Analysis of microstrip circular patch antennas

An analysis of the circular microstrip disc antenna is presented which uses an orthogonal mode representation of the current distribution on the disc. The convergence of the analysis with number of modes is considered and the accuracy of resonant frequency calculations estimated as ¿¿ 1%for 40 modes. Good agreement with experimental results is obtained for resonant frequency and bandwidth calcualtions. The results are compared with those of previous approximate analyses, and the range of antenna parameters for which the approximate results are useful identified. Examples of current distributions and radiation polar diagrams are given. The influence of surface waves is considered, and it is concluded that they may limit the upper frequency at which the substrated may be used. For an ¿¿r of 2.32, this is estimated as being 21 GHz/substrate height (mm).