Extended analysis of closed-ring microstrip antenna

An extended analysis for the radiation characteristics of a closed-ring microstrip antenna is presented. The general closed form expression for the total energy stored is derived by utilising the properties of the cylindrical functions. Known closed form expressions for its radiation field based on the cavity model are also used to derive general expressions for the radiated power in a converging series form, by utilising the properties of the Gauss´ hypergeometric function and by using Euler´s transformation. The expressions are used to set the relation between efficiency and bandwidth, taking into account ohmic and dielectric losses. It is shown that different structures can have the same performance at the critical frequency. At the higher frequencies, narrower ring structures can have small Q-factors, high gain and large bandwidth. This is opposite to the behaviour of the structures at low frequencies.