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.