Improved Handset Antenna Performance via an Electrically Extended Ground Plane

A novel and practical approach is presented providing improved antenna performance without enlarging the antenna or the ground plane. The approach electrically extends the ground plane using wire(s) that behave as surface metal extensions of the ground plane. The wire extensions can be accommodated within typical handset housing or as part of the stylish metal used on the handset’s exterior perimeter; hence don’t require enlargement of the device. Consequently, this approach avoids the costs and limitations traditionally associated with physically lengthening of a ground plane. Eight variations are presented and compared with baseline antenna performance. Both far-field patterns and near-field electromagnetic scans demonstrate that the proposed approach controls the electrical length of the ground plane and hence its chassis wavemodes, without negatively impacting the characteristics of the antenna. Improvements in performance of up to 56% in bandwidth at 900？MHz and up to 12% in efficiency with a reduction of up to 12% in the specific absorption rate (SAR) are achieved. An 8% increase in efficiency with a 1.3% improvement in bandwidth and a 20% reduction in SAR is achieved at 1880？MHz. Thus, improvements in bandwidth are achieved without compromising efficiency. Further, improvements at lower frequencies do not compromise performance at higher frequencies. 1. Introduction Handset users increasingly demand smaller and lighter devices, coupled with long battery life. Unfortunately, compactness, which results in slim and shortened device form factors, is often achieved at the cost of degraded antenna performance. This undesirable tradeoff has inspired numerous research efforts to find a more attractive balance between providing conveniently small and stylish handset dimensions while preserving acceptable antenna performance. In this effort, the influence of the mobile-phone-environment-related parameters, such as chassis (ground plane) size and the antenna position on the ground plane, have been thoroughly investigated, see for example [1–8]. It is known that the total radiation bandwidth of the mobile device is defined by both antenna properties and the chassis physical dimensions [1]. In [5], the authors show that if the chassis is resonant at the antenna-operating frequency, the bandwidth will increase significantly. A more detailed analysis in [1] demonstrated the chassis effects on both specific absorption rate (SAR) and radiation efficiency. It was demonstrated that the resonance of the chassis leads to an increase in SAR and a decrease in radiation