Earth Station

An earth station is a ground station that transmits to and receives from a communication satellite through its antenna, RF chain, modem and baseband equipment.

Subsystem	Function
Antenna system	Focuses transmitted and received microwave energy
HPA	High-power amplifier for the uplink
LNA / LNB	Low-noise amplifier / block for the weak downlink
Upconverter	IF $\to$ uplink RF frequency
Downconverter	Received RF $\to$ IF / baseband
Modem	Modulation, demodulation, coding, framing
Tracking system	Keeps the antenna pointed at the satellite (if needed)
Monitor and control	Supervises alarms, power and performance

Earth-station subsystems.

Earth station: transmit chain (codec$\to$modem$\to$up-conv$\to$HPA) and receive chain (LNA$\to$down-conv$\to$modem$\to$output) sharing a duplexer, dish, tracking and monitor/control.

Caution

Key Formula — Parabolic-dish gain and figure of merit

$$G=\eta\!\left(\frac{\pi D}{\lambda}\right)^{\!2},\qquad G_{dBi}=10\log_{10}\!\left[\eta\!\left(\frac{\pi D}{\lambda}\right)^{\!2}\right],$$$$\frac{G}{T}(dB/K)=G_{dBi}-10\log_{10}T_s.$$

Here $\eta$ is aperture efficiency, $D$ the dish diameter and $\lambda$ the wavelength; $T_s$ is the system noise temperature. A high G/T (receive gain relative to system noise temperature) is the single figure of merit for downlink reception — larger dish and lower-noise front end both raise it.