Enhancing the Pattern Roundness for Handset Antennas using Reactive Loads

In this paper, an efficient and systematic design method for enhancing the pattern roundness of the handset antenna is proposed, providing more reliable links for terminal communications. Based on the platform of the handset antenna, an N-port network is constructed on the top part of the handset using discrete ports. Full-wave simulations are then carried out to obtain the impedance matrix and the single-port-excited patterns. Based on the impedance matrix, pattern synthesis is formulated as a multi-objective optimization problem and solved using the algorithm of NSGA-II. A WLAN antenna on the metallic-frame based handset is designed, with remarkable improvement in pattern roundness using only two lumped components. Specifically, the in-band gain of the proposed antenna is reduced by about 1.5 dB compared with the reference monopole antenna. More importantly, the original deep nulls are reduced, improving the SNR at many directions. The optimized handset antenna was fabricated and measured, with the measured results agreeing well with the simulated ones.