4. Ground Station

4.1 Overview

The ground station is a component on the Earth system that communicates with the satellite. It is in charge of transmitting commands up and gathering the downlink data such as telemetry or payload data that the satellite transmits back.

Our primary concern for this project is downlink reception. The system is designed to receive the Ku-band signal at approximately 13.95 GHz. A motorized gimbal allows the antenna to track the satellite and maintain a stable link as it passes overhead in space.

4.2 Problem Statement

Telemetry and payload data are continuously transmitted by satellites, we only can receive this data with a suitable ground-based system to receive the downlink. Furthermore, without a proper receiving setup, we are unable to monitor the satellite’s status and carry out our mission.

The main challenge for our ground station system will be maintaining a stable Ku-band link from the satellite to the ground station, as the satellite is in constant motion. The ground equipment must track the satellite accurately in order to receive the signal reliably, this ensures that the link will not be interrupted.

The issue for our project was straightforward: Commercial ground-station solutions are inappropriate for the particular communication requirements of this project since they do not support the downlink frequency of 13.95 GHz that we need.
Therefore, we are required to build our own ground station that is capable of tracking the satellite’s movement, moving the ground station satellite dish to track and accurately face the targeted satellite to be able to receive the 13.95GHz downlink at the same time.

4.3 Objective

Designing and implementing a Ku-Band downlink system that can receive satellite signals at 13.95 GHz is the primary goal of the Ground Station subsystem. This entails creating a tracking system and an end-to-end receiving chain to guarantee constant alignment with satellites in orbit.

Both software and physical components are integrated into the project. While the software takes care of tracking, control, and data management, the hardware concentrates on signal capture and conversion.

4.4 System Scope

4.4.1 Hardware Scope:

• 1 m Ku-Band Dish Reflector
• RHCP/LHCP Feedhorn
• PLL LNB
• Software Defined Radio (SDR)
• Gimbal and Controller (Newmark GM-12E-3A + NSC-G3-E)

4.4.2 Software Scope:

• Python-based tracking and control
• Integration with GPS and TLE data
• Real-time interpolation for smooth gimbal motion

4.5 System Overview

4.5.1 Ground Station System Overview (Flowchart)

4.5.2 Component Functions

Satellite (Ku-Band, 13.95 GHz)

Transmits downlink signals to the Ground Station on the Ku-Band frequency.
Provides telemetry and payload data for reception and analysis.
Dish Reflector (1 m Ku-Band)
Collects and focuses weak satellite signals onto the Feedhorn.
Mounted on a two-axis gimbal for real-time satellite tracking.
Feedhorn (RHCP/LHCP)
Ensures correct signal polarization (Right- or Left-Hand Circular).
Directs the focused signal from the dish into the LNB.
PLL LNB (Phase-Locked Loop Low Noise Block)
Amplifies weak signals from the Feedhorn.
Converts the high-frequency Ku-Band signal to a lower intermediate frequency (IF).
Maintains signal stability using a phase-locked loop.
Software-Defined Radio (SDR)
Converts the analog IF signal into a digital stream.
Decodes the DVB-S2 (Digital Video Broadcast) signal format for analysis.

Control PC
Receives and processes the digital data from the SDR.
Interfaces with the Python-based tracking and gimbal control system.

4.5 Current Progress

The ground station’s software subsystem is about 90% complete. Real-time satellite tracking is now possible because of the complete implementation of the gimbal tracking and control framework, which integrates GPS inputs with Two-Line Element (TLE) orbital data. The azimuth and elevation angle commands are smoothed using Piecewise Cubic Hermite Interpolation (PCHIP), which ensures steady and continuous pointing of the antenna without any sudden changes.

Hardware-wise, the NSC-G3-E motion controller and the Newmark GM-12E-3A gimbal have been integrated with the Gimbal Control System software. The system can carry out tracking commands smoothly, with no discernible jitter or uneven movement, according to preliminary motion testing.

The 1-meter Ku-band dish, the RHCP/LHCP feedhorn, and the PLL-stabilized LNB are the remaining parts needed for the RF receive chain that are still awaiting delivery. Following the delivery of these parts, the entire ground station can be assembled. End-to-end testing will then be conducted to assess the system’s dependability in acquiring and decoding the 13.95 GHz downlink signal.

4.6 Groundstation Hardware Components

4.6.1 1 m Ku-Band Dish Reflector (NS-FM(Ku)-100)

The 1 m Ku-Band Flyaway Antenna Dish Reflector will serve as the main receiving antenna for downlink signals in the 13.75–14.5 GHz range.

