Showing papers on "Reflective array antenna published in 1990"

Practical Antenna Handbook

Abstract: This edition contains BASIC computer programs for antenna design and impedance matching, expanded coverage of long-wire directional antennas and radio-wave propagation theory, and new material on small loop direction-finding antennas. It presents practical projects, providing nuts-and-bolts information on an array of antenna types, including: high frequency dipole, vertically polarized HF, multi-band and tunable wire, hidden and limited-space, directional-phased vertical and directional beam, VHF/UHF transmitting and receiving antennas, antennas for shortwave reception, microwave antennas and mobile, marine and emergency antennas. Also explained are circuits and methods for matching antenna load impedance to an RF source or transmission line, antenna measurement and adjustment methods, antenna measurement and adjustment methods, antenna grounding techniques and how to use the Smith chart as a problem-solving device.

Superconducting antennas

Abstract: It is noted that the advent of high-T/sub c/ superconducting materials has prompted a reexamination of the opportunities for improving antenna performance. Areas where superconductors have potential are considered, including superdirective arrays; large millimeter wavelength arrays; electrically small antennas; matching of electrically small antennas, including large transmitting antennas, and of superdirective arrays; switched line or single line phasers for electronic scanning of arrays; and traveling wave arrays where the transmission line phase velocity controls the beam angle. It is concluded that arrays above 5 GHz will benefit from low conduction, and probably also from low dielectric losses. Matching of electrically short antennas, both small (high-frequency) and large (low-frequency), and of arrays of moderate superdirectivity, will allow significant efficiency improvement. >

A concentric array for low and medium frequencies

Abstract: It is shown that a concentric array of improved directivity Corum elements disposed about a central tower, driven by appropriate source amplitudes, produces a Fourier series approximation to any desired vertically polarized radiation pattern in the plane of the array. The antenna system is of special interest to broadcasters (where protected contours and interference levels are legally constrained) and also to other medium- and low-frequency users who require a vertically polarized directional array. An elementary example of the pattern synthesis technique is presented. >

Superconducting antennas

Abstract: The applicability of superconductors to antennas is examined with emphasis on the roles of external and internal fields. Six potential implementations have resulted. These are superdirective arrays, millimeter-wavelength arrays, electrically small antennas, matching of antennas, phasers for electronic scanning, and traveling-wave array feeds. Most superdirective arrays are still impractical, because of high Q and strict tolerances. Large millimeter arrays appear feasible, due to a major reduction in feed losses. For electrically small antennas, high Q again limits applicability. However, matching of small superdirective arrays and all electrically small antennas, including large transmit antennas, is very attractive, as matching network losses are greatly reduced. Switched-line phasers offer a major size reduction; phase control by means of temperature of a single line poses some problems. Traveling-wave array beam steering by means of temperature also appears possible. The last two utilize the kinetic inductance provided by thin films. >

Evaluation of adaptive phased array antenna, far-field nulling performance in the near-field region

Abstract: A theory for analyzing the behavior of adaptive phased array antennas illuminated by a near-field interference test source is presented. Conventional phased array near-field focusing is used to produce an equivalent far-field antenna pattern at a range distance of one to two aperture diameters from the adaptive antenna under test. The antenna is assumed to be a linear array of isotropic receive elements. The interferer is assumed to be a bandlimited noise source radiating from an isotropic antenna. The theory is developed for both partially and fully adaptive arrays. Results are presented for the fully adaptive array case with single and multiple interferers. The results indicate that near-field and far-field adaptive nulling can be equivalent. The adaptive nulling characteristics studied in detail are the array radiation patterns, adaptive cancellation, covariance matrix eigenvalues, and adaptive array weights. >

Interleaved helix arrays

Abstract: Arrays of helical antennas are desired for operation at spaced-apart frequencies, such as 1.5 and 2.5 GHz. In order to reduce mutual coupling between the antenna elements of the lower-frequency array, they are spaced apart by more than λ. Grating lobes occur due to the spacing. The lengths of the lower-frequency helices are adjusted to move the nulls in their radiation patterns into congruence with the unwanted peaks of the array pattern, thereby suppressing the grating lobes. In order to reduce the total area of the combined arrays, the higher-frequency antennas of the second array are interleaved with the elements of the first array. At the higher frequency, the antenna elements of the second array are spaced apart even further, in terms of wavelength, than the elements of the first array, so mutual coupling of the antennas of the second array is reduced even more than in the first array. The number of turns of the helices of the second array are adjusted to bring nulls of the individual radiation patterns into coincidence with the unwanted grating lobes.

