New considerations in the design of low-cost probe-fed truncated corner microstrip antennas for GPS applications

Antennas produce circularly polarized waves when two orthogonal field components with equal amplitude but in phase quadrature are radiated. Probe-fed microstrip patches, classified as resonator-type antennas, are able of satisfying these requirements [1]. Nowadays, design procedure for truncated corner square patches and also for the almost square radiators is available in the literature, for instance in [2, 3]. Following this procedure, antennas with excellent axial-ratio (AR) in the operating frequency can be synthesized. Unfortunately, their input impedances are inherently inductive, mainly if thick substrates are used. A useful method of compensating for the inductance is to etch a capacitive gap on the patch, concentric (or not) with the feed probe [4, 5]. In this paper, instead of applying this standard method, a new approach is used to design truncated corner patches, printed on thick substrates. The purpose is to get the best axial-ratio and return loss at the same frequency.