No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

It has been known for a number of years that the noise figure of a simple receiving system is directly proportional to the conversion efficiency of the mixer. Any improvement in this will have great bearing on the performance of a communications system, offering the possibility of an increased range of reception. The narrow-band open - circuit lattice mixer has been shown theoretically, under certain conditions, to produce a loss approaching zero. Exploratory low frequency circuits have given conversion power losses as low as 1 dB. The increasing use of communication systems at microwave frequencies brings with it the demand for low-loss mixers at these higher frequencies. As the frequency of operation increases, the parasitic diode reactance's have a more pronounced effect on the mixer performance. The original work presented here analyses the effect of the parasitic diode package capacitance on the performance o f a narrow-band open - circuit lattice mixer. The main conclusion to be drawn from the analysis is that for practical diodes used with local oscillator powers normally encountered in microwave mixers, the conversion power-loss of the mixer will, generally, be less than 1.5 dB. Another important result from the analysis is that the optimum terminating resistances are considerably reduced when even small amounts o f package capacitance (eg. 0.1 pF) are present. This may be considered as being an advantage when matching the lattice to a 50 Ω coaxial system. An experimental mixer at L-band constructed by the author using lumped circuit components, gave a 2.8 dB conversion power loss at 20mW of local oscillator drive. This was a considerable improvement on existing commercial models. Had it been a broad-band lattice mixer, it would have given as 3.6 dB minimum conversion loss. On the other hand a narrow-band mixer would have given 3.75 dB minimum. The practical mixer circuit was a modification of the one first analysed in detail by Kulesza, in that the input transformer was resonated. This configuration solved the problem of feeding the local oscillator at the input of the lattice. The 25 MHz. 3 dB band-width of the mixer would be considered sufficiently large enough for use in a communications network. Less power at the local oscillator, frequency was required when comparing this mixer with some 2-diode; mixers; in some cases producing a power saving of 50%. Experimental verification of the analytical work on the effect of diode capacitance gave within 0.9 dB of the theoretical values for low values of capacitance and for local oscillator drive levels used in practice. Finally, the 'K' mixer parameters for the case when diode package capacitance is present in a narrow-band open-circuit lattice mixer are solved. These will be of importance to any future analytical work on lattice mixers.

No description available.

Newer technologies like Electric Vehicles (EVs) and Distributed Generation (DG) are being viewed as potential harmonic distortion threats for the distribution systems which are already facing increased harmonic stress due to the increased use of the non-linear home appliances in the recent years. Therefore, it is necessary to evaluate and analyze the harmonic distortion due to the various non-linear home appliances, EV battery chargers and DG inverters to give a clear picture of the future scenario. So that future technologies can be accommodated in the distribution systems while the existing harmonic distortion threats are dealt with. This research work investigates the harmonic spectrums of various non-linear residential loads, battery chargers and DG inverters which are then deployed to perform various simulations of the distribution systems, using Electrical Transient Analyzer Program (ET AP), considering several different scenarios. A high penetration level of non-linear residential loads is considered to simulate the current scenario. The results show high level of harmonic distortion at the Point of Common Coupling (PCC). The investigation is then extended to simulate the future scenarios by considering advent of the EV s and DG. The results indicate a significant increase in the Total Harmonic Distortion in the Voltage (THDv) in the presence of EVs and DG, at the PCC. Currently, Demand Side Management (DSM) strategies are primarily being designed based upon the daily load profile only. This research work gives a different perspective for the DSM based upon "Daily Harmonic Profile" developed by combining the experimental and simulation results. The results indicate that throughout the day, the THDv has a value of more than 1.5 % with per hour average THDv being equal to 3.25 %. The-situation worsens if the increased winter loading is considered to investigate the daily harmonic profile. This research work also explores the potential impacts of the developed profile on the DSM schemes to control the harmonic distortion in the future distribution systems.

This thesis is concerned with the design and fabrication of flexible textile wearable antennas integrated with the newly introduced artificial materials known as high impedance surfaces (HIS). With the rapid growth and use of wireless communication systems more and more people are taking advantage of portable computing systems on daily basis. Also with the advancement in electronic industry new and sophisticated wireless devices have been introduced which are being used closed to human body. For user convenience there is an increasing need for integrating antennas on or in the clothing. The conventional antennas being rigid and obtrusive to user movements have limitations. There is a need of antennas made of flexible textile materials that can be part of user clothing defined as wearable antennas. Also with the miniaturisation trend in electronic industry, antenna designers are facing a challenge to come up with a compact, low profile,multi function efficient antenna designs occupying a small physical space. By integrating antennas in user clothing this limited space problem can also be resolved. With the easy availability of electro textile materials it is now possible to manufacture complete fabric antennas. The entire design cycle of wearable fabric antennas starting from material selection to prototype fabrication and antenna testing was carried out in this thesis. A novel technique for antenna fabrication using electro textile material is proposed that will have major implications on wearable computing industry. The use of HIS for antenna performance enhancement is growing at a rapid pace. In this thesis a modified wearable form of HIS defined as non uniform HIS is presented and successfully integrated with antenna for improved performance under low profile limitation. The HIS was also integrated with normal patch antenna to reduce its size and improve its gain and impedance bandwidth. These wearable antennas were then tested under real operating conditions. The measured results validated the design idea and showed that there are many possibilities for these unique artificial materials to be exploited for future wearable on body communication antennas.