D.A. Robertson

University of St Andrews, Saint Andrews, Scotland, United Kingdom

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Publications (38)19.48 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The corrugated or scalar feedhorn has found many applications in millimeter wave and sub-millimeter wave systems due to its high beam symmetry, relatively low sidelobe levels and strong coupling to the fundamental mode Gaussian beam. However, for applications such as millimeter wave cosmology, space-based experiments, or even high performance imaging, there is a generic requirement to reduce the size of horns whilst maintaining very high levels of performance. In this paper we describe a general analytic methodology for the design of compact dual-profiled corrugated horns with extremely low sidelobe levels. We demonstrate that it is possible to achieve -50 dB sidelobe levels, over wide bandwidths with short horns, which we believe represents state-of-the-art performance. We also demonstrate experimentally a simple scalar design that operates over wide bandwidths and can achieve sidelobes of better than -40 dB, whilst maintaining a frequency independent phase center. This design methodology has been validated experimentally by the successful manufacture and characterization of feedhorns at 94 GHz and 340 GHz for both radar and quasi-optical instrumentation applications.
    IEEE Transactions on Antennas and Propagation 01/2013; 61(4):1714-1721. · 2.33 Impact Factor
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    ABSTRACT: A software-based method for estimating and compensating for chirp non-linearity in frequency-modulated continuous wave radars is described. The method is based on the phase-gradient algorithm and time-domain warping of the dechirped signal. The method is demonstrated both on typically and severely non-linear chirps. The retrospective application is demonstrated on archive radar data.
    IET Radar Sonar ? Navigation 04/2011; · 0.92 Impact Factor
  • A.B. Rogers, D.G. Macfarlane, D.A. Robertson
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    ABSTRACT: Millimeter wave radar has shown to be of great use in the field of volcanology in terrain mapping applications. One area less studied to date is its use in ash cloud monitoring applications. In order for this to be realized, a quantitative study of the dielectric properties of volcanic rock and ash is required. In this letter, we present a method for accurately determining the complex dielectric permittivity of volcanic samples using a quasi-optical technique on the pellets of pulverized rock and present the results obtained. When averaged across our sample set, the results show agreement with those obtained by previous authors for both the permittivity of the volcanic material at lower frequencies and the permittivity of other rocks at millimeter wave frequencies. The results also show good levels of consistency between the multiple splits of each sample. In order to relate the measurements of the porous collections of ash to a continuous rock equivalent that is needed for use in the distributed target radar equation, mixing formulas are required. A measurement technique is presented for validating the mixing formulas using pressed pellets and loose ash. Böttcher's formula is found to be both accurate and sufficient for our purposes and is used further to relate our measurements to the continuous rock equivalents. These equivalents show that, for andesitic ash, the radar reflectivity factor may be taken to be an average value of K = |(ε - 1)/(ε + 2)|<sup>2</sup> = 0.39 ± 0.03 , showing no measurable deviation from that reported previously at frequencies of up to 19 GHz.
    IEEE Geoscience and Remote Sensing Letters 04/2011; · 1.82 Impact Factor
  • R.I. Hunter, D.A. Robertson, G.M. Smith
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    ABSTRACT: We present results for the complex refractive index and characteristic relative impedance of various commercially supplied solid absorbing materials at W-band (75-110 GHz). A waveguide measurement technique is described, together with the model that is fitted to the measured data. The accuracy of this method was verified with measurements of the well known dielectric material Rexolite 1422. Results are presented for Eccosorb MF-110, MF-114, MF-117, Ferrosorb, and TK-RAM. Knowledge of the electromagnetic properties of absorbing materials enables the design and manufacture of high performance waveguide or quasi-optical loads which find widespread application as thermal calibration targets and beam terminations in radar, spectroscopy, remote sensing, plasma diagnostics and astronomy.
    IEEE Microwave and Wireless Components Letters 01/2011; 21(7):389-391. · 1.78 Impact Factor
  • D.G. Macfarlane, D.A. Robertson
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    ABSTRACT: The MMW Group at the University of St Andrews has constructed a fast scanning, high resolution 94GHz FMCW radar named SAFIRE. We present SAFIRE imagery and outline the practical limitations of the radar in terms of the trade offs between scanning speeds, FMCW sweep times, range resolution, data sampling, processing and display requirements.
    Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on; 10/2010
  • A.B. Rogers, D.G. Macfarlane, D.A. Robertson
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    ABSTRACT: Methods for determining the dielectric permittivity of rock samples at millimetre wave frequencies have been investigated. A quasi-optical approach using pellets of powdered samples was found to work well, avoiding the dimensional restrictions of small waveguides. The permittivity of volcanic rock and ash samples was measured, providing valuable data for MMW radar remote sensing of terrain and ash clouds.
    Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on; 01/2010
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    ABSTRACT: Combinations of high range resolution, long standoff ranges and the requirement for moving target indication in LFMCW radars tend to increase the required signal sampling rate. A simple method of calculating a suitable sub-sampling rate to down-convert the signal by exactly aliasing the required information is described, providing a means of dramatically reducing the sampling rate. The technique is demonstrated in numerical simulations and with a mm-wave radar.
    01/2010;
  • D.G. Macfarlane, D.A. Robertson, M.R. James
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    ABSTRACT: The AVTIS remote sensing instrument is a custom built millimetre wave sensor that has been developed as a practical field tool for remote sensing of volcanic terrain at active lava domes. We present validation of the MMW radiometry of a volcanic scene by comparison with coincident infrared imagery.
    Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on; 01/2010
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    ABSTRACT: Exogenous growth of Peléean lava domes involves the addition of lava from a central summit vent and mass wasting on the flanks as rockfalls and pyroclastic flows. These processes were investigated at the Soufrière Hills Volcano, Montserrat, between 30 March and 10 April 2006, using a ground-based imaging millimeter-wave radar, AVTIS, to measure the shape of the dome and talus surface and rockfall seismicity combined with camera observations to infer pyroclastic flow deposit volumes. The topographic evolution of the lava dome was recorded in a time series of radar range and intensity measurements from a distance of 6 km, recording a southeastward shift in the locus of talus deposition with time, and an average height increase for the talus surface of about 2 m a day. The AVTIS measurements show an acceleration in lava extrusion rate on 5 April, with a 2-day lag in the equivalent change in the rockfall seismicity record. The dense rock equivalent volumetric budget of lava added and dispersed, including the respective proportions of the total for each component, was calculated using: (1) AVTIS range and intensity measurements of the change in summit lava (∼1.5 × 106 m3, 22%), (2) AVTIS range measurements to measure the talus growth (∼3.9 × 106 m3, 57%), and (3) rockfall seismicity to measure the pyroclastic flow deposit volumes (∼1.4 × 106 m3, 21%), which gives an overall dense rock equivalent extrusion rate of about 7 m3·s−1. These figures demonstrate how efficient nonexplosive lava dome growth can be in generating large volumes of primary clastic deposits, a process that, by reducing the proportion of erupted lava stored in the summit region, will reduce the likelihood of large hazardous pyroclastic flows.
    Journal of Geophysical Research 01/2008; · 3.17 Impact Factor
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    ABSTRACT: The EIKs described have demonstrated capability to provide mmW power suitable for improved ESR and NMR systems. The performance of EIKs at 94 GHz and 220 GHz is reviewed and possibilities for future improvement in performance, including increasing frequency, will be discussed. Presented data are supported by information provided by various academic and industrial customers.
    01/2008;
  • R.J.C. Middleton, D.A. Robertson
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    ABSTRACT: A highly versatile and exact approach to range point response prediction for linear frequency modulated continuous wave radars is described. The approach involves direct measurement of the chirp frequency profile and exact numerical computation of the point response by simulation of the de-chirp compression process. A test radar is used to image a point-like target. The results are used to validate the computational method, and demonstrate excellent agreement.
