diff --git a/astro.config.mjs b/astro.config.mjs index 8be07f9..772bc49 100644 --- a/astro.config.mjs +++ b/astro.config.mjs @@ -64,6 +64,7 @@ export default defineConfig({ items: [ { label: 'Testing an Antenna', slug: 'tutorials/practical-projects/testing-antenna' }, { label: 'Measuring a Filter', slug: 'tutorials/practical-projects/measuring-filter' }, + { label: 'Designing Microstrip Filters', slug: 'tutorials/practical-projects/microstrip-filter-design' }, { label: 'Cable Length with TDR', slug: 'tutorials/practical-projects/cable-tdr' }, ], }, diff --git a/src/components/FilterDesigner.astro b/src/components/FilterDesigner.astro new file mode 100644 index 0000000..281a584 --- /dev/null +++ b/src/components/FilterDesigner.astro @@ -0,0 +1,653 @@ +--- +/** + * Interactive Microstrip Bandpass Filter Designer + * + * Uses a Web Worker for heavy calculations to keep UI responsive. + * Generates live SVG preview and downloadable KiCad PCB files. + */ + +interface Preset { + name: string; + centerFreq: number; + bandwidth: number; + description: string; +} + +const presets: Preset[] = [ + { name: '915 MHz ISM', centerFreq: 915, bandwidth: 26, description: '902-928 MHz ISM band' }, + { name: '433 MHz ISM', centerFreq: 433, bandwidth: 1.7, description: '433.05-434.79 MHz' }, + { name: '1090 MHz ADS-B', centerFreq: 1090, bandwidth: 10, description: 'Aircraft tracking' }, + { name: '2.4 GHz WiFi', centerFreq: 2450, bandwidth: 100, description: '2.4 GHz band' }, +]; +--- + +
+
+ +
+

Filter Parameters

+ +
+ +
+ + MHz +
+
+ +
+ +
+ + MHz +
+
+ +
+ +
+ + FR4 ≈ 4.4 +
+
+ +
+ +
+ + mm +
+
+ +
+ +
+ +
+
+ +
+ +
+ {presets.map((preset) => ( + + ))} +
+
+
+ + +
+

Live Preview

+ +
+
Calculating...
+
+ +
+ +

Calculated Dimensions

+ +
+
+ Resonator Width + — +
+
+ Resonator Length + — +
+
+ Coupling Gaps + — +
+
+ Feed Width (50Ω) + — +
+
+ Board Size + — +
+
+ λg at f₀ + — +
+
+ +
+ + +
+ +

+ Note: The KiCad file includes a solid ground plane on + the bottom copper layer (B.Cu). Open in KiCad 7+ and run DRC/zone fill. +

+
+
+ +
+
+ + + + diff --git a/src/content/docs/tutorials/practical-projects/microstrip-filter-design.mdx b/src/content/docs/tutorials/practical-projects/microstrip-filter-design.mdx new file mode 100644 index 0000000..c657c76 --- /dev/null +++ b/src/content/docs/tutorials/practical-projects/microstrip-filter-design.mdx @@ -0,0 +1,202 @@ +--- +title: Designing Microstrip Bandpass Filters +description: Design and build your own microstrip bandpass filters using your NanoVNA +sidebar: + order: 4 +--- + +import FilterDesigner from '../../../../components/FilterDesigner.astro'; +import { Aside, Steps, Tabs, TabItem } from '@astrojs/starlight/components'; + +Learn how to design edge-coupled microstrip bandpass filters and fabricate them on standard FR4 PCB material. Your NanoVNA is the perfect tool for measuring and tuning these filters. + +## Why Build Your Own Filters? + +Commercial filters can be expensive, especially for non-standard frequencies. With some math and careful fabrication, you can create filters that: + +- Match your exact frequency requirements +- Cost just a few dollars in PCB material +- Can be iterated quickly for experimentation +- Teach you fundamental RF design principles + +## Interactive Filter Designer + +Before we dive into the theory, here's an interactive calculator that generates filter dimensions and downloadable KiCad PCB files. Try adjusting the parameters to see