Regional Nodes are a great way to connect with local fellow AMTA members and offer opportunities for those interested in antenna measurements to participate on a personnel level.
The principal aim of the node is to extend the AMTA world to those members of the Antenna Community belonging to academic and industrial, civil, and military organizations who have not had the opportunity to attend the AMTA annual symposium and to include them in the AMTA world thanks to the initiatives planned by the node, such as this AMTA workshop.
The workshop programme is available in the 18th ASA Conference Programme on DAY 1: Wednesday 14 February
1. Measuring the Station Beams of the Low Frequency Radio Telescope Ska-Low
Abstract:
SKA-Low is currently under construction, as the low frequency component of the SKA Observatory. It is planned to comprise 512 “stations’’; each such station will consist of 256 dual-polarised log periodic dipole arrays (SKALA), deployed in a constrained random pattern within a circle of diametre 38 metres. The specified frequency range for SKA-Low is 50-350 MHz. “Low frequency” is of course relative; this range very largely overlaps the VHF communications band. The ionosphere effectively precludes terrestrial radio astronomy at lower frequencies, hence the designation. This is an approximately 7:1 bandwidth, which is an exceptionally large ratio for an array. As the frequency increases, the array goes from being very dense to very sparse; the transition from dense to sparse is at approximately 100 MHz.
Most dish-based radio telescopes operate from approximately 1 GHz upwards. These were traditionally prime-fed parabolic dishes (e.g. Westerbork, VLA). These dishes were often measured using holographic techniques, and a description of the process may be found in. Due to the high accuracy of the antennas as built and their symmetry, cardinal plane measurements were often sufficient. A dish has a very significant amount of collecting area (usually in the order of hundreds of square meters), and a variety of astronomical radio sources provide suitable sources for measurements in-situ.
For low-frequency radio telescopes such as SKA-Low, the measurement issues are very different. Firstly, an aperture array is not simply a dish projected onto the ground. The mutual coupling between closely spaced elements results in individual element patterns changing significantly with both frequency and position within the array. Since these individual elements are used to calibrate the station, their properties should ideally be measured to confirm computational simulations. A successful campaign using a UAV with a test source was undertaken in 2019 on the AAVS2 prototype, which was partially completed at the time. However, UAV tests in situ are greatly complicated by both the weather and strict drone laws in Australia. A significant issue with measuring an SKA-Low station using drones relates to its electromagnetic size. The Rayleigh distance (2D2/) is around 3 300m at 350 MHz, well into the airspace regime. This greatly exceeds the permitted altitude of 120m for drone operation set by CASA. Even at 50 MHz, this distance is around 500m. Computational studies have shown that mutual coupling extends far across the array, so one needs to take the entire diametre into account for accurate results, especially at low frequencies. Near-field to far-field transforms are another obvious possibility, although the accuracy requirement on drone positioning is demanding.
SKA-Low is a full digital array; the output of each element (the “voltages’’) are digitised close to the antennas. As such, one would expect that astronomical sources could be used as is done with dishes for each element. The issue here is that each antenna has a collecting area of only a square metre or two at best, and there are very few astronomical sources (other than the sun) which are powerful enough to be detectable. This method can of course be used to probe the station beam. The most promising method shown to date is to treat the station as an interferometric array. The visibilities (the products of the “voltages’’ at each element) weight the observed sky with the pattern of each element, and results have demonstrated good agreement between element patterns inferred from such observations and direct computational simulations. The paper will also briefly touch on recent work on holographic methods for aperture arrays.
David B. Davidson1
ICRAR-Curtin, 1 Turner Ave, Bentley, WA 6102 Australia
David was born in the UK but grew up and was educated in South Africa. He completed his Bachelors, Honours and Masters degrees in electrical engineering at Pretoria University. His PhD and DEng were awarded by Stellenbosch University in 1991 and 2017 respectively.
David started his career at the (South African) CSIR, and then moved to Stellenbosch University, where he worked for almost 30 years before taking early retirement in 2017. At that time he held the SKA SARChI chair at Stellenbosch, and was also a Distinguished Professor. He retains a position at SU as Professor Extraordinary.
In 2018, he joined the International Centre for Radio Astronomy Research at Curtin University. He recently stepped down as Director of Engineering of ICRAR, and is currently departmental chair of Electrical and Computer Engineering at Curtin. David has worked on computational electromagnetics and its applications throughout his career, and published extensively, including two books. In 2012, he became a Fellow of the IEEE for his contributions to this field. He is currently listed on the Elsevier-Stanford University List of the World’s Top 2% Scientists.
