Characterizing the Effects of Mutual Coupling on the Performance of a Miniaturized GPS Adaptive Antenna Array

This paper describes the design of a compact, M-code capable, four element GPS adaptive antenna arrays made from stacked patch microstrip antenna elements. Possible applications for these antenna arrays are in military airborne platforms where the space available for installing antennas is very limited. To meet future GPS M code requirements, the antenna elements were designed for a bandwidth of 24 MHz. The size of the entire array assembly including the metal ground plane on which it is mounted is 4.625"; the size of the array itself is even smaller—only 3.5" square. The array also has a low profile with a height of just 1.2" including the radome cover. The size of the microstrip antenna elements has been reduced in size to fit within this aperture by using high dielectric constant substrate materials. The technical challenge in the design was to reconcile conflicting requirements imposed by the small antenna size and the wider 24 MHz bandwidth demanded by the M-code. Each element in the array fed by a self-diplexing feed consisting of coaxial probes connected to surface mount quadrature hybrids for circular polarization. Satisfactory M—code performance of the antenna array has been demonstrated by measuring the signal fidelity of the correlation peak using an M-code transmitter, down-converter and receiver built at MITRE. The results of mutual coupling measurements on this circularly polarized array are described with their impact on array design. The antenna patterns and other pertinent performance characteristics of this array are being measured. These results will be described in a future paper.