Design of log-periodic two-stacked circular loop antenna

By taking into consideration the high gain characteristics of a circular twin-loop antenna and by distributing this antenna in a log-periodic arrangement, an antenna with a wide bandwidth was proposed. Equivalent circuits for the loop part and its transmission line part were established to perform a numerical analysis. After examining its properties, data to design such an antenna were obtained. In particular, the reason why this antenna had a high gain and wide bandwidth through its current distribution was clarified. Based on the design data of this paper, an antenna was constructed and its performance was measured. As a result, its half-power bandwidth was about 80 deg for the E-plane and 45 deg for the H-plane with a sharp directivity. Over a wide bandwidth of about 360 MHz for the 3-dB bandwidth, VSWR was less than about 2.2 and the directivity gain was more than about 10 dB. From these data, the validity of the present design method was confirmed. Thus, at present, the proposed antenna is a wideband antenna with a structure that has the highest gain.