Low-impedance transmitter antenna for multi-antenna WCDMA handsets

The possibility of building compact, low-ohmic antennas suitable for mobile handsets is investigated. An F-antenna is built with a self-impedance of 10 Ω instead of the commonly used 50 Ω. Low impedance is chosen to minimize voltages in circuits prior to the antenna, in this case an adaptive matching network designed in CMOS or a similar process. To optimize this adaptive matching network, the antenna structure is two-fold: one antenna for transmission and one for reception. A resulting benefit is increased isolation between transmitter and receiver, as shown for a typical case. The 10 Ω antenna has an average efficiency of over 70% and an omnidirectional pattern; isolation increases by distance and reaches about 10dB at 4 cm.