Howard C. Reader

Comb-Generator Characterization

We characterize a 50-GHz comb generator with a sampling oscilloscope. With careful control of the input power, input harmonics, and comb generator temperature, we measure the output spectrum with a standard uncertainty of 0.1 dB and 0.5deg. We correct the measurements for time-base distortion, impedance mismatch, an inline attenuator, and the complex frequency response of the oscilloscopes sampler. We also report on the stability of the comb-generator spectrum and the effects of the recorded time windows, drive levels, and temperature. These results provide general guidelines for practioners of high-speed measurements and a benchmark for future inter-laboratory comparisons of harmonic phase-reference calibrations.

Small Corona Cage for Wideband HVac Radio Noise Studies: Rationale and Critical Design

Corona cages are used in overhead power line studies to investigate physical mechanisms involved in corona discharge and to predict radio noise generation. In this paper, we design a small laboratory corona cage to investigate wideband radio noise generation on practical HVac conductor bundles. We introduce and describe cage design criteria including the insulation of the cage mesh. Our measurement method generates data that can be used to calculate the characteristics of both fair-weather and foul-weather radio noise for interference studies over a wide bandwidth. We achieve this through time-domain measurements obtained on an 8-bit, 100-MHz sampling card. Single and multiple corona pulses are studied and we propose a single corona pulse source excitation function for small cages.

S-parameter measurements yielding the characteristic matrices of multiconductor transmission lines

A frequency-domain method is presented, which yields accurate characteristic matrices of uniform multiconductor transmission lines (MTLs). It uses simple two-port network analyzer S-parameter measurements of a set of open-circuit and short-circuited MTL configurations. The method eliminates the need for voltage and current probes, which introduce errors. Transversely inhomogeneous MTLs can be accurately characterized in their quasi-TEM propagation regime. The influence of the skin effect on the inductance matrix is taken into account. The technique was used to determine the inductance and capacitance matrices of a low-loss three-conductor ribbon cable above a ground plane. Comparisons with numerically and analytically obtained data are given. Measurements are found to be repeatable for lines of length /spl Lscr/</spl lambda//4. The /spl lambda//4 requirement is not found to be a restriction in the megahertz regime and only plays a role as line-end effects become significant at gigahertz frequencies. The obtained accuracy is significantly better than previously reported results.

Radio Frequency Interference and Lightning Studies of a Square Kilometre Array Demonstrator Structure

We study the radio frequency interference and lightning protection of the South African Square Kilometre Array demonstrator: the Karoo Array Telescope. Increasingly-realistic scale models of the demonstrator have been built and computationally modeled using FEKO. Minimally-invasive S-parameter measurements are made on physical scale models in an anechoic chamber with good agreement to simulation. The modeling has enabled insightful investigations into current paths and field distributions for interference mitigation and structure lightning protection, with direct bearing on the demonstrator implementation.

Calibrated waveform measurement with high-impedance probes

We develop an on-wafer waveform calibration technique that combines a frequency-domain mismatch correction to account for the effects of the probe on the measurement with an oscilloscope calibration. The mismatch correction is general and can be applied to any type of microwave probe, including scanning and internal-node probes for noninvasive integrated-circuit tests. We show that, for the commercial high-impedance probe we used, this calibration approach allows accurate on-wafer waveform reconstruction for a variety of probe ground configurations.

Wideband and Narrowband HVDC Conductor Corona Test Methods for Radio Noise Prediction

Various conductor corona test methods have been used to predict corona performance of HVAC transmission lines. Due to the formation and build-up of space charge, it is unclear whether the same methods can be used for corona performance of HVDC conductors. We investigate the use of a large corona cage, a short test line, and a small corona cage at high altitude to generate RI data. Wideband excitation functions are derived using time- and frequency-domain techniques. These generation functions are compared to CISPR standard narrowband measurements as well as published empirical RI prediction formulas. We find that a small corona cage cannot be used to accurately predict the RI performance of HVDC transmission lines at high altitude.

HVDC Corona Space Charge Modeling and Measurement

An electrometer circuit is designed and developed to measure the ion-space charge created during HVDC corona events. The interpretation of the electrometer output and visualization of various discharge processes are facilitated by a particle-in-cell computational code. The time it takes for the space charge to be created during a single monopolar corona event to reach the ground electrode in a corona test method is computed for a small corona cage, a short test line, as well as a large corona cage. This complements results obtained by the authors in another paper where it is shown that a small corona test cage cannot be used to predict the RI performance of HVDC conductors due to the space charge buildup in the small electrode gap.

MeerKAT RFI environment modeling and metrology

Our research group has contributed to the characterization and mitigation of radio frequency interference (RFI) associated with telescope and infrastructural developments for the Karoo Array Telescope. The Karoo core site is found in the Northern Cape of South Africa. The scale and computational modeling of systems and telescopes, along with actual site testing of RFI and mitigation procedures, will be outlined in this overview paper. A challenge for RFI management for South African and Australian future Square Kilometre Array developments will be posed.

South African SKA demonstrator systems: Evolving RFI mitigation investigations

The South African SKA demonstrator is founded on the Karoo Array Telescope (KAT). A holistic approach to radio frequency interference (RFI) mitigation has been adopted from the outset. We describe our groups contribution to this evolving effort. We consider the RFI beginning from the 100 km powerlines, through to the site base equipment and continue right up to the KAT-7 telescopes. A site survey was conducted with systems initially deactivated and then individually switched on to determine signature characteristics. More detailed studies include analysis of telescope pedestal shielding interfaces and cable transfer impedance.

Karoo Array Telescope: Lightning protection issues and RFI

A computational electromagnetic (CEM) code and a reduced scale model were used to characterize the design of the Karoo Array Telescope (MeerKAT), South Africas demonstrator for the Square Kilometer Array (SKA). Different excitation techniques were used in the CEM code and are compared to actual scale model measurements in an anechoic chamber. With verified computational modeling, the optimized lightning down conductor layout and earth termination system interconnections were investigated, keeping cost and RFI in mind.