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A novel design methodology for the successful implementation of high efficiency class E frequency multipliers is presented in this work. An innovative class E configuration is proposed for a frequency tripler that provides an advantage over the conventional designs, by allowing a 50 %duty cycle drive with a realisable load for 100 %DC-to-RF efficiency operation. A novel quantitative analysis of class E networks is developed that aids in the rapid yet accurate assessment of circuit performance. The first-order analysis provides an intuitive evaluation of class E operation and harmonic content of the switch waveforms. The analysis is shown to be applicable to both class E amplifiers and multipliers, providing closed-form equations for an intelligent first design. The proposed class E tripler configuration is evaluated using this technique and is shown to be a practically viable solution for achieving high DC-to-RF efficiency. Techniques involved in the design and implementation of the novel frequency tripler are investigated, and three microstrip circuits are presented that provide high drain efficiency, high unwanted harmonic rejection and low DC power consumption. Innovative design of the input matching circuit that exploits the nonlinear input capacitance of the device, and the output matching circuit that simultaneously provides appropriate harmonic terminations and unwanted harmonic rejection, ensure a simultaneously high achievable conversion gain and DC-to-RF efficiency. Practical demonstration of the three novel circuits display the highest reported DC-to-RF efficiency and conversion gain for m~crowave frequency triplers to date. Trade-oITs between circ.uit complexity,size and simultaneously achievable high efficiency and high conversion gain are identified and elucidated with the three novel designs.

Electron multipacting is a resonant process by which electrons build-up under the influence of a radio-frequency (RF) field. This process can occur in evacuated RF equipment such as the input coupler of accelerator cavities. The superconducting RF cavities designed by Cornell University, that are used in a number of synchrotron light sources including the DIAMOND Light Source, have had a history of vacuum breakdown in the CESR ring at Cornell with frequencies that would be inappropriate for a reliable synchrotron facility. This work aims to understand and correct the problem and ensure smooth operation of the cavities. The cause of the vacuum breakdown hindering the cavities’ operation at Cornell was identified as being multipactor in the rectangular input coupler waveguide. Prior studies carried out by R.L. Geng at Cornell University identified a number of solutions which he proposed to verify experimentally. Two series of experiments were carried out at Cornell University on short waveguide sections. The first session allowed us to observe, measure and attempt to suppress multipactor using techniques such as a longitudinal static magnetic bias field and a groove cut along the waveguide centreline. While the first technique was found to be quite effective, since a relatively weak 10G field was found to be sufficient to achieve complete multipactor suppression, the groove did not allow such total suppression of the multipactor though it did mitigate its effects. The second experimental session was designed to complement the first. The waveguide allowed the testing of other methods such as multiple grooves, a ridge in place of the groove, or surface coatings. The ridge proved to be as effective as a groove with regards to multipactor suppression, while multiple grooves proved to increase rather than reduce the total multipacting current. The waveguide could also be heated or cooled to study the effect of baking the surface as well as that of condensed gases. Surface coatings were tested and found to have the expected effect of lowering the multipactor current, but the surface areas covered as well as the vacuum quality achieved were insufficient to conclusively validate the use of coatings as a means of achieving multipactor-free operation of the coupler. Both series of experiments provided extensive measurements of electron currents at various locations on the waveguide and at a range of RF power levels; these were compared to simulations of multipactor developed using the MAGIC PIC code. The code results and the simulations were found to agree closely when using a secondary electron model including backscattered low energy electrons. The code was able to predict the effectiveness of a ridge, as well as agreeing with experimental observations. Instead of sharply defined multipactor bands as predicted by simple multipactor models, the multipactor current (above a certain power level) does not disappear completely even though it may show peaks and troughs for various values of the RF power. In conclusion, the magnetic bias is the only proven method to ensure multipactor-free operation of the CESR-type cavities. A ridge or a groove cut along the centreline of the waveguide could be a simple, passive way of limiting and retarding the effects of multipactor in the input coupler, while coatings should certainly be considered, though more research is needed to fully validate the concept.

A high bandwidth-efficiency modulation scheme is demanded for supporting a high-data rate communications, and so a highly linear transmitter is needed. Applying a linearisation technique to the transmitter can achieve this goal. In this thesis, there are three main topics which are investigated. They are mixer linearisation, the vector modulator based on the reflection-type attenuator and transmitter linearisation. For the first topic, there are two contributions in this thesis. The first technique is the application of the feedforward (FF) technique to linearise a downconversion mixer. It is shown for the first time that the FF technique for a mixer is simplified to a be a single loop rather than the conventional doubleloop structure, leading to a lower complexity and a high-linearity mixer. The second proposed technique applied to a mixer is a harmonic injection technique. The technique simply injects the difference-frequency tone to the input of a mixer. It is shown from the simulations and the experiments that the technique can improve the linearity significantly without trading off the power efficiency. Apart from the mixer linearisation topic, there are three contributions concerning with the reflection-type attenuator (RTA). The first is the feedback reflection attenuator based on Field-Effect Transistors (FETs). It has been found that applying resistive feedback can improve the attenuation range of the RTA and also the phase-distortion by trading-off the input and output return losses. The RTA size is comparable to the size of the conventional RTA which suffers from the phase-distortion. For variable attenuator applications, this structure can improve the attenuation range over the conventional RTA. For bi-phase modulator application, the structure is 50% smaller than the balanced structure based on the conventional RTA, which is needed for correcting the phase-distortion. The second contribution for this topic is the demonstration of an improved structure for a vector modulator (VM) based on the RTA. To avoid the phase distortion problem, the full balanced structure is needed and hence a large chip area is consumed. A simple technique to compensate the phase distortion and balance the amplitude for the whole control voltage range is proposed by adding an extra source inductor and a shunt resistor at the MESFET's drain. The aforementioned problems are overcomed and the circuit size is 50% of the balanced VM. In addition, the baseband signals for the proposed structure are reduced to 2, compared to 4 channels for the balanced VM. The third contribution is the study of the nonlinearity distortion in the RTA, The analysis technique is based on the power series model, The results provide the criteria for selecting the active devices to obtain the small nonlinearity distortion. Linearisation techniques for the whole transmitter are also under the research in this thesis. There are three contributions to the topic; The first technique is applying the FF technique for the whole transmitter. The advantage of the technique is the capability of reducing the distortion not only from the main power amplifier but also for the modulator. The second technique is a proposed topology for a low-cost millimetre-wave transmitter. The structure has low complexity since it composes of only 3 main parts, i.e. a VM, a medium/high-power oscillator and a DSP processor. The DSP part provides multi-functionality to the structure. These functions include baseband predistortion, channel filtering, modulation technique, to name the few. The last contribution of this topic is the improved LINC structure, so called adaptive predistortion LINC, to correct the phase/gain imbalances. The proposed technique shows the capability to overcome this effect, which can degrade the distortion performance in LINC.

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