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In this paper, the addition of an EM-coupled element to the printed planar monopole antenna is investigated. While remaining simple to construct, modifications to the EM-coupled element are shown to reduce the lower edge frequency of the 10 dB impedance bandwidth by up to ∼19% (280 MHz at 1.5 GHz). The radiation patterns for these antennas are characteristic of monopole antennas - i.e. omnidirectional in the azimuth plane with a at the zenith - and are consistent within +/- 2 dB across their useful impedance bandwidths. By optimizing the feed arrangements on these antennas a 10 dB impedance bandwidth ratio of over 3:1 can be achieved. This technique yields the ability to construct a smaller antenna, in comparison to a simple printed planar monopole antenna, for a given frequency range. The antennas considered in this paper operate between 1.3 and 5.5 GHz, making them suitable for numerous mobile and portable applications. Measured results are compared to antenna simulations using transmission line modelling.
Evans, J., Lerma, F., & Ammann, M. (2004) Printed planar monopole antenna with electromagnetically coupled elements. High Frequency Postgraduate Student Colloquium, pp.81-86. 6-7 September, 2004, doi:10.1109/HFPSC.2004.1360358