The design of end-fire antenna with log-period directors

This paper presents the design and implementation of a novel wide bandwidth end fire antenna with log-periodic directors. The feeding structure of the proposed antenna includes a balun which is formed using a pair of microstrip to slot line transitions. The proposed antenna has three resonant frequencies in the operating frequency band. Both simulation and measurement results show that the operating frequency band of the antenna for S11 <; -10 dB covers the wide bandwidth (5GHz-10GHz), and the relative bandwidth is 67%. Far field measurements in azimuth plane and elevation plane show that the radiation patterns are stable and end fire within the operating band at frequencies of 5GHz, 7GHz, 8GHz, 10GHz. The proposed antenna radiates a well defined end fire beam, with a front-to-back ratio > 20dB and cross polarization level below -29dB. The dimension of the proposed antenna is 26mm × 27mm. Good return loss and radiation pattern characteristics are obtained and measured results are presented to validated the usefulness of the proposed antenna structure for wide bandwidth end fire applications.