Showing papers on "Conformal antenna published in 1983"

Antenna Diversity Performance in Mitigating the Effects of Portable Radiotelephone Orientation and Multipath Propagation

Abstract: Antenna diversity can mitigate signal impairments caused by random angular orientation and multipath radio propagation when using portable radiotelephones. Cumulative distributions of signal-to-noise ratio ( S/N ) were determined for antenna diversity using realistic orientation and multipath propagation models. In a random orientation and multipath propagation environment with -6 dB average crosspolarization coupling, two-branch selection diversity with two perpendicular antennas yields an S/N distribution with the same slope as two-branch selection diversity in the fixed-oriented mobile radio environment. The distribution for random orientation is about 4.5 dB worse, however, than the mobile radio distribution.

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.

A coma-corrected multibeam shaped lens antenna, part II: Experiments

Abstract: A dielectric lens based on the shaping technique described in Part I of this communication was fabricated and tested. This lens was shaped to control the sidelobes and zoned for improved scanning characteristics. Basic antenna measurements were conducted and excellent performance results have been observed. In the prototype lens system with unmatched surfaces, a 4 dB crossover between adjacent beams of -30 dB sidelobes was obtained. The beam was scanned up to \pm 12\deg without significant coma degradations. This coma-corrected zoned lens was developed for satellite multibeam applications. The multibeam antenna so designed not only reduces the total costs and the payload burden, but also enhances the system reliability and the overall gain compared to a conventional design because no complex feed network is required.

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.

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.

Self-Cohering an Airborne e Radio Camera

Abstract: By distributing antenna elements or small subarrays throughout the skin of an aircraft, a large portion of the airframe can act as an electromagnetic transducer. The basic problem associated with such a design is that uncertainties in element locations due to the nonrigidness of the airframe induce phase errors. Self-cohering techniques are required to compensate for those errors. Four such techniques are presented here.

Adaptive antenna design considerations for satellite communication antennas

Abstract: Satellite communication systems must often be designed to operate in the presence of interfering signal sources. Conventionally, bandspreading via signal modulation is often used to combat such unwanted interference. Recently, interest has been focused on supplementing the conventional interference reduction achieved via bandspreading by using antenna radiation pattern shaping achievable with adaptive nulling antennas. Because of the well defined field of view of the earth seen by a satellite at geosynchronous altitude (i.e. a ± 9° cone angle) and the relatively `clean' multipath environment seen by the high-gain `earth-looking' antennas which must be used (as compared with low-gain adaptive antennas on aircraft, or antennas located in a terrestrial environment), it is possible to determine several useful trends unique to this class of adaptive antenna systems. The paper addresses the general considerations inherent in choosing the fundamental antenna and adaptive processor design parameters relative to geosynchronous satellite adaptive systems. The following topics are developed in detail: (a) Choice of antenna types: Phased array against the multiple beam antenna (b) Nulling resolution: Minimum tolerable separation between interference and signal (user) sources (c) Nulling bandwidth: Frequency-independent weighting against frequency-dependent weighting (for example tapped delay lines) (d) Factors affecting the performance of adaptive antenna systems: Channel tracking errors, weighting circuit imperfections etc.

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.

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°

Control of large space antennas

Abstract: The NASA large space antenna missions, the performance requirements, and the resulting control technology requirements are summarized.

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.

Shape determination/identification for large space antennas

Abstract: An integrated hardware/software system, SHADES, for shape determination and identification; a three dimensional multipoint sensor; multipoint sensor data; batch processing; and scanning algorithms are discussed.

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.