Multi-frequency and wide-band VSWR characteristics of loop antennas

Typically, loop antennas are constructed from a single wire and have a round or square shape. Antennas with more than two loops located in the same plane have been investigated, but a more detailed investigation of such multi-loop (ML) antennas is required for design purposes. This paper presents a theoretical investigation of two types of loop antenna and reveal their radiation characteristics. First, an antenna composed of discrete N loops is investigated. This kind of antenna is designated as a discrete ML antenna. The discrete ML antenna is excited using proximity coupling from an inverted L-shaped wire. The frequency response of the VSWR is calculated and the number of minima is discussed. Second, the investigation is directed toward a modified ML antenna in which the corners of the N loops are connected by wires. It is revealed that the modified ML antenna has a wideband VSWR frequency response, unlike the discrete ML antenna.