A Novel Calibration Instrument to Compensate the Effect of a Wet Radome in Weather Radars

A Novel Calibration Instrument to Compensate the Effect of a Wet Radome in Weather Radars Jorge L. Salazar-Cerreno, Nafati A. Aboserwal and Boon Leng Cheong Advanced Radar Research Center (ARRC) University of Oklahoma, Norman, 72073

In general, any radome should provide electromagnetic transparency and structural strength to protect the antenna. Electromagnetic transparency consists of low reflections, low transmission loss, and minimum distortion of polarization-dependent antenna patterns. Structural strength is related to wind loading, stability, and integrity for mitigating environmental conditions, such as temperature, humidity, and pressure. For operational systems, the radome is the essential component, since it minimizes the high wind load, reduces the need for a heavy and expensive pedestal, provides consistent nominal temperatures that facilitate the operation and maintenance, and improves the life cycle cost of the system. One adverse effect of the radome is the performance degradation of radio signals when they operate in the presence of water or ice. Water accumulated on the radome surface can significantly affect the radar signal. Depending on the frequency of operation, rain and wind conditions, shape, and material, a radome can significantly attenuate, reflect, and depolarize the radar or communication signals. For frequencies below S band, the impact of wet radomes is relatively small and cannot be considered critical for radar operation. However, for higher frequencies water formation on the radome surface can significantly deteriorate the transmit and receive signals. The attenuation of radio signals on satellite systems that operate between 17 and 22 GHz has been extensively analyzed in the past regarding the large attenuation in the radio signals caused by water accumulation on the radome surface. (Gibble 1964; Blevis 1965; Cohen and Smolski 1966; Anderson 1975; Hendrix et al. 1989; Chang 1985; Fenn 1997; Crane 2002, Bechini et al, 2010, Fraiser et al, 2013, Kurri et al, 2009, Manz et al, 1999, Merceret et al, 2002 and Schneebeli et al, 2012). The electrical performance of a radome for a dual-polarized phased-array antenna under rain conditions was analytically evaluated by Salazar (Salazar et al, 2014). In the proposed model, the attenuation, reflections, and induced cross polarization are evaluated for different rainfall conditions and radome types. Numerical results were compared with radar data obtained in the Next Generation Weather Radar (NEXRAD) and Collaborative Adaptive Sensing of the Atmosphere (CASA) systems, and good agreement was found. In this work the author presents a calibration instrument that enables the characterization and correction of the adverse effect of the radome under presence of rain. The instrument uses a unique setup based on an accurate vector reflectometer and customized dual-polarized antenna probe to capture the power reflections of the radome (dry and wet). Data collected is used to calibrate out the attenuation and reflection of the radar signals due to the wet radome.

References.

Anderson, I., 1975: Measurements of 20-GHz transmission through a radome in rain. IEEE Trans. Antennas Propag., 23, 619–622, doi:10.1109/TAP.1975.1141134. Bechini, R., V. Chandrasekar, R. Cremonini, and S. Lim, 2010: Radome attenuation at X-band radar operations. Proc. Sixth European Conf. on Radar in Meteorology and Hydrology, Sibiu, Romania, ERAD, P15.1. [Available online at http:// www.erad2010.org/pdf/POSTER/Thursday/02_Xband/ 01_ERAD2010_0346_extended.pdf.] Blevis, B., 1965: Losses due to rain on radomes and antenna reflecting surfaces. IEEE Trans. Antennas Propag., 13, 175–176, doi:10.1109/TAP.1965.1138384. Cohen, A., and A. Smolski, 1966: The effect of rain on satellite communications earth terminal rigid radomes. Microwave J., 9, 111–121. Crane, R. K., 2002: Analysis of the effects of water on the ACTS propagation terminal antenna. IEEE Trans. Antennas Propag., 50, 954–965, doi:10.1109/TAP.2002.800701. Fenn, A. J., 1997: Measurements of wet radome transmission loss and depolarization effects in simulated rain at 20 GHz. 10th International Conference on Antennas and Propagation, Vol. 1, IEEE Conf. Publ. 436, 474–477. Frasier, S. J., F. Kabeche, J. Figueras i Ventura, H. Al-Sakka, P. Tabary, J. Beck, and O. Bousquet, 2013: In-place estimation of wet radome attenuation at X band. J. Atmos. Oceanic Technol., 30, 917–928, doi:10.1175/JTECH-D-12-00148.1. Frech, M., 2009: The effect of a wet radome on dualpol data quality. 34th Conf. on Radar Meteorology, Williamsburg, VA, Amer. Meteor. Soc., P13.15. [Available online at https://ams.confex. com/ams/34Radar/techprogram/paper_155405.htm.] ——, Kurri,M., and A. Huuskonen, 2008:Measurements of the transmission loss of a radome at different rain intensities. J. Atmos. Oceanic Technol., 25, 1590–1599, doi:10.1175/2008JTECHA1056.1. NOVEMBER 2014 S A L A Z A R - C E R R E ÑO ET AL. 2429 Manz, A., L. Handwerker, M. Löffler-Mang, R. Hannesen, and H. Gysi, 1999: Radome influence on weather radar systems with emphasis to rain effects. Preprints, 29th Int. Conf. on Radar Meteorology, Montreal, Québec, Canada, Amer. Meteor. Soc., 918–921. Merceret, F. J., and J. G. Ward, 2002: Attenuation of weather radar signals due to wetting of the radome by rainwater or incomplete filling of the beam volume. NASA Tech. Memo. NASA/TM— 2002-211171, 16 pp. [Available online at http://ntrs.nasa.gov/ archive/nasa/casi.ntrs.nasa.gov/20020043890.pdf.] Schneebeli, M., J. Sakuragi, T. Biscaro, C. F. Angelis, I. Carvalho da Costa, C. Morales, L. Baldini, and L. A. T. Machado, 2012: Polarimetric X-band weather radar measurements in the tropics: Radome and rain attenuation correction. Atmos. Meas. Tech., 5, 2183–2199, doi:10.5194/amt-5-2183-2012. Salazar-Cerreño, Jorge L, V. Chandrasekar, Jorge M. Trabal, Paul Siquera, Rafael Medina, Eric Knapp, and David J. McLaughlin, 2014: A drop size distribution (dsd)-based model for evaluating the performance of wet radomes for dual-polarized radars. J. Atmos. Oceanic Technol., 31, 2409–2430. doi: http://dx.doi.org/10.1175/JTECH-D-13-00208.1