A Shared-Aperture Decoupling Network (SADN) for Dual-Band Differentially-Fed Antenna (DFA) Array

This paper proposes a dual-band shared-aperture decoupling network (SADN) to suppress mutual coupling in a dual-band antenna array. The array consists of two high-band (HB) patches and two low-band (LB) patches, all fed differentially. The SADN addresses both in-band coupling between the two HB antennas and between the two LB antennas, as well as cross-band coupling between the LB and HB antennas. The SADN can adapt to multi-band DFA arrays with different frequency ratios. To validate the design principle, a dual-band DFA array operating at 18.5 GHz and 28 GHz with a frequency ratio of 1:1.51 was designed, fabricated, and tested. The fractional bandwidths of the two bands are 6.0% and 10.1%, respectively. Within both bands, the isolation between any ports exceeds 26 dB. Compared to the case without the SADN, significant isolation improvements ranging from 15 dB to 45 dB have been achieved.