2. NSI-MI Advanced Antenna Measurements Technologies
Abstract:
An overview of NSI-MI solutions and installed systems to meet customers’ antenna test needs including satellite, radar and other sophisticated antennas, radome, RCS and Hardware-in-the-loop for aerospace defense and commercial applications.
John Wen
John Wen is Director, International Business Development for NSI-MI Technologies. He is responsible for sales and market development in designated countries in the East Asia and Pacific Rim market. Prior to this assignment, John was the Regional Sales Manager of Nearfield System Inc. (NSI), responsible for all sales effort and customer support for Asia, primarily China and Japan, since 2003.
Prior to joining NSI, John served ten years with Hewlett Packard (China) then later Agilent USA in various sales and marketing, manufacturing and management positions supporting RF Microwave, Wireless and Telecom Communication, Production test solutions products of HP/Agilent divisions in the US, Europe and Asia.
John holds a Bachelor of Science Degree in Electronic Engineering from Beijing University of Aeronautics and Astronautics. After graduation, John was an EMC engineer for China Aviation Polytech Research Institute working on national and industrial EMC standards planning, preparation and promotion for eight years. Over his career, John has been active in a number of industry and professional organizations, including the IEEE Antenna and Propagation Society and the Antenna Measurement and Techniques Association.
3. Tuning and Adjustment of Bandpass Filters
Abstract:
This AMTA tutorial presentation is a practical introduction to the tuning of all-pole coupled-resonator bandpass filters. It draws heavily upon M. Dishal’s seminal 1951 paper “Alignment and Adjustment of Synchronously Tuned Multiple-Resonant-Circuit Filters” [1].
The equivalent circuit of a coupled-resonator bandpass filter will be introduced first, followed by a brief discussion of the filter’s properties both at the centre frequency and in its stopbands. It will be shown that the “alternating open-short-open” method of filter tuning arises as the logical consequence of the filter’s architecture. Based on this, a step-by-step procedure for tuning bandpass filters will be introduced and explained.
The tuning procedure will then be demonstrated on sample filters. The method outlined in Dishal’s paper will be demonstrated first. The procedure will then be updated in stages to cater for advances in test and measurement technology since the 1950s to match the equipment available in the attendees’ laboratories, such as SWR meters, spectrum analysers, and finally vector network analysers.
If time permits, methods of measuring the resonator coupling coefficients will be demonstrated.
Robert Shaw
Robert Shaw graduated from electrical engineering at the University of Sydney in 1985. His first position was at OTC, in the Cable Systems Engineering group. He was then transferred to the R&D group, where he worked on optical fibre systems. In 1989 and 1991 he was seconded to CIT-Alcatel in France as part of a technology transfer arrangement, and then worked for Alcatel-TCC for six months in 1992 prior to undertaking theological studies at Moore College. On graduating from Moore, he worked briefly at Optical Systems Design, before obtaining a position with CSIRO Radiophysics in early 1996. Robert worked on radio propagation measurements and experimental radio communication systems, then designed the low-noise amplifiers for the ASKAP radio telescope array. In 2014 he moved over to CSIRO Space and Astronomy, where he has worked on various receiver projects as an analog, RF and microwave design engineer.
Robert’s area of expertise is RF and microwave test and measurement.
4. Title: Multiple directions of arrival using CATR OTA measurements
Abstract:
This talk will summarise a novel method using multiple compact antenna test range (CATR) reflectors to perform simultaneous multiple angle measurements for 5G devices that are capable of beam-forming in the millimetre wave frequency range. The objective of this setup is to reproduce configurations involving multiple base-stations radiating from different directions. One of the applications is radio resource management (RRM) testing, where the execution of mobility procedures and radio link monitoring of a 5G millimetre wave device are evaluated.
Bio:
Boris Tovirac is Aerospace and Defence Segment Lead for Test & Measurement Division in Rohde & Schwarz Australia. Prior to joining Rohde & Schwarz Test & Measurement Division, Boris worked as System Engineer for R&S Communications Department, RF Design Engineer at GME Electrophone and Antenna Design Engineer at Hills Industries. Boris holds a degree in Telecommunications from the University of South Australia.
5. Terahertz antenna measurement techniques
Abstract:
Recently there has been growing interest in sub-millimeter and terahertz wave technologies. With vast underutilized bands, these frequencies offer exciting opportunities for high speed wireless communications and unique imaging techniques. In both cases radiating frontends are critical and as such we have worked to develop a range of suitable antennas including all-dielectric endfire antennas, metamaterial transmitarrays and quasi-optical systems with 3D printed materials. Here, we would like to present our experience characterizing these antennas and the various experimental techniques we employ including, automated far-field radiation pattern measurements, near-field beam profiling, as well as introductions to imaging and terahertz communications demonstrations.
