Gain enhancement of microwave antennas by dielectric-filled radomes

Structural constraints can require that the space within a radome can be filled with a rigid lightweight material, and the question arises as to whether the presence of this material can improve, rather than impair, the performance of the associated microwave antenna. Using a simplified model based on rectangular geometry, it is shown that a slab of material having an appropriate relative permittivity can increase the antenna gain by 3¿7 dB for typical cases. Computations carried out using modal methods indicate that there is a pronounced periodic gain variation with slab length; this is confirmed by experiment for both planes of polarisation. The practical implementation of the enhancement technique is discussed and illustrated by typical airborne radar applications. Loss effects in the dielectric material are shown to be negligible and some simplified design data relevant to linear arrays are compiled in an Appendix.