Receiver Design
Figure 1 contains a preliminary block diagram of the proposed beacon receiver for each Earth station. The V-band receiver antenna is directly connected to an orthomode transducer (OMT), which separates the received signal into vertically and horizontally polarized components. Separating these components allows for the measurement of depolarization. The signals are passed through a directional coupler, amplified by ultra-low noise LNAs (see the Front-End Technology Selection and Downlink Budget section) and downconverted to the first IF stage (Ka-band). The Ka-band IF signals are split and delivered to a radiometer and to a digital receiver (through a second IF stage).
The radiometers enable the measurement and characterization of relatively slow fading mechanisms such as gaseous attenuation and cloud attenuation and correct for measurements inaccuracies introduced by receiver gain and satellite EIRP fluctuations. The radiometers and digital receiver need to be calibrated regularly to compensate for receiver gain fluctuations. This is accomplished by periodically injecting a reference noise temperature into the receiver using a stable, known noise source [1]. This noise source is injected through a roughly 20 dB directional coupler to minimize losses in the main signal path and to prevent noise source on/off state impedance mismatches from “load-pulling” the main signal path. A radiometer calibrated in this manner is known as a “noise-adding radiometer.”
In addition to the beacon receiver shown in Figure 1, a meteorological data acquisition station will be located at each Earth station. This station will record all local meteorological parameters of interest. This data, along with the data from the radiometer and the digital beacon receiver, will be sampled and stored on a local computer for processing off-site. More information on the data acquisition and post-processing is contained in the “V-band Beacon Experiment Plan” section.
Figure 1. Preliminary block diagram of Earth station V-band beacon receiver (click to enlarge).
References:
[1] J. M. Riera, A. Benarroch, P. Garcia-del-Pino, J. M. Garcia-Rubia, “Simultaneous Beacon and Radiometer Propagation Measurements in the Ka-Band,” European Conference on Antennas and Propagation (EuCAP), Apr. 2011.