A Wideband Planar Endfire Antenna With High Front-to-Back Ratio

This work presents a novel wideband endfire antenna by combining a driven dipole, a quasi-dipole reflector, and a parasitic dipole on a planar structure together with the radiation from a magnetic dipole to produce a wide and stable radiation pattern over the entire operating bandwidth. The suggested antenna structure exhibits an enhanced radiation pattern for a planar magentoelectric (ME) dipole antenna with high front-to-back (F/B) ratio. An L-shaped feedline integrated with a balun is adopted to excite the lower part (the driven dipole and the quasi-dipole reflector) and the upper part (the driven dipole and the parasitic dipole) of the antenna. Through a proper arrangement for both parts, the antenna has high capability in suppressing back radiation to produce directional radiation pattern to its endfire direction. In addition, a half loop is added at the lower part of the antenna to achieve an equivalent magnetic-dipole radiation to control the stability and low back lobe in radiation pattern by the complementary sources contributed from the ME-dipole radiator. A prototype of the proposed antenna shows an impedance bandwidth (the reflection coefficient
$ < -10$
dB) of 68% from 1.75 to 3.55 GHz with a stable radiation pattern and a peak gain of 8.23 dBi. The antenna has the F/B ratio of over 15 dB throughout the entire bandwidth.