A Low-Cost 2 $\times$ 2 Planar Array of Three-Element Microstrip Electrically Steerable Parasitic Array Radiator (ESPAR) Subcells

A low-cost electrically scanned phased array utilizing microstrip patch electrically steerable parasitic array radiator (ESPAR) subarray cells is presented for the first time. Four single-layer three-element ESPAR subarray cells at one-wavelength spacing are uniformly illuminated by a corporate feed network consisting of microstrip Wilkinson power dividers and ring hybrids. The array is scanned using a combination of ESPAR capacitive mutual coupling control and microstrip switched delay line phase shifters at the subarray level to achieve a scanning range from -20^° to +20^° while maintaining high return loss. The ESPAR coupling technique allows a 50% reduction in the number of phase shifters used by utilizing a full wavelength subcell spacing, resulting in excellent performance with inexpensive fabrication. The fabricated prototype exhibits boresight gain of 12.1 dBi with low scan loss and 7.0-dB worst case sidelobe level. The array is compared quantitatively to thinned arrays with and without parasitic elements to illustrate this advantageous technique. A functional prototype is fabricated and measured and is aptly predicted by the full-wave model.