A high directivity broadband aperture coupled patch antenna using a metamaterial based superstrate

This paper describes an antenna design for wideband high directivity operation using an aperture coupled patch antenna as the feeding source and an FSS (frequency selective surface) based structure as the superstrate for high directivity. The new antenna device combines the wideband characteristic of the aperture coupled antenna and the desirable characteristics of the FSS structure as a superstrate for high performance operation. A coplanar waveguide (CPW) feed design is used to obtain wideband performance for the feeding antenna. Both single layer and double layer based FSS designs are studied for improvement of directivity. The performance is further enhanced by using an air gap between the patch on a thin film substrate and the CPW and aperture structures on an FR4 substrate and also between the layers of a double layer FSS design. The air gaps can be produced using micromachined PMMA rims for low cost construction. An impedance bandwidth in excess of 50% has been obtained for a centre frequency of 10 GHz. The antenna device exhibits a directivity of about 13.6 dBi. A 1-dBi ripple radiation bandwidth as high as ~42% has been achieved.