A Novel Coplanar-Strip-Based Excitation Technique for Design of Broadband Circularly Polarization Antennas With Wide 3 dB Axial Ratio Beamwidth

In this communication, a novel excitation technique for the design of a single-point-fed compact low-profile wide-slot antennas with broadband circular polarization (CP) and wide 3 dB axial ratio (AR) beamwidth is presented. Two inverted L-shaped parasitic strips placed coplanar to the microstrip line of an asymmetric coplanar waveguide (CPW) and a horizontal strip that protrudes from the vertical edge of the backside ground plane of the substrate are used for CP excitation. The overall footprint of the structure is only L
_s
× W
_s
= 0.3λ
₀
× 0.28λ
₀
when measured at the lowest operating frequency. The antenna prototype has been experimentally validated. The measured results indicate that a wide impedance bandwidth of 72% (2.26-4.85 GHz) and a CP bandwidth of 66% (2.44-4.87 GHz) can be achieved. In addition to the wideband characteristics in terms of the impedance bandwidth and CP, a stable bidirectional radiation pattern with a wide 3 dB beamwidth of 85° ± 5° is obtained for 58% of the total CP bandwidth without involving any complex circuitry. Furthermore, by placing a flat metallic reflector behind the antenna, a unidirectional radiation pattern is produced without changing the geometrical dimensions of the proposed antenna. The average realized gain of the antenna without a reflector is 3.3 dBi, whereas it increases up to 6.3 dBi with the substrate-size reflector.