Showing papers on "Reflective array antenna published in 1991"

The first demonstration of an optically steered microwave phased array antenna using true-time-delay

Abstract: The concept of true-time-delay steering for phased array antennas and its advantage over phase shifters in broadband applications are described with particular emphasis on the potential advantages offered by fiber-optic delay lines. The system architecture of the phased array antenna and the design and performance of the fiber-optic time-shifter networks in the antenna are described. The radiation patterns of the phased array antenna at L and X bands are presented. Using semiconductor laser switching to implement the delay times, the absence of beam squint in the antenna pattern and its frequency was switched from L to X band is demonstrated. >

Millimeter-wave design of wide-band aperture-coupled stacked microstrip antennas

Abstract: K-band aperture-coupled stacked microstrip antennas are studied and numerical results based on the solution of integral equations solved in the spectral domain are presented. The effects of varying physical parameters of the structure are investigated with the goal of designing millimeter-wave wideband microstrip antennas. Antennas with different characteristics are then analyzed and compared with experimental data. Bandwidths in excess of 20% are obtained and applications to phased array antennas are discussed. >

Linear conformal antenna array for scanning near end-fire in one direction

Abstract: A linear conformal array antenna consisting of double-ridged waveguide elements which are all tapered in the E-plane or the H-plane. The array of waveguide elements is fed by a Gent lens whose amplitude and phase characteristics can be adjusted to cause the waveguide element array to produce a desired radiation pattern. The linear array antenna, which has been tapered in the E-plane, can be operated to scan an electromagnetic endfire beam in one predetermined direction with a maximum scan loss of 3 dB. The array of waveguide elements can be substantially conformal with the fuselage of an airborne craft carrying the linear array antenna, thereby reducing aerodynamic drag and radar cross section. The linear array antenna has a bandwidth that is greater than an octave wide.

Practical Phased Array Antenna Systems

Abstract: Electronic scanning radar systems (ESRS) design and architecture antenna array fundamentals Antenna array fundamentals phased array elements array feeds case study - design of air defence ESRS compact, constrained feed phased array for AN/SPY-1 limited scan arrays limited scan arrays computer control of a multifunction radar computer control of a multifunction radar.

System for determining direction or attitude using GPS satellite signals

Abstract: For determining spatial orientation based on the carrier phase of signals received from a set of GPS satellites, an antenna array (16) includes a number of antennas (20a, 20b, 20c) coupled to GPS radio receivers (22a, 22b, 22c), a mechanism (28, 30) for reconfiguring the positions of the antennas (20a, 20b, 20c) within the array (16) and a signal processing module (24) for processing the data collected by the antennas (20a, 20b, 20c) and the receivers (22a, 22b, 22c). The mechanism (28, 30) for reconfiguring the antenna array (16) is adapted for exchanging the positions of one pair of antennas (20b, 20c) and for rearranging the antennas (20a, 20b, 20c) from collinear (Fig. 8a, Fig. 8b) into non-collinear patterns (Fig. 8c). Phase measurements are taken by the antennas and their associated receivers, both before and after antenna exchange and after antenna rearrangement in order to provide the data necessary to determine direction or attitude.

Beamforming structure for modular phased array antennas

Abstract: A combination of doubly folded parallel plate beam combiners or dividers, configured to produce a desired composite beam for use in arrays of antenna elements. The doubly folded combiner or divider functions to expand a transmitted beam, or contract a received beam, in one selected plane. In a transmit mode, a single beam can be expanded first in one direction by a first divider, then expanded in a perpendicular direction by a stack of additional dividers coupled to the first. Optional phase shifting circuits provide beam steering as desired. Second and other additional beams can be processed in the same manner, to produce a composite output of multiple beams for transmission by an antenna array. Another aspect of the invention involves the use of a beam forming structure of this type in conjunction with an array of transmit/receive microwave modules providing amplification and phase shifting functions, and an array of printed circuit antenna elements. With appropriate phase shifting controls, a composite beam transmitted or received by the array or antenna elements can be steered independently in azimuth and elevation, using much less complex control circuitry than a conventional phased array antenna system.

Reversible time delay beamforming optical architecture for phased-array antennas

Abstract: A phased array antenna system has optical architecture comprising free space delay units and associated spatial light modulators compatible for operation with temporally incoherent or coherent laser light to produce signals having selected time delays to actuate antenna elements of an antenna array to transmit electromagnetic radiation at a selected beam angle from the phase array. The same optical architecture is used to process electromagnetic signals detected by the antenna array to produce an output signal for display or processing which corresponds to the radiation detected at the selected beam angle.

Comparison of six microwave antennas for hyperthermia treatment of cancer: sar results for single antennas and arrays.

