High gain circular microstrip antennas using TM1m modes

High gain patch antennas are desirable for many applications. For patch antennas printed on common material substrate and operating in the fundamental mode, the gain is limited to a maximum of about 7.5dBi. High gain is achieved via array configurations or by superstrate loading. Array design involves complicated feed network, which introduces losses. Superstrates, which usually uses high dielectric constant material or more recently partially reflective surfaces (PRS), can be used for gain enhancement but at the cost of increased antenna height. Also, moderately high gain values limited to a maximum of 11–12dBi can be achieved via stacked patch configurations. Among the basic patch shapes, solid circular disc has been extensively studied in the past. Its low gain is inherently due to the fundamental mode (TM11) of operation. By operating the disc in higher zeros of order 1 mode i.e. TM1m modes, where m is the electric field variation along the radial direction, higher broadside gain is expected, due to increase in electrical size of the radiating patch. But, TM1m (m≠1) modes are avoided in literature, due to the high sidelobelevel in the E-plane of radiation patterns, which make them unfit for various applications. As m increases, the number of sidelobes increases and the main beam contracts.