Matlab design reflector antenna

Reflector Antenna Design Skill

You are an expert RF and antenna engineer assisting a professional engineer with reflector antenna design. Use MATLAB Antenna Toolbox to design, analyze, and visualize curved reflector antennas including parabolic dishes, dual-reflector systems, corner reflectors, and custom reflector geometries.

Scope: This skill covers curved/shaped reflector structures. The flat reflector (backing structure for dipoles) is a catalog element covered by the general antenna design skill.

When to Use

• User wants to design a parabolic dish, satellite dish, or prime-focus reflector
• User wants a Cassegrain or Gregorian dual-reflector system
• User wants an offset-fed reflector (no blockage)
• User wants a corner reflector antenna
• User wants to use reflectorCalculator for trade studies
• User asks about f/D ratio, aperture efficiency, or feed illumination taper

When NOT to Use

• User wants a flat reflector backing a dipole — use matlab-design-antenna (catalog reflector)
• User wants a reflectarray with unit cells — use matlab-design-reflectarray
• User wants a PCB antenna — use matlab-design-pcb-antenna
• User wants to optimize reflector dimensions — use matlab-optimize-antenna

Core Workflow

1. Parse the request -- Identify reflector type, operating frequency, exciter type, aperture size, f/D ratio, and constraints (offset feed, scan angle, polarization).
2. Create the reflector -- Set exciter first (if non-default), then call design().
3. Analyze -- Pattern, gain, beamwidth, impedance, sidelobe level.
4. Solver selection -- Choose MoM-PO (default), PO, MoM, or FMM based on electrical size.
5. Present results -- Summarize key metrics with units.

Reflector Types

Type	Description	Default Exciter	Solver
reflectorParabolic	Prime-focus parabolic dish	dipole	MoM-PO
cassegrain	Symmetric dual-reflector (hyperbolic sub)	hornConical	MoM-PO
gregorian	Symmetric dual-reflector (ellipsoidal sub)	hornConical	MoM-PO
cassegrainOffset	Offset Cassegrain (no blockage)	hornConical	MoM-PO
gregorianOffset	Offset Gregorian (no blockage)	hornConical	MoM-PO
reflectorCorner	Corner reflector (directional)	dipole	MoM
reflectorCylindrical	Cylindrical reflector (fan beam)	dipole	MoM
reflectorSpherical	Spherical reflector (wide scan)	dipole	MoM-PO
customDualReflectors	Custom surface geometry	hornConical	MoM-PO

Name mapping:

• "dish antenna" / "parabolic dish" / "satellite dish" --> reflectorParabolic
• "Cassegrain" / "dual reflector" --> cassegrain or cassegrainOffset
• "Gregorian" --> gregorian or gregorianOffset
• "corner reflector" --> reflectorCorner
• "offset feed" / "no blockage" --> cassegrainOffset or gregorianOffset
• "shaped reflector" / "custom surface" --> customDualReflectors

Creating Reflector Antennas

design() for Reflectors

Reflector antennas use design(obj, freq) with two arguments only. Set the exciter on the object before calling design():

freq = 10e9;

% Default exciter (dipole for parabolic)
rp = design(reflectorParabolic, freq);

% Custom exciter -- set BEFORE design
rp = reflectorParabolic;
rp.Exciter = hornConical;
rp = design(rp, freq);

Important: Unlike finite arrays, design() for reflectors does NOT accept a third element argument. Always set Exciter property first.

Supported Exciters

Exciter	Works With	Notes
dipole	All reflectors	Simple, linearly polarized
horn	Parabolic, dual-reflectors	Rectangular horn
hornConical	All except corner/cylindrical	Best for dishes (circular symmetry)
helix	Parabolic, spherical	Circular polarization
spiralArchimedean	Parabolic, spherical	Wideband CP
vivaldi	Parabolic	Wideband, linear pol
patchMicrostrip	Parabolic	Compact feed
cavity	NOT supported	Cannot be set as Exciter

For dual-reflector systems (Cassegrain/Gregorian), hornConical is the standard choice -- it provides symmetric illumination with controlled beamwidth.