Abstract: Interstitial techniques of inserting catheters into tumors for the purpose of applying therapeutic irradiation and hyperthermia are in widespread use. Several miniature microwave antenna designs are currently used for these treatments. These include multisection, hot-tip, 2- and 3-node, dipole and helical antennas, all of which are commercially available. The antenna designs are diverse enough to have a dramatic effect on the power deposition patterns either as single antennas or when used in arrays. Aside from the dipole antenna, most of the antennas have never been evaluated experimentally or theoretically in arrays, although the array configuration is used in the vast majority of all clinical treatments. Power deposition or SAR (specific absorption rate) tests were run in muscle equivalent phantom. Single antennas were evaluated at 400 points in a plane and isoSAR contours drawn, normalized to maximum SAR. Single antennas were also compared in large and small diameter catheters to evaluate catheter dependent antenna performance. The dipole, multisection, hot-tip and helical antennas were evaluated in arrays of four antennas located at the corners of a square, spaced 2.0 cm apart. Arrays of antennas were evaluated at 441 points in three planes orthogonal to the antenna axes. Results in the single antenna studies showed that the dipole was less affected by snugness of catheter fit than the multisection, hot-tip or helical antennas. In large catheters, the latter three antennas showed more extreme tip heating performance. The 2- and 3-node antennas deposited only 20% SAR in the distal 30 mm of antenna length. In arrays, the multisection, hot-tip, and dipole antennas all yielded 80–90% SAR centrally in the central measurement plane. Comparing the three antennas, the dipole array deposited 20% more power centrally in a plane near the insertion point, and the multisection and hot-tip antenna designs deposited 10% more central power in a plane near the antenna tips. The helical antenna array deposited only 30% SAR centrally in the plane near the antenna tips and in the central plane. Only 10% SAR was measured centrally near the insertion point, as expected for tip-heating antennas. Finally, the clinical significance of the results is discussed as applied to human tumors undergoing hyperthermia treatments.

Yagi-Uda array for millimetre-wave imaging

Abstract: An imaging array consisting of five Yagi-Uda antennas in a dielectric has been constructed for 50 GHz that has antenna patterns suitable for millimetre-wave applications. Crosstalk levels of less than −30 dB between adjacent antennas in an f/1.0 imaging array have been measured in 5 GHz model experiments

Subsurface target identification radar

Abstract: Subsurface target identification radar includes an antenna array, a rotary encoder, a radar controller, a polarization switching circuit, and transmitter and receiver circuits. The antenna array is constituted by dipole antennas having plane triangle elements. The antennas are disposed at angular intervals of 120° with respect to a rotated symmetric point of the array. The rotary encoder generates a distance pulse every time the radar travels a presetted distance. The radar controller sequentially generates three switching pulses within one period on the basis of the distance pulse from the rotary encoder. The polarization switching circuit selects an arbitrary dipole antenna as a transmitting antenna from the antenna array, selects an arbitrary dipole antenna, other than the selected antenna, as a receiving antenna, and changes a combination of selected antennas every time the switching pulse is generated by the radar controller. The transmitter and receiver circuits transmit/receive electromagnetic waves through the selected antennas.

Microstrip base station antennas for cellular communications

Abstract: Four base-station antenna products using microstrip technology have been developed for use in cellular communications. The antennas operate in the 800-900-MHz range and are designed to work in a 60 degrees sectored arrangement. The main product is a half-cylinder three-beam radome-enclosed antenna. There are three microstrip planar array panels within the half-cylindrical radome. Each microstrip planar array panel illuminates one 60 degrees sector, and all three panels fit into the half-cylindrical structure to provide RF coverage over 180 degrees . An electromechanical down-tilt actuator has also been designed into the structure to provide individual remote elevation adjustment to each panel. The antenna is in use in the Bell Cellular network. Its aesthetics and performance improvements in operations and maintenance have proven to be a big advantage in densely populated urban and suburban areas. >

Mode matching analysis of arrays of stepped rectangular horns and application to satellite antenna design

Abstract: Satellite antennas commonly use reflectors with array feeds. In such cases the efficient illumination of the reflector is crucial in the design of the arrays. Methods in use to improve the illumination efficiency of the array include partially loading the horns with dielectric, or employing multi-mode horns. The author describes the analysis of an array of multimode stepped rectangular horns, including the effect of mutual coupling, using the mode matching method. It has already been used in a study of the Hughes Aircraft Company's HS601C satellite Ku-band antennas and some results obtained are outlined herein.< >

Effects of circular and linear polarized antennas on wideband propagation parameters in indoor radio channels

