Millimetre-wave limited-scan array using small lenses

In a phased array with limited-scan capability, the radiating element spacing is larger than one half wavelength and the element gain is higher than its full-scan counterpart to avoid grating lobes. This paper presents a new high-gain element made of a microstrip patch at the focal point of a small lens of only three wavelengths in diameter. Simulations showed that the lens still focuses the electromagnetic energy in spite of being electrically small. However, the focal region is quite spread out and the focal length is different from that predicted by geometrical optics. Fabrication and tests of a single element and a four-element array showed good agreement with theory. One application for a limited-scan array is an electronic tracking antenna for a fixed satcom terminal looking at a geosynchronous satellite stabilized in azimuth but not in elevation, as is often the case with military satellites.