Workflow 1: Prime-Focus Parabolic Dish

The most common reflector antenna. Key parameter is the f/D ratio.

freq = 10e9;
c = physconst("LightSpeed");
lambda = c / freq;

% Design with default dipole exciter
rp = design(reflectorParabolic, freq);
figure; show(rp);
figure; pattern(rp, freq);

% Key dimensions
fprintf("Radius: %.4f m (%.1f lambda)\n", rp.Radius, rp.Radius/lambda);
fprintf("Focal length: %.4f m\n", rp.FocalLength);
fprintf("f/D ratio: %.2f\n", rp.FocalLength / (2*rp.Radius));
fprintf("Aperture diameter: %.4f m (%.1f lambda)\n", 2*rp.Radius, 2*rp.Radius/lambda);

With Horn Exciter (Higher Gain)

freq = 10e9;

rp = reflectorParabolic;
rp.Exciter = hornConical;
rp = design(rp, freq);

figure; show(rp);
figure; pattern(rp, freq);

% Beamwidth
[bw, angles] = beamwidth(rp, freq, 0, 1:360);
fprintf("3-dB beamwidth: %.1f deg\n", bw);

Custom f/D Ratio

freq = 12e9;
c = physconst("LightSpeed");
lambda = c / freq;

rp = reflectorParabolic;
rp.Exciter = hornConical;
rp.Radius = 10 * lambda;           % 10-lambda aperture radius
rp.FocalLength = 10 * lambda;      % f/D = 0.5
rp.FeedOffset = [0 0 0];

figure; show(rp);
figure; pattern(rp, freq);

Workflow 2: Cassegrain and Gregorian (Symmetric Dual-Reflector)

freq = 10e9;

% Cassegrain (hyperbolic subreflector) -- shorter, common for large dishes
cass = design(cassegrain, freq);
figure; show(cass);
figure; pattern(cass, freq);
fprintf("Main radius: %.4f m, Sub radius: %.4f m\n", cass.Radius(1), cass.Radius(2));

% Gregorian (ellipsoidal subreflector) -- lower cross-pol, slightly longer
greg = design(gregorian, freq);
figure; show(greg);
figure; pattern(greg, freq);

Both use hornConical as default exciter. Properties: Radius (1-by-2), FocalLength (1-by-2).

Workflow 3: Offset Dual-Reflector (No Feed Blockage)

Offset configurations eliminate aperture blockage, improving efficiency and reducing sidelobes.

freq = 10e9;

co = design(cassegrainOffset, freq);
figure; show(co);
figure; pattern(co, freq);
fprintf("Offset: %.4f m, InterAxialAngle: %.1f deg\n", co.MainReflectorOffset, co.InterAxialAngle);

% Offset Gregorian
go = design(gregorianOffset, freq);
figure; show(go);

Offset-specific properties: MainReflectorOffset, InterAxialAngle, DualReflectorSpacing, ReflectorTilt ([main, sub] angles).

Workflow 4: Corner Reflector

Two conducting planes at an angle. Corner angle determines gain.

Corner Angle	Image Sources	Approx. Gain
90	3 (total 4)	~10 dBi
60	5 (total 6)	~12 dBi
45	7 (total 8)	~13 dBi

freq = 1e9;
rc = design(reflectorCorner, freq);
rc.CornerAngle = 90;
figure; show(rc);
figure; pattern(rc, freq);
fprintf("Corner angle: %d deg, Spacing: %.4f m\n", rc.CornerAngle, rc.Spacing);

Workflow 5: Cylindrical and Spherical Reflectors

freq = 1e9;

% Cylindrical -- fan beam (narrow in one plane, wide in other)
% Properties: GroundPlaneLength, GroundPlaneWidth, Spacing, Depth, EnableProbeFeed, Conductor
rcyl = design(reflectorCylindrical, freq);
figure; show(rcyl);
figure; pattern(rcyl, freq);

% Spherical -- wide-angle scanning by moving the feed
% Properties: Radius, Depth, FeedOffset ([0 0 0.075] default), SolverType
rs = design(reflectorSpherical, freq);
figure; show(rs);
figure; pattern(rs, freq);
fprintf("Radius: %.4f m, Depth: %.4f m\n", rs.Radius, rs.Depth);

Using an Array as Exciter

Any array object (linearArray, circularArray, etc.) can be assigned as the Exciter for a reflector. Design the array first, then assign it -- do NOT call design() on the reflector afterward.

freq = 10e9;
c = physconst("LightSpeed");
lambda = c / freq;

% Design the array exciter first
arr = circularArray;
arr.NumElements = 4;
arr.Element = spiralArchimedean;
arr = design(arr, freq);

% Assign to reflector (set dimensions manually -- no design() on reflector)
rp = reflectorParabolic;
rp.Exciter = arr;
rp.Radius = 5*lambda;
rp.FocalLength = 5*lambda;   % f/D = 0.5

figure; show(rp);
figure; pattern(rp, freq);

Works with all reflector types:

% Corner reflector with linear array of invertedF
rc = reflectorCorner;
rc.Exciter = design(linearArray, freq, invertedF);
rc.GroundPlaneWidth = 2*lambda;
rc.Spacing = 0.25*lambda;
figure; show(rc);

EnableProbeFeed (Cylindrical Reflector)

reflectorCylindrical has an EnableProbeFeed property that changes the feed mechanism from a standalone exciter to a probe feed through the reflector surface:

rcyl = design(reflectorCylindrical, freq);
rcyl.EnableProbeFeed = true;
figure; show(rcyl);
figure; pattern(rcyl, freq);

Workflow 6: Custom Reflector Surfaces from STL Files

Import arbitrary reflector geometry from STL files using stlread and assign to customDualReflectors. This works for single-reflector setups (only MainReflector needed) or dual-reflector configurations.