The crow's nest antenna-experimental results

Abstract: The experimental radar system CNA-512 is introduced. Its core is a spatial array consisting of 512 statistically distributed microstrip antennas. The object is to demonstrate radar operation over 360 degrees without need for mechanical antenna rotation. The CNA-512, working at X-band, is designed for a look-direction-independent beamwidth of 2.7 degrees . The positions of the single elements (microstrip loop antennas) were determined via a 3D-Taylor density distribution. Each antenna element is to be equipped with a separate T/R-module, from which 60 have been realized in the first step. The array is subdivided into 32 subgroups with combination on the RF level; the individual signal outputs are down-mixed and digitized, allowing monopulse operation and adaptive null steering. Phase calibration for beamforming is achieved by the measurement of relative phases at a few reference elements inside the sphere. First experiments with the CNA-512 showed that transmit-receive operation and phase-steering work as projected. >

Coplanar waveguide fed phased array antenna

Abstract: A K-band four-element linear phased array of printed dipole antennas has been designed and tested. This array radiates in the end fire direction and is suitable for large two-dimensional arrays. A coplanar waveguide (CPW) is used for the microwave distribution system. A CPW to twin strip transition is used to interface with the printed dipole antennas. MMIC (microwave monolithic integrated circuit) phased shifters are used for phase control. This array demonstrates the advantages of CPW for MMIC integration and microwave signal distribution. The radiation characteristics of the antenna are excellent. >

Applications of photonic technology to phased array antennas

Abstract: The photonic features that can benefit the system performance of airborne and ground-based array antennas are enumerated. It is pointed out that the wide instantaneous bandwidth is probably the most attractive characteristic, holding great promise for performance improvement of future radar, communication, and electronic warfare systems. The impact of photonic technology on the array architecture design is discussed. The development of a dual-band transmit array (X-band and L-band) controlled by a time shift beamforming network is considered. >

Optical techniques for reconfiguring microwave phased arrays

Abstract: 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. >

Array antenna with forced excitation

Abstract: Low profile array antennas for aircraft achieve improved performance with excitation circuits providing forced excitation of radiating elements to generate signals of desired relative phase and amplitude at the elements. Excitation circuits are structured for use of reactive turning for wideband operation. Monopole or slot array antennas, each including three or more radiating elements, can be grouped as antenna systems.

An infinite array model for printed phased array antennas with arbitrary multilayer geometries

Abstract: A general infinite array analysis and related software code, UNIFY, have been developed for printed phased array antennas composed of arbitrary multilayer geometries. The analysis is described, and a few examples are presented: a microstrip dipole coupled to an inclined covered microstrip feed line, an aperture coupled microstrip antenna with radome, and a dual aperture coupled microstrip antenna for circular polarization. >

Metal-strip-loaded rectangular dielectric rod leaky-wave antennas: experimental verification of a new simple theory

Abstract: An earlier simple and accurate theory for the class of metal-strip-loaded dielectric antennas is extended to the case of narrower antennas, where the width to grating period is significantly less than 4 to 1. This extension is based on the effective dielectric constant method, and is therefore very simple. Careful measured data for two representative structures, a wide antenna and a narrow one, are presented, and it is shown that the theories for both cases are sufficiently accurate for engineering design. Comparisons between measurement and theory demonstrate the validity of the theories for both the wide and narrow cases, verifying the earlier theory for wider antennas and the current extension to narrower widths. The theory and its simple extension are shown to be sufficiently accurate for the design of millimeter-wave antennas with prescribed characteristics. >

Vehicle terminal antennas for mobile satellite applications

Abstract: A review of three classes of antennas for data and voice terminals is presented. The first one is a conically shaped beam low-gain antenna for data terminals. Drooping dipoles, quadrifilar helices, and microstrip antennas are described. These antennas can be simple and inexpensive . The second type of mobile terminal antennas are medium gain: microstrip mechanically steered arrays, microstrip electronically steered arrays, and adaptive arrays with a simple beam-steering system. The third type is a high-gain fixed terminal antenna. The noise temperature and G/T values of some antennas are discussed. The results of the vehicle terminal antennas program at AK Electromagnetique in support of developing North American mobile and fixed satellite services are summarized. >

