matlab-design-pcb-antenna

# PCB Antenna Design Skill

You are an expert RF and antenna engineer assisting a professional engineer with PCB antenna design. Use MATLAB Antenna Toolbox `pcbStack` to build multi-layer printed circuit board antennas with custom metal patterns, configure feeds and vias, analyze performance, and generate Gerber files for fabrication.

## When to Use

- User wants to design a PCB antenna or printed antenna from scratch
- User wants to build a multi-layer antenna stackup
- User wants to convert a catalog antenna (patchMicrostrip, pifa) to pcbStack
- User wants to add custom metal patterns, slots, or parasitic elements to a PCB
- User asks about probe feed, edge feed, or aperture-coupled feed on a PCB
- User wants to export Gerber files for antenna fabrication
- User wants to add via stitching or shorting vias

## When NOT to Use

- User wants a simple catalog antenna analysis — use `matlab-design-antenna`
- User wants a matching network — use `matlab-design-matching-network`
- User wants a reflectarray with unit cells — use `matlab-design-reflectarray`
- User wants to design a curved reflector — use `matlab-design-reflector-antenna`

## Core Workflow

1. **Parse the request** -- Identify the antenna type, operating frequency, substrate, number of layers, feed method, and any constraints (board size, connector type).

2. **Design the stackup** -- Create a `pcbStack` with the correct layer ordering: metal shapes and dielectric objects, top-to-bottom.

3. **Configure feeds and vias** -- Set `FeedLocations` with correct layer indices, add vias for grounding or stitching.

4. **Analyze** -- Compute impedance, S-parameters, radiation pattern, and bandwidth.

5. **Export** -- Generate Gerber fabrication files with connector footprints.

## Layer Stack Construction

This is the most error-prone step. The `Layers` property is a cell array specified **top-to-bottom**, alternating between metal shapes and dielectric objects.

```matlab
% 3-layer: patch on FR4 with ground plane
subHeight = 1.6e-3;
sub = dielectric("FR4");

p = pcbStack;
p.BoardShape = antenna.Rectangle(Length=60e-3, Width=60e-3);
p.BoardThickness = subHeight;       % MUST be set BEFORE Layers
p.Layers = {patch, sub, ground};    % {metal(1), diel(2), metal(3)}
```

### Critical Rules

1. **Set `BoardThickness` BEFORE `Layers`** -- Setting `Layers` always overwrites the dielectric thickness with the current `BoardThickness`. If you set Layers first, the dielectric gets the default 10 mm thickness, and setting BoardThickness afterwards does NOT fix it. To suppress the warning, also set `sub.Thickness` to the same value as `BoardThickness` before assigning Layers.

2. **Layer indices reference cell array positions** -- In `FeedLocations` and `ViaLocations`, layer numbers are cell array indices (1, 2, 3, ...), not metal-only indices. In `{metal, diel, metal}`, the metals are at indices 1 and 3.

3. **First and last entries are typically metal** -- but dielectric layers can also appear as the first or last entry when needed (e.g., radome above the top patch, or substrate beneath the bottom feed layer). Example: `{diel, patch, diel, slottedGround, diel, feedLine}`.

4. **`BoardThickness` = total dielectric below top metal** -- For multi-substrate stacks, this equals the sum of all dielectric thicknesses.

### 3-Layer Stack (Most Common)

```matlab
% {topMetal(1), dielectric(2), bottomMetal(3)}
p.Layers = {patch, sub, ground};
p.FeedLocations = [x, y, 1, 3];    % sig=1(top), gnd=3(bottom)
```

### 2-Layer Stack (Air Dielectric)

When only two metal layers are specified with no dielectric object, the stack assumes air as the dielectric between them:

```matlab
% {topMetal(1), bottomMetal(2)} -- air dielectric assumed
p.Layers = {radiator, ground};
p.FeedLocations = [x, y, 1, 2];    % sig=1(top), gnd=2(bottom)
```

### 5-Layer Stack (Aperture-Coupled)

```matlab
% {radiator(1), upperSub(2), slottedGround(3), lowerSub(4), feedLine(5)}
p.BoardThickness = upperSubHeight + lowerSubHeight;
p.Layers = {radiator, upperSub, slottedGround, lowerSub, feedLine};
p.FeedLocations = [x, y, 5, 3];    % sig=5(feedLine), gnd=3(ground)
```

### Substrate Materials

| Material | EpsilonR | LossTangent | Use Case |
|----------|----------|-------------|----------|
| `"FR4"` | 4.8 | 0.026 | Prototyping, low cost |
| Custom `"RO4003C"` | 3.55 | 0.0027 | High-frequency, low loss |
| `"Teflon"` | 2.1 | 0.0002 | Very low loss |
| `"Air"` | 1.0 | 0 | 2-layer stacks with physical spacer |

For materials not in the built-in catalog, create a custom dielectric:

```matlab
sub = dielectric(Name="RO4003C", EpsilonR=3.55, LossTangent=0.0027, Thickness=h);
```

## Shape Operations for Metal Patterns

All shapes are in the `antenna` namespace. Build complex metal patterns using boolean operations.

### Available Shapes

| Shape | Key Properties |
|-------|---------------|
| `antenna.Rectangle` | `Length`, `Width`, `Center`, `NumPoints` |
| `antenna.Circle` | `Radius`, `Center`, `NumPoints` |
| `antenna.Ellipse` | `MajorAxis`, `MinorAxis`, `Center` |
| `antenna.Polygon` | `Vertices` (N-by-3 matrix) |
| `antenna.Triangle` | `InputType` ("SSS"/"SAS"/"ASA"), `Side`, `Angle` |

### Boolean Operations

```matlab
% Union: combine shapes
patchWithFeed = patch + feedLine;

% Subtraction: cut slots, notches, holes
gndWithSlot = ground - slot;
eNotch = patch - notch1 - notch2;

% Intersection: overlap region
overlap = shape1 & shape2;
```

### Geometric Transforms

```matlab
% Translate
shifted = translate(shape, [dx, dy, 0]);

% Rotate (requires axis definition, or use rotateZ convenience)
rotated = rotate(shape, angleDeg, [0 0 0], [0 0 1]);
rotated = rotateZ(shape, angleDeg);

% Mirror (for symmetric geometries — fractals, bowties, balanced structures)
mirrored = mirrorX(copy(shape));    % mirror across Y-axis
mirrored = mirrorY(copy(shape));    % mirror across X-axis

% Copy (duplicate before transforming to preserve original)
shapeCopy = copy(shape);

% Scale
bigger = scale(shape, fa