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No description available.

Despite the increased availability of digital frequency dividers operating up to several gigahertz, analogue dividers offer lower power consumption and higher operating frequencies. Among the different types of analogue microwave frequency dividers, parametric dividers based on passive circuits still fill a unique niche due to their simplicity and low cost. However, their major drawbacks have been their high input threshold powers and high conversion losses. Also to obtain higher division ratios, several divide-by-two circuits are usually cascaded, with the required amplitude for the input and output signals needing pre- and post-amplifiers, further complicating the circuit. In the present study, the above disadvantages are overcome by active parametric frequency dividers. This thesis presents the analysis, design and measured results of parametric frequency dividers utilizing pseudomorphic High Electron 1'1obility Transistors (pHEMTs) in place of traditional varactor diodes along with a novel circuit approach. The major advantage of using active devices is the potential for high conversion gain eliminating the need for amplification if further division is required. The active parametric frequency dividers described in this study use coupled microstrip transmission lines and two pHEMTs in a balanced configuration. A 2 GHz to 1 GHz divider is designed and fabricated, with measurements showing a 10% bandwidth, +18 dB maximum conversion gain and a lo~ input power threshold level of -14 dBm. The divider has a fundamental frequency rejection of better than 37 dBc at the output, and rejection of other harmonics of more than 22 dBc, with similar results for a lower frequency divider circuit converting 1 GHz to 0.5 GHz. A significant improvement in performance compared to previous designs is demonstrated.

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No description available.

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A new numerical approach based on least-squares error minimization is studied for the accurate analysis of electromagnetic problems. The approach whic~ is applicable in principle to any field problem has two specific advantages over the existing methods; firstly, it is rigorously convergent in contrast to point-matching or Fourier rnatching; secondly, free parameters can be chosen to guide convergence between a generally decreasing upper bound and an increasing lower bound. The first structure that is analysed by the new approach is an abrupt coaxial-to-circular waveguide junction, The device is of interest in immittance standardization and measurement. Values of the equivalent discontinuity capacitance of the junction are evaluated to an accuracy of within +0.1 femto farads. These results confirm independent published figures, and can be used for standards work. Another' structure that is studied is in support of the work on microwave dielectric measurements, where a microwave bridge is used with the material under test ,filling a length of a rectangular waveguide. In making measurements, corrections and optimizing the layout, theoretical results are needed for the scattering coefficients of a dielectric taper in the bridge. Again using the least-squares approach, the problem here is successfully solved. Two automatic and efficient schemes are proposed and developed which give accurate resultsfor a wide range of frequency, taper angle, and dielectric permittivity. Theory is also developed, related to measurement on a dielectric slab in the bridge, to account for the sample only partially filling the waveguide. The effects on the inferred metallic and dielectric losses are analysed, and accurate results are presented

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