The research carried out and detailed in this thesis presents several techniques applied to frequency selective surfaces (FSS) with an emphasis on propagation control in the built environment. Issues are explored such as interference reduction and frequency reuse, security applications or propagation enhancement by reducing the effects of multi path and the wireless black spots or nulls that it produces. A band-stop active FSS (AFSS) has been designed operating in the WLAN band of 2.45GHz. The structure consists of annular ring. elements with PIN diodes as the semiconductor switches. The surface is two-state, being reflective with the diodes forward biased and transparent when zero biased. The design is single sided and includes an efficient distribution method of the de biasing by employing RP chokes. A prototype surface is constructed and its transmission response measured for a range of angles of electromagnetic wave incidence. A dual-band passive band-stop FSS is designed operating in the WLAN bands of 2.45GHz and 5GHz. The annular ring design introduces "traps" to FSS, where a trap is a parallel tuned circuit and behaves as a frequency selective switch, presenting a low or high impedance state depending upon the band of operation. Similarly the technique is applied to an annular slot design where the parallel tuned circuit is replaced with a series tuned circuit. For both designs prototype surfaces were constructed and evaluated for dual-band operation, with transmission response measurements carried out over a range of angles of electromagnetic wave incidence. A new AFSS structure known as the "phase plate" is introduced. A phase plate is a AFSS backed by a solid rear reflective surface spaced some distance away and modulated at a rate to modify wireless coverage nulls in enclosed environments, improving signal distribution in that space. A 2.45GHz experimental phase plate is constructed and evaluated, both by static phase shift measurements and observing its operation in a multi path environment with the successful filling of a wireless null. To demonstrate its performance a just discernible signal in the noise floor of the measurement receiver is brought some 20dB above it.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:590061 |
| Date | January 2011 |
| Creators | Taylor, P. S. |
| Publisher | University of Kent |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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