  A unique three-band patch antenna for high accuracy ranging between nodes in
open-loop coherent distributed antenna arrays is presented. Open-loop coherent
distributed operations require accurate relative position knowledge between
nodes to enable distributed beamforming operations. For the highest accuracy,
the inter-node ranging will typically occur at frequencies higher than the
frequency of the signal transmitted by the distributed array (the coherent
action signal) to enable wider bandwidth signals to be used, however it is
important that the inter-node ranging measure the distance between the antennas
transmitting the coherent action signal. In this work, a three-band antenna is
presented that is designed to support distributed beamforming at 1.88 GHz and
high-accuracy ranging using a sparse, two-tone waveform operating near 9.5 and
10.5 GHz. The two-tone waveform is supported by a slotted patch antenna
surrounded by a larger patch antenna supporting the 1.88 GHz array signal. The
antennas are concentrically designed to ensure that the phase centers of the
ranging antenna and the coherent action antenna are closely aligned. Simulated
and measured performance shows phase center displacement of approximately
lambda/10 relative to the coherent action signal, while maintaining S11 below
-10 dB at each band.
