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 /spl Omega/ instead of the commonly used 50 /spl Omega/. 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 /spl Omega/ antenna has an average efficiency of over 70% and an omnidirectional pattern; isolation increases by distance and reaches about 10dB at 4 cm.