Showing papers on "Reflective array antenna published in 1984"

Directive properties of antennas for transmission into a material half-space

Abstract: The directive properties of antennas for transmission into a material half-space are investigated. In a practical situation, the antennas might be located in air with the directive transmission into the earth. The field of a general antenna over the half-space is expressed as a spectrum of plane waves. The integrals representing the field are evaluated asymptotically to obtain the "geometrical optics" field of the antenna, and this field is used to define quantities that describe the directive properties of the antenna (pattern function, gain, and directivity). Numerical results are presented for infinitesimal electric and magnetic horizontal dipole antennas in a dielectric half-space, region 1, with directive transmission into the adjacent dielectric half-space, region 2, and the ratio of permittivities \epsilon_{2}/\epsilon_{1} greater than one. The theory for the infinitesimal dipoles completely explains the directive properties previously obtained for the resonant circular-loop antenna over a material half-space. Measured field patterns and gains for dipole and loop antennas near an interface between air and fresh water are in good agreement with the theory.

Generalisation of the concept of equivalent radius of thin cylindrical antennas

Abstract: The concept of equivalent radius of electrically thin cylindrical antennas is well known in the case of metallic antennas in homogeneous dielectric media. It is possible, however, to define equivalent radius also in cases of thin cylindrical antennas in the presence of arbitrarily cylindrically shaped dielectric and/or magnetic materials. The approach is essentially a quasistatic energy approach. It enables a large number of complicated problems of such antennas to be reduced to the equivalent problem of a cylindrical antenna of circular cross-section with an appropriate single-type dielectric or (preferably) magnetic cover, which can be solved with ease. Illustrative examples, including those of strip antennas on a dielectric substrate, indicate high accuracy of the results obtained by the proposed theory.

Phased array antennas with binary phase shifters

Abstract: Steerable phased array antennas of the tapered type in which the antenna ment power is maximum at the center of the array and tapers off on either side thereof. The phase shifters of each antenna element are of the binary digital type with the number of stages and hence the phase accuracy being maximum for the high power center antenna elements and tapering off on either side thereof. Redundant stages for the binary phase shifters can be provided to increase reliability.

Switchable antenna for the VHF and UHF frequency bands

Abstract: This invention concerns an antenna switchable between the VHF and UHF frequency bands. This antenna incorporates a capacitive element, disposed at a specified distance from a reflecting surface mounted on the body of the vehicle. For VHF, tuning is obtained by a fixed self-inductance in parallel and a variable self-inductance in series with the capacitive element. The latter comprises various sections which can be short-circuited by switches. For UHF, the variable self-inductance is totally short-circuited and the fixed self-inductance is disconnected by a switch; then, plates form, with the reflecting surface and the capacitative element, a "manchette" antenna. This switchable antenna can in particular be mounted on an airplane.

Array Sidelobes, Error Tolerance, Gain, and Beamwidth

Abstract: : In this report, we present a set of universal probability curves that the array error tolerance, illumination function, achievable sidelobe level, and the designed sidelobe level. We show that this set of probability curves can be used to find a lower designed sidelobe level to achieve a better error tolerance. The relations of array directivity gain and beamwidth with respect to illumination function are also discussed. These parameters can be conveniently used for this design procedure without detailed knowledge of the array illumination. Originator supplied keywords include: antenna, phased array, and array errors.

Extending the R-2R lens to 360°

Abstract: The R.2R lens is a remarkable microwave device that provides perfect focusing, giving multiple simultaneous antenna beams from a circular or cylindrical array. However, the perfect focusing of the R-2R brings with it a serious limitation on angular coverage as a result of the angular doubling that enters when the array elements in the antenna are connected to the launcher elements on the lens periphery. We have now found a way to modify the R-2R concept so that a full circle of array elements can be mapped onto a full circle of beam ports. The new mapping makes use of hybrid junctions and either four or six physical lenses. The interconnections result in 360\deg of simultaneous antenna beams, each of which can be used both for transmission and for reception.

Phased antenna array for wind profiling applications

Abstract: A diagonal phased antenna array for use as a wind profiler by means of Doer shift measurements comprises a plurality of Yagi-Uda antennas which are oriented in a predetermined direction such that Yagi-Uda antennas have a polarization 45° offset from the principal planes of operation of the antenna array resulting in similar radiation patterns subject to a geometric taper in the array aperture with respect to the principal planes.

Feed displacement correction in a space fed lens antenna

Abstract: A space fed microwave lens antenna for deployment in outer space or other remote, hazardous or unattended location. Electronic means are provided for compensating for errors in the mechanical displacement of the phased array feed elements from the phased array lens elements.

