A compact, low-profile, broadside radiating two-element Huygens dipole array facilitated by a custom-designed decoupling element

A compact, low-profile, broadside radiating, two-element Huygens dipole array is developed for in-band full-duplex (IBFD) applications. Each radiating element is a multilayer near-field resonant parasitic (NFRP) design that is electrically small with ka = 0.76 at its resonance frequency, f₀ = 1.511 GHz. The center-to-center distance between the elements is only 0.3λ₀. The array's outstanding performance is facilitated by a custom-designed decoupling element. This specially engineered scatterer is printed on an additional layer and consists of a pair of meander-line resonators connected by a metallic strip. The overall height of the entire system is only λ₀/20.3. The passive decoupling element operates as several electrically small electric dipoles whose scattered fields mitigate the interactions between the two radiators. It provides very high isolation levels between them and improves the overall directivity of the array. The optimized array was fabricated, assembled, and tested. The measured results, in good agreement with their simulated values, confirm that the developed decoupling structure not only increases the peak isolation level from 14.4 to 50.4 dB but it also improves the peak realized gain in the broadside direction by 0.5 dB and the corresponding front-to-back ratio (FTBR) value by 14.4 dB.