Iridium Satellite Spot Beam Coverage on the US
This example shows how to generate and visualize Iridium satellite spot beams on the US map. The Iridium satellite antenna array is created using Phased Array System Toolbox. The satellite position is generated and viewed using Satellite Communications Toolbox. The spot beam coverage map is displayed as the antenna array is steered.
Introduction
The Iridium satellite system is a low-Earth-orbit (LEO) satellite constellation system that provides high-quality voice and data communications. This system consists of 66 satellites distributed along six polar orbital planes. Each satellite’s main mission array (MMA) is a 120-element L-band uniform rectangular array (URA). The MMA can generate 48 fixed spot beams towards earth using analog beamforming technology.
Create an Iridium Satellite Main Mission Array
An Iridium satellite adopts a 12-by-10 element URA as its MMA. Configure the MMA using Uniform Rectangular Array.
% Iridium satellite frequency freqLow = 1616e6; % Hz freqHigh = 1626.5e6; % Hz freq = (freqLow + freqHigh)/2; % Hz % Determine the wavelength lambda = physconst('LightSpeed')/freq; % Define array size in row and column nrow = 12; ncol = 10; % Define row and column element spacing drow = lambda/2; dcol = lambda/2; % Configure Iridium 120-element MMA iridiumArray = phased.URA(... 'Size',[nrow ncol],... 'ElementSpacing',[drow dcol],... 'Lattice','Triangular'); iridiumArray.Element.BackBaffled = true; % View Iridium MMA figure viewArray(iridiumArray)
View the 3D directivity pattern of Iridium MMA.
% Plot 3D directivity pattern of Iridium MMA
figure
pattern(iridiumArray,freq)
Create Satellite Scenario
Create a satellite scenario using satelliteScenario (Satellite Communications Toolbox). Specify a start time and duration of 60s for the scenario.
% Define start and end time startTime = datetime(2021,3,17,22,52,0); % 17 March 2021 10:52 PM UTC stopTime = startTime + minutes(1); % 17 March 2021 10:53 PM UTC sampleTime = 60; % s % Configure satellite scenario sc = satelliteScenario(startTime,stopTime,sampleTime);
Set Keplerian elements of an Iridium satellite such that the satellite passes above the US.
% Define the semimajor axis of the orbit of the satellite semiMajorAxis = (6371 + 780)*1e3; % m % Define the shape of the orbit of the satellite eccentricity = 0; % Define the inclination angle inclination = 86.4; % degrees % Define the argument of periapsis argOfPeriapsis = 0; % degrees % Define the right ascension of ascending node raan = 55; % degrees % Define the true anomaly trueAnomaly = 38; % degrees
Configure the Keplerian elements of the Iridium satellite using the satelliteScenarioViewer (Satellite Communications Toolbox) object.
% Configure Iridium satellite iridiumSat = satellite(sc, semiMajorAxis, ... eccentricity, ... inclination, ... raan, ... argOfPeriapsis, ... trueAnomaly, ... Name = "Iridium Satellite", ... OrbitPropagator = "two-body-keplerian");
View satellite scenario by using satelliteScenarioViewer (Satellite Communications Toolbox).
% Satellite scenario
v = satelliteScenarioViewer(sc,ShowDetails=false); 
Configure Iridium Satellite 48 Spot Beam
The Iridium satellite has 48 spot beams. These beams are arranged in 4 tiers. The following figure shows the spot beam indices and the 4-tier structure with different tiers drawn in different colors.
% Number of spot beams numSpotBeam = 48; % Define 48 spot beam indices in 4 tiers tier1 = [16,32,48]; % inner-most beams tier2 = [13:15,29:31,45:47]; % inner-middle beams tier3 = [8:12,24:28,40:44]; % outer-middle beams tier4 = [1:7,17:23,33:39]; % outer-most beams % Define transmission parameters maxRange = 5e6; % m transmitterPower = 11; % watts thetaoffset = [11,19,33,45]; % degrees % Define signal strength range sigstrengthlow = -105; % dBm sigstrengthhigh = -95; % dBm sigstrengths = sigstrengthlow:sigstrengthhigh; sigcolors = [sigstrengthlow,sigstrengthhigh];
Display Iridium Satellite 48 Spot Beam Coverage on the US
The 48 spot beams are formed using transmit beamforming at the Iridium satellite. Configure steering vector of the Iridium array using phased.SteeringVector.
