Showing papers on "Reflective array antenna published in 1983"

A modular approach for the design of microstrip array antennas

Abstract: A method for the design of medium gain (15-25 dB) microstrip array antennas is described. A modular approach is utilized in which a given antenna is used as a building block for higher gain antennas. A series of X -band antennas were built in this way, and the results seem to validate the usefulness of the method.

Novel method of multiplexing radiocommunication antennas using circular-array configuration

Abstract: This paper describes the application of a circular array for the central antenna of base/repeater stations in mobile communication systems. The antenna is fed from a multiple-port feed network, which offers a number of electrically independent patterns which have omnidirectional coverage. The nature of the network is described showing how it can provide isolation between multiple transmitters and receivers. Experimental results are presented which suggest that 30 dB isolation can be achieved over an octave bandwidth.

Loop antennas for directive transmission into a material half space

Abstract: The horizontal circular loop and the coaxial array of loops above a material half space are studied as antennas for directive transmission into the half space In a practical situation the loops might be located in air with the directive transmission into the earth In determining the optimum geometry for the single loop and the array, the far-zone field patterns and directivities of these antennas when placed over lossless dielectrics are considered first The directive properties for the lossless dielectric are found to be indicative of those for the same antenna over a medium with low loss when proper account is taken of the exponential attenuation experienced in the lossy medium Parametric studies are used to obtain the maximum directivities for these antennas For the single loop of resonant size, the optimum height over the interface is determined, and for the two-element array consisting of a driven loop of resonant size with a single parasite, the optimum size and spacing of the parasitic reflector are found Measured electric field patterns and gains of model antennas above an interface between air and fresh water are in good agreement with the theoretical results

Twin aperture phased array lens antenna

Abstract: A phased array lens antenna which includes a lens having two faces disposedubstantially at a right angle to each other. Transmit-receive modules which include phase-shifters are shared between the two lens faces. Two lens antennas positioned in back-to-back relationship about a ship superstructure scan 360°.

Small angular beamwidth antenna system

Abstract: A relatively narrow beamwidth (10° or less) receiving antenna patt is formed at the receiver end of a radio frequency transmission link where a plurality of radiating sources are operating in a dense communications environment. The antenna pattern comprises the difference between two antenna receiving patterns where the beamwidth of one pattern is wider by a predetermined angular amount than the other pattern. In the preferred embodiment, a phased linear array of antenna elements is operated as two sets of elements wherein one set of elements comprising a number of elements less than the total number of elements provides a beamwidth that is broadened by a predetermined angular sector greater than the beamwidth formed by the entire array. The antenna elements are progressively phase shifted to provide overlapping beam patterns and the pattern of one set of elements is scanned so that one side of both patterns are substantially coincident. The received signals from the elements developing the two antenna patterns are respectively combined and linearly subtracted to provide cancellation of all the received radiation except over the small angular sector defined by the difference between the two patterns.

Time division adaptive retransmission for reducing signal impairments in portable radiotelephones

Abstract: Multiple-antenna receiving-diversity was shown previously to be effective in mitigating the effects of random angular orientation and multipath radio propagation for portable radiotelephones. This paper shows that time-division adaptive retransmission used with appropriate antenna configurations can also mitigate these effects. The retransmission configurations require fewer antennas than the receiving diversity configurations for a given improvement in relative signal-to-noise ratio (S/N). Cumulative distributions of S/N were determined for adaptive retransmission and diversity using random orientation and multipath propagation models. Distributions of S/N for systems with two antennas at the portable set and two appropriately polarized antennas at the Portable Radiotelephone Terminal (PORT) are similar to distributions for two branch selection diversity in the fixed-oriented mobile radio environment. Systems with one portable antenna and two PORT antennas have distributions with slopes similar to two branch mobile radio distributions but the distributions for the portables range from 3 to 7 dB worse.

