Rapid and Accurate Measurement of Polarization and Fading of Weak VHF Signals Obliquely Reflected from Sporadic-E Layers

Chris Deacon, Ben A. Witvliet, Cathryn Mitchell, Simon Steendam

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Abstract

In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction.

Original languageEnglish
Article number9301351
Pages (from-to)4033-4048
Number of pages16
JournalIEEE Transactions on Antennas and Propagation
Volume69
Issue number7
Early online date21 Dec 2020
DOIs
Publication statusPublished - 1 Jul 2021

Bibliographical note

Publisher Copyright:
© 1963-2012 IEEE.

Funding

ACKNOWLEDGMENT The authors thank the designer of the LFA Yagi antennas, Justin Johnson of InnovAntennas Ltd, for the antenna model used in our simulations and Marcus Walden for discussions on the limiting polarization in magneto-ionic propagation. The authors also thank the University of Bath, which sponsored Chris J. Deacon’s Ph.D. research, the U.K. Natural Environment Research Council for Cathryn N. Mitchell’s KE Fellowship, NE/P006450/1, and the Radiocommunications Agency Netherlands for the use of its FEKO antenna simulation software. All data created during this research are openly available from the University of Bath Research Data Archive.

FundersFunder number
Natural Environment Research CouncilNE/P006450/1

Keywords

  • Brewster angle
  • ionosphere
  • polarization
  • radio noise
  • radio wave propagation
  • sporadic-E (Es)
  • very high frequency (VHF)

ASJC Scopus subject areas

  • Electrical and Electronic Engineering

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