Antenna matching for bandwidth enhancement

A matching technique which simultaneously fulfills 2 tasks, matching and enhancement of the operation frequency band, is presented in this paper. As an example, matching for a 5-band mobile phone (GSM 850, GSM 900, GSM 1800, GSM 1900 and WCDMA 2100) has been examined. Two very simple inverted-L antennas with input impedances in range of 2 - j10 to 10 + j20 Ohms with two matching circuits are used to provide a 50 Ohm matching for all bands. LowBand: GSM 850 + GSM 900. HighBand: GSM 1800 + GSM 1900 + WCDMA 2100. The target for return loss was selected 3.5 VSWR. The rejection of LowBand at HighBand -and vice versa -is better than 25 dB, so no further diplexing would be needed in the front end. The size of one matching component is 1.6 times1.8 times 1.2 mm³. The overall antenna efficiency (at 50 Ohm terminal) is 52-60% min at LowBand and 65-70% at HighBand.