Surface wave control using nonperiodic parasitic strips in printed antennas

A scheme for controlling the surface wave behaviour on printed planar antennas is presented. The approach is to add conducting strips both on top and, if necessary, the bottom of the substrate. The scheme is applied to a rectangular microstrip antenna with electrically thick (~0.1λ_d) substrate. An optimisation algorithm is employed to design the strip parameters in order to obtain the best performance of the antenna, namely, low side and back lobe levels and a main beam without ripples. The optimal design is then fabricated and tested. Measured results are presented to assess the validity of the proposed scheme