matlab-analyze-rcs

# RCS Analysis Skill

You are an expert RF and antenna engineer assisting a professional engineer with radar cross section analysis. Use MATLAB Antenna Toolbox to compute and visualize monostatic and bistatic RCS.

## When to Use

- User wants to compute monostatic or bistatic radar cross section
- User asks about RCS of a platform, antenna, or array
- User wants to compare RCS across polarizations (HH, VV, HV, VH)
- User needs to select an EM solver (PO, MoM, FMM) for RCS computation
- User wants to analyze RCS of a dielectric target

## When NOT to Use

- User wants antenna radiation pattern (not scattering) — use `matlab-design-antenna` or `matlab-design-array`
- User wants to install an antenna on a platform and compute its pattern — use `matlab-analyzing-installed-antennas`
- User wants plane wave excitation analysis (induced currents, DOA) — use `matlab-analyzing-plane-wave-excitation`

## Core Workflow

1. **Parse the request** -- Identify the target object (platform, antenna, or array), frequency, angular sweep, polarization, and monostatic vs. bistatic mode.

2. **Create the target** -- Load or build the scattering object:
   ```matlab
   % Platform from STL file
   plat = platform(FileName="target.stl", Units="m");

   % Or use an antenna/array object directly
   ant = design(horn, freq);
   ```

3. **Compute RCS** -- Call `rcs()` with appropriate arguments:
   ```matlab
   figure;
   rcs(plat, freq, azimuth, elevation, Polarization="VV");
   ```

4. **Report results** -- Summarize peak RCS, angular location, and polarization. Include units (dBsm).

## Supported Objects

The `rcs` function works on all of these object types:

| Object Type | Examples |
|-------------|---------|
| Platform | `platform` (STL/STEP/IGES geometry) |
| Installed antenna | `installedAntenna` (antenna on platform) |
| Antenna elements | `dipole`, `horn`, `patchMicrostrip`, `reflectorParabolic`, `cassegrain`, etc. |
| Arrays | `linearArray`, `rectangularArray`, `circularArray` |

## rcs Function Reference

### Syntax

```matlab
% Plot mode (no outputs -- generates polar plot automatically)
rcs(object, freq)
rcs(object, freq, azimuth, elevation)
rcs(___, Name=Value)

% Data mode (capture values)
[rcsval, azimuth, elevation] = rcs(object, freq)
[rcsval, azimuth, elevation] = rcs(___, Name=Value)
```

When called with no output arguments, `rcs` generates a polar plot. When outputs are captured, no plot is created.

### Input Arguments

| Argument | Type | Default | Description |
|----------|------|---------|-------------|
| `object` | platform, antenna, or array | -- | Target for RCS computation |
| `freq` | positive scalar (Hz) | -- | Analysis frequency |
| `azimuth` | scalar or vector (deg) | 0 | Azimuth angle(s) for monostatic sweep |
| `elevation` | scalar or vector (deg) | 0:5:360 | Elevation angle(s) for monostatic sweep |

### Name-Value Arguments

| Name | Values | Default | Description |
|------|--------|---------|-------------|
| `Polarization` | `"VV"`, `"HH"`, `"HV"`, `"VH"` | `"VV"` | Transmit-receive polarization |
| `Solver` | `"PO"`, `"MoM"`, `"FMM"` | `"PO"` | Electromagnetic solver |
| `CoordinateSystem` | `"polar"`, `"rectangular"` | `"polar"` | Plot coordinate system |
| `Scale` | `"log"`, `"linear"` | `"log"` | Output scale (dBsm or m^2) |
| `Type` | `"Magnitude"`, `"Complex"` | `"Magnitude"` | Return magnitude or complex value |
| `UseGPU` | `"off"`, `"on"`, `"auto"` | `"off"` | GPU acceleration for PO solver |
| `TransmitAngle` | 2-by-1 vector [az; el] | `[0; 0]` | Bistatic transmit direction (deg) |
| `ReceiveAngle` | 2-by-M matrix [az; el] | -- | Bistatic receive directions (deg) |
| `Range` | positive scalar (m) | far-field | Observation distance for near-field RCS |

## Monostatic RCS

In monostatic mode, the transmitter and receiver are co-located. Sweep azimuth or elevation to map the RCS pattern.

**One of `azimuth` or `elevation` must be a scalar.** You cannot sweep both simultaneously -- `rcs` only produces 1D angular cuts, not 2D maps.

### Elevation Sweep (Fixed Azimuth)

```matlab
freq = 10e9;
plat = platform(FileName="plate.stl", Units="m");

az = 0;
el = 0:1:90;

% Auto-plot
figure;
rcs(plat, freq, az, el, Polarization="HH");

% Or capture data
[sigma, ~, ~] = rcs(plat, freq, az, el, Polarization="HH");
```

### Azimuth Sweep (Fixed Elevation)

```matlab
az = 0:1:360;
el = 45;

figure;
rcs(plat, freq, az, el, Polarization="VV");
```

### Comparing Polarizations

```matlab
az = 0:1:180;
el = 0;

sigma_hh = rcs(plat, freq, az, el, Polarization="HH");
sigma_vv = rcs(plat, freq, az, el, Polarization="VV");

figure;
plot(az, sigma_hh, az, sigma_vv, LineWidth=1.5);
grid on;
xlabel("Azimuth (deg)");
ylabel("RCS (dBsm)");
legend("HH", "VV", Location="best");
```

### 2D RCS Map

To produce a 2D azimuth-elevation RCS map, loop over one angle and collect 1D cuts:

```matlab
az = 0:5:355;
el = 0:5:90;
sigmaMap = zeros(numel(az), numel(el));
for i = 1:numel(az)
    sigmaMap(i, :) = rcs(plat, freq, az(i), el, Polarization="VV");
end

figure;
imagesc(el, az, sigmaMap);
xlabel("Elevation (deg)");
ylabel("Azimuth (deg)");
colorbar;
title(sprintf("RCS Map at %.1f GHz (VV, dBsm)", freq/1e9));
```

This can be slow for fine angular resolution. Use coarse steps (5-10 deg) first, then refine regions of interest.

## Bistatic RCS

In bistatic mode, the transmitter and receiver are at different locations. Use `TransmitAngle` and `ReceiveAngle` instead of the `azimuth`/`elevation` positional arguments.

```matlab
% Incident wave from broadside (az=0, el=90)
txAngle = [0; 90];

% Sweep receive direction in elevation at az=0
rxEl = 0:5:360;
rxAngle = [zeros(size(rxEl)); rxEl];

figure;
rcs(plat, freq, TransmitAngle=txAngle, ReceiveAngle=rxAngle, Polarization="HH");
```

`TransmitAngle` is a 2-by-1 vector `[azimuth; elevation]`. `ReceiveAngle` is a 2-by-M matrix where each column is one receive direction `[azimuth; elevation]`.

## Solver Selection

| Solver | Best For | Mesh Requirement | Speed