The analysis of balanced feed antenna structures for use in integrated antenna-transceivers

For software defined radio and, indeed, any ultrawide band communications system, it is essential that good control of the antenna's pattern characteristics (coverage and polarisation) is maintained over the entire frequency of operation (possibly several GHz). In this paper, the radiation properties of a number of two-port antenna configurations are compared with their single-feed counterparts. A wire dipole, wire loop and a planar antenna (essentially an air-dielectric patch antenna) are all analysed. All three types could easily be fabricated in a printed circuit form and integrated with the front-end wireless circuitry. Full far-field radiation patterns have been measured at several frequencies over the range 1750 - 3500 MHz, and antenna directivity and cross-polarisation levels determined. For all the dual-feed arrangements considered, the maximum co-polar levels were always greater than 12 dB above the maximum cross-polar levels, and the power in the total co-polarisation was always greater than 90.4% of the total power radiated. The results show that, in all cases, the radiation performance of the single-feed arrangements varied considerably with frequency, while the dual-feed arrangements guarantee pattern integrity and low levels of cross-polarisation over the whole range considered.