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Traditional methods for RF beamforming require significant amounts of power, making them difficult to deploy in some low-power applications. A simple, fully-passive, low-loss technique for Radio Frequency (RF) beamforming is realized by serially combining the antennas in an array using transmission-line transformers (without magnetic components) incorporated into the feed line and a programmable admittance placed in shunt across each antenna’s feed port. Utilizing the feed structure for signal combining eliminates the need for additional RF combining structures. Further, taking advantage of the symmetry inherent in a phased array, we propose a new method for passive phase shifting that only requires one tunable element per antenna. The proposed fully-passive beamformer is demonstrated on an FR4 printed circuit board with a linear, two-element, array of half-wave dipoles at 2.05 GHz using a digitally tunable capacitor as the programmable admittance. A loss in array gain of 1.07 dB is realized when compared to an identical array with ideal phase combining.

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