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An elsewhere in the world of antenna technology.

The theory associated with DBF's ability to manipulate the appearance and response of an antenna pattern seems almost mystical, but progress is being made in translating the theory into practice. Several DBF applications and hardware advances in several adjunct fields deserve special recognition.

Andrew SciComm (Garland, TX) has developed various beamforming technologies for both military and commercial applications. An HF Digitally Adaptive Beamforming subsystem is a case in point. This M antenna system is able to null up to M-1 undesired (jamming) signals and form a beam directed at a desired signal location. The typical system consists of four to as many as eight antennas. Current activity is aimed at improving the required algorithms and transitioning to a VXI form factor. VHF and UHF versions of the system are under consideration.

Scientists at Roke Manor (Romsey, Hampshire, England), the research arm of Siemens Plessey, have been involved in advanced antenna beamforming since the early 1970s. Digitally adaptive beamforming has been applied to the Multifunction Electronically Scanned Adaptive Radar (MESAR) developed in conjunction with the UK Defence Research Agency. The MESAR consists of some 1,000 S-band active phased-array elements. While standard phase shifters provide electronically controlled beam steering, each output is then combined into one of 16 subarrays for adaptive beamforming. Each subarray feeds its own receiver channel for conversion to digital I and Q basebands. The 16 I/Q channels are adaptively beamformed using complex weight multipliers to provide protection against up to 15 sidelobe or mainbeam jammers.

Siemens Plessey has also entered into a strategic alliance with the Watkins-Johnson Co. (Palo Alto, CA) to interface advanced communications digital receiver technology into Roke Manor adaptive array processing and DBF algorithms. In this HF communications application, super-resolution DF processing provides improved readability in the direction of signal interest, while nulling other unwanted co-channel signals.

The ability to generate numerous antenna beams in arbitrary directions poses a challenge to measurement instrumentation. Antenna patterns are generally measured with instrumentation receivers that measure the response of the antenna as a function of angle off boresight. Conventional antenna pattern receivers perform a few thousand measurements per sec. For an antenna system capable of synthesizing hundreds of thousands of different patterns, however, the measurement time per pattern must be greatly reduced. To fill this need, the Aeroflex Lintek Corp. (Powell, OH) has produced the elan antenna-measurement system. The elan system is capable of collecting four million samples/sec at frequencies from 100 MHz to 100 GHz. This increased measurement speed not only reduces test time but in some cases can lead to new insights, such as a study of the time-varying response of an adaptive DBF antenna as its pattern evolves.

A portable kit of antennas intended for cellular telephone applications in the Nordic 450, AMPS and TACS bands has been introduced by Electro-Metrics (Johnstown, NY). Consisting of directional Yagis and omnidirectional antennas covering the 430- to 470-MHz and 824- to 960-MHz range, along with required preamplifiers, switch, filters and cables, the kit allows antennas to be assembled in the field without tools.
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Author:Herskovitz, Don
Publication:Journal of Electronic Defense
Date:Jul 1, 1996
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