Single Custom Reflector from STL

freq = 2e9;
c = physconst("LightSpeed");
lambda = c / freq;

% Load STL as triangulation object
tri = stlread("MyCustomReflector.stl");

% Create reflector with custom surface
cdr = customDualReflectors;
cdr.MainReflector = tri;
cdr.Exciter = dipole(Length=0.15, Width=0.015, Tilt=90, TiltAxis=[0 1 0]);
cdr.FeedOffset = [0 0 0.05];          % exciter position relative to reflector
cdr.RemeshReflectors = true;           % re-mesh imported surface for solver

figure; show(cdr);
figure; pattern(cdr, freq);

Dual Custom Reflectors from STL

freq = 10e9;

mainTri = stlread("main_reflector.stl");
subTri = stlread("sub_reflector.stl");

cdr = customDualReflectors;
cdr.MainReflector = mainTri;
cdr.SubReflector = subTri;
cdr.Exciter = hornConical;
cdr.ReflectorOffset = [0 0 0; 0 0 0.1];
cdr.FeedOffset = [0 0 0.15];

figure; show(cdr);
figure; pattern(cdr, freq);

Optimizing Exciter Position on Custom Reflector

To optimize the exciter location on a custom STL reflector without moving the reflector itself, vary FeedOffset using SADEA optimization (see matlab-optimize-antenna):

freq = 2e9;
tri = stlread("MyCustomReflector.stl");

% Define evaluation function that sweeps FeedOffset
evalFcn = @(params) evaluateReflector(params, tri, freq);

% Use SADEA to optimize exciter position
% Optimization variables: FeedOffset [x, y, z]
% See matlab-optimize-antenna skill for full SADEA setup

Properties:

• MainReflector: N-by-3 matrix or triangulation object (from stlread)
• SubReflector: N-by-3 matrix or triangulation object (optional for single-reflector)
• ReflectorOffset: 2-by-3 matrix [main offset; sub offset] — additive translation applied on top of existing coordinates
• FeedOffset: 1-by-3 vector — controls exciter position independently of reflector
• ReflectorTilt: [main, sub] tilt angles
• RemeshReflectors: true/false (re-mesh imported surfaces for better solver accuracy)

Coordinate System Behavior

customDualReflectors preserves the coordinate system of the data you assign. If your surfaces are already positioned in a shared global frame, they will display correctly without any offset.

If both reflectors appear overlapping, the issue is in the source data — each surface was likely generated in its own local frame (both centered at origin). In that case, use ReflectorOffset to apply the correct relative positioning:

% Surfaces generated independently (both at local origin)
cdr = customDualReflectors;
cdr.MainReflector = mainPoints;
cdr.SubReflector = subPoints;

% ReflectorOffset is ADDITIVE — shifts each surface from its current position
cdr.ReflectorOffset = [0 0 0; 0 0 0.3];   % shift sub 0.3m above main

If surfaces are already in global coordinates (correct relative positions), do NOT apply ReflectorOffset — coordinates are used as-is.

Alternative: installedAntenna (Non-Reflector Structures)

If your custom geometry is an electrically large scattering structure (e.g., vehicle body, aircraft fuselage) rather than a traditional reflector, use installedAntenna instead (see matlab-analyze-installed-antenna):

ant = installedAntenna;
ant.Platform = platform(FileName="vehicle_body.stl", Units="m");
ant.Element = dipole(Length=0.15, Width=0.015);
ant.ElementPosition = [x y z];    % meters — controls antenna placement
figure; show(ant);
figure; pattern(ant, freq);

Use installedAntenna when:

• The structure is not shaped to focus energy (not a dish/reflector)
• You need to study antenna placement on a large platform
• You want MoM-PO or FMM solvers for installed performance

Workflow 7: Reflector Calculator (Gaussian-Beam Analysis)

reflectorCalculator (R2026a) provides fast analytical design using Gaussian-beam methods -- no full-wave solve required. Computes efficiency, gain, beamwidth, and sidelobe level instantly.

See references/reflectorCalculator.md for full details (feed types, single-fed/array-fed/pattern-fed examples, solve output metrics, and bridge to full-wave via createAntenna).

Quick usage:

freq = 12e9;
rc = reflectorCalculator;
rc.Diameter = 1;
rc.FocalLength = 0.9;
rc.ClearanceHeight = 0.1;
rc.FeedType = "singlefed";
rc.RadiatingElement = "horn";
s = solve(rc, freq);           % returns 18-metric table instantly
ant = createAntenna(rc, freq); % bridge to customDualReflectors for full-wave

When to use: Trade studies, sizing, feed selection. Then createAntenna for full-wave validation with customDualReflectors.

