$\mathrm{K} / \mathrm{K}_{\mathrm{a}}$-Band Shared-Aperture Dual-Circularly Polarized Lens Array Antenna for Geostationary Satellite Communications

We present a low-loss shared-aperture dual circularly polarized <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4 \times 4$</tex> lens array antenna for full-duplex geostationary satellite communications in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${K} / {K}_{\mathrm{a}}$</tex>-band. The proposed array has a periodicity of approximately <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2 \lambda$</tex> in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{K}_{\mathrm{a}}$</tex>-band and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.5 \lambda$</tex> in the K-band, with the resulting grating lobes suppressed by highly directive array element patterns. Two separate sequential rotation feed networks (for the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${K}_{a}$</tex>-bands) are implemented using a combination of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$H$</tex>-plane ridged waveguides and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E$</tex>-plane rectangular waveguides. The feed works for the two bands are stacked. The performance of the proposed lens array is validated using full-wave simulations in CST. In the receiving band of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$17.7-20.2 \text{GHz}$</tex>, the array achieves a right-hand circular polarization with an axial ratio lower than 2 dB, a realized gain of 23 dBic, a total antenna efficiency of more than 85 %, and a return loss higher than 10 dB. In the transmitting band of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$27.5-30 \text{GHz}$</tex>, the array achieves a left-hand circular polarization with an axial ratio lower than 1.5 dB, a realized gain of 27 dBic, a total antenna efficiency of more than 80 %, and a return loss higher than 10 dB.