Compressive 2-D delay line architecture for time steering of phased-array antennas

Abstract: SUMMARY We have presented an optical approach to true-time, wide-angle steering ofphased array antennas which may be applied to antennas having a large number ofelements (1O) operating at frequencies from UHF to X bands in both transmit andreceive modes and capable of multi-beam operation. The approach uses a binarydelay-line architecture for delay-line compression and array-partioning conceptsfor antenna-element compression which in combination result in a realisticpractical overall architecture having a manageable amount of hardware. Theapproach utilizes the unique property of wavelength multiplexing to achieveoptimum hardware compression. Detailed design of a practical system will dependon the particular specifications desired for a specific antenna. 7 . ACKNOWLEDGMENTS This work was supported by the Air Force Rome Air Development Center underContract No. F30602-87-C-0166. 8 . REFERENCES 1. R. A. Soref, "Programmable time-delay devices," Applied Optics, Vol. 23,3736, 1984.2. A. M. Levine, "Fiber-optic phased array antenna system for RF transmission,"U.S. Patent. No. 4028702, 1977.3. H. F. Taylor, "Optical fiber devices for signal processing," Proc. SPIE,Vol. 209, 159, 1979.4. B. Lagerstroem, et al., "Integrated optical delay line signal processor,"Proc. OFC/IOOC, Paper WK2, 1987.5. A. P. Goutzoulis, D. K. Davies, and J. M. Zomp, "Prototype binary fiberoptic delay line," Optical Engineering, Vol. 28, No. 11, 1193, (1989).

Performance of a Spherical Array Antenna Fabricated by Vacuum Forming Technique

Abstract: In this paper, a spherical array antenna applicable to mobile satellite communications is discussed. The beam scanning characteristics of the directive gain of spherical and planar arrays are examined by computer simulation, and it is shown that the gain reduction of a spherical array is suppressed about 2 dB at a scan angle of 60° compared with that of a planar array. Mechanical and electrical performance of a vacuum formed hemispherical array is introduced. Experiment results show the feasibility of easily fabricated conformal arrays with good electrical performance.

Propagation of an intense microwave beam from a phased array

Abstract: Phased array antenna systems are capable of radiating very intense microwave beams. However, while propagating through the atmosphere and the ionosphere the beam intensity can be significantly reduced by several mechanisms which are not of concern to less intense radiation. This paper discusses qualitatively the propagation energy loss associated with powerful phased arrays.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical beam-former for microwave phased array antennas

Abstract: Presents a new beam forming technique for use in optically controlled phased array antennas The system 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 a description of the experimental implementation and results for a system operating at L-band

An experimental investigation of a 16*16 microstrip array with stacked parasitic elements

Abstract: An experimental investigation of a 16*16 microstrip array of rectangular patch radiating elements is reported. Results for the radiation characteristics and impedance bandwidth of the array with and without stacked parasitic elements are presented. The measured impedance bandwidth of the array with stacked parasitic elements is more than twice as broad as the bandwidth of the array with single patch elements, and is about twice that of a single stacked parasitic patch antenna. >

Antennas for direct to home reception of DBS television

Abstract: Outdoor units were required for domestic DBS TVRO stations. Satellites had been ordered to provide 59 dBW EIRP or more, as had receivers incorporating custom DMAC integrated circuits and eurocypher modules. It was established that an antenna aperture width of about one foot would be required and that the antenna could be either a parabolic dish or a flat plate array. Research confirmed that both flat plate arrays and offset-feed parabolic reflector antennas are acceptable to the market. Two Squarial arrays and two reflectors were made available by approved manufacturers in time for launch of BSB programmes. The antennas are designed to facilitate installation by professionals and by the DIY enthusiast. An installation display facility was incorporated in the receiver to monitor the DMAC bit error rate.

Circularly-polarized omnidirectionnal antenna with maximum horizontal gain

Abstract: Association of three half-wave dipole antennas (A1-A3) spaced uniformly in the same plane and arranged concentrically with a fourth antenna (A4) situated at an equal distance from each of the three half-wave antennas and in a plane perpendicular to them so as to form a network of antennas fed with currents of like phase and like amplitude, the diameter of the circle containing the radiating elements of the three half-wave antennas being equal to one half- wavelength lambda 0 in air at the mean operating frequency, this dimension being reducible by the dielectric constant epsilon r when the set of antennas is embedded in a homogeneous dielectric medium. Application to omnidirectional ground-ground or ground-air transmissions in a disturbed surrounding medium.

