A High‐Efficiency L‐Band Planar Array Antenna Using a Shielded Suspended Stripline Feed Network on a Lossy FR‐4 Substrate

ABSTRACT

This paper presents a high‐efficiency L‐band planar array antenna employing a shielded suspended stripline feed network on a conventional FR‐4 substrate. Although achieving high efficiency on FR‐4 is generally challenging because of its relatively high dielectric loss tangent, the proposed feed network mitigates substrate loss by realising quasi‐air propagation characteristics with an effective permittivity close to unity. The antenna consists of a 6 × 6 planar array of cross‐slot‐coupled corner‐truncated patch elements for left‐hand circular polarisation (LHCP), and a sequential rotation feeding scheme based on four quarter subarrays with 90° phase offsets is adopted to improve the axial ratio at the array level. The fabricated antenna uses a 0.2‐mm‐thick FR‐4 PCB integrated with upper and lower metallic shielding enclosures. Experimental results show a measured peak gain of 23.25 dBi and a system‐level antenna efficiency exceeding 84% over the operating band from 1.52 to 1.675 GHz, with a boresight axial ratio below 1.51 dB across the entire band. These results confirm that high‐efficiency planar array antennas can be realised on a lossy FR‐4 substrate, making the proposed design a promising candidate for L‐band satellite ground terminal applications.