Posts Tagged
‘Marcus Walden’

By Marcus C. Walden

Abstract: This paper presents the antenna G/T degradation incurred when communications systems use very inefficient receive antennas. This work is relevant when considering propagation predictions at HF (2-30 MHz), where it is commonly assumed that antennas are efficient/lossless and external noise dominates over internally generated noise at the receiver. Knowledge of the antenna G/T degradation enables correction of potentially optimistic HF predictions. Simple rules-of-thumb are provided to identify scenarios when receive signal-to-noise ratios might be degraded.

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By Marcus C. Walden

Abstract: This paper describes the design and characterization of a frequency-scanning meanderline antenna for operation at 60 GHz. The design incorporates SIW techniques and slot radiating elements. The amplitude profile across the antenna aperture has been weighted to reduce sidelobe levels, which makes the design attractive for radar applications. Measured performance agrees with simulations, and the achieved beam profile and sidelobe levels are better than previously documented frequency-scanning designs at V and W bands.

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By Marcus C. Walden, Timothy Jackson & William Gibson

Abstract: This paper presents an initial empirical path-loss propagation model for communication links operating at streetlight/roof-top heights over the ranges of 100 m to 10 km in urban and suburban environments. The statistical path-loss model presented uses data taken from a significant number of deployed street-light telemetry systems transmitting in the licence-exempt/ ISM bands at 868 and 915 MHz. This propagation model provides a valuable tool for network planning where typical cellular propagation models might not be appropriate.

I. INTRODUCTION: Telensa Ltd. operate a network of street-light telemetry systems for a variety of customers (e.g. local and county councils) for control and monitoring of street lights. This capability is becoming desirable for energy efficiency and for service maintenance; for example, to switch off unnecessary lighting and/or to identify failing lights.

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By Marcus C. Walden

Abstract: This paper presents a comparison of Chilton ionosonde critical frequency measurements against vertical-incidence HF propagation predictions using ASAPS (Advanced Stand Alone Prediction System) and VOACAP (Voice of America Coverage Analysis Program). This analysis covers the time period from 1996 to 2010 (thereby covering solar cycle 23) and was carried out in the context of UK-centric near-vertical incidence skywave (NVIS) frequency predictions. Measured and predicted monthly median frequencies are compared, as are the upper and lower decile frequencies (10% and 90% respectively). The ASAPS basic MUF predictions generally agree with fxI (in lieu of fxF2) measurements, whereas those for VOACAP appear to be conservative for the Chilton ionosonde, particularly around solar maximum. Below ~4 MHz during winter nights around solar minimum, both ASAPS and VOACAP MUF predictions tend towards foF2, which is contrary to their underlying theory and requires further investigation. While VOACAP has greater errors at solar maximum, those for ASAPS increase at low or negative T-index values. Finally, VOACAP errors might be large when T-SSN exceeds ~15.

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