Recent works have shown that the size reduction of printed dipole antennas was possible thanks to a proper shaping of the radiating element. Following the same idea (choice of suitable shape), a shortened slot fed patch antenna exhibiting two step discontinuities, is described, analysed and optimized with a simple transmission line model. The shortening ratio (ρ) can reach 80% for matched antenna, printed on a substrate with a low dielectric constant (εr=2.2). The calculated results of input impedance are validated by experiment.

A cavity model well suited for computed-aided design is developed to synthesize the dimensions of patches for a given resonant frequency, an input resistance and a substrate. The antennas which have been investigated are rectangular patches fed with either a microstripline or a coaxial probe.