Negative impedance converter for antenna matching

Tade, Oluwabunmi O. (2014). Negative impedance converter for antenna matching. University of Birmingham. Ph.D.

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Abstract

This thesis describes research into Negative Impedance Converters (NIC) for antenna matching. There are many applications that require small wideband antennas, from mobile phones and devices which are being required to cover larger frequency bands to cognitive radios that are expected to operate within any frequency band with minimum reconfiguration. However, fundamental limits on antennas such as the Chu-Harrington and Bode-Fano restricts the bandwidths obtainable from small antennas and antennas matched using conventional Foster reactive elements. However, non-Foster elements realised using NICs have been shown to provide wideband matching of antennas independent of frequency.

In this thesis, a non-Foster element is designed based on Linvill’s model. A drawback on NIC is stability therefore a new stability analysis is developed and reported in this thesis which correctly predicts the frequency of oscillation. With the aid of this new stability analysis, a 1.5GHz NIC prototype is developed, operating up to 1.5 GHz. Its performance in terms of noise and linearity are also characterized. Another novel NIC schematic is also introduced in the thesis; it makes use of a single transistor and a pair of coupled lines. Because of its use of a single transistor, stability is less critical and hence it is able to achieve a working frequency of 6GHz. Its performance is compared with the NIC based on Linvill’s model.

The coupled line NIC has been integrated with an antenna and this prototype shows the expected wideband performance with good gain. System implications of using NICs within an antenna is discussed.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):