15-05-2013, 03:53 PM
Experimental Two-Element Time-Modulated Direction Finding Array
Abstract
A two-element time-modulated array system is configured to
operate as a direction finding antenna. The signal from each element of the
array is time switched to provide a phase modulated output in which the
depth of modulation is dependent on the angle of arrival of the received
signal. Details of an experimental system designed to operate at 2400 MHz
are presented and the results are compared to theoretical predictions.
INTRODUCTION
Conventional radio direction finding (RDF) systems often use an
array of two or more antennas and use either phase-comparison or amplitude-
comparison of the received signals to determine direction of
arrival information [1]. In both of these techniques directional information
is derived by processing array data at the receive signal frequency.
In recent publications we proposed an alternative approach to
direction finding using the concept of a time-switched array [2], [3].
The time-switched array system uses simple signal processing techniques
to provide a directional main beam and pattern nulls at harmonic
frequencies.
SYSTEM DESCRIPTION
The time-switched array system is shown schematically in Fig. 1 and
consists of two antenna elements separated by a distance d. Each element
is assumed to exhibit an Omnidirectional radiation pattern in the
plane of the diagram. The output from each element is connected to
the array output via a switch in the feed line; the element switching
waveforms and switching period are also defined in Fig. 1. A complete
analysis of the system may be found in [2] but for the purpose of this
contribution we will assume that the elements are alternately switched
on and off with an equal mark-space ratio square wave switching .
CONCLUSION
Details of an experimental two element time-switched array system
have been presented. The signals to each element of the array are time
switched to provide a phase modulated output signal in which the depth
of modulation is dependent on the angle of arrival of the received signal.
The angular response of the array at the fundamental frequency of the
received signal exhibits a directional response at broadside, while the
response at the first harmonic of the switching frequency exhibits a
deep null. Measured results from the experimental system confirm the
basic operation of the system.