feat(plotly): implement smith-chart-basic (#3869)

## Implementation: `smith-chart-basic` - plotly

Implements the **plotly** version of `smith-chart-basic`.

**File:** `plots/smith-chart-basic/implementations/plotly.py`

**Parent Issue:** #3792

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/21047488889)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/smith-chart-basic/implementations/plotly.py

@@ -0,0 +1,221 @@
+""" pyplots.ai
+smith-chart-basic: Smith Chart for RF/Impedance
+Library: plotly 6.5.2 | Python 3.13.11
+Quality: 91/100 | Created: 2026-01-15
+"""
+
+import numpy as np
+import plotly.graph_objects as go
+
+
+# Reference impedance
+Z0 = 50  # ohms
+
+# Generate sample impedance data (antenna-like frequency sweep)
+np.random.seed(42)
+freq = np.linspace(1e9, 6e9, 50)  # 1-6 GHz
+
+# Simulate realistic antenna impedance trajectory
+# Starting inductive, moving through resonance to capacitive
+t = np.linspace(0, 2 * np.pi, 50)
+z_real = 25 + 40 * np.sin(t / 2) ** 2 + 5 * np.random.randn(50)
+z_imag = 60 * np.cos(t) + 10 * np.sin(2 * t)
+
+# Normalize impedance
+z_norm = (z_real + 1j * z_imag) / Z0
+
+# Calculate reflection coefficient (gamma)
+gamma = (z_norm - 1) / (z_norm + 1)
+gamma_real = gamma.real
+gamma_imag = gamma.imag
+
+# Create figure
+fig = go.Figure()
+
+# Draw Smith chart grid - constant resistance circles
+r_values = [0, 0.2, 0.5, 1, 2, 5]
+theta_grid = np.linspace(0, 2 * np.pi, 200)
+
+for r in r_values:
+    # Constant resistance circle: center at (r/(r+1), 0), radius 1/(r+1)
+    center_x = r / (r + 1)
+    radius = 1 / (r + 1)
+    circle_x = center_x + radius * np.cos(theta_grid)
+    circle_y = radius * np.sin(theta_grid)
+    # Clip to unit circle
+    mask = circle_x**2 + circle_y**2 <= 1.01
+    circle_x_clipped = np.where(mask, circle_x, np.nan)
+    circle_y_clipped = np.where(mask, circle_y, np.nan)
+    fig.add_trace(
+        go.Scatter(
+            x=circle_x_clipped,
+            y=circle_y_clipped,
+            mode="lines",
+            line=dict(color="rgba(100,100,100,0.4)", width=1),
+            hoverinfo="skip",
+            showlegend=False,
+        )
+    )
+
+# Draw constant reactance arcs
+x_values = [0.2, 0.5, 1, 2, 5]
+
+for x in x_values:
+    # Constant reactance arc: center at (1, 1/x), radius 1/x
+    center_y = 1 / x
+    radius = 1 / x
+    arc_theta = np.linspace(-np.pi, np.pi, 400)
+    arc_x = 1 + radius * np.cos(arc_theta)
+    arc_y = center_y + radius * np.sin(arc_theta)
+    # Clip to unit circle
+    mask = (arc_x**2 + arc_y**2 <= 1.01) & (arc_x >= -1)
+    arc_x_clipped = np.where(mask, arc_x, np.nan)
+    arc_y_clipped = np.where(mask, arc_y, np.nan)
+    fig.add_trace(
+        go.Scatter(
+            x=arc_x_clipped,
+            y=arc_y_clipped,
+            mode="lines",
+            line=dict(color="rgba(100,100,100,0.4)", width=1),
+            hoverinfo="skip",
+            showlegend=False,
+        )
+    )
+    # Negative reactance (mirror)
+    fig.add_trace(
+        go.Scatter(
+            x=arc_x_clipped,
+            y=-arc_y_clipped,
+            mode="lines",
+            line=dict(color="rgba(100,100,100,0.4)", width=1),
+            hoverinfo="skip",
+            showlegend=False,
+        )
+    )
+
+# Draw horizontal axis (real axis)
+fig.add_trace(
+    go.Scatter(
+        x=[-1, 1],
+        y=[0, 0],
+        mode="lines",
+        line=dict(color="rgba(100,100,100,0.5)", width=1),
+        hoverinfo="skip",
+        showlegend=False,
+    )
+)
+
