Contactless Wheeler cap concept for antenna radiation efficiency measurements

A new design for Wheeler cap is introduced that does not require contacts for the cavity cap to the ground plane. The concept is based on adding a flange of magnetic conductor that is parallel to the ground plane to suppress the waves from leaking out. The magnetic conductor is artificially realized using the electromagnetic bandgap (EBG) concept, which usually has a limited bandwidth. However, a cascaded design concept is used to widen the bandwidth beyond what is normally achievable. Since the cascading concept requires large flange size, a new compact EBG unit cell is designed and the bandwidth is limited to about 4:1. As such, the Wheeler cap becomes able to make measurements for wideband antennas and make it possible to use the same cap for varieties of antennas without the need for the cavity contact with the ground plane. Exact and simplified full wave models verify the proposed approach.