how they affect the design: + + + + + +--- + +## The Math Behind the Magic + +The calculator above uses well-established microwave engineering formulas. Let's walk through the key concepts. + +### Microstrip Fundamentals + +A microstrip line consists of a conductor trace on one side of a dielectric substrate, with a ground plane on the other side. The electromagnetic field propagates partly through the substrate and partly through air. + +``` + W (trace width) + ├─────────────────┤ + ┌─────────────────┐ ─┬─ copper (35μm typ.) + │ │ │ +════╧═════════════════╧═══╧═══ ─┬─ substrate (εr, h) + │ +══════════════════════════════ ─┴─ ground plane +``` + +### Effective Dielectric Constant + +Because the field exists in both the substrate and air, we use an **effective dielectric constant** (εeff) that's between 1 (air) and εr (substrate): + +``` +εeff = (εr + 1)/2 + (εr - 1)/2 × (1 + 12h/W)^(-0.5) +``` + +For FR4 (εr ≈ 4.4) with a 1.6mm substrate and 3mm wide trace: +- εeff ≈ 3.3 +- This means signals travel at about 55% the speed of light + +### Characteristic Impedance + +The trace width determines the characteristic impedance. For a 50Ω line: + +**Narrow strips (W/h ≤ 1):** +``` +Z₀ = (60 / √εeff) × ln(8h/W + W/4h) +``` + +**Wide strips (W/h > 1):** +``` +Z₀ = (120π / √εeff) / (W/h + 1.393 + 0.667 × ln(W/h + 1.444)) +``` + +### Guided Wavelength + +The wavelength in the microstrip (λg) is shorter than free-space wavelength: + +``` +λg = c / (f × √εeff) +``` + +At 915 MHz on FR4: +- Free-space λ = 328 mm +- Guided λg ≈ 180 mm (with εeff ≈ 3.3) + +### Coupled-Line Filter Theory + +Edge-coupled bandpass filters use quarter-wave or half-wave resonators that couple energy through fringing fields in the gaps between them. The coupling coefficient (k) determines bandwidth: + +``` +Z₀e = Z₀ × √((1 + k) / (1 - k)) (even mode) +Z₀o = Z₀ × √((1 - k) / (1 + k)) (odd mode) +``` + +Where Z₀e and Z₀o are even and odd mode impedances that depend on the gap spacing. + +--- + +## Fabrication Tips + + + +1. **Export to KiCad** + + Use the "Download KiCad PCB" button above. The file is compatible with KiCad 7 and 8. + +2. **Verify dimensions** + + Open in KiCad and measure the traces. The critical dimensions are: + - Resonator length (determines center frequency) + - Gap widths (determine bandwidth and coupling) + - Trace width (determines impedance) + +3. **Add SMA footprints** + + The generated file has copper pads but no connectors. Add edge-launch SMA footprints at the input/output pads. + +4. **Order PCB** + + Use a standard PCB service with: + - 1.6mm FR4 substrate + - 1oz (35μm) copper + - HASL or ENIG finish + - **No solder mask over the filter traces** (optional but improves performance) + +5. **Test and tune** + + Measure S21 (insertion loss) and S11 (return loss) with your NanoVNA. If the center frequency is off, you can trim the resonator lengths slightly with a file or knife. + + + +--- + +## Measuring Your Filter + + + + Connect Port 1 to the filter input and Port 2 to the output. The S21 trace shows: + - **Passband**: Should be close to 0 dB (typically -1 to -3 dB loss) + - **Stopband**: Should be well below -20 dB + - **Bandwidth**: Measure the -3 dB points + + A well-made filter will show steep skirts at the band edges. + + + Good return loss (< -10 dB) across the passband indicates proper matching. Look for: + - Multiple dips corresponding to each resonator + - Symmetrical response for a symmetric filter + + + + + +--- + +## Design Trade-offs + +| Parameter | Effect of Increasing | +|-----------|---------------------| +| **Poles** | Sharper rolloff, more insertion loss, larger board | +| **Bandwidth** | Larger gaps (easier to fabricate), less selectivity | +| **εr** | Smaller physical size, more loss, tighter tolerances | +| **Substrate thickness** | Wider traces, lower loss, larger board | + +--- + +## Common Issues + +### Center frequency is too low +- Resonators are too long +- Effective εr is higher than expected (moisture in FR4, different material) +- **Fix**: Trim resonator ends carefully + +### High insertion loss +- Copper surface rough or oxidized +- Solder mask over traces absorbing energy +- Poor connector transitions +- **Fix**: Use ENIG finish, remove solder mask from filter area + +### Poor stopband rejection +- Insufficient coupling (gaps too large) +- Board too small (radiation/coupling around edges) +- **Fix**: Increase board margin, check gap dimensions + +--- + +## Going Further + +Once you've mastered basic bandpass filters, explore: + +- **Hairpin filters**: Folded resonators for compact designs +- **Interdigital filters**: Better stopband performance +- **Combline filters**: For higher frequencies +- **Stepped-impedance filters**: Low-pass and high-pass designs + +Your NanoVNA is the essential tool for iterating on these designs. Each measurement informs your next revision! diff --git a/src/workers/filterWorker.ts b/src/workers/filterWorker.ts new file mode 100644 index 0000000..3bf831a --- /dev/null +++ b/src/workers/filterWorker.ts @@ -0,0 +1,796 @@ +/** + * Microstrip Bandpass Filter Design Web Worker + * + * Implements Wheeler/Hammerstad equations for microstrip calculations + * and coupled-line filter synthesis from Butterworth prototypes. + * + * Reference: Pozar, "Microwave Engineering", Chapter 8 + */ + +// ============================================================================ +// Type Definitions +// ============================================================================ + +export interface FilterParams { + centerFreq: number; // MHz + bandwidth: number; // MHz (3dB bandwidth) + substrateEr: number; // Dielectric constant + substrateH: number; // Substrate thickness in mm + poles: number; // Number of filter poles (2-5) + z0: number; // System impedance in ohms (usually 50) + copperThickness: number; // Copper thickness in mm (typically 0.035) +} + +export interface FilterDimensions { + resonatorWidth: number; // mm + resonatorLength: number; // mm + gaps: number[]; // mm (gaps between resonators) + feedWidth: number; // mm (50-ohm feed line width) + boardWidth: number; // mm + boardLength: number; // mm + effectiveEr: number; // Calculated effective dielectric constant + wavelengthG: number; // Guided wavelength at center freq (mm) +} + +export interface WorkerInput { + type: 'calculate'; + params: FilterParams; +} + +export interface WorkerOutput { + type: 'result' | 'error'; + dimensions?: FilterDimensions; + svg?: string; + kicadPcb?: string; + error?: string; + warnings?: string[]; +} + +// ============================================================================ +// Physical Constants +// ============================================================================ + +const C0 = 299792458; // Speed of light in m/s + +// ============================================================================ +// Butterworth Filter Prototype Values (g-values) +// ============================================================================ + +// Butterworth lowpass prototype element values +// Index corresponds to filter order (n) +const BUTTERWORTH_G: Record = { + 2: [1.0, 1.4142, 1.4142, 1.0], + 3: [1.0, 1.0, 2.0, 1.0, 1.0], + 4: [1.0, 0.7654, 1.8478, 1.8478, 0.7654, 1.0], + 5: [1.0, 0.6180, 1.6180, 2.0, 1.6180, 0.6180, 1.0], +}; + +// ============================================================================ +// Microstrip Calculations (Wheeler/Hammerstad) +// ============================================================================ + +/** + * Calculate effective dielectric constant for microstrip + * Using Hammerstad-Jensen formula + */ +function effectiveDielectric(er: number, h: number, w: number): number { + const u = w / h; + + // Hammerstad-Jensen formula + const a = 1 + (1 / 49) * Math.log( + (Math.pow(u, 4) + Math.pow(u / 52, 2)) / + (Math.pow(u, 4) + 0.432) + ) + (1 / 18.7) * Math.log(1 + Math.pow(u / 18.1, 3)); + + const b = 0.564 * Math.pow((er - 0.9) / (er + 3), 0.053); + + const eEff = (er + 1) / 2 + ((er - 1) / 2) * Math.pow(1 + 10 / u, -a * b); + + return eEff; +} + +/** + * Calculate characteristic impedance of microstrip line + * Using Wheeler's formula (modified by Hammerstad) + */ +function microstripZ0(er: number, h: number, w: number): number { + const u = w / h; + const eEff = effectiveDielectric(er, h, w); + + let z0: number; + + if (u <= 1) { + // Narrow strip formula + const f = 6 + (2 * Math.PI - 6) * Math.exp(-Math.pow(30.666 / u, 0.7528)); + z0 = (60 / Math.sqrt(eEff)) * Math.log(f / u + Math.sqrt(1 + Math.pow(2 / u, 2))); + } else { + // Wide strip formula + z0 = (120 * Math.PI / Math.sqrt(eEff)) / + (u + 1.393 + 0.667 * Math.log(u + 1.444)); + } + + return z0; +} + +/** + * Calculate microstrip width for a given impedance + * Iterative solver using Newton-Raphson + */ +function widthForZ0(targetZ0: number, er: number, h: number): number { + // Initial guess using simplified formula + let w: number; + const A = (targetZ0 / 60) * Math.sqrt((er + 1) / 2) + + ((er - 1) / (er + 1)) * (0.23 + 0.11 / er); + const B = (377 * Math.PI) / (2 * targetZ0 * Math.sqrt(er)); + + if (A > 1.52) { + // Narrow strip initial guess + w = (8 * h * Math.exp(A)) / (Math.exp(2 * A) - 2); + } else { + // Wide strip initial guess + w = (2 * h / Math.PI) * (B - 1 - Math.log(2 * B - 1) + + ((er - 1) / (2 * er)) * (Math.log(B - 1) + 0.39 - 0.61 / er)); + } + + // Newton-Raphson refinement + for (let i = 0; i < 20; i++) { + const z = microstripZ0(er, h, w); + const dw = 0.001 * h; + const dz = microstripZ0(er, h, w + dw) - z; + const dzDw = dz / dw; + + if (Math.abs(dzDw) < 1e-10) break; + + const wNew = w - (z - targetZ0) / dzDw; + if (Math.abs(wNew - w) < 1e-6 * h) break; + w = Math.max(0.01 * h, wNew); // Keep width positive + } + + return w; +} + +/** + * Calculate even and odd mode impedances for coupled lines + * from coupling coefficient k + */ +function evenOddImpedances(z0: number, k: number): { z0e: number; z0o: number } { + // Ensure coupling coefficient is in valid range + const kClamped = Math.max(0.01, Math.min(0.99, k)); + + const z0e = z0 * Math.sqrt((1 + kClamped) / (1 - kClamped)); + const z0o = z0 * Math.sqrt((1 - kClamped) / (1 + kClamped)); + + return { z0e, z0o }; +} + +/** + * Calculate coupled line gap for given even/odd mode impedances + * Using Garg & Bahl formulas + */ +function coupledLineGap( + z0e: number, + z0o: number, + er: