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()`:

```matlab
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.

```matlab
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)

```matlab
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

```matlab
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)

```matlab
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