Abstract: Results are presented from an experiment that used a variety of antennas inside two buildings. An important result is that directional circularly polarized (CP) antennas reduce RMS delay spreads when compared with omnidirectional and directional linearly polarized (LP) antennas at identical locations. The variation of RMS delay spread over distances of several wavelengths is also greatly reduced when CP antennas are used in place of LP antennas with similar gains. >

Method of managing beams formed by phased array antennas and apparatus therefor

Abstract: A method of managing beams transmitted and received by a plurality of phased array antennas. In a search mode, the phased array antennas transmit searching pulses synchronously in a search mode. In a tracking mode, targets tracked by the phased array antennas are divided to a plurality of groups on the basis of pulsed repetition rate. Then, for the respective divided groups, transmission timings of tracking pulses to be sent form the phased array antennas are calculated by using ranges of the targets belonging to the respective groups so that transmission and reception operations do not occur simultaneously, thereby enabling the simultaneous usage of the phased array antennas.

Determination of array feed excitation to improve performance of distorted or scanned reflector antennas

Abstract: The performance degradation of distorted and/or scanned reflector antennas is manifested primarily in a decrease in peak gain and in an increase in radiation pattern sidelobes. The author discusses a procedure for determination of the excitation coefficients of the array feed in order to approximate the 'ideal' performance for both gain and sidelobes. Representative results of 6 GHz are presented for a hexagonal array of 1.5 lambda diameter dual-mode horns with center-to-center spacing of 1.5 lambda , to compensate for the surface distortion of one offset aperture of a mesh deployable reflector antenna. >

Null beam forming by phase control of selected elements in phased‐array antennas

Abstract: In phased-array antennas, nulls of the radiation pattern can be formed in the direction of undesired wave by controlling only the phase excitation without affecting the main beam. However, the computation time becomes very large when an antenna with a large number of elements is analyzed and it becomes very difficult to counteract the variation of wave boundary instantly. Here, based on the exact calculation of phase value by the method of plane-wave synthesis, the foremen-tioned elements are selected which contribute more to the null formation, and the method of controlling only the phase of the selected elements is presented. Using this method, the computation time can be reduced. Moreover, the depth of nulls and the gain of the main beam obtained in this way is the same as that produced by controlling the phase of all the antenna elements. As a result of numerical simulation and experiments of null forming in the phased-array antenna using a 5-bit phase shifter, deep nulls with the level of less than -40 dB could be formed without decreasing the gain of the main beam.

Characterization of standing wave movement by in-line antennas

Abstract: The interaction of incident radiowave fields with multiple-port antennas on a moving vehicle is investigated. The interest is for in-line antennas which trace identical paths through a standing wave field and receive similar, but not identical, (time-displaced) signals as the mobile moves through typical multipath environments. The investigation quantifies the similarity of the received signals using the average peak cross-correlation of the envelopes. This, as a function of the antenna spacing, offers a quantitative assessment of the effective movement of standing wave fields. However, when the antenna spacing is less than 0.5 wavelengths, the peak cross-correlation measure is strongly perturbed by the mutual coupling effects of terminated antennas. For the 851 MHz measurements reported, the speed range of 15 km/h to 50 km/h (12 to 40 wavelengths per second) did not consistently affect the results for antenna spacings of up to 1.44 m (4.1 wavelengths). >

Self-steering. self-focussing phased array for SHARP

Abstract: Attention is given to SHARP (Stationary High Altitude Relay Platform), a proposed electrically powered light aircraft which will fly on station at 21000 m altitude for months on end. receiving its power from the ground. Its mission is to carry a transmitter and antenna for broadcasting, microwave relay, mobile communications or radar, at far less cost than a satellite. A large ground antenna transmits microwave power to the aircraft were the power is captured by an array of antenna-rectifiers and is used to propel the aircraft and to power the payload. It is assumed that a phased array will be used, and the phases of the elements adjusted to steer and focus the beam. The proposed system is self-focusing and self-steering: wherever the aircraft goes the beam points at it and is focused on it. The system has been simulated on a small scale with a 5 by 5 square array using Advanced Basic. >

Compact and directive transient antennas

Abstract: Following an analysis of TEM structures, a brief discussion of the transient sources used is given, and a review of the biconic properties outlined. The effect of resistive loading is then considered. Next, some successful designs of planar fin and planar horn antennas radiating fast transient pulsed fields are presented. Finally, arrays of such horns are considered. >

Optimized Antennas for Mobile Communication Base Stations

Abstract: This is a synopsis of work conducted to improve the electrical and mechanical performance of antennas used for mobile communication base stations. To accomplish this we first consider the propagation characteristics to determine the optimal antenna pattern. In addition, the antennas mechanical size and profile are minimized to improve its appearance and mounting ease. The end result of this work is an antenna that has superior performance in terms of virtually every antenna and mechanical specification. This was achieved by the use of a specially constructed microstrip patch element in conjunction with technology for beam shaping and the use of environmentally proven materials. The present use for such antennas is for the 900MHz GSM and 1.8GHz PCN systems base stations but freedom in the design frequency range, polarization, and array configurations allow for a considerably wider range of applications.

