integrated phased arrays with ferrite control

A new class of electrically scanned antenna arrays for the millimeter wave range is described. The antenna is based on a planar integrated ferrite travelling wave structure and is controlled by the magnetization of ferrite elements. Experimental antennas operating in the 8-mm wave range have the following electrical parameters: beamwidth 2 to 4°, two dimensional scanning ±20°, loss about 3 to 4 dB     

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.     

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 technique for broadbanding phased arrays

An optical method for broadbanding a phased array is considered. A narrow band feed-through aperture lens comprised of pick-up elements, radiating elements, and360degtype phase shifters is fed by a small feed array with an intervening passive lens. The lens has fixed frequency-sensitive properties. The feed array has variable time delay compensators which are selected in accordance with the desired scan angle in the far field. Using geometrical optics, design formulas are derived that relate bandwidth and scan angle to the minimum number of variable time delayers. To demonstrate performance, diffraction theory is used to calculate patterns, sidelobe levels, and efficiencies as a function of bandwidth and scan angle out to50degscan for several aperture sizes. In the worst cases, the optical system provides somewhat less gain than the comparable constrained subarray antenna; however, it always provides much better sidelobe levels.     

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°     

Analysis of integrated optics parametric oscillators

An almost analytical model for the analysis of integrated optics parametric oscillators is proposed. A comprehensive discussion of the static device characteristics of a doubly resonant oscillator with varying parameters of the optical cavity which influence the operation conditions (single and double pass and resonant pump) is presented. A detailed discussion of the evolution towards the singly resonant condition and the possibility of hysteretic behavior is also included     

Analysis of finite phased arrays of circular microstrip patches

A method is presented for analyzing a finite planar array of circular microstrip patches fed by coaxial probes. The self- and mutual impedances between array elements are calculated using the method of moments with the dyadic Green's function for a dielectric layer on a ground plane. The patch circuits are determined by using the reaction integral equation. The active input impedance as well as the active element pattern of the array are computed from a knowledge of the resultant patch currents. The calculated results for two-element and eight-element linear arrays are in good agreement with experimental data. The active reflection coefficient and element pattern for the center and edge elements of a two-dimensional array as a function of scan angle are also presented     

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.     

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.     

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     

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.     

Correcting phased arrays for multipath or for conformal topography

The theoretical basis for a calibration scheme for phasedarray antennas is presented. A modified beamforming matrix is produced that will correct for the effects of multipath propagation. An extension of this is that, since it is not necessary to know the exact disposition of the array elements, the same scheme can be used to derive beamformers for conformal arrays.     

Circularly symmetric RF commutator for cylindrical phased arrays

A new feed concept is described which greatly simplifies the problem of commutating the RF distribution system of a cylindrical phased array. The feed consists of a circular parallel-plate radial transmission line with a central set of probes and a ring of peripheral probes. The array of probes in the center can be phased to produce an amplitude distribution in the parallel-plate line in any given direction. Proper setting of only two phase shifters connected to the central probes can cause any sector of the peripheral probes to be excited with the proper amplitude distribution necessary to produce a directive pattern with low sidelobes as well as a monopulse difference pattern when the peripheral probes are connected, through collimating phase shifters, to the active radiating elements of a cylindrical array. The cylindrical array can be scanned through360degin fine increments by continued indexing of the amplitude distribution generated by the central probes. ExperimentalLband hardware, built to prove the feed technique, is described. Nine central probes in a 0.25-inch thick 21-in diameter model produced a cardioid distribution and an orthogonal figure-eight distribution which could be commutated together by adjustment of two phase shifters. Measured insertion loss between the central probes and 48 peripheral probes showed only 0.1-dB loss over a 6-percent band. Coupling measurements between the three available central terminals indicated isolation between the various ports of 23-35 dB. The minimum insertion loss and the corresponding transmission phase between the central feed and the peripheral probes was shown to be independent of the setting of the two control phase shifters which were set to have conjugate phase shift.     

Infinite phased arrays of cavity-backed patches

An analysis of the radiation properties of infinite phased arrays of probe-fed circular microstrip patches backed by circular cavities using a rigorous Green's function/Galerkin's method is presented. The effect of substrate thickness on both scan volume and bandwidth performance is considered. Results are compared to those of infinite arrays of conventional probe-fed circular patch antennas