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Direct Link To This Post Topic: RF Equipment - Satellite Ground Station Components
    Posted: 07/August/2015 at 22:48
RF Equipment - Ground Station Components
In these tutorials we will look at the various component parts that make up a satellite ground station and the typical practices that engineers employ during satellite ground station engineering projects.
Radio Frequency (RF) Equipment

Feed System
The antenna feed is the start point of the receive chain and the end point of the transmit chain. The feed can be of a simple design with just one transmit and one receive waveguide ports for one frequency band and one polarisation or more complex with multiple ports for multiple frequency bands and dual polarisations for both transmit and receive. There are also feeds which have additional ports for the antenna tracking system such as Mono-pulse feed systems.

Transmit and Receive Waveguide Filters
The feed usually connects to waveguide filters to prevent unwanted transmissions out of band and unwanted reception out of band. This helps to isolate the transmit and receive paths as well as reduce interference.

Waveguide Filter Combining Networks
In order to connect multiple HPAs to the same feed port polarisation (for multiple carriers) it is necessary to filter the individual HPA outputs to restrict the operating bandwidths and then combine these in waveguide combiners. The result is a reduction in interference and minimal loss of power as would be the case if you simply route multiple carrier signals through a single HPA. The HPA would need to be backed off (input attenuated) by a large amount to avoid saturation and unwanted intermodulation.

High Power Amplifiers (HPA)
The transmitter is called a High Power Amplifier which can be of either a Travelling Wave Tube Amplifier (TWTA) or Solid State Power Amplifier (SSPA) design. The latter is less sensitive to shock and vibration and is often used in outdoor environments as it is a cheaper design although does not yet have the power to match the TWTA design. This is changing though and new technologies are producing ever more powerful SSPAs.

Waveguide Couplers
At the output of the HPA, and the input of the LNA, can usually be found Waveguide Couplers. These can be used to measure the RF power at the HPA output by connecting a power meter or for signal injection at the LNA.

Low Noise Amplifiers (LNA)
The low noise amplifier is a critical component in the performance of the antenna system being a fundamental part of the G/T calculation. The better the LNA the more signal is available at the LNA output compared to the noise level. See our tutorials on G/T calculation for more information.

Low Noise Block downconverter (LNB)
The LNB is essentially the same as the LNA except it has a built-in block downconverter which reduces loss and enables the RF signals to be received and immediately be converted to IF signals.

Block Converters
These are frequency converters that convert one frequency band to another without any tuning required. An example of this is Ku Band to L Band conversion where all Ku Band frequencies are down converted to l band frequencies and visa versa for the up conversion.

As with the LNB, which is a combined LNA and block down converter (LNB) the HPA can also be provided with a built-in block up converter (BUC). In small VSAT systems this combined HPA and BUC is simply called a BUC but for large ground stations with much higher power amplifiers the TWTA or SSPA is described as including the BUC.

In the next Tutorial we will look at the IF equipment.

Edited by Satcoms UK - 30/August/2015 at 22:38
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