Effect of The Dish Angle on The Wet Antenna Attenuation Mostafa H. Ahfayd Electronic and Communication Department High Institute of Engineering,Regdaleen,Libya malnagh@yahoo.com Abstract -Rain attenuation is a major factor to demean the system performance at frequencies above 10 GHz. This paper deals with wet antenna attenuation at Ku band with different elevation angles and rain rate. throughout the Ku band propagation experiment, it was discovered that the rain water on the antenna caused signiicant attenuation. It is necessary to estimate the losses caused by water on the antenna in order to separate these losses from the atmospheric propagation losses. The experiment was done at USM Engineering Campus to study the attenuation for the physical parameters. At Ku band the RF signal was generated by a signal generator and transmitted via horn antenna. The signal was received using a smooth offset antenna of 61 cm by 54 cm (Astro dish) and measured using a spectrum analyzer. To simulate the rain rate, PVC pipes with equally distant bores were implemented. Three cases were considered: First, one pipe was used to simulate low rain rate; second, two pipes were used to simulate medium rain rate; third, three pipes were used to simulate heavy rain rate. In addition, the tap was used to control the low of water to get more values of rain rate. The total attenuation ofRF signals due to water layer on the feed and on the relector feed was found to be 3.1 dB, at worst case. On the other hand, the attenuation of the RF signal due only to feed was 2.S1 dB, so major attenuation occurred was from feed. Keywords- Anntena; Attenuation; pipe; Frequncy I. INTRODUCTION The rain effect on surface or on the parabolic relector and on the feed window is considerable at higher requencies. It depends on antenna geometry, elevation angle, rain rate, etc. [7] Recent studies show that these losses are signiicant for the measurement of excess attenuation due to rain [1,5]. Wet antenna losses are required to be subtracted rom the measured attenuation in order to get the propagation losses accurately. The effect of water on the surface of relector and radome of feed window are of growing interest in satellite communications. Experimenters speculate that the effect could be responsible for more than 3 dB of attenuation at Ka-band; however few experiments have been conducted. The simple experiment of spraying water irst on the ACTS propagation terminal (APT) antenna relector and later on the feed window was conducted in the fall of 1993 ater satellite transmissions were acquired but Abdalla M. Hanashi . Computer Engineering Department, Faculty of Engineering, University of Zawia, Zawia, Libya ahanashi@yahoo.com before the oficial start of the ACTS propagation experiment [6]. The result was generally less than 0.3 dB of attenuation due to water droplets on the feed and the attenuation due to water droplets on the relector was l.9 dB at 27.5 GHz and l.0 dB at 20.2GHz. According to Hendrix, et al. [11], the water on the surface of a radome due to rain lows down in three different forms: a laminar sheet, rivulets and as droplets. The form of the water low on a spherical Radom is dominated by the hydrophobic properties of the radome [II]. The higher the rain intensity the longer the rain water stays as droplets. The attenuation of droplets is smaller than the attenuation caused by a continuous ilm or by rivulets due to the fact that the attenuation mechanism of droplets is relatively weak because of scattering compared to the absorption and relection caused by a continuous ilm [10]. A campaign to examine experimentally the magnitude of the wet antenna problem was undertaken at several of the ACTS propagation experiment sites. [2,3], reported attenuation values in excess of 9 dB produced by spraying water on the APT antenna. Similar sprayer measurements were made at the ACTS experiment sites in British Columbia [9]. The latter experiment included rain gauge measurements to detemine the rain rate produced by the sprayer. In each case, the experiments were made on clear sky days and the reported attenuation was due only to the water sprayed on the antenna. In one of the experiments, the relector had been sprayed with a hydrophobic coating in an attempt to eliminate the water layer but with no success. Acosta (1998) reported results of a comparison between observations made using two closely spaced antennas, one shielded rom rain and the other exposed to the rain. He observed more than 4 dB of attenuation attributable to water on the exposed antenna at rain rates up to 40 mm/h. The low rate was controlled so repeatable experiments could be made at the same effective rain rate. The measured attenuation values were 2 dB for the wet feed window at 20.2 GHz and 27.5 GHz and the total relector plus feed window attenuation values of 3.9 and 6.3 dB at 20.2 and 27.5 GHz, respectively, at a rain rate of 40 mm/h. A methodology for system design has been developed rom the earlier work: radomes may 978-1-4799-3351-8/14/$31.00 ©2014 IEEE