A mechanism to electrically enlarge the ground plane of handset antennas: A bandwidth enhancement technique

There is a need of developing new techniques for enhancing the bandwidth of handset antennas without increasing the antenna volume in order to incorporate more frequency bands into the cell phones. The technique to enhance the bandwidth proposed herein consists in adding a conductive strip connected to the ground plane at the opposite edge of the handset antenna location. Conductive strip tunes the ground plane mode to effectively improve the bandwidth at the low frequency region (∼900 MHz) while keeping the same antenna volume. An electrical model is used to give an insight into the behavior concluding that the conductive strip is a useful mechanism to improve the bandwidth. The model demonstrates that the length of the conductive strip can be reduced by inductive or dielectric loading, as well as by reducing its height. Simulations and measurements show how the conductive strip excites the resonance of the ground plane mode improving the bandwidth and validating the electrical model predictions. The proposed technique is applied to a dual-band (900-1800 MHz) planar inverted F-antenna providing a measured bandwidth enhancement of 1.6 times when using the strip at the low frequency region while keeping the same performance at the high frequency region (∼1800 MHz).