    Radar, 2008 International Conference on; 01/2008
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    ABSTRACT: Exogenous growth of Peléean lava domes occurs by addition of lava from a central summit vent and mass wasting on the flanks as rockfalls and pyroclastic flows, forming an apron of talus. We observed this process at the Soufrière Hills Volcano, Montserrat between 30 March and 10 April 2006 using a ground-based imaging mm-wave radar, AVTIS, to measure the shape of the dome surface.From a time series of range and intensity measurements at a distance of six kilometres we measured the topographic evolution of the lava dome. The locus of talus deposition moved to the southeast with time and the talus surface grew upwards on average at about 2 metres per day. The AVTIS measurements show an acceleration in lava extrusion rate on 5 April, with a 2-day lag in the equivalent rockfall seismicity record. We account for the budget of lava addition and dispersal during the eleven days of measurements using: AVTIS range measurements to measure the talus growth (7.2 Mm3, 67%), AVTIS range and intensity measurements to measure the summit lava growth (1.7 Mm3, 16%), and rockfall seismicity and visual observations to measure the pyroclastic flow deposits (1.8 Mm3, 17%). This gives an overall dense rock equivalent extrusion rate of about 9.7 m3s-1. These figures demonstrate how efficient non-explosive lava dome growth can be in generating large volumes of primary clastic deposits, and how this process could also reduce the propensity for large hazardous pyroclastic flows. andrews.ac.uk/~mmwave/mmwave/avtis.shtml
    AGU Fall Meeting Abstracts. 12/2007;
  • D.G. Macfarlane, D.A. Robertson
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    ABSTRACT: The millimetre wave group at the University of St. Andrews is constructing a fast scanning, high resolution 94 GHz FMCW radar named SAFIRE. The radar is designed to provide real time imagery of close range scenes both indoors and outdoors as part of a programme for public education on the specific topic of millimetre wave imaging. We present an outline of the design motivation and performance required for fast sampled close-range radar in a cluttered environment.
    Microwave Conference, 2007. European; 11/2007
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    ABSTRACT: We report on the use of a versatile 94GHz FMCW instrumentation radar to assess optimum hardware configurations for a variety of co-polar and cross-polar target classification studies. Phase noise and sweep linearity are critical parameters in FMCW radars and optimising them is a key objective of any high performance radar system. We have made a systematic comparison of fundamental sources (bias tuned Gunn, varactor tuned Gunn) and multiplied sources (commercial YIG based sweeper, YIG tuned oscillator, permanent magnet YIG tuned oscillator) to ascertain their relative phase noise contributions and FMCW sweep linearities at 94GHz. The radar will also be used to investigate the effect on target return signal coherence as a function of time for different sources. We present details of the calibration against the radar range equation and the effects of variable sweep bandwidth (and hence range resolution). The radar can also be configured for arbitrary polarisation (V, H, +45, -45, RC, LC) and demonstrates high polarisation isolation (33dB) which is required for the accurate assessment of cross-polar radar cross section (RCS), and we will present preliminary results for standard targets and clutter.
    Infrared and Millimeter Waves, 2007 and the 2007 15th International Conference on Terahertz Electronics. IRMMW-THz. Joint 32nd International Conference on; 10/2007
  • D.G. Macfarlane, D.A. Robertson
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    ABSTRACT: Millimetre wave (MMW) imaging is a fast moving technological area which has seen major advances in the last few years and is now offering practical solutions across a wide spectrum of imaging applications. Despite this, the technology is largely unknown and poorly understood by the general public. Under a UK EPSRC partnership for public engagement grant, the millimetre wave group at the University of St Andrews has partnered with exhibit development company FifeX Ltd to construct a touring exhibition designed to showcase the alternative view of the world provided by MMW remote sensing, illustrating the science principles behind the technology. The group is providing the centrepiece of the programme, a 94 GHz FMCW radar named SAFIRE (St Andrews fast imaging radar equipment). SAFIRE uses a frequency multiplied 7G Hz source to provide a low power (+2.5 dBm) 94 GHz carrier with a 750 MHz modulation bandwidth (i.e. a radar range resolution of 0.2 m). SAFIRE has a single zenith-pointing antenna scanned in azimuth via a rotating mirror angled at 45 degrees to the antenna axis to generate a PPI display of the immediate scene surrounding the radar (the maximum range is 25 m). Since real time imagery is essential for a project of this type the PPI is refreshed at minimum rate of 4 Hz. We present an outline of the motivation for the radar design and the expected system performance.
