Compact Active Multiband Cellular Antenna for Mobile Handsets

Abstract

A small active controllable cellular antenna for mobile phones has been designed and evaluated. With a switch on top of the radiator different frequency bands can be chosen. The antenna is based on a dual band IFA design but number of bands are increased to four. Two different radiator branches can be activated by the switch which results in a frequency shift. In one state the antenna covers the GSM 850 MHz and 1800 MHz bands and in the other state the GSM 900 MHz and 1900 MHz bands are covered. This means the antenna size is same as a dual band antenna but it covers four frequency bands. Size is 38times7times1 mm. Adding active circuits to an antenna to achieve frequency control normally results in high losses and low gain antenna. With this solution the performance remains and radiation efficiency (gain) is very high and similar to a passive antenna