Design of a Portable DF System with Simple and Compact Structure Operating at 875 Mhz GSM Band

Abstract

This paper reports a portable GSM direction finding system operating at 875 MHz frequency band with simple and compact structure. In the system, array of receiver antennas are placed together with other RF components including amplifiers, power dividers, phase comparators, an analog to digital converter and a processor unit. With help of the developed algorithm phase comparison between the receiver antenna channels is obtained and angle estimation is done. The developed algorithm was first run on a constructed system test setup that involves a digital oscilloscope connected to the receiver antennas in a laboratory environment. Later, the digital oscilloscope in the test setup was replaced with the RF components mentioned above such that a portable receiver system with compact structure was obtained. Direction finding experiments were repeated with the designed portable receiver system in the laboratory and in open space. Results show that with the designed system angle of a transmitter is found very accurately such that the maximum angle error between the estimated and the exact angle values of the transmitter antenna was found to be equal to 3.5° in the open space experiments for the transmitter antenna positioned at an angle between -60° and 60° on the horizontal plane same with the receiver antennas. Also, it is observed that the difference between the estimated and the exact angle values has an increasing trend with the exact angle absolute value. The findings indicate that the designed portable direction finding system is promising to be used for applications requiring accurate angle estimation of GSM signals.