Broad-Band Matching of Antennas using Dual-Mode Radiators

This paper describes a new method for increasing the bandwidth of microwave antennas. This is achieved by recognizing that microstrip patch antennas may support two orthogonal resonant modes, or polarizations. These resonant modes may be modelled by a simple filter network, consisting of two coupled resonators, which represents the input impedance of such a dual-mode antenna. A novel and simple method of maximizing the bandwidth of the input reflection coefficient of a dual-mode antenna, by suitable choice of resonator couplings is presented. This method provides a theoretical bandwidth improvement of more than 300% when compared with a single mode antenna. The result is experimentally confirmed. From a practical point of view the method could have useful application in the design of antennas for mobile phones.