Enhancing multiple-aperture Ka-band Navy SATCOM antennas with electronic tracking and reflectarrays

In naval SATCOM applications, there are advantages to using multiple antenna panels, each of limited scan range covering only a portion of the required hemisphere. For mechanical steering, the depth of each panel can be reduced by dividing the required aperture into multiple, smaller, sub-apertures at the cost of needing coherent combining. Two enhancements to multiple sub-aperture systems are presented. First, a method, akin to radar monopulse tracking techniques, is introduced that uses the multiple sub-beams for fine acquisition and tracking of the downlink signal. The individual sub-beams are steered to point slightly off center. A portion of the downlink signal from each beam is tapped off, detected, and used in an algorithm to compute the pointing error of the combined antenna beam center. This error estimate is used in a feedback loop to track the downlink signal. In the second enhancement, the sub-aperture antennas are implemented using reflectarray reflectors. Printed reflectarrays are used in place of conventional parabolic dishes. To minimize the design complexity of the feeds, the reflectarray elements are designed to transform the linear polarization from the feeds to circular polarization. The reflectarray design is capable of handling both right-hand and left-hand circular polarization. Furthermore, the reflectarray is designed with separate focal points for the transmit and receive signals. This removes the need for an orthomode transducer and for diplexers, resulting in considerable cost and weight savings. A Ka-band implementation is described.