Almost-periodic linear arrays

Abstract: A novel scheme is described here for the nonuniform placement of elements in a linear array. By leaving the constraints of the periodic-spacing domain and entering the larger domain of almost-periodic spacing, one is allowed additional degrees of freedom for optimizing the radiation characteristics of the array.

Vehicle-caused pattern distortion at 800 MHz

Abstract: The choice of mounting location and the antenna configuration used will effect system performance. The azimuth plane radiation patterns presented in this paper illustrate that it is possible to reduce the effects of the vehicle by choosing appropriate antennas. History has shown that the roof location gives the most omnidirectional coverage, but reality has shown that some customers, and to a lesser extent some vehicles just do not permit antennas and the associated transmission lines to be neatly installed in the roof. It's at this point that the alternatives must be understood and the patterns presented here are intended to further one's understanding.

Sidelobe reduction for phased array antennas using digital phase shifters. Part 1: One bit phase weighting

Abstract: A novel method for sidelobe reduction in phased array antennas is described, using equal-amplitude elements with randomised phase reversals to create an effective taper. Peak sidelobe levels of -18.8 dB for a 128 element array and -20.2 dB for 256 elements can be obtained with 9 and 27 phase reversed elements respectively. The associated gain reduction is between 1 and 2 dB. Statistical theory is used to explain the results.

A New Vor-Antenna in Slot-Technology

Abstract: The general necessity for an improved VOR-antenna is outlined and the related specifications are summarized The development and the design of a new VOR-antenna is described The basic theory and the resulting radiating elements are discussed and the hardware resulting, an array of staggered loop antennas and interlaced double slot radiators, is outlined Specific details are presented The achieved results and the measuring technique are described A vertical cross-polar-field-suppression of more than 20 dB and a bearing error < ± 1° have been achieved up to 60°-elevation without the need for a polarisation cage The cone of silence is reduced to ± 30°

VLF, LF and MF Antennas

Abstract: Since antenna dimensions and frequencies scale in inverse proportion, the antennas discussed are not unique to the lower frequency bands. In fact some of the results presented in this Chapter were measured at scale model frequencies on an antenna pattern range. The same antenna fundamentals apply at any frequency, but with a few important differences. At the higher frequencies, a quarter wavelength or a half-wavelength becomes a practical dimension, and at HF, VHF and UHF monopole antennas can be elevated, remote from the ground beneath. The radiation pattern for vertical elevation angles below the horizon must therefore be considered, and the 3 dB gain attributed to ground-based monopole antennas, because they radiate over a hemisphere rather than a sphere does not apply. Also, ground loss resistance does not scale directly with frequency. The emphasis in this Chapter is on vertical antennas, or antennas that radiate dominantly vertical polarization, for use at the lower frequencies, and therefore discussion about ground losses, radiation efficiency, etc. refer to this application.

Off-axis scanning of cylindrical lenses

Abstract: Two aspects of cylindrical lens antennas excited by off-axis transform feeds are explored. First, the properties of the subarrays formed by the feeds at various off-axis locations are investigated to evaluate their potential for forming sector coverage patterns. Secondly, the use of transform feeds is investigated for the purpose of providing multiple scanning beams with low sidelobes and high directivity. The basic equations are presented without derivation because the method of analysis for antennas of this type with on-axis feeds is well established. The contribution of this paper is to investigate how the pattern characteristics are modified by moving the feed-axis, along a prescribed curve.

A New Amplitude and Phase Control Concept for Microstrip Phased Array Antennas

Abstract: The design and performance of a receiving 8-element microstrip antenna array for X-band operation is discussed. A new phase and amplitude control concept using electronically tunable antenna loads is presented which has been employed in the design of a planar phased array antenna with integrated control network.

A circularly-polarized UHF array antenna with a broadband axial null

Abstract: The characteristics of an 8-element circular array antenna developed for possible application with a satellite crosslink communication system are described. The array elements are excited in rotating phase of the second mode ( e^{j2\phi} mode) to provide a conical-shape pattern with an axial (earth pointing) null. Theoretical and scale measurement results are presented.