Low profile antenna performance study. Part 2: Broadband antenna techniques survey

This report is Part II of a three part series of reports investigating small antennas, their bandwidth and efficiency capabilities. Reviews and brief outlines of techniques published in the literature over the past 10-20 years, for broadbanding antennas are provided in this report. Experimental results from measurements of the Goubau antenna, a low-profile antenna (=0.05 lambda at the lowest operating frequency) are presented to show that this antenna possesses an octave bandwidth, regarding both impedance and radiation characteristics. Numerical results for some top-loaded structures are presented and matching network element variations are determined in order to estimate the bandwidth. It is shown that approximately 2:1 and approximately 4:1 increases in bandwidth are achieved when top-loading is applied to the stub and the loop antenna, respectively, and an L-network is used for tuning and matching. It is concluded that there may be several small but broadband antenna configurations possible from a clever (but as yet unknown) combination of the ideas and techniques presented in this report.