Updated Link Budget

Based on the updated values, the link budget can be currently reestimated with the following parameters:

The link budget suggests that no significant performance losses will be expected even after accounting for real world effects such as reduced amplifier output, and that real world losses are marginal.

Link Test Results Analysis

The link test was partially successful in that it demonstrated over the air data transmission and recovery. It further revealed that we would need to account for roughly 35 dB of missing link performance. While this is a high number, it is suspected that the primary cause of this deficit is due to the implementation of the test setup and antenna misalignment The contributing factors are explained below:

1. High receiver noise temperature: Higher baseline noise is encountered at lower elevations. This is primarily due to thermal noise from the earth’s surface, as well as the background atmospheric noise that enters the receiver as its line of sight passes through the earth’s atmosphere. The link test was conducted at approximately 1.6 degrees of Elevation, and the receiver noise was consequently estimated at ~300K, up from the nominal 107K at a 30 degree elevation used in most link calculations. This would result in a 4 dB loss in link budget.
2. 

3. RX Antenna misalignment: Given the extremely narrow beamwidth of the receive side antenna, it is extremely sensitive to any form of misalignment. This would include initial pointing errors caused during the initialization of the station, and also due to any installation allowances. During the test, it was observed that the signal strength would vary if there was wind, suggesting some form of wobbling of the dish/gimbal. A sensitivity study was further conducted to assess the effects of pointing misalignment on the ground side. Additional work will be conducted to reduce shaking of the antenna during wind loading conditions.

4. TX Antenna Misalignment: While the beamwidth of the TX antenna is much larger - approximately 20 degrees - it can still be subject to alignment errors. This is more so given that there was no proper mounting designed for it during the conduct of the test, beyond using the range finder to position it in the general direction of the ground station. For future testing purposes, more work will be undertaken to ensure consistent alignment of the TX antenna. This might include 3D printing a testing mount for it.

5. Rain Attenuation: On the day the results were collected, there was some light rain that occurred midway through the test. This could have resulted in higher than expected rainfall losses, contributing to reduced link performance. This is a known issue in Ku band and the link has been designed to operate at a 99% availability.

RX Antenna Misalignment Sensitivity Study

The RX ground segment antenna can be assumed to follow the gain distribution of a parabolic antenna. Therefore the gain profile (to a -10 dB contour) can be analytically approximated. While it is not within the scope of this report to provide the mathematical derivation of this approximation, there are online calculators which can be used for this purpose. After obtaining the gain profile for a 1m reflector at 13.95 GHz, a simple polynomial curve was fitted to it which allows us to approximate the antenna gain as a function of angular offset.

The sensitivity of the ground station to pointing errors was determined for 2 cases - one at 30 degree elevation and another at 90 degrees. Variations of the receiving antenna’s G/T ratio was calculated based on the above polynomial. To maintain ideal performance, the resulting performance curve indicates that the antenna must be pointed to within a 0.5 degree beamwidth cone of uncertainty. This places the antenna pointing requirement at 0.25 degrees or better.

Requirements Fulfilment:

Specifications	Requirement Met	Remarks
Targeted Data Rate: 2.6 Mbps Targeted Bandwidth: 2 MHz Nominal	Yes	Data Transmitted and recovered at QPSK ¾ at target bandwidth
Modulation Scheme: DVBS2 MODCOD: QPSK3/4 Nominal, Adjustable depending on link conditions	Yes	Data transmitted and recovered at QPSK3/4, with DVBS2 Modulation
Frequency: 13.95 GHz	Yes	Transmission frequency confirmed with Spectrum Analyzer
VSAT Aperture: 1m Targeted EIRP (Transmit Power + Antenna Gain): 10W (40 dBm)	Yes, Partial	Operation with 1m dish confirmed with degraded link budget due to testing inaccuracies Effective EIRP at 38 dBm, link analysis shows no significant degradation in performance
Payload Envelope: 1U (~10 x 10 x 10cm) Power Envelope < 30W	Yes	Measured Power Consumption : ~28W

	Theoretical	Updated	Remarks
Transmitted Power	33 dBm	31 dBm	Real Values after accounting for Antenna S11 Loss at -9 dB
RX Antenna Gain	41 dB	39 dB*	Actual Gain estimated at 0.6 deg pointing error- see sensitivity study
TX Antenna Gain	10 dB	10 dB*	14 dB peak, derated to 10 dB to allow 20 degree beamwidth
RX Noise Temperature	107K	107K	At 30 degrees elevation

	Theoretical	Link Test Conditions	Remarks
Transmitted Power	33 dBm	31 dBm	Real Values after accounting for Antenna losses at S11 of -9 dB
RX Antenna Gain	41 dB	41 dB*	Actual Gain Varies based on Pointing Accuracy - see sensitivity study
TX Antenna Gain	10 dB	10 dB*	10 dB to allow for pointing
RX Noise Temperature	107K	300K	Higher noise temperatures due to low elevation during link test