% Configure steering vector for spot beam beamforming steeringvector = phased.SteeringVector("SensorArray",iridiumArray);
Obtain Iridium satellite position using states (Satellite Communications Toolbox) function of the satelliteScenarioViewer (Satellite Communications Toolbox) object.
% Obtain Iridium satellite position iridiumpos = states(iridiumSat,startTime,"CoordinateFrame","geographic");
Create the satellite as a txsite (Antenna Toolbox) in siteviewer (Antenna Toolbox), which supports terrestrial RF propagation analysis and visualization.
% Configure site viewer to view spot beams viewer = siteviewer('Terrain','none'); % Loop beam index to plot 48 spot beams for beamIdx = 1:numSpotBeam % Configure phi/theta angles for each spot beam if any(ismember(beamIdx,tier1)) k = find(beamIdx == tier1); phi = 360/numel(tier1)*(k-1); % degrees theta = thetaoffset(1); % degrees elseif any(ismember(beamIdx,tier2)) k = find(beamIdx == tier2); phi = 360/numel(tier2)*(k-1); % degrees theta = thetaoffset(2); % degrees elseif any(ismember(beamIdx,tier3)) k = find(beamIdx == tier3); phi = 360/numel(tier3)*(k-1); % degrees theta = thetaoffset(3); % degrees else k = find(beamIdx == tier4); phi = 360/numel(tier4)*(k-1); % degrees theta = thetaoffset(4); % degrees end % Convert steering angle from phi/theta form to azimuth/elevation form azel = phitheta2azel([phi;theta]); % Set transmit beamforming weights for a spot beam sv = steeringvector(freq,azel); iridiumArray.Taper = sv'; % Configure the transmit site for a spot beam spotbeam = txsite("Name","Iridium-Next Satellite Tx",... "Latitude",iridiumpos(1), ... "Longitude",iridiumpos(2), ... "AntennaHeight",iridiumpos(3),... "Antenna",iridiumArray,... "AntennaAngle",[0;-90],... "TransmitterFrequency",freq,... "TransmitterPower",transmitterPower); % Plot 3D beam pattern in animation pattern(spotbeam) % Display coverage map coverage(spotbeam,"freespace",... 'MaxRange',maxRange,... 'SignalStrengths',sigstrengths,... 'ColorLimits',sigcolors) end
Summary
This example shows how to create an antenna array using Phased Array System Toolbox. This example also shows how to generate a satellite scenario using Satellite Communications Toolbox. Through this example, you learned how to display different beams generated by an antenna array on a map.
Reference
[1] Attachment EngineeringStatement SAT-MOD-20131227-00148. https://fcc.report/IBFS/SAT-MOD-20131227-00148/1031348. Accessed 9 June. 2023.
[2] Attachment Exhibit A SAT-MOD-20131227-00148. https://fcc.report/IBFS/SAT-MOD-20131227-00148/1031240. Accessed 9 June. 2023.
[3] Manual for ICAO Aeronautical Mobile Satellite (Route) Service, Part 2-Iridium, Draft v4.0. https://www.icao.int/safety/acp/Inactive%20working%20groups%20library/ACP-WG-M-Iridium-8/IRD-SWG08-IP05%20-%20AMS(R)S%20Manual%20Part%20II%20v4.0.pdf. Accessed 9 June. 2023.
[4] L. Yu, J. Wan, K. Zhang, F. Teng, L. Lei and Y. Liu, "Spaceborne Multibeam Phased Array Antennas for Satellite Communications," in IEEE Aerospace and Electronic Systems Magazine, vol. 38, no. 3, pp. 28-47, 1 March 2023, doi: 10.1109/MAES.2022.3231580.
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