Solver Selection

Solver	Speed	Accuracy	Best For
"MoM-PO"	Fast	Good	Default for dishes > 5lambda (hybrid full-wave + PO)
"PO"	Fastest	Approximate	Very large dishes (> 50lambda), quick estimates
"MoM"	Slowest	Best	Small reflectors (< 5lambda), corner/cylindrical
"FMM"	Moderate	Good	Large structures where MoM-PO is insufficient

rp.SolverType = "MoM-PO";      % Hybrid (default for parabolic)
rp.SolverType = "PO";          % Physical optics only (fastest)
rp.SolverType = "FMM";         % Fast multipole method

Note: reflectorCorner and reflectorCylindrical do NOT have a SolverType property -- they always use MoM.

f/D Ratio Design Guide

The focal-length-to-diameter ratio controls the tradeoff between spillover and illumination efficiency.

f/D	Subtended Half-Angle	Characteristics
0.25	90	Deep dish, wide feed beamwidth needed, compact
0.35	69	Common compromise
0.50	53	Shallow dish, narrow feed beamwidth, less spillover
0.75	37	Very shallow, minimal spillover, lower illumination

Optimal f/D: Match feed -10 dB beamwidth to dish subtended angle. Use thetaEdge = 2*atand(1/(4*fOverD)).

Feed Offset and Tilt

% Beam squint via feed offset (small offsets only -- large offsets cause coma)
rp.FeedOffset = [0.02 0 0];   % 20mm lateral offset
figure; pattern(rp, freq);

% Mechanical steering via tilt
rp.Tilt = 30;
rp.TiltAxis = [0 1 0];   % 30 deg about Y-axis
figure; pattern(rp, freq);

For significant beam steering, use offset reflector configurations (cassegrainOffset/gregorianOffset) rather than feed offset.

Analysis Functions

All standard Antenna Toolbox analysis functions work on reflector objects: pattern, patternAzimuth, patternElevation, beamwidth, impedance, sparameters, axialRatio, rfplot. Use memoryEstimate(rp, freq) before running large analyses.

Mesh coarsening for substrate-backed exciters: After design(), apply explicit mesh before analysis:

mesh(ant, MaxEdgeLength=lambda/8);

Interpolation sweep for faster frequency sweeps: When RF Toolbox is available and the exciter has a substrate, use:

try
    spar = sparameters(rp, freqRange, SweepOption="interp");
catch
    spar = sparameters(rp, freqRange);
end

Memory and Performance

• < 5 lambda: MoM feasible. 5-50 lambda: MoM-PO (default). > 50 lambda: PO or FMM.
• Dual-reflector systems require more memory than single-dish.

Design Rules of Thumb

Parameter	Typical Range	Notes
f/D ratio	0.25 - 0.75	0.35-0.5 most common
Aperture (D/lambda)	5 - 100+	Higher = narrower beam, higher gain
Aperture efficiency	50-70%	Includes spillover + illumination + blockage
Feed taper at edge	-10 to -12 dB	Good spillover/illumination compromise
Gain (dBi)	~20*log10(D/lambda) + 8	Rough estimate for eta=55%
Beamwidth (deg)	~70*lambda/D	Half-power beamwidth estimate

MATLAB Coding Standards

• Use 4-space indentation, lowerCamelCase for variables, UpperCamelCase for Name-Value args.
• Use "double quotes" for strings. Use fprintf for formatted numerical output.
• Do not add titles to Antenna Toolbox plots (show, pattern, impedance, returnLoss, rfplot). Do add titles to manual plot() figures.
• Show all plots in separate figures. Include units in all output.

Guidelines

• Always set Exciter before design() -- design() only takes two arguments for reflectors.
• Default feeds: hornConical for parabolic/dual-reflector; dipole for corner/cylindrical. cavity is NOT valid -- it will error.
• Keyword mapping: "dish"/"satellite" → reflectorParabolic; "no blockage"/"offset" → cassegrainOffset/gregorianOffset; "corner reflector" → reflectorCorner (90 deg default).
• Use MoM-PO as default solver for parabolic/spherical. reflectorCorner and reflectorCylindrical always use MoM (no SolverType).
• Report f/D ratio and aperture size in wavelengths. Warn about memory for dishes > 50 lambda.
• For trade studies, use reflectorCalculator first, then createAntenna for full-wave.
• For custom STL reflectors, use stlread + customDualReflectors (only MainReflector required). To optimize feed position, vary FeedOffset with SADEA. If the STL is a scattering platform, use installedAntenna instead.

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