Grating Lobe Mitigation in Series-Fed Patch Periodic Leaky-Wave Antenna Using Parasitic Monopoles

It is shown that the grating lobes issue of periodic leaky-wave antennas (P-LWAs) can be mitigated using parasitic monopoles placed between the antenna's unit cells. Due to the periodicity nature of P-LWAs, infinite number of space harmonics are excited, but only one space harmonic should radiate to achieve single-beam radiation. As the beam scans to the forward direction, a second space harmonic starts to radiate creating a double beam, a main beam and a grating lobe in opposite directions. Here, we present a simple and low-cost technique to overcome the grating-lobe issue in series-fed patch (SFP) P-LWA by inserting parasitic monopoles at each unit cell to reduce its radiation in the grating lobe direction, while maintaining the main beam. Moreover, the concept of parasitic monopoles and their effect on the radiation pattern of the unit cell is addressed and later validated by full-wave simulation and measurement results for an SFP P-LWA broadside frequency at 6.1 GHz. The results show that the grating lobes are reduced by about 10 dB and therefore, the scanning range is extended in the forward direction from 15 degrees for the conventional SFP P-LWA to 29 degrees for the proposed SFP P-LWA with parasitic monopoles.