A parasitic stacked patch antenna element for use in a 44 GHz MMIC phased array

The current 44 GHz MMIC (monolithic microwave integrated-circuit) antenna arrays, with active devices located on the same substrate as the radiating elements, typically require GaAs substrate thicknesses of about 5 mils for optimal active component performance. This substrate thickness would severely restrict the bandwidth of conventional microstrip antennas. This problem has been largely overcome by using a stacked patch antenna element, which can yield bandwidths of greater than 20% in some cases. Using a 10.5 dielectric-constant material for the lower substrate, six waveguide simulators were used to measure the active impedance of the scaled 44 GHz stacked patch antenna element as a function of (1) the dielectric constant of the cover material, (2) the air gap spacing between the lower and upper substrates, and (3) the radius of the cover patch. The voltage-standing-wave ratios (VSWRs) for the stacked patch element for each scan condition as a function of the dielectric cover parameters are given in a table. The air-gap spacing and upper patch radius were empirically determined so that the VSWRs for each scan condition were mutually minimized. In this manner the VSWR was held relatively constant across the measured scan range of the array.<
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