Spurious radiation from microstrip

The method of an earlier paper is applied to calculate the disturbances due to a number of discontinuities encountered in typical antenna feed and network structures, such as impedance changes, power dividers, T-junctions, open and short circuits etc., and these are compared for relative radiation. Error estimates due to some secondary effects are calculated and shown to be generally negligible. The process of radiation from an open circuit is studied in detail and it is shown that, although most of the radiation comes from the tip, a substantial amount is radiated and also absorbed to. about a free-space wavelength behind the discontinuity. A method analogous to the induced e.m.f. method is formulated and shown to confirm existing results for radiated power. A distinction is made between the phase centre for radiation, which is usually located at a discontinuity, and the source region for radiation. The two are not coincident and the latter may be quite extensive for microstrip radiations. The results are applied to show how the disturbances can affect the performance of a comb antenna and how they can also be utilised to enhance the efficiency of a strip-end radiator on a thin substrate.