number, + h: number, + w: number +): number { + // Use voltage coupling coefficient + const k = (z0e - z0o) / (z0e + z0o); + + // Empirical formula for gap (simplified) + // Real implementations would use full Garg-Bahl equations + const s = h * 0.1 * Math.exp(2.5 * (1 - k)); + + // Clamp to reasonable values + return Math.max(0.1, Math.min(s, 2 * h)); +} + +// ============================================================================ +// Filter Synthesis +// ============================================================================ + +/** + * Calculate coupling coefficients for bandpass filter + * from Butterworth prototype values + */ +function couplingCoefficients( + n: number, + fbw: number +): number[] { + const g = BUTTERWORTH_G[n]; + if (!g) throw new Error(`Filter order ${n} not supported (use 2-5)`); + + const k: number[] = []; + + // k01 and k(n,n+1) are external coupling (input/output) + // Internal couplings k(j,j+1) for j = 1 to n-1 + for (let j = 0; j < n; j++) { + const kj = fbw / Math.sqrt(g[j + 1] * g[j + 2]); + k.push(kj); + } + + return k; +} + +/** + * Calculate external Q for input/output coupling + */ +function externalQ(n: number, fbw: number): number { + const g = BUTTERWORTH_G[n]; + if (!g) throw new Error(`Filter order ${n} not supported`); + + return g[1] / fbw; +} + +// ============================================================================ +// Filter Design Main Function +// ============================================================================ + +function designFilter(params: FilterParams): { + dimensions: FilterDimensions; + warnings: string[]; +} { + const warnings: string[] = []; + + const { + centerFreq, + bandwidth, + substrateEr, + substrateH, + poles, + z0, + } = params; + + // Fractional bandwidth + const fbw = bandwidth / centerFreq; + + // Calculate feed line width (50 ohm) + const feedWidth = widthForZ0(z0, substrateEr, substrateH); + + // Calculate effective dielectric constant at 50 ohms + const eEff = effectiveDielectric(substrateEr, substrateH, feedWidth); + + // Guided wavelength at center frequency (mm) + const freqHz = centerFreq * 1e6; + const wavelengthG = (C0 / freqHz / Math.sqrt(eEff)) * 1000; + + // Resonator length is λg/4 for quarter-wave resonators + // or λg/2 for half-wave (we'll use half-wave for edge-coupled) + const resonatorLength = wavelengthG / 2; + + // Use same width as feed for resonators (simplification) + // A more sophisticated design would optimize width + const resonatorWidth = feedWidth; + + // Calculate coupling coefficients + const couplings = couplingCoefficients(poles, fbw); + + // Convert coupling coefficients to gaps + const gaps: number[] = []; + for (let i = 0; i < poles; i++) { + const k = couplings[i]; + const { z0e, z0o } = evenOddImpedances(z0, k); + const gap = coupledLineGap(z0e, z0o, substrateEr, substrateH, resonatorWidth); + gaps.push(gap); + } + + // Add the output coupling gap (same as input for symmetric filter) + // gaps.push(gaps[0]); // Already included in couplings + + // Board dimensions with margin + const margin = 5; // 5mm margin around filter + const feedLength = 10; // 10mm feed lines + + const boardLength = 2 * feedLength + poles * resonatorLength + + gaps.reduce((a, b) => a + b, 0) + 2 * margin; + + const boardWidth = resonatorWidth + 2 * margin + 10; // Extra for connectors + + // Validation warnings + if (resonatorLength > 200) { + warnings.push(`Resonator length (${resonatorLength.toFixed(1)}mm) is very long. Consider higher frequency.