Theoretical and experimental advances in two-port injection matched antennas

Kihogo, Peter Mgaya (2022). Theoretical and experimental advances in two-port injection matched antennas. University of Birmingham. Ph.D.

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Abstract

The bandwidth enhancement of two-port single radiator patch antennas for wireless communications is studied through single resonance and frequency tunability using the injection matching technique. The approach uses the variations of the relative amplitude \(\gamma\) and phase shift \(\varphi\) between the two coherent excitation signals at port two of the antenna to modulate the terminal impedances at the two ports, which simultaneously matches the two ports of the antenna to the 50 \(\Omega\) coherent sources. Particular focus is paid to the active modulation of the electrical length of the patch antenna to enhance the bandwidth of an electrically small antenna.
Wide bandwidth greater than 64% is attained from the two-port proximity-fed patch antenna with approximately stable omnidirectional H-plane radiation patterns, radiation efficiency higher than 99% and total efficiency higher than 89% across the antenna passband through excitation of two characteristic modes of the antenna with \(\gamma=1\) and \(\varphi=180^o\) applied to the antenna. Also, the fractional bandwidths of 67% and 19% with radiation efficiency higher than 98% and total efficiency higher than 84% across the antenna passband are attained from a patch antenna through a non-progressive frequency tuning of the antenna modes with \(\gamma=1\) and \(\varphi=180^o\), and \(\gamma=1\) and \(\varphi=0^o\), respectively. It is further shown that other \(\gamma\) and \(\varphi\) combinations apart from \(\gamma=1\) and \(\varphi=180^o\) or \(\gamma=1\) and \(\varphi=0^o\) can only affect the matching of the attained differential or common mode resonances.
Besides, an electrically small operation with electrical length \(ka=0.81\), radiation and total efficiencies of 93%, and a -10 dB fractional bandwidth of 2.7% at a 1.423 GHz centre frequency has been attained on a patch antenna which is incorporated with a slow-wave structure, through the application of the injection matching technique. It is further shown that the use of lumped elements for tuning the two-port injection matched antennas to an electrically small frequency of operation is not feasible because of the narrowband matching behaviour of the lumped elements, which causes significant variations in the applied \(\gamma\) and \(\varphi\).
Also, the reciprocity analysis of the two-port injection matched antennas shows that the same feeding network arrangement used by the antenna in transmit mode can be fed by an injection matched antenna in the receive mode. Besides, the two-port injection matched antennas can work reciprocally with any other antenna with similar radiation characteristics.
The high bandwidths attained by the two-port injection matched antennas are attributed to the excitation of the multiple characteristic modes of the antenna through the application of the injection matching technique. However, all these features are attained at the expense of complex driving circuitry, which is not always advantageous to realise.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):