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IEEE Transactions on Antennas and Propagation
Volume 48 Number 8, August 2000

Table of Contents for this issue

Complete paper in PDF format

A Two-Element Antenna for Null Suppression in Multipath Environments

William F. Young, Benjamin Belzer, Member, IEEE and Robert G. Olsen Fellow, IEEE

Page 1161.

Abstract:

The design of a two-element antenna for portable transceivers is considered. The antenna consists of a dipole terminated with a parallel loop-capacitor combination. The antenna has a single feed at a point on the loop opposite the junction and does not require external combining circuitry. The capacitor creates a phase shift between the dipole and loop currents,thereby greatly reducing the probability of deep nulls in the received signal when the antenna is deployed in free-space or in the vicinity of a fixed reflector,where standing wave patterns occur. Theoretical and simulation studies based on multiple incident/reflected plane wave fields typical of multipath environments are used to quantify the reduction in null probability. Simulation results are presented for three antenna types: a dipole antenna, a loop-dipole antenna without a capacitor, and the loop-dipole antenna with capacitor. The results are verified by field measurements on an automated outdoor test range, where the incidence angle and distance from the reflector are varied. With a single incident plane wave, the loop-dipole-capacitor (LDC) design reduces the probability of deep nulls in the received signal by up to two orders of magnitude at low signal-to-noise ratios (SNRs) when compared with the standard dipole antenna and the loop-dipole antenna without the capacitor. The performance advantage of the new design decreases as the number of incident waves increases; however,it performs at least as well as the dipole antenna in all cases studied.

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