Envisioning an Endfire Circularly Polarized Antenna: Presenting a Planar Antenna with a Wide Beamwidth and Enhanced Front-to-Back Ratio

We present a design approach to a novel nonturnstile planar endfire circularly polarized (CP) antenna with a widened beamwidth and an enhanced front-to-back ratio. This approach combines a semicircular magnetic dipole and a V-shaped open loop to widen the azimuthal beamwidth at first. Then, to further enhance the front-to-back ratio, the V-shaped loop is appropriately rotated with respect to its feed apex. The tradeoff between the azimuthal beamwidth and the front-to-back ratio is theoretically revealed based on the approximate closed-form radiation pattern functions. Antenna prototypes are simulated accordingly, and they are then designed and measured to validate the design approach. The measured impedance bandwidth for |S 11 | l-10 dB covers a frequency range of 2.25-2.5 GHz (10.5% in fraction), and the axial ratio (AR) bandwidth of l3 dB is 2.3-2.57 GHz (11.1% in fraction). The measured 3-dB AR beamwidths of the proposed antenna are equal to 180d and 115d in the elevational and azimuthal plane, respectively, at 2.35 GHz. In addition, the measured in-band average frontto- back ratio reaches up to 13.7 dB.