A high gain antenna system for airborne satellite communication applications

Abstract: A high gain antenna for commercial aviation satellites communication is discussed. Electromagnetic and practical design considerations as well as candidate systems implementation are presented. An evaluation of these implementation schemes is given, resulting in the selection of a simple top mounted aerodynamic phased array antenna with a remotely located beam steering unit. This concept has been developed into a popular product known as the Canadian Marconi Company CMA-2100. A description of the technical details is followed by a summary of results from the first production antennas.

Adaptive phase compensation for distorted phased array by minimum sidelobe response criteria

Abstract: Nonpoint sources are used as the beamforming source for distorted phased array antennas. Since adaptive phase compensation is a nonlinear optimization problem, an appropriate solution is found. A noniterative solution is presented which utilizes a priori knowledge about the sidelobe region of the target field, which is the nonilluminated region of a radar illuminator, to find a phase vector which minimizes the array response in that region. An approximate solution of this phase vector can be found by solving a standard adaptive array problem. Computer simulation results are presented to demonstrate the performance of the proposed algorithm. >

Design of omnidirectional slot antennas with vertical polarization

Abstract: The design of thin omnidirectional transmitting antennas with vertical polarization is discussed. The antenna is realized as a broadside slot array in order to make use of the simplicity and high power-handling capabilities of this principle. The design of the antennas was accomplished by the use of an equivalent circuit. The radiating elements are characterized by series elements connected through a transmission line with characteristic impedance Z/sub I/. If the equivalent circuit is terminated by a short the array is said to be resonant or standing-wave fed. For a termination Z/sub I/ the array is said to be nonresonant or traveling-wave fed. As an example, the measured azimuth and elevation radiation patterns of a resonant slot array with eight radiating bays of slots are presented. The directivity of the antenna was measured at about 10 dB. >

An equivalent model for practically used dipole-type antenna elements

Abstract: A simple equivalent model is presented which represents antenna elements that make up various types of TV receiving array antennas. The model gives a unified representation of eight different types of antenna elements, such as loaded and unloaded folded types, conventional dipole types, loaded and unloaded parasitic element types, etc. This model can be used to conveniently analyze the radiation characteristics of many array antennas which are made by combining these dipole-type elements into various TV receiving antennas. >

Low-sidelobe phased array characteristics using planar near-field scanning

Abstract: A low-sidelobe phased-array antenna was investigated both theoretically and experimentally using the planar near-field scanning technique at a distance of less than one wavelength from the antenna aperture. The theory was applied to a monopole phased array, and it was shown that a theoretical V-dipole probe can accurately model the observed experimental array performance using a waveguide probe. The presence of nonpropagating grating lobes in the plane-wave spectrum has been observed using theory and measurements. Results indicate that the near-field sample spacing must be chosen such that aliases of the grating lobes do not appear in the visible space region. The theory presented can also be applied in the radiating near-field region and to other array thin-wire elements such as dipoles. >

Element response to an incident plane wave of a VHF circular array antenna above lossy ground

Abstract: A circular array receiving antenna is highly attractive for radio direction finding because of its geometrically circular symmetry and, thereby, the periodicity of its electromagnetic features, such as mutual coupling between elements of the array, when its beam is scanned electronically through 360 degrees. In radio direction finding systems, the elements of an array are considered to be sensors for the incoming wave. One of our principal concerns is the response of each element in the array to a plane wave. It will be treated as the input data vector for the digital signal processing system. The output voltage of an antenna element in a circular array, however, does not directly represent the amplitude and phase of the incident wave hitting the element antenna because of mutual coupling between the elements and the effect of lossy ground with a complex dielectric constant, e r . In this paper, an analytical treatment and numerical results for the element response are provided. The discrete image theory and the method of moments are employed.

The measurements column (antenna gain measurement)

Abstract: Four different methods for measuring the gain of circularly polarized antennas under test are presented. Errors that result from these measurements are discussed. The errors presented would form part of an overall error budget analysis. >