Single-Layer and Wideband Filtering Antenna With Small Footprint Based on Nonuniform Grid Array

A single-layer and wideband antenna with a small footprint and a good filtering response is developed based on the nonuniform grid array. First, the advantages of the conventional grid array antenna (GAA) in terms of miniaturization and closer multiresonances are demonstrated through comparison with a conventional microstrip patch antenna (MPA). Then, based on the analysis of these resonances in GAA, two evolution processes are implemented to improve the performance. On the one hand, the grid units are adjusted, i.e., the GAA turns into a nonuniform GAA (NUGAA). On the other hand, a coplanar L-probe and two pairs of short slots are integrated into the NUGAA. The former evolution makes the three resonance modes in GAA aligned, and thus the bandwidth is extended; meanwhile, this step introduces the radiation null (RN) at the lower operational band edge. The latter evolution generates the RN at the upper operational band-edge, which, together with the lower RN, leads to a skirt selectivity and preferable out-of-band rejection level; meanwhile, this step modifies the resonant mode in the higher band, and ensures a broadside radiation pattern with a consistent polarization. Finally, the optimized NUGAA with a compact size of $0.45\times 0.28\times 0.055\lambda _{0}<^>{3}$ is fabricated and measured, demonstrating excellent agreement with the simulation results. The proposed design achieves a bandwidth of 3.08-3.71 GHz (18.8%) with more than 21.5 dB out-of-band suppression level. Moreover, the bandwidth-to-volume ratio (BVR) reaches $0.027\times 10<^>{3}$ / $\lambda _{0}<^>{3}$ .