The Excitation of Circular Polarization in Microwave Cavities

The usefulness of exciting a single circularly-polarized mode in a microwave cavity is indicated. A matrix method is presented then for the analysis of the operation of various components, such as transition pieces and differential phase shifters on waves propagating in waveguides with two degenerate orthogonal modes. This method is applied to describe three distinct systems for generating the desired circular polarization in a cavity that is coupled directly to the side wall of a waveguide. The final system, which involves a minimum of critical adjustments, is described in more detail, and its performance is indicated. It is shown that purely circular radiation can be set up along the axis of the cavity. However, the largest preponderance of one rotating mode over the other which can be set up, if one averages over the entire cavity volume, is 11.5 to 1. This value is obtained with the TE11n modes.