J.B. de Swardt

Low phase noise cylindrical cavity oscillator

A low phase noise oscillator operating at 9.2 GHz is presented. A cylindrical metal cavity with air as dielectric is used as the resonator. To minimize the phase noise of the oscillator, the resonator must be designed to have a high quality factor (Q-factor). A high Q-factor is obtained by designing the resonator to operate in the TE011 mode. A tuning screw is used to tune the resonant frequency without significantly affecting the Q-factor, while also separating the resonant frequencies of the degenerate TE011 and TM111 modes. The signal is coupled to the resonator by means of rectangular apertures. The coupling is designed to minimize the phase noise of the oscillator. A dual mode waveguide filter was developed and inserted into the oscillator loop in order to prevent oscillation at unwanted frequencies. The output signal of the oscillator was measured at different locations in the loop and clearly showed that the resonator can be used as a filter to minimize the phase noise. Phase noise levels of -115 dBc/Hz and -146 dBc/Hz were obtained at offset frequencies of 10 and 100 kHz.

The design of optimal phase tracking current controlled attenuators

Multi-channel receivers often require good phase tracking between channels. If a PIN diode current controlled attenuator (CCA) is needed in each channel, the individual CCAs should track in phase over the full control range. Variations in PIN diode complex impedance as well as component tolerances will cause phase tracking errors in a family of CCAs. A method to compare CCA topologies in terms of phase tracking performance is developed. By using sensitivity analysis and defining a single root sum square measure for comparing attenuator topologies, an optimum topology is identified for implementing an electronically controlled variable attenuator. The results clearly show that the cascade parallel quarter-wave attenuator topology will have the smallest phase tracking error within a family of CCAs.

Cancellation of colocated allied jamming signals in communication receivers

The use of high power jammers on vehicles for Improvised Explosive Device (IED) detonation prevention and strategic enemy communications jamming, allows for high levels of noise and interference to couple from the jamming systems to the co-located on-board communications radio receivers. The high levels of jammer noise desensitise communication receivers and render them less effective. The use of phase and amplitude variation through the use of analog vector modulation circuitry as well as power level error detection are evaluated for a noise and interference cancellation system. In this paper, the design and implementation of a prototype are discussed and performance of the prototype is measured in order to assess the design strategy and the usefulness of vector modulation circuits in cancellation systems.

Power control of a domestic microwave oven

Microwave ovens are widely used for research purposes, many times incorrectly. Understanding how the microwave power is controlled will give the researcher insight into the experimental results obtained. Microwave power resolution and system time response are the main figures of merit for evaluating the quality of a microwave power controller. A 700 Watt domestic microwave oven was modified using a TRIAC to control the magnetron input power. The resulting microwave output power measurements were used to evaluate the initial system. Further modifications were made with the intention to improve the identified figures of merit. Combining desired characteristics from existing magnetron power control strategies allowed the design of a custom power controller suited for rooibos tea sterilization. The system shows improvement in response time and power resolution, while transformer losses are also taken into account. This paper will focus on the hardware changes made and the motivation behind the changes. Therefore, illustrating how a domestic microwave oven can be modified to suit various research applications.

Multipath modelling in a dual-frequency phase-comparison FMCW radar

The unique configuration and application of the Active Protection System (APS) radar sensor, developed by Reutech Radar Systems, requires the development of a novel multipath interference model. This paper derives a mathematical model for the effects of specular multipath interference (primarily due to ground reflections) on the received signals of a dual-frequency phase-comparison FMCW radar. Two formulas are derived, one describes the change in amplitude and the other describes the change in phase due to specular multipath. This has interesting and previously unknown effects when Range-Doppler processing is applied to the corrupted input signal. Simulation results and measurements are presented to corroborate the theory.

Simple pattern synthesis for microwave dielectric heating

Synthesis of microwave field patterns by interference of frequency coherent, phase modulated signals is proposed as a novel technique for dielectric heating. Particular delay/phase differences result in a distinct set of base patterns. Weighted and averaged the desired heat patterns are then synthesized. Alongside, a unified, clearer large signal source model for injection locking is introduced.

Oscillator analysis using the waveform balance technique

A new method for analysing autonomous nonlinear circuits using the ‘waveform balanc’ technique is described. When analysing oscillator circuits, this method overcomes the difficulties normally encountered in determining the exact frequency of oscillation. A highly nonlinear oscillator is analysed and the results are compared to a time domain analysis and measurement results.

Slotline coupled varactor tuning of voltage controlled oscillators

A novel electronic means of tuning a dielectric resonator oscillator has been developed. The varactor control element is electromagnetically coupled to the resonator by means of a slotline. The easily manufactured circuit has a relatively wide tuning range. It is ideally suited for narrowband VCOs (voltage-controlled oscillators). The configuration lends itself to an inexpensive and reproducible manufacturing process.<<ETX>>A novel electronic means of tuning a dielectric resonator oscillator has been developed. The varactor control element is electromagnetically coupled to the resonator by means of a slotline. The easily manufactured circuit has a relatively wide tuning range. It is ideally suited for narrowband VCOs (voltage-controlled oscillators). The configuration lends itself to an inexpensive and reproducible manufacturing process. >