Investigations of SIW Leaky-Wave Antenna for Endfire-Radiation With Narrow Beam and Sidelobe Suppression

A new substrate integrated waveguide (SIW) leaky-wave antenna is investigated for endfire-radiation with a narrow beam and sidelobe suppression. Maximum directivity conditions for endfire-radiation from line sources with different amplitude distributions are theoretically discussed as a design aid. Interestingly, for endfire beams it is seen that designs that have a lower sidelobe level can also have a higher directivity, contrary to what is normally encountered for broadside beams. An SIW leaky-wave antenna with tapered transverse slots on only the top and bottom planes is presented. Compared with a previous leaky-wave antenna having uniform transverse slots on the top plane, the presented leaky-wave antenna has a main beam that can radiate exactly at endfire and also has a lower sidelobe level. The design of the low sidelobe antenna is based on the leaky mode, which loses physical significance as the beam is scanned to the endfire direction. Nevertheless, the antenna retains a good beam shape and a low sidelobe level when it radiates at endfire. A prototype is made, and measured results are consistent with theoretical and simulated results.