A shape-first, feed-next design approach for compact planar MIMO antennas

Employing characteristic mode theory (CMT), a shape-first feed-next design methodology for compact planar antennas is proposed, which facilitates rapid and systematic design of self-matched, multi-port antennas with optimal bandwidth and high isolation. First, the optimal antenna shape with multiple self-resonant modes is synthesized using a binary genetic algorithm. Then, the optimal feed positions that provide good input matching and high isolation between the excitation ports are specified using a virtual probe modeling technique. A two-port microstrip antenna with an electrical size of 0.45λ d × 0.297λ d is designed, fabricated and measured. The measured operating frequency is within 1% of the full wave simulation, and the overall S parameter characteristics and far field patterns agree well with the simulation result, validating our design methodology. Mutual coupling S 21 < −35 dB at the center frequency is achieved in this design.