    Infrared and Millimeter Waves, 2007 and the 2007 15th International Conference on Terahertz Electronics. IRMMW-THz. Joint 32nd International Conference on; 10/2007
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    ABSTRACT: Next generation millimetre wave radars and pulsed electron spin resonance (ESR) instruments require complex pulse sequences consisting of very short, high power pulses that are pulse-to-pulse phase coherent. We have previously demonstrated 200 mW coherent pulses at 94 GHz with pulse lengths as short as 110 ps, and showed how they can be used to make high range resolution radar measurements. We now report results where a commercial extended interaction Klystron amplifier (EIKA) is used to amplify these pulses to kW power levels for use in advanced pulse ESR instrumentation. The instantaneous bandwidth of the EIKA now limits the minimum pulse length, but we demonstrate 1 kW peak power pulses down to 1.5 ns, dropping to 0.8 kW at Ins and 0.25 kW at 800 ps. We demonstrate that complex high power pulse sequences can be used in a mm-wave pulse ESR system, and also report on the level of broadband noise or "dark noise" from the amplifier (when there is no input signal), which can limit receiver sensitivity. We also detail the average power handling characteristics of various quasi-optical components.
    Infrared and Millimeter Waves, 2007 and the 2007 15th International Conference on Terahertz Electronics. IRMMW-THz. Joint 32nd International Conference on; 10/2007
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    ABSTRACT: Standing waves between transmit and receive feedhorns in quasi-optical systems often limit the achievable performance of mm-wave and sub-mm-wave instrumentation. Even with high performance corrugated feedhorns and perfect frequency independent optics, significant standing waves can occur because of the resonant build-up of higher order modes between feedhorns. In this paper we describe a new design of wideband corrugated feedhorn that significantly reduces standing wave effects, is scalable to any frequency, is shorter than standard horns and is suitable for a wide range of optical configurations. In addition it produces far-field beam patterns with much reduced sidelobes. We will describe the theory behind this new feedhorn design, outline scaling laws and present experimental results confirming the analysis.
    Infrared and Millimeter Waves, 2007 and the 2007 15th International Conference on Terahertz Electronics. IRMMW-THz. Joint 32nd International Conference on; 10/2007
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    ABSTRACT: We describe a 94GHz pulsed Electron Spin Resonance (ESR) spectrometer capable of delivering arbitrary pulse sequences at kW power levels with sub-nanosecond timing resolution, where it is possible to detect coherent signals close to the thermal noise level within one nanosecond of the final pulse. Such a spectrometer represents a remarkable step forward, very significantly increasing excitation bandwidth and system deadtime compared to current state of the art. This level of performance has only become possible due to many technical advances in mm-wave technology (pulse generators, loads, isolators, switches, antennas), and these are outlined within the paper.
    Infrared and Millimeter Waves, 2007 and the 2007 15th International Conference on Terahertz Electronics. IRMMW-THz. Joint 32nd International Conference on; 10/2007
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    R. I. Hunter, D. A. Robertson, P. Goy, G. M. Smith
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    ABSTRACT: Faraday rotators using permanently magnetized ferrite materials are used to make quasi-optical isolators and circulators at millimeter wave and sub-millimeter wave frequencies that have far higher performance than their waveguide equivalents. This paper demonstrates state-of-the-art performance for four-port quasi-optical circulators with 60-dB isolation, 0.2-dB insertion loss, and better than 80-dB return loss for devices centered at 94 GHz. A method is presented for the accurate characterization of the complex permeability and permittivity of permanently magnetized ferrites via a series of frequency and polarization dependent transmission and reflection measurements. The dielectric and magnetic parameters for the sample are determined by fitting theoretical curves to the measured data. These fitted parameters are then used in a model for a complete quasi-optical Faraday rotator, including matching layers, allowing the accurate design and fabrication of these devices for any specific operational frequency band in the millimeter wave and sub-millimeter wave regime. Examples are given showing typical results and demonstrating how temperature cycling can significantly improve the temperature stability of these devices, while allowing fine tuning of the center frequency. We also indicate the performance possible at higher frequencies to above 1 THz and outline performance of truly planar isolators where lossy polarizer material is built into the Faraday rotator matching structure
    IEEE Transactions on Microwave Theory and Techniques 06/2007; · 2.23 Impact Factor
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    ABSTRACT: Described is a simple method to produce sub-nanosecond phase coherent pulses with rise times and fall times of at least 80 ps at power levels in excess of 200 mW at 94 GHz. The duration and timing of these pulses are controlled by fast input logic, and pulses as short as 110 ps have been achieved. The technique is easily extended to both higher and lower frequencies, and produces pulses with an infinite extinction ratio suitable for amplification to higher power levels
    Electronics Letters 02/2007; · 1.04 Impact Factor