Small crossed-slot radiating elements for phased array applications

Abstract: Two small cavity-backed crossed-slot antenna configurations are described that offer simple design and easy frequency tuning, and are light-weight, low-loss, and low-cost, The slots in these antennas are end-loaded. The end loading makes the slots effectively longer and hence reduces their resonance frequency. Therefore, relatively small radiating elements can be achieved for large-angle-scanning phased-array antennas. These antennas have good RF characteristics and provide a relatively wide bandwidth. >

Multifrequency phased array aperture

Abstract: A shared antenna aperture has two or more sets of interleaved antenna elements. Open-ended waveguides are used for the elements of the higher frequency antenna array and are selectively interconnected to form the elements of the other sharing antenna arrays. Plates are used to short walls of adjacent waveguides to form notch antennas. Coaxial feeds are used to excite the notches at a lower frequency than the waveguides. In one embodiment, the notch antennas formed of two interconnected waveguides operate at half the frequency of the waveguides. To form a third sharing antenna, four adjacent waveguides are interconnected to form notch antenna elements and these notches are excited at an even lower frequency.

Development of L-band feed arrays for INMARSAT-3

Abstract: The author gives a general review of some of the aspects of the development of the feed arrays for the L-band transmit and receive antenna arrays on INMARSAT-3. The work described has been carried out over the last two years in the Antenna Group at Matra Marconi Space Portsmouth. Some of the initial trade-offs in the design are described leading to the development of the BSE array in the current design. Details of the design techniques and the final implementation of the array feeds are described. >

A general method for treating infinite arrays of antennas printed on protruding dielectric substrates

Abstract: A full-wave approach has been developed to analyze a wide variety of radiating elements (including the dipole element with feed lines) printed on one side of a protruding substrate in an infinite array environment. The method is outlined, and examples of results are presented for the dipole element fed by a coplanar strip transmission line. >

Fast determination of the element excitation of active phased array antennas

Abstract: An element excitation method which provides a simple and fast way of determining the excitation of antenna elements in an active phased array as a function of the amplitude and phase setting is presented. These element ions can be used to align the amplitude and phase settings of the antenna elements of an active phased array for a desired radiation pattern. The complex electric field has to be measured in only one observation point in the far field of the antenna as a function of the element's amplitude and phase settings. The method is described in detail and excellent experimental results are shown. >

Multimatrix beamforming for semi-active antennas at L-band

Abstract: The authors review several aspects of payload system design for L-band Mobile missions. Direct radiating, imaged array and focussed array antenna solution options are briefly discussed. The INMARSAT-3 multimatrix antenna design is described and performance results presented. The extension of the concepts to future L-band payloads for regional coverage is outlined.

Characteristics of frequency scanning elliptical array

Abstract: It is considered that the radiation field of an end-fed elliptical array whose main beam points toward the array normal and whose elements are equally-spaced in the ellipse is the output of a time-invariant system. On the basis of the linear system, the transfer function of this system is obtained and the formula is presented. The time required for the establishment of a steady pattern is considered. >

Millimetrewave Antennas

Abstract: Antennas designed for use at millimetrewaves and sub-millimetrewaves are reviewed. The use of these parts of the spectrum for communications, radar and remote sensing is growing rapidly and with it the demand for high performance antennas. Many novel designs have been developed to exploit the unique characteristics of millimetrewaves. The short wavelength means fine tolerances which has led to precision and efficient reflectors and feed horns. The paper reviews the current position for reflectors, lenses, horns, planar antennas, travelling wave antennas and integrated antennas.

Aircraft antenna with correction of errors introduced by a coning of the antenna beam and by aircraft banking

Abstract: Array antennas (120) for aircraft use have a shiftable center of radiation. The antenna beam of a group of laterally spaced array antennas (110,112,114,116,118) is steered and the beam shape is controlled by relative shifting (122) of the centers of radiation of the arrays. Beam tilting in a fuselage mounted system of array antennas uses controlled selection of active antennas.

Printed Yagi antennas as a focal plane array in an imaging system

Abstract: Describes an experimental investigation of a two-dimensional X-band 5*5 array of printed Yagi antennas usable as the focal plane array in an imaging system with f/D approximately 1. E- and H-plane patterns have been measured and aperture efficiencies have been calculated. The results have been compared with a 5*5 constant-width slot antenna (CWSA) array. >