COMPACT NEGATIVE-PERMITTIVITY MICROSTRIP PATCH ANTENNA FOR END-FIRE RADIATION

We propose a compact microstrip patch antenna that uses a negative permittivity substrate to achieve an end-fire radiation pattern. The antenna is designed to operate at X-band frequencies with a patch footprint of 0.9[lambda] x 0.05[lambda] and a thickness of [lambda]/20. We show that loading a narrow patch with a negative permittivity substrate introduces an effective shunt inductance that resonates with the strong fringing capacitance of the patch. At resonance, the electric field is vertically polarized and approximately uniform across the patch, producing transverse nulls that improve the directivity of the antenna. The negative permittivity substrate is implemented using a thin-wire effective medium with four vias spread across the patch. The antenna is matched to 50 [OMEGA] using a quarter-wavelength transformer. The fabricated antenna operates at 10.8 GHz with a peak return loss of 30 dB and a bidirectional directivity of 10.7dBi. The antenna has a 10-dB impedance bandwidth of 3.8% and radiates with a simulated efficiency of 93%.