Low-Profile Magnetic Loop Monopole Antenna Based on a Square Substrate-Integrated Cavity

A low-profile monopole antenna with height below lambda(0)/16 is proposed. The antenna is based on a square substrate-integrated cavity radiating through apertures in its four side walls. This effectively creates a small square loop of magnetic currents, which radiates omnidirectionally as an electric monopole. The antenna cavity has a side length of less than lambda(0)/3 and thus resonates in the monomode region, in a fundamental TM11 mode. This means that the structure is robust in terms of feeding and manufacturing tolerances, as no parasitic modes can be excited. The designs of the cavity and the feed are introduced in detail. The measurement results from a manufactured prototype operating at 5.9 GHz show good agreement with simulations and validate the proposed approach.