Radiation Pattern Analysis of Aircraft Mounted GPS Antennas and Verification Through Scale Model Testing

Abstract

This paper presents results of scale model measurements and electromagnetic simulations to determine the gain, polarization characteristics and antenna patterns of aircraft mounted GPS antennas. Of particular interest is the antenna gain and polarization at negative elevation angles between -30° and -90° to evaluate pulsed in-band Radio Frequency Interference (RFI) in the L5-Band caused by DME, TACAN, JTIDS/MIDS and ATC systems radiating in the ARNS Band. Patterns in the L1-Band have also been investigated to help in assessing RFI in this frequency band. The scale model measurements were made on a 1/10 scale model of a Beechcraft 1900 C aircraft. The measured scale model results were then used to verify the accuracy of the NEWAIR computer code developed by Ohio State University for predicting the airborne antenna patterns. There is excellent agreement between the measurements and simulations using the NEWAIR code for antenna patterns at two different antenna locations on the Beechcraft 1900 C aircraft. The NEWAIR code was also used for computing the radiation pattern of a GPS antenna on a Boeing 737. The results obtained from these investigations indicate that a maximum gain value of -10 dBi with vertical polarization should be used at the negative elevation angles between -30° and -90° for estimation of RFI in the L5 frequency band.