Electrically Small, Planar, Frequency-Agile, Beam-Switchable Huygens Dipole Antenna

An electrically small, planar, frequency-agile, beam-switchable Huygens dipole antenna is investigated in this article. The near-field resonant parasitic (NFRP) design incorporates an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL) that function as the electric and magnetic NFRP elements, respectively. A varactor diode is integrated into each of these NFRP elements to facilitate simultaneous tuning of its operating frequency and switching its main beam direction. By changing the capacitance values of these two varactor diodes, the antenna realizes two independent, antipodal, unidirectional endfire radiating states with similar realized gain (RG) and front-to-back ratio (FTBR) values within virtually the same frequency-agile ranges. The experimental results demonstrate that the developed antenna exhibits a 5% frequency-agile fractional impedance bandwidth in both of its two oppositely directed endfire states. The antenna is electrically small at the highest frequency of this bandwidth ( {ka}_{high} < 0.86 ) and has measured relatively high radiation efficiency (RE >67.7%), peak RG (2.1-3.19 dBi), and FTBR (5.61-13.4 dB) values, together with stable and uniform radiation patterns, over this frequency-agile range.