Bandwidth enhancement of internal WWAN antenna using an inductively coupled plate in the small‐size mobile phone

By adding a small inductively coupled plate of size 10 × 45 mm 2 to the system ground plane of the mobile phone with a short length of 60 mm only, wide lower and upper bands of its internal WWAN antenna (a printed monopole slot antenna in this study) to respectively cover the GSM850/900 and GSM1800/1900/UMTS bands can be obtained. The coupled plate is connected and vertically oriented to the system ground plane through a 10‐nH chip inductor, which effectively causes the small coupled plate to resonate at about 925 MHz. A new resonant mode contributed by the coupled plate is hence provided to enhance the bandwidth of the antenna's lower band, which is quickly decreased with decreasing ground plane length of the mobile phone. With the coupled plate added to the ground plane of length 60 mm, the obtained lower‐band bandwidth is about the same as that of the internal WWAN antenna for the ground plane of length 105 mm and without the coupled plate. Further, the antenna's upper band for the short ground plane of length 60 mm can still have wide bandwidth for both the cases with and without the coupled plate. Detailed effects of the inductively coupled plate on the bandwidth enhancement of the internal WWAN antenna are analyzed.