The low transmit power of the satellite combined with the large free-space path losses of the system make SNR the constraining parameter of the ground receiver. This system is thus designed with minimal losses before the LNA, and a cryogenically-cooled LNA is used to drastically decrease its noise figure. As shown in [1], a cryogenically-cooled LNA can provide a noise figure of easily 4-5 dB less than a room-temperature LNA, thus increasing overall SNR by roughly 4 dB.

The ground station receiver uses an orthomode transducer to split the incoming signal - which has been Faraday shifted from a single linear polarization to a combination of vertical and horizontal polarization - into vertically and horizontally polarized components, which are then individually mixed down and can be compared in the signal processing unit to characterize the polarization shift.

A radiometer is used on one leg of the receiver to experimentally measure the background noise, as described in the experiment section. The received signal is filtered out with an additional BPF, isolating noise power for the radiometer measurement.

The rest of the system is very similar to the satellite receiver chain: a two-stage superheterodyne configuration is used to improve image rejection and downconversion accuracy. Note the vastly improved LNA noise figure - 0.6 dB versus 5 dB in the satellite - leading to a total noise figure of 3.56 dB versus 7.00 dB in the satellite.

Table 1 gives the key parameters of this system, and Figure 2 shows the layout.

Table 1: Ground Receiver Key Parameters

Figure 1: Ground Station Receiver Block Diagram