Frequency- and Pattern-Reconfigurable Antenna Pair Fed by a Frequency-Swappable Diplexer

A compact frequency- and pattern-reconfigurable antenna pair fed by a varactor-controlled frequency-swappable diplexer is presented. The diplexer consists of two identical frequency-selective units integrated symmetrically on the output ports of a T-junction equal-power divider. Each unit consists of a 50-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> transmission line equipped with two short-ended stubs loaded with two varactors. By changing the bias voltage applied onto these two varactors, specific frequencies are enabled or disabled to pass through the transmission line, yielding frequency selectivity. Importantly, unlike conventional diplexers, it can also allow these two frequency bands to pass through. Consequently, the simple and unique diplexer topology allows the frequency-selective units to have a low insertion loss, compact size, and two interchangeable operation frequencies by only swapping their bias voltages. The diplexer offers three operation modes, namely, 2.45 GHz at Channel-1 while 5.8 GHz at Channel-2, 5.8 GHz at Channel-1 while 2.45 GHz at Channel-2, and both the channels working simultaneously at 2.45 GHz, 5.8 GHz, or both the frequencies. An antenna pair separated by a metal plate and fed by the diplexer is then proposed to obtain frequency-swappable directional patterns. Measured results on a fabricated prototype illustrate successful operation of the three expected diplexer states, which correspondingly creates diplexed directional or bidirectional radiation patterns of the antenna pair. All these findings demonstrate a unique concept for the realization of dual-band frequency- and pattern-reconfigurable antennas.