In the project, a test bed for antenna tracking systems of earth stations operating in the QV-band is developed. The test bed emulates the antenna servo system, the ground station RF front end, the ACU and the tracking receiver, as well as the propagation properties of the channel including scintillations, fading and refractive effects in the atmosphere. Aim of the project is to verify the tracking performance with respect to different station setups and control algorithms in order to support the design of antenna tracking systems in QV-band.
The challenge of this project is to build a flexible system that is able to support the design process for ground stations in terms of antenna tracking operated on different sites considering local tropospheric effects and various tracking methods.
Especially at Q/V band, the tracking system has to cope with atmospheric propagation effects which are more severe than those experienced at Ku and Ka band. These effects include an increase of gaseous, rain and cloud attenuation with steeper fade slopes, as well as stronger scintillations caused by tropospheric turbulence. Furthermore refracting effects become more relevant.
The development of new earth stations in QV-band can be effectively aided, when the design of the antenna tracking system can be verified and optimized cost effectively in the test bed developed in the course of this project.
The Q/V-band antenna tracking system test bed supports the following features:
Orbit generator: Based on ephemeris data it defines the actual orbit position of the spacecraft to be used as a reference.
Orbital data degradation: The actual orbital information made available for the control of the ground station could differ from the actual one because of latency, update frequency and accuracy issues. These effects are simulated by this module.
Atmospheric channel model: It simulates the effects of the atmosphere on the electromagnetic wave transmitted by the satellite beacon and received by the ground station.
These effects include the variations of amplitude and of angle of arrival according to actual spacecraft orbit and location of the ground station.
The model requires a set of atmospheric parameters, the actual satellite position and the frequency of the satellite beacon as input parameters.
RF front end and antenna simulator: This sub-system describes the variation of the signal at the output of the antenna according to direction of arrival of the electromagnetic wave, as well as the effects of the antenna front-end and network for down-conversion to IF on the RF signal to (gain, linearity and noise). The RF antenna parameters and the frequency of the satellite beacon are required input parameters.
Tracking receiver simulator: It simulates the effects of the radio receiver that converts the tracking error signal from IF to a baseband error signal.
Antenna control unit: It provides algorithms for tracking, e.g. step track, orbit prediction tracking or monopulse. The antenna control unit issues commands to the antenna servo simulator controlling the antenna pointing and reads the antenna position encoders. In the project the antenna control unit is an off-the-shelf model from Vertex.
Antenna Servo Simulator: It includes a simulator of the time response of the antenna servo mechanism, based on the antenna mechanical properties, including effects of wind loading and emulates the antenna position encoders.
Pointing loss and Statistical toolbox: This subsystem calculates various statistical measures like the resulting tracking errors or the pointing losses at the frequencies of the telecom services provided by the ground antenna.
The basic architecture of the Q/V-band antenna tracking system test bed is shown in the diagram below.
This project consist of the following tasks:
- State-of-the-art review of channel models for Q/V-band and identification of necessary improvements
- State-of-the-art review of earth stations including antenna tracking systems and RF front ends
- Architectural design
- Definition of an operational scenario for verification of the test bed (Reference system is the Alphasat TDP5 Q/V-band earth station in Graz)
- HW implementation and software development
- Test case execution and performance verification against the reference system
This project is successfully completed.