Multi-band matching technique for microstrip patch antenna transceivers

A new method of multi-band matching for circular microstrip patch antennas is presented. The input impedance of circular patch antennas can be represented as a second order ladder network of coupled resonators where each resonator is coupled to a load resistor. Using analysis based on microwave filter theory, the antenna can also be used as a dual-band antenna exploiting the fact that structures such as circular, square or triangular microstrip patch antennas can support two orthogonal resonant modes. A theoretical method of incorporating an external matching network with the dual-mode polarisation property of a microstrip patch antenna network is presented. This enables an antenna fed by two ports to be matched at four distinct frequencies, and achieve good isolation between the two feeding ports. This is the first time where the dual-mode polarisation property of circular microstrip patch antennas is successfully utilized with a matching network to maximise the performance of single layer microstrip patch antennas. The simulation results are confirmed with an experimental quad-band circular microstrip patch antenna realisation.