Circularly Polarized Quasi-Absorptive Filtering Phased Array for Millimeter-Wave SATCOM

A circularly polarized (CP) quasi-absorptive filtering phased array of the stacked patch antenna is presented for millimeter-wave (mmWave) satellite communications (SATCOM). A parasitic square ring and cruciform strip are introduced to the stacked and driven patches, giving a radiation null for the lower and upper bandedge, respectively. A three-branch quadrature hybrid is used to feed the filtering stacked patch antenna for circular polarization, with the isolated port being terminated by a 50 Ω resistor. The incident power in the lower stopband can be largely absorbed by the resistor, whereas that in the upper stopband is mostly reflected to the input port, showing a quasi-absorptive filtering property. For demonstration, a 10×10 CP quasi-absorptive filtering phased array operating at 26 GHz was designed, fabricated, and measured. Its impedance is matched from 24.72 to 27.88 GHz, with the measured out-of-band suppression levels being over 15.2, 15.5 and 17.2 dB for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 0°, 30° and 45°, respectively. The measured maximum scan loss is 2.3 dB for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 45°. The sequential rotation technique is used to improve the axial ratio (AR). The measured AR remains below 3 dB within the reported impedance bandwidth throughout the scanning.