Specifications:

Material: Carbon Fibre (lightweight, high stiffness)
Polarization: Circular
Antenna Type: Offset Parabolic
Drive Mode: Manual
Gain: 42.59 + 20 lg (f / 13.85) dBi
Operating Frequency: 13.75 – 14.5 GHz
Surface Accuracy (RMS): ≤ 0.5 mm
First Sidelobe: ≤ –14 dB
3 dB Beamwidth (Mid-Band): 1.32°
Interface: WR-75

This reflector provides high gain and low surface error, ensuring efficient signal focusing and minimal distortion for Ku-band reception.

For the dish reflector, carbon fibre (density: 1.5-2g/cm³) was selected over aluminium (density: 2.8g/cm³) and steel (density: 7.8g/cm³) after comparing the weight, durability and long-term performance of each material. Steel was ruled out early mainly due to its heavy weight and the tendency to rust easily which is undesirable for a moving mount that needs to react quickly.

Aluminium performed better in terms of weight when compared to steel. However it still adds a noticeable load to the gimbal and it oxidises over time which would require regular upkeep. Carbon fibre, on the other hand, is significantly lighter around 40 to 50 percent lighter than aluminium while still being stiff. This reduces mechanical strain on the gimbal motors and allows the tracking system to move more smoothly due to the lower weight. Another practical advantage is that carbon fibre does not corrode, as a result the reflector can remain outside without experiencing surface degradation. Although carbon fibre costs more upfront, the combination of strength, stability and low maintenance made it the most suitable material choice for our 1m dish reflector.

4.6.2 Ku-Band Feedhorn (NS-FM(Ku)-100)

The Ku-Band Circular Polarization Feedhorn (RHCP/LHCP) which we will be using is used to capture and polarize the incoming signal reflected from the dish surface before directing it to the LNB. It ensures proper circular polarization alignment to match the satellite’s transmission.

Specifications:

Frequency Range: 13.75 – 14.5 GHz (Ku-Band Rx)
Polarization: Circular (RHCP / LHCP)
Interface: WR-75
F/D Ratio: 0.5

This feedhorn was selected for its compatibility with the WR-75 interface and its ability to support dual circular polarization (RHCP and LHCP). Circular polarization minimizes signal loss due to orientation mismatch and improves link stability under varying weather and tracking conditions, making it ideal for Ku-band satellite communications.

4.6.3 Ku-Band PLL LNB (Atron A500-137-142N05)

The Atron A500-137-142N05 Ku-Band PLL Low Noise Block (LNB) downconverts the high-frequency Ku-band signal into a lower intermediate frequency (IF) for processing by the Software Defined Radio (SDR). It uses a Phase-Locked Loop (PLL) design for enhanced frequency stability and low phase noise.

Specifications:

Input Frequency: 13.7 – 14.2 GHz
Output Frequency: 900 – 1400 MHz
Local Oscillator Frequency: 12.8 GHz
Noise Figure: ≤ 0.8 dB
Conversion Gain: 55 – 65 dB (60 dB typ.)
Interface: WR-75 waveguide (with groove)
Output Connector: F-type or N-type female
Operating Temperature: −40°C to +60°C
Waterproof Rating: IP67

Performance Note:
This LNB was chosen for its low noise figure and high stability which are essential for maintaining signal integrity in Ku-band reception. The IP67-rated body ensures durability for outdoor operation, and the PLL design provides superior frequency accuracy compared to traditional DRO-based LNBs.

4.6.4 Gimbal Control System (Hardware Setup)

The Newmark GM-12E-3A is the main 2-axis mount we’re using to move the dish. It’s meant for setups that need accurate pointing like antennas or small optical systems. For our project the 1-metre Ku-band dish sits on this gimbal so it can follow the satellite as it moves across the sky during a pass.

The unit runs on NEMA 23 stepper motors and they’re paired with worm gears and optical encoders so the movement is quite controlled without noticeable backlash. It can swing about ±90° in both azimuth and elevation which is enough for us to track most passes cleanly and accurately.

We also use the Newmark NSC-G3-E controller to drive the gimbal. It talks to the PC over Ethernet (RS-232) and the software would send the pointing commands through it. The controller then handles the closed-loop side of things and smooths out the motion so the gimbal doesn’t jerk around when it updates its angles.

The GM-12E-3A and the NSC-G3-E together form the core of the pointing system. Once the tracking script feeds into the satellite’s location. This setup keeps the dish pointed at the right spot from start to finish of a pass.