Bio:
Withawat Withayachumnankul (Senior Member, IEEE) received the bachelor’s and master’s degrees in electronic engineering from the King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok, Thailand, in 2001 and 2003, and the Doctorate degree in electrical engineering with a Dean’s Commendation from the University of Adelaide, Adelaide, SA, Australia, in 2010. In 2010, he was awarded a 3-year Australian Research Council (ARC) Postdoctoral Fellowship. In 2015, he was a Research Fellow of the Japan Society for the Promotion of Science (JSPS) with the Tokyo Institute of Technology, Meguro City, Japan. He has been a Visiting Researcher with Osaka University, Suita, Japan, in recent years. He is currently an Associate Professor with the University of Adelaide, and the Founding Leader of the Terahertz Engineering Laboratory. He has authored and co-authored more than 100 journal publication, and has supervised nine Ph.D. students to completion. His research interests include terahertz waveguides, antennas, radar, communications, and metrology. In recent years, he has been a lead investigator for four Australian Research Council (ARC) grants, totalling to over AUD 1.5 M. He is currently the Track Editor of the IEEE Transactions on Terahertz Science and Technology. Between 2017 and 2018, he was the Chair of the IEEE South Australia Joint Chapter on Microwave Theory and Techniques (MTT) $ \& $ Antennas and Propagation (AP). He was the recipient for the IRMMW-THz Society Young Scientist Award 2020.
Harrison Lees received the BE (Honours) degree in electrical and electronics engineering from The University of Adelaide, Adelaide, SA, Australia, in 2020. In 2022 he was awarded the IEEE MTTS Graduate Fellowship. In 2023 he was a Best Student Paper finalist at the 48th International Conference on Infrared Millimeter and Terahertz Waves. He is currently working toward the Ph.D degree in electrical and electronic engineering with the Terahertz Engineering Laboratory, The University of Adelaide, Adelaide, SA, Australia.
His research interests include terahertz waveguides and systems for applications in sensing, non-destructive evaluation, and communication.
6. Axial Ratio measurements of Small Antennas and Feeds
Abstract:
The standard way to measure the axial ratio(AR) of antennas is to use a rotating linearly polarised(LP) antenna as the test antenna. As pointed out many years ago , this method requires careful consideration of any reflected signals for accurate results. Using a circularly polarised(CP) test antenna reduces the reflection problem since virtually all the incident signal on the test antenna is absorbed. but it is very difficult to get a CP antenna that is sufficiently close to the
ideal such that the AR of the CP test antenna does not affect the overall measured AR. Using a rotating LP antenna can take considerable measurement time if readings are required over a wide frequency range. An alternative technique is to take readings with the LP antenna set to three rotational angles with respect to the antenna under test(AUT). By choosing rotational angle steps of 45 deg or 60 deg, the AR can be directly determined as can the alignment angle of the major axis of the AUT. This method can be readily implemented on a small test range and avoids the necessity for a rotating joint.
Similarly, if the CP test antenna method is used, the uncertainty in the AR measurement due to the non zero AR value of the test antenna can be removed by taking measurements at two rotation angles offset by 90edg. Both of these methods along with results are described in this paper.
Dr John Ness
John was a co-founder of EM Solutions in 1998, in which he is the Chief Technology Officer. He also plays an active role in the governance and strategic leadership of EMClarity.
John has a B.E. (Electrical), PhD and a BA from the University of Queensland and has been involved in the telecommunications industry since the 1970s. His specialist expertise is in electromagnetic analysis applied to products such as high-power amplifiers, antennas, filters and feed networks. John helped set up Mitec as a public company in 1987, which became the basis for the RF/microwave industry in Queensland, Australia.
Prior to that John had worked in Sydney on the Interscan microwave landing system for the Australian aviation industry, which brought together the expertise of CSIRO, the Australian government and industry to create new technology and eventually companies. From Interscan through to EM Solutions he has developed products for radar, telecommunications and radioastronomy satellites, ground station equipment for miniature to large-scale earth stations, remote sensing equipment and microwave links. John has taken out patents in antennas and microwave heating applications.
In 2010 John was awarded the prestigious Clunies Ross Award by the Academy of Technological Scientists and Engineers for excellence in innovation.