Basics of Satellite Ground Station Hardware

A ground station, earth station, or earth terminal is the terrestrial radio system used in extraplanetary telecommunications with spacecraft and satellites. Ground stations are used to communicate, bidirectionally, with satellites and spacecraft, or receive electromagnetic energy in the radio frequency spectrum from astronomical sources. Given the nature of extraplanetary communications, ground stations and satellites/spacecraft typically communicate with microwave and millimeter-wave signals, which are extremely weak upon reception. Hence, electrically large parabolic antennas have been common in the past as ground station antennas. More recent ground station systems for massive satellite constellations in low earth orbit are now instead using active antenna array systems with beamsteering technology.

Key components of ground station hardware are its antenna system, extremely linear transmitters, and highly sensitive receivers. In some cases, automatic tracking systems are also necessary to maintain synchronization between the satellites/spacecraft’s directional antenna and the ground station antenna. In some cases a ground station may have multiple antennas or several satellite/spacecraft communication systems, and may also be distributed in a broad region to track multiple satellites or provide spatial diversity. There is also a growing trend of networked ground station systems that are both modular and powered by open source software and internet-based control, monitoring, and communication to better facilitate modern satellite networks.

To maintain the utmost in sensitivity and signal integrity, many traditional ground station communication systems relied on dedicated and discrete modulation/demodulation and data handlers. It is becoming more common to use software-defined systems. Moreover, earlier ground station hardware used multiple frequency translation stages for both the transmit and receive pipelines. With higher frequency direct digital synthesis and direct digital sampling technology, less frequency translation stages are now necessary. For K and Ka band satellite communications there is still a need for multiple frequency translation stages as digital-to-RF and RF-to-digital direct conversion electronics aren’t widely capable of millimeter-wave frequency operation.

Given the extremely weak signals from extraplanetary communication sources, in some cases the receiver network of a ground station system may be cryogenically cooled to lower the noise figure of the low-noise-amplifier and critical components. This is because the noise floor is the limiting low-end factor of a ground station’s dynamic range, and to reduce the added noise figure of RF devices and components cooling can be used to mitigate some of the thermal noise generated by these signal chain components. It is also important to design a ground stations receive system to avoid introduction of nonlinearities, spurs, or harmonics that could otherwise reduce the signal integrity of the receiver pipeline.

Interference from noise sources is also a high concern for ground stations, as the receiver section is optimized for sensitivity and may be susceptible to desensitization from interference sources in and out of the band of interest. Hence, extremely selective filters are often used after input amplification stages following the antenna. Though these highly selective filters tend to have higher attenuation in the passband, eliminating out of band interference in noise is often a greater priority. Multiple filters are typically used throughout the receiver pipeline to further reduce out of band noise, harmonics, and spurs from the frequency translation and amplification stages.