Abstract
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.
Highlights
Handset users increasingly demand smaller and lighter devices, coupled with long battery life
We show that the wire extensions compare with a performance improvement when the ground plane is physically extended and this is shown through the near-field EM field intensity scans in the HAC plane
We accomplish the more desirable solution by electrically extending the length of the ground plane using wires that are placed outside the surface of the ground plane
Summary
Handset users increasingly demand smaller and lighter devices, coupled with long battery life. 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. Previous efforts [5, 9, 10] have consistently demonstrated that the optimal dimensions of the ground plane, for achieving the best antenna performance, are those that enable resonance. This has significant consequences for low frequencies, including the 800 MHz and 900 MHZ GSM bands and the proposed 700 MHz band for LTE in the USA.
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