Contiguous Broadband Circularly Periodic High Impedance Surface Integrated with a Spiral Antenna

A broadband circularly periodic High Impedance Surface (HIS) is designed and integrated with a broadband spiral antenna to enable unidirectional broadband performance in a low-profile format. Performance is demonstrated between 2–6 GHz covering three contiguous sub-bands centered at 2.4 GHz, 3.5 GHz, and 5.0 GHz. The design methodology aligns the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">± 90∘</tex> reflection-phase of consecutive sub-bands to enable good performance at the center of each sub-band, as well as the overlapping frequencies in between. The phase response is verified using simulations to ensure zero-degree reflection-phase at each sub-band design frequency and the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">± 90∘</tex> reflection-phase at overlapping sub-band frequencies. A broadband spiral antenna is integrated with the HIS by placing the antenna above the HIS at a height of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.09λ</tex> with respect to the lowest frequency of operation. This HIS-backed spiral antenna is enclosed in an aluminum cavity to further suppress back-lobe radiation. The antenna S11, gain and radiation pattern data are presented to demonstrate the broadband performance of the integrated antenna structure.