4.6.5 Adapter

The adapter is the piece that enables us to attach the 1-metre Ku-band dish to the GM-12E-3A gimbal as well as to ensure that the dish sits firmly on the mount and that the weight is spread out properly so the gimbal doesn’t get stressed. It also helps keep the dish lined up with the gimbal’s rotation so the pointing angles stay accurate.

Currently, we have yet to design the adapter because we’re still waiting for the detailed drawings from the dish supplier. Without the exact hole layout and mounting surface dimensions we can’t start modelling it. Once the specs come in we’ll proceed to sketch it out and build it ourselves.

When we get to the design stage we’ll probably go for something that’s strong but light and not one that would rust easily. Materials like aluminium or maybe even carbon-fibre plates are on the table mainly because they won’t add too much weight or extra torque for the gimbal motors to deal with. We’ll also try to keep the shape simple so assembling everything isn’t a hassle.

4.6.6 Software Defined Radio (SDR)

As of now, the SDR component of the ground station is still a work in progress. Our team is exploring the use of a Software-Defined Radio capable of receiving and decoding DVB-S2 signals which is commonly used for satellite communication. We are currently focused on tracking and mechanical integration first and the signal acquisition and decoding pipeline will be developed and updated in later project phases.

4.7 Challenges

4.7.1 Past Challenges

During the initial integration and testing phase, one major challenge we encountered was the mechanical limitation of the Newmark GM-12E-3A gimbal used for satellite tracking. The gimbal, controlled via the Galil NSC-G3-E motion controller, has mechanical rotation limits of ±90° on both the Azimuth and Elevation axes.

Initially, the Elevation axis limits were incorrectly configured, with the rotation range capped at straight up (vertical) and straight down (vertical). This configuration restricted the gimbal’s ability to follow satellite trajectories across the sky, as it could not perform smooth tracking along the horizontal plane. Consequently, when executing the tracking code, the system frequently ran into limit errors, preventing complete coverage of the required azimuth–elevation coordinates.

To resolve this issue, the team performed mechanical adjustments to the elevation axis, reconfiguring its range of motion to allow full rotation across the horizontal plane. As shown in the images above, the gimbal’s reference or home position is as shown in the middle image with the modified limits (right & left) now enabling tracking of satellites across both sides of the sky above the horizon.

This modification successfully eliminated the tracking errors and ensured continuous, unrestricted motion for real-time satellite tracking.

4.7.2 Current Challenges

Right now, one of the major issues we’re facing is the wiring around the gimbal. When the GM-12E-3A moves around especially in azimuth or elevation, the cables sometimes would get tangled or rub against the sharp edges of the frame. There were also instances where the wires would get hooked on parts of the mount which is not ideal. If this issue is not addressed, it could block the motion or mess up with the signal. In the worst case scenario, it might even damage the cables entirely. Currently, we’re looking at different ways to manage the routing efficiently. We are currently exploring several cable-management solutions such as proper cable guides, using flexible cable chains, or even going for a slip-ring setup so the wires don’t twist at all. We just need to ensure that the cables are kept clear while the gimbal moves freely. Once the cable layouts are sorted, the system should be able to run a lot more smoothly and safely during long tracking sessions.

4.8 Future Plans

Looking ahead, the team will focus on completing the remaining stages of the Ground Station development. The key upcoming milestones include:

Hardware Integration
For the hardware side, the next step is basically getting everything connected and making sure the whole setup works as intended. Once the last few parts come in, we’ll proceed to put the dish, feedhorn, LNB, SDR, and the control PC into one complete chain. After once everything is mounted, we’ll run a few simple signal tests just to check that all the components can talk to each other properly.
Receiver Hardware Development
For the receive chain, the plan is to figure out which setup gives us the cleanest Ku-band signal. Once we have all the parts on hand then we’ll put the LNB and SDR (DVB-S2) together and start adjusting their settings to see what works best. Most of the work here is just tuning things so the signal comes in steadily without too much noise messing it up.
Gimbal Cable Management Redesign
We also need to sort out the wiring issue on the gimbal. Right now the cables tend to twist or get caught when the mount rotates too much, so we’re looking at better ways to route them. It might be as simple as adding proper cable guides, or we might be considering going for a slip-ring setup if we need full rotation without the wires getting tangled.
Full-System Testing and Calibration
The last part of our work will consist of the full system test. We’ll run the gimbal tracking together with the RF chain and see how everything behaves in real time whether the dish follows the satellite accurately or the signal shows up cleanly and if the data can be decoded without dropping out. After that, we’ll proceed to fine-tune the pointing and signal settings so the satellite stays aligned and the downlink remains stable.