feat(ggplot2): implement smith-chart-basic

plots/smith-chart-basic/implementations/r/ggplot2.R

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+#' anyplot.ai
+#' smith-chart-basic: Smith Chart for RF/Impedance
+#' Library: ggplot2 3.5.1 | R 4.4.1
+#' Quality: 89/100 | Created: 2026-05-20
+
+library(ggplot2)
+library(ragg)
+
+# --- Theme tokens -----------------------------------------------------------
+THEME       <- Sys.getenv("ANYPLOT_THEME", "light")
+PAGE_BG     <- if (THEME == "light") "#FAF8F1" else "#1A1A17"
+INK         <- if (THEME == "light") "#1A1A17" else "#F0EFE8"
+INK_SOFT    <- if (THEME == "light") "#4A4A44" else "#B8B7B0"
+OKABE_ITO   <- c("#009E73", "#D55E00", "#0072B2", "#CC79A7",
+                 "#E69F00", "#56B4E9", "#F0E442")
+
+# --- Smith chart grid -------------------------------------------------------
+theta <- seq(0, 2 * pi, length.out = 361)
+
+# Outer unit