An accurate technique for measuring the on-axis axial ratio of circularly polarized feed systems

A method for swept-frequency measurement of the on-axis axial ratio of circularly polarized feed systems is described. The method is suitable for measuring the resultant axial ratio of a feed plus horn assembly. The performance of the feed (diplexer) alone may also be measured by using a simple terminating horn designed for very low reflection coefficient. A comparison with established techniques shows advantages for the new method, either in simplicity or accuracy. The precautions necessary to achieve the high degree of accuracy obtainable are also considered.