+# Draw unit circle (boundary)
+boundary_theta = np.linspace(0, 2 * np.pi, 200)
+fig.add_trace(
+    go.Scatter(
+        x=np.cos(boundary_theta),
+        y=np.sin(boundary_theta),
+        mode="lines",
+        line=dict(color="#306998", width=2),
+        hoverinfo="skip",
+        showlegend=False,
+    )
+)
+
+# Plot impedance locus
+freq_ghz = freq / 1e9
+hover_text = [f"{f:.2f} GHz<br>Z = {z_real[i]:.1f} + j{z_imag[i]:.1f} Ω" for i, f in enumerate(freq_ghz)]
+
+fig.add_trace(
+    go.Scatter(
+        x=gamma_real,
+        y=gamma_imag,
+        mode="lines+markers",
+        line=dict(color="#306998", width=4),
+        marker=dict(size=10, color="#FFD43B", line=dict(color="#306998", width=2)),
+        name="Impedance Locus",
+        text=hover_text,
+        hoverinfo="text",
+    )
+)
+
+# Add frequency labels at key points with varied positions to avoid overlap
+label_configs = [
+    (0, 40, -40),  # 1.0 GHz - upper right
+    (16, -50, -30),  # 2.6 GHz - left
+    (32, 50, 30),  # 4.3 GHz - right
+    (49, 40, -50),  # 6.0 GHz - upper right
+]
+for idx, ax_offset, ay_offset in label_configs:
+    fig.add_annotation(
+        x=gamma_real[idx],
+        y=gamma_imag[idx],
+        text=f"{freq_ghz[idx]:.1f} GHz",
+        showarrow=True,
+        arrowhead=2,
+        arrowsize=1,
+        arrowwidth=2,
+        arrowcolor="#306998",
+        ax=ax_offset,
+        ay=ay_offset,
+        font=dict(size=16, color="#306998"),
+        bgcolor="white",
+        bordercolor="#306998",
+        borderwidth=1,
+        borderpad=4,
+    )
+
+# Mark center (matched condition)
+fig.add_trace(
+    go.Scatter(
+        x=[0],
+        y=[0],
+        mode="markers",
+        marker=dict(size=15, color="#FFD43B", symbol="x", line=dict(color="#306998", width=3)),
+        name="Matched (Z = Z₀)",
+        hoverinfo="name",
+    )
+)
+
+# Update layout
+fig.update_layout(
+    title=dict(text="smith-chart-basic · plotly · pyplots.ai", font=dict(size=28), x=0.5, xanchor="center"),
+    xaxis=dict(
+        title=dict(text="Real(Γ)", font=dict(size=22)),
+        tickfont=dict(size=18),
+        range=[-1.15, 1.15],
+        scaleanchor="y",
+        scaleratio=1,
+        showgrid=False,
+        zeroline=False,
+    ),
+    yaxis=dict(
+        title=dict(text="Imag(Γ)", font=dict(size=22)),
+        tickfont=dict(size=18),
+        range=[-1.15, 1.15],
+        showgrid=False,
+        zeroline=False,
+    ),
+    template="plotly_white",
+    legend=dict(
+        x=0.02, y=0.98, font=dict(size=18), bgcolor="rgba(255,255,255,0.9)", bordercolor="#306998", borderwidth=1
+    ),
+    margin=dict(l=80, r=80, t=100, b=80),
+)
+
+# Add resistance labels on the right
+r_labels = [(0, "0"), (0.2, "0.2"), (0.5, "0.5"), (1, "1"), (2, "2"), (5, "5")]
+for r, label in r_labels:
+    x_pos = r / (r + 1) + 1 / (r + 1)
+    if x_pos <= 1.0:
+        fig.add_annotation(x=x_pos, y=0, text=label, showarrow=False, font=dict(size=14, color="gray"), yshift=-20)
+
+# Add reactance labels at chart boundary
+reactance_label_positions = [
+    (1, 0.85, 0.52, "+j1"),  # +j1 label
+    (1, 0.85, -0.52, "-j1"),  # -j1 label
+    (0.5, 0.6, 0.8, "+j0.5"),  # +j0.5 label
+    (0.5, 0.6, -0.8, "-j0.5"),  # -j0.5 label
+]
+for _x, lx, ly, label in reactance_label_positions:
+    fig.add_annotation(x=lx, y=ly, text=label, showarrow=False, font=dict(size=14, color="gray"))
+
+# Save as PNG and HTML
+fig.write_image("plot.png", width=1600, height=900, scale=3)
+fig.write_html("plot.html")