A novel dual-fed, self-diplexing PIFA and RF front-end (PIN-DF2-PIFA)

The concept of using a dual-fed, self-diplexing PIFA with a highly optimized RF front-end has been analyzed. The feed structure is arranged to provide both diplexing action and impedance broadbanding in the best technology available in a mobile phone - the technology currently used to fabricate the antenna. The measured average total efficiency (including the effects of mismatch) of the design presented, including the antenna, diplexing and transmit/receive switching, is 81% at the GSM band and 72% at the DCS band. The return loss is particularly good in the transmit bands at less than -16 dB in the GSM band and -11 dB in the DCS band. This is expected to yield further efficiency improvements in the subsequent RF circuitry of a phone. Improved performance can be traded for either bandwidth or antenna size. The bandwidth can be approximately doubled using this technique (for a return loss of -6 dB) with a small loss of average efficiency. This loss of efficiency is more than recovered by the highly efficient diplexing action of the antenna in combination with the out-of-band impedance presented by SAW filters. Alternatively, the antenna may be reduced in size by a factor of approximately two.