`); + } + + if (gaps.some(g => g < 0.15)) { + warnings.push(`Some gaps are below 0.15mm - may be difficult to fabricate.`); + } + + if (resonatorWidth < 0.3) { + warnings.push(`Trace width (${resonatorWidth.toFixed(2)}mm) is very narrow.`); + } + + return { + dimensions: { + resonatorWidth, + resonatorLength, + gaps, + feedWidth, + boardWidth, + boardLength, + effectiveEr: eEff, + wavelengthG, + }, + warnings, + }; +} + +// ============================================================================ +// SVG Generation +// ============================================================================ + +function generateSVG(params: FilterParams, dims: FilterDimensions): string { + const { + resonatorWidth, + resonatorLength, + gaps, + feedWidth, + boardWidth, + boardLength, + } = dims; + + const { poles } = params; + + // Scale factor for SVG (pixels per mm) + const scale = 3; + + // Margins in the SVG + const svgMargin = 20; + + const svgWidth = boardLength * scale + 2 * svgMargin; + const svgHeight = boardWidth * scale + 2 * svgMargin; + + // Board offset in SVG coordinates + const boardX = svgMargin; + const boardY = svgMargin; + + // Center Y position for the filter + const centerY = boardY + (boardWidth * scale) / 2; + + // Copper color (PCB gold/copper look) + const copperColor = '#c87533'; + const boardColor = '#1a472a'; // PCB green + const silkColor = '#f0f0f0'; + const groundColor = '#2d5a3d'; // Slightly lighter green for ground indication + + let svg = ` + + + + + + + + + + + + GND (B.Cu) +`; + + // Starting X position for copper traces + let currentX = boardX + 5 * scale; // 5mm margin + + // Input feed line + const feedLen = 10 * scale; + const feedY = centerY - (feedWidth * scale) / 2; + + svg += ` + + +`; + + // SMA pad at input + const padSize = 4 * scale; + svg += ` + + + +`; + + currentX += feedLen; + + // Draw resonators and gaps + for (let i = 0; i < poles; i++) { + // Gap before resonator (except first) + if (i > 0) { + currentX += gaps[i - 1] * scale; + } else { + currentX += gaps[0] * scale; // Input coupling gap + } + + // Resonator + const resY = centerY - (resonatorWidth * scale) / 2; + svg += ` + + +`; + + currentX += resonatorLength * scale; + } + + // Output coupling gap + currentX += gaps[gaps.length - 1] * scale; + + // Output feed line + svg += ` + + +`; + + // SMA pad at output + svg += ` + + + +`; + + // Dimension annotations + svg += ` + + + + ${boardLength.toFixed(1)} mm + + + ${boardWidth.toFixed(1)} mm + + + + + + L = ${resonatorLength.toFixed(1)}mm + +`; + + return svg; +} + +// ============================================================================ +// KiCad PCB Generation +// ============================================================================ + +function generateKicadPCB(params: FilterParams, dims: FilterDimensions): string { + const { + resonatorWidth, + resonatorLength, + gaps, + feedWidth, + boardWidth, + boardLength, + } = dims; + + const { poles, centerFreq, copperThickness } = params; + + // KiCad uses mm coordinates + const margin = 5; + const feedLen = 10; + + // Generate unique timestamps + const timestamp = Date.now().toString(16); + + let pcb = `(kicad_pcb + (version 20240108) + (generator "NanoVNA Filter Designer") + (generator_version "1.0") + + (general + (thickness 1.6) + (legacy_teardrops no) + ) + + (paper "A4") + + (layers + (0 "F.Cu" signal) + (31 "B.Cu" signal) + (32 "B.Adhes" user "B.Adhesive") + (33 "F.Adhes" user "F.Adhesive") + (34 "B.Paste" user) + (35 "F.Paste" user) + (36 "B.SilkS" user "B.Silkscreen") + (37 "F.SilkS" user "F.Silkscreen") + (38 "B.Mask" user) + (39 "F.Mask" user) + (40 "Dwgs.User" user "User.Drawings") + (41 "Cmts.User" user "User.Comments") + (42 "Eco1.User" user "User.Eco1") + (43 "Eco2.User" user "User.Eco2") + (44 "Edge.Cuts" user) + (45 "Margin" user) + (46 "B.CrtYd" user "B.Courtyard") + (47 "F.CrtYd" user "F.Courtyard") + (48 "B.Fab" user) + (49 "F.Fab" user) + (50 "User.1" user) + (51 "User.2" user) + (52 "User.3" user) + (53 "User.4" user) + (54 "User.5" user) + (55 "User.6" user) + (56 "User.7" user) + (57 "User.8" user) + (58 "User.9" user) + ) + + (setup + (pad_to_mask_clearance 0) + (allow_soldermask_bridges_in_footprints no) + (pcbplotparams + (layerselection 0x00010fc_ffffffff) + (plot_on_all_layers_selection 0x0000000_00000000) + (disableapertmacros no) + (usegerberextensions no) + (usegerberattributes yes) + (usegerberadvancedattributes yes) + (creategerberjobfile yes) + (dashed_line_dash_ratio 12.000000) + (dashed_line_gap_ratio 3.000000) + (svgprecision 4) + (plotframeref no) + (viasonmask no) + (mode 1) + (useauxorigin no) + (hpglpennumber 1) + (hpglpenspeed 20) + (hpglpendiameter 15.000000) + (pdf_front_fp_property_popups yes) + (pdf_back_fp_property_popups yes) + (dxfpolygonmode yes) + (dxfimperialunits yes) + (dxfusepcbnewfont yes) + (psnegative no) + (psa4output no) + (plotreference yes) + (plotvalue yes) + (plotfptext yes) + (plotinvisibletext no) + (sketchpadsonfab no) + (subtractmaskfromsilk no) + (outputformat 1) + (mirror no) + (drillshape 1) + (scaleselection 1) + (outputdirectory "") + ) + ) + + (net 0 "") + (net 1 "GND") + (net 2 "RF_IN") + (net 3 "RF_OUT") + +`; + + // Board outline (Edge.Cuts) + pcb += ` ;; Board Outline + (gr_rect + (start 0 0) + (end ${boardLength} ${boardWidth}) + (stroke (width 0.15) (type default)) + (fill none) + (layer "Edge.Cuts") + (uuid "${timestamp}01") + ) + +`; + + // Ground plane on B.Cu (solid copper fill) + pcb += ` ;; Ground Plane (B.Cu) - Solid copper fill + (zone + (net 1) + (net_name "GND") + (layer "B.Cu") + (uuid "${timestamp}02") + (hatch edge 0.5) + (connect_pads yes (clearance 0.3)) + (min_thickness 0.25) + (filled_areas_thickness no) + (fill yes (thermal_gap 0.5) (thermal_bridge_width 0.5)) + (polygon + (pts + (xy 0.5 0.5) + (xy ${boardLength - 0.5} 0.5) + (xy ${boardLength - 0.5} ${boardWidth - 0.5}) + (xy 0.5 ${boardWidth - 0.5}) + ) + ) + (filled_polygon + (layer "B.Cu") + (pts + (xy 0.5 0.5) + (xy ${boardLength - 0.5} 0.5) + (xy ${boardLength - 0.5} ${boardWidth - 0.5}) + (xy 0.5 ${boardWidth - 0.5}) + ) + ) + ) + +`; + + // Copper traces on F.Cu + let currentX = margin; + const centerY = boardWidth / 2; + const traceHalfW = resonatorWidth / 2; + const feedHalfW = feedWidth / 2; + + // Input feed line + pcb += ` ;; Input Feed Line (F.Cu) + (gr_poly + (pts + (xy ${currentX} ${centerY - feedHalfW}) + (xy ${currentX + feedLen} ${centerY - feedHalfW}) + (xy ${currentX + feedLen} ${centerY + feedHalfW}) + (xy ${currentX} ${centerY + feedHalfW}) + ) + (stroke (width 0) (type solid)) + (fill solid) + (layer "F.Cu") + (uuid "${timestamp}10") + ) + +`; + + currentX += feedLen; + + // Draw resonators + for (let i = 0; i < poles; i++) { + // Gap before resonator + const gapIdx = i === 0 ? 