Synthesis of random antenna array patterns with prescribed nulls

Abstract: Under study is a method devised to reduce sidelobes of thinned random antenna arrays over specified angular sectors. The thinned array is assumed random in the sense that the nominal location of the elements is known, but their actual position may vary randomly. It is shown that by imposing adequately dense pattern nulls, it is possible to reduce the sidelobes effectively in the region of the nulls. The problem is formulated as a set of points in the radiation pattern, which are constrained to specified values. The unknowns are the excitations, or weights, applied to the array elements. In the general case, the linear system of equations is consistent and has an infinite number of solutions. The solution selected optimizes the pattern in a minimum variance sense. Quantitative relations are derived for the pattern change and the gain cost associated with the imposed pattern nulls. Several examples are included to illustrate the results.

A variable power dual mode network for reconfigurable shaped beam antenna

Abstract: A three output port variable power dual mode network is described. This network can be useful in driving a three element feed array feed of a communication satellite antenna to provide a dual mode reconfigurable shaped beam pattern.

Potential Measurement Errors Due to Mutual Coupling Between Dipole Antennas and Radio Frequency Absorbing Material in Close Proximity

Abstract: The mutual coupling between dipole antennas and radio frequency absorbing material was determined experimentally. A comparison of the mutual coupling before and after wall treatment is presented. These results can be used to determine the minimum distance which should be maintained between a dipole antenna and radio frequency absorbing material. A broadband antenna and several quarter-wave monopoles near resonance were measured.

Highly Efficient Two-Dimensional Printed Antenna Array with a New Feeding Network

Abstract: A printed broadside two-dimensional array of anti resonant dipoles at the frequency of 17 GHz with a gain of 28 dB is presented. A new concept of radiating elements and subarrays feeding is applied, thus providing high efficiency. The array is fed by tapered distribution in both planes, so that the side lobes suppression is better than 21.5 dB.

An integrated planar microwave antenna array with feeding by magnetostatic surface waves and electronic beam steering

Abstract: Investigations are presented dealing with integrated substrate structures to excite and guide magnetostatic surface waves feeding a planar antenna array. An equivalent circuit model is utilized to describe surface wave feeding and radiation. It is shown that phase and amplitude distribution of the suggested integrated array can be controlled by simple methods. The amplitude results from the configuration of the surface wave transducers, whereas the phase of the individual radiation elements is tunable by applying an external magnetic bias field. 5 and 4-element arrays for S- and C-hand, resp., are realized and scan angles up to \pm45\deg have been achieved.

A new class of broadband time domain element space antenna array processors

Abstract: This paper describes a new approach to the design of broadband element space antenna array processor which can handle a variety of steering situations. The approach is applicable to array processor without pre-steering, with coarse pre-steering and exact pre-steering. Furthermore, the approach presented enables mismatch between signal model and actual signal scenario to be incorporated in the problem formulation. Analytical as well as simulation results on the new class of antenna array processors are presented.

Bounds of Uncertain Interference Between Closely Located Antennas

Abstract: The uncertainty in the characteristics of two antennas located close together and operating at different frequencies is considered. The formulations of antenna performance indexes on one antenna by admittance parameters are obtained with respect to the load impedance at the feed point of the other antenna. All the antenna performance indexes obtained here are expressed as the ratio of quadratic functions of the load impedance, and exact formulas are derived for the quick calculation of their bounds with respect to the load impedance which is uncertain and changes with frequency.

Pattern synthesis of array fed reflector antennas

Abstract: Phased array reflector antennas are used in practice for beam scanning in a limiting range of angles. Compared with the complete phased array systems, these antennas have a simple structure and can be constructed with a smaller cost. These arrayss fed reflector antennas can be replaced with generalized array antennas by considering the secondary radiation pattern of each feeding element of the array element pattern. This paper is a theoretical study of the maximization of the gain and suppression of the sidelobes for this generalizeed array. These problems are important for pattern synthesis. From the study, it was found that the computation time of the synthesized secondary pattern can be reduced for the array fed reflector antenna due to exploitation of the secondary element patterns. Also, the array excitation distribution optimum for the desired pattern can easily be determined from the theory of the generalized array. These findings have been confirmed experimentally by means of an X-band linear array fed reflector antenna.

Effects of a spacecraft on the performance of a UHF yagi array antenna

Abstract: The performance of a 2 \times 2 array of UHF Yagi-Uda antennas mounted adjacent to a DSCS III spacecraft is investigated. RF measurements are made of the antenna peak (nadir) gain, edge-of-earth (EOE) gain, pattern and axial ratio characteristics for various locations of the array with respect to the spacecraft. The measured results are compared with those of an isolated array.

End-fire hybrid array antennas

Abstract: A heuristic approach useful in the design of end-fire array antennas is described. When an array is scanned "beyond end fire," the last elements of the array, in the direction of the end-fire beam, generally receive net power transmitted by other elements of the array. This received power might conceivably be recirculated and reradiated at the price of substantial complexity in the feed network. It is relatively simple to absorb this power in appropriate resistive loads at the price of reduced gain. The resulting end-fire antenna is a hybrid-array consisting of two classes of elements: elements excited directly and elements excited parasitically. A compromise termination of these parasitic elements in reactive loads especially determined to preserve desired pattern characteristics is examined.