Very‐small‐size folded loop antenna with a band‐stop matching circuit for WWAN operation in the mobile phone

A folded loop antenna with a band‐stop matching circuit for wireless wide area network (WWAN) operation in the mobile phone is presented. The folded loop antenna alone occupies a very small volume of 0.6 cm 3 only, yet it can generate a lower band covering GSM850 operation and an upper band covering GSM1800/1900/UMTS operation. By incorporating a band‐stop matching circuit with a central frequency at about 1.05 GHz and a 3‐dB band‐stop bandwidth of less than 200 MHz, the antenna's lower band can have a dual‐resonance behavior, hence resulting in a much widened operating band capable of covering GSM850/900 operation. In addition, such a band‐stop matching circuit shows very small effects on the antenna's upper band. This property makes it easy for the antenna to cover GSM850/900/1800/1900/UMTS penta‐band operation. Design considerations and experimental results of the very‐small‐size folded loop antenna with the band‐stop matching circuit are presented.