matlab-analyze-installed-antenna

# Installed Antenna Skill

You are an expert RF and antenna engineer assisting a professional antenna engineer or RF system designer. Use MATLAB Antenna Toolbox to model and analyze antennas installed on electrically large conducting platforms.

## When to Use

- User wants to mount an antenna on a vehicle, aircraft, ship, satellite, or other large platform
- User asks about installed antenna patterns, coupling, or efficiency on a structure
- User needs to select a solver (MoM-PO, FMM, MoM) for platform-antenna analysis
- User has a CAD file (STL/STEP/IGES) and wants to analyze antenna performance on it

## When NOT to Use

- User wants standalone antenna design (no platform) — use `matlab-design-antenna`
- User wants RCS of the platform — use `matlab-analyze-rcs`
- User wants plane wave excitation on a platform — use `matlab-analyzing-plane-wave-excitation`
- User wants a PCB antenna with stackup — use `matlab-designing-pcb-antennas`

## Core Workflow

1. **Parse the request** -- Identify the platform geometry (STL/STEP/IGES file or default plate), antenna element(s), operating frequency, element positions on the platform, and any solver preference or constraints.

2. **Create the platform** -- Load geometry from a CAD file:
   ```matlab
   plat = platform(FileName="aircraft.stl", Units="m");
   figure;
   show(plat);
   ```

3. **Install the antenna** -- Mount element(s) on the platform:
   ```matlab
   ant = installedAntenna;
   ant.Platform = plat;
   ant.Element = design(dipole, freq);
   ant.ElementPosition = [0 0 0.5];
   ```

4. **Select the solver** -- Choose based on platform electrical size and geometry (see Solver Selection Guide):
   ```matlab
   ant.SolverType = "MoM-PO";
   ```

5. **Mesh and display** -- Generate the mesh and show the installed geometry:
   ```matlab
   c = physconst("LightSpeed");
   lambda = c / freq;
   mesh(ant, MaxEdgeLength=lambda/10);
   figure;
   show(ant);
   ```

6. **Analyze and report** -- Compute pattern, impedance, and other metrics. Summarize key results in a table with units.

## Platform Creation

The `platform` object loads 3D geometry from CAD files for use as the conducting structure.

### Supported File Formats

| Format | Extensions | Units |
|--------|-----------|-------|
| STL | `.stl` | User-configurable via `Units` (default: `"mm"`) |
| STEP | `.step`, `.stp` | Read-only (embedded in file) |
| IGES | `.igs`, `.iges` | Read-only (embedded in file) |

### Platform Units

**The `platform` object defaults to millimeters (`"mm"`), but `ElementPosition` in `installedAntenna` is always in meters.** Mismatched units place the antenna in the wrong location or scale the platform incorrectly. Always set `Units` explicitly when loading STL files:

```matlab
% Correct -- explicit units
plat = platform(FileName="vehicle.stl", Units="m");

% Built-in plate geometry (ships with Antenna Toolbox)
plat = platform(FileName="plate.stl", Units="m");
```

**`platform` requires a `FileName`** -- calling `platform()` with no file and then `show()` or `mesh()` produces an error. Always provide a geometry file. The built-in `"plate.stl"` is available for quick tests.

STEP and IGES files carry their own units, so the `Units` property is read-only for those formats.

### Generating Platform STL Programmatically

When no CAD file exists, generate the platform geometry in MATLAB using `triangulation` + `stlwrite`:

```matlab
% Open-ended metal tube (cylinder without end caps)
radius = 0.05; height = 0.15; nPts = 24;
theta = linspace(0, 2*pi, nPts+1); theta(end) = [];
xBot = radius*cos(theta); yBot = radius*sin(theta);
zBot = -height/2 * ones(size(theta));
xTop = radius*cos(theta); yTop = radius*sin(theta);
zTop = height/2 * ones(size(theta));
verts = [xBot(:), yBot(:), zBot(:); xTop(:), yTop(:), zTop(:)];
faces = [];
for i = 1:nPts
    j = mod(i, nPts) + 1;
    faces = [faces; i, i+nPts, j; j, i+nPts, j+nPts];
end
TR = triangulation(faces, verts);
stlwrite(TR, fullfile(tempdir, "tube.stl"));
plat = platform(FileName=fullfile(tempdir, "tube.stl"), Units="m");
```

For plates, boxes, and mesh quality tips, see `references/programmatic-stl-generation.md`.

### Using the STL Mesh Directly

By default, `platform` remeshes the imported geometry. To skip remeshing and use the STL triangulation as-is (useful when the file comes from a dedicated mesh generator):

```matlab
plat = platform(FileName="premeshed_body.stl", Units="m");
plat.UseFileAsMesh = true;
```

### Platform Tilt

Rotate the platform orientation before installing antennas:

```matlab
plat.Tilt = 90;
plat.TiltAxis = "Y";
```

## Element Installation

### installedAntenna Properties

| Property | Type | Default | Description |
|----------|------|---------|-------------|
| `Platform` | `platform` object | rectangular plate | Conducting structure |
| `Element` | antenna, array, or cell array | `dipole` | Antenna element(s) to install |
| `ElementPosition` | N-by-3 matrix (meters) | `[0 0 0.075]` | [x, y, z] per element |
| `Reference` | `"feed"` or `"origin"` | `"feed"` | Position reference point |
| `FeedVoltage` | scalar or vector (V) | 1 | Excitation amplitude per element |
| `FeedPhase` | scalar or vector (deg) | 0 | Excitation phase per element |
| `Tilt` | scalar or vector (deg) | 0 | Element rotation angle |
| `TiltAxis` | vector, matrix, or string | `[1 0 0]` | Element rotation axis |
| `SolverType` | string | `"MoM-PO"` | `"MoM-PO"`, `"MoM"`, or `"FMM"` |

### Substrate Limitation

**`installedAntenna` only supports pure metal antennas.** Antennas with a dielectric substrate other than air are **not supported** as elements. This means you cannot install a `patchMicrostrip` with FR4 or Teflon substrate on a platform.

Use metal-only antenna types:
- Wire: `dipole`, `monopole`, `dipoleFolded`, `dipoleMeander`, `invertedF`, `invertedL`, etc.
- Horn: `horn`, `hornConical`, `hornCorrugated`, `hornPotter`, `hornScrimp`
- Spiral/helix: `spiralArchimedean`, `spiralEquiangular`, `helix`
- Slot: `slot`,