Study of Unidirectional/Bidirectional Pattern—Reconfigurable Antenna With Impedance Match of Two Modes

This letter presents a butterfly-shaped pattern-reconfigurable antenna featuring unidirectional/bidirectional (U/B) radiation patterns and broadband stable gain. This paper innovatively utilizes the coupling effect between two reflective elements to achieve impedance matching for the antenna's bidirectional radiation pattern. Pattern reconfiguration is realized by controlling two pairs of PIN diodes integrated onto parallel twin lines via dedicated DC control circuits. The bidirectional pattern occurs when two driving units are fed with equal-amplitude and anti-phase currents, which are spaced at 0.5λ₀ apart (at 4.5 GHz). This feeding configuration, combined with coupling effects between reflective elements, enables the bidirectional pattern. The stable gain stems primarily from the director and reflector units. A prototype was fabricated and measured, yielding an overall antenna size of 0.87λ₀×0.87λ₀×0.015λ₀ at 4.5 GHz. The measured overlapping impedance bandwidths for the three patterns are 16.5% (4.34–5.12 GHz). The measured overlapping 0.5-dB stable gain bandwidths for the three patterns are 14.9% (4.34–5.04 GHz). This coverage encompasses the 5 G n86 (4.4–4.9 GHz) and n90 (4.9–5.0 GHz) bands, enabling flexible deployment in high-density scenarios like urban areas and stadiums.