Novel compact harmonic-suppressed planar-fed microstrip antenna

Two novel designs for a planar-fed compact microstrip antenna are presented and discussed. With the proper selection of inserted slits, together with slot loading of the correct dimensions and positions, reduced size operation can be achieved whilst also maintaining an input impedance of 50 Ω which facilitates the use of a direct 50 Ω microstrip-line feed without an external matching network. The design technique and measured results for two configurations are shown, in which it is demonstrated that a size reduction of up to 40% can be achieved. The measured radiation pattern achieves low cross polarisation levels of below -20 dB for one configuration. This compact antenna is also capable of suppressing 2^nd and 3^rd order harmonics.