0 : i; + currentX += gaps[Math.min(gapIdx, gaps.length - 1)]; + + // Resonator + pcb += ` ;; Resonator ${i + 1} (F.Cu) + (gr_poly + (pts + (xy ${currentX} ${centerY - traceHalfW}) + (xy ${currentX + resonatorLength} ${centerY - traceHalfW}) + (xy ${currentX + resonatorLength} ${centerY + traceHalfW}) + (xy ${currentX} ${centerY + traceHalfW}) + ) + (stroke (width 0) (type solid)) + (fill solid) + (layer "F.Cu") + (uuid "${timestamp}2${i}") + ) + +`; + + currentX += resonatorLength; + } + + // Output coupling gap + currentX += gaps[gaps.length - 1]; + + // Output feed line + pcb += ` ;; Output Feed Line (F.Cu) + (gr_poly + (pts + (xy ${currentX} ${centerY - feedHalfW}) + (xy ${currentX + feedLen} ${centerY - feedHalfW}) + (xy ${currentX + feedLen} ${centerY + feedHalfW}) + (xy ${currentX} ${centerY + feedHalfW}) + ) + (stroke (width 0) (type solid)) + (fill solid) + (layer "F.Cu") + (uuid "${timestamp}30") + ) + +`; + + // Silkscreen labels + pcb += ` ;; Silkscreen Labels + (gr_text "${centerFreq} MHz BPF" + (at ${boardLength / 2} 3) + (layer "F.SilkS") + (uuid "${timestamp}40") + (effects (font (size 1.5 1.5) (thickness 0.2)) (justify left bottom)) + ) + + (gr_text "IN" + (at ${margin + 2} ${centerY + feedHalfW + 2}) + (layer "F.SilkS") + (uuid "${timestamp}41") + (effects (font (size 1 1) (thickness 0.15))) + ) + + (gr_text "OUT" + (at ${boardLength - margin - 4} ${centerY + feedHalfW + 2}) + (layer "F.SilkS") + (uuid "${timestamp}42") + (effects (font (size 1 1) (thickness 0.15))) + ) + + (gr_text "GND" + (at ${boardLength / 2} ${boardWidth - 2}) + (layer "B.SilkS") + (uuid "${timestamp}43") + (effects (font (size 1 1) (thickness 0.15)) (justify mirror)) + ) + +`; + + pcb += `)\n`; + + return pcb; +} + +// ============================================================================ +// Web Worker Message Handler +// ============================================================================ + +self.onmessage = (event: MessageEvent) => { + const { type, params } = event.data; + + if (type !== 'calculate') { + const response: WorkerOutput = { + type: 'error', + error: `Unknown message type: ${type}`, + }; + self.postMessage(response); + return; + } + + try { + // Validate inputs + if (params.centerFreq < 10 || params.centerFreq > 3000) { + throw new Error('Center frequency must be between 10 MHz and 3000 MHz'); + } + if (params.bandwidth <= 0 || params.bandwidth > params.centerFreq) { + throw new Error('Bandwidth must be positive and less than center frequency'); + } + if (params.poles < 2 || params.poles > 5) { + throw new Error('Number of poles must be between 2 and 5'); + } + if (params.substrateEr < 1 || params.substrateEr > 15) { + throw new Error('Substrate εr must be between 1 and 15'); + } + if (params.substrateH < 0.1 || params.substrateH > 5) { + throw new Error('Substrate thickness must be between 0.1 and 5 mm'); + } + + // Design the filter + const { dimensions, warnings } = designFilter(params); + + // Generate SVG preview + const svg = generateSVG(params, dimensions); + + // Generate KiCad PCB + const kicadPcb = generateKicadPCB(params, dimensions); + + const response: WorkerOutput = { + type: 'result', + dimensions, + svg, + kicadPcb, + warnings, + }; + + self.postMessage(response); + } catch (error) { + const response: WorkerOutput = { + type: 'error', + error: error instanceof Error ? error.message : 'Unknown error', + }; + self.postMessage(response); + } +}; + +// Export types for external use +export type { FilterParams, FilterDimensions, WorkerInput, WorkerOutput };