On the Use of W-Band for Deep-Space Communications

In this article, the performance of W-band (90 GHz) over a Deep Space Network’s 34-m beam-waveguide (BWG) antenna is analyzed in terms of its average data return. In order to do so, data were collected from various sources about the performance of various W-band components. In addition, equations for calculating the W-band atmospheric noise temperature from water vapor radiometer 31.4-GHz sky-brightness measurements were obtained. Using these data it is shown that, even if the W-band link is operated optimally, due to weather effects the efficiency of the 34-m BWG antenna needs to be significantly improved from its current 18 percent efficiency to greater than 50 percent efficiency in order for the W-band link to return on the average significantly more (>2 dB) data than an optimum Ka-band link. I. Introduction With the push towards lower-weight and higher-speed spacecraft, the Deep Space Network is looking into using higher radio frequencies. This has a distinct advantage over the use of optical communications in that it uses existing DSN ground tracking facilities with some evolutionary modifications. Currently, the DSN is in the process of implementing Ka-band (32-GHz) tracking capabilities at all its tracking facilities. The next logical step is to look beyond Ka-band to W-band (90 GHz) to see whether or not W-band offers any significant advantage over Ka-band. This article reports on this inquiry. The article is organized as follows: In Section II, the link equation for the average data rate is introduced and its optimization is discussed. This lays the foundation for the comparison of W-band’s performance with that of Ka-band. As there are currently no W-band spacecraft or ground station components in existence for deep-space use, most of the analysis has been based on the experience and understanding of experts in various fields relating to deep-space communications. In Section III, the sources for the parameters used in this article as well as the formula for converting Ka-band water-vapor radiometer sky-brightness measurements to W-band zenith atmospheric noise-temperature measurements are given. In Section IV, equations in Sections II and III are used to calculate the value of “weather percentile” for the optimum performances for Ka-band, X-band, and W-band. (The term “weather percentile” is used as a shorthand to refer to the zenith atmospheric noise temperature associated with a fixed value of the cumulative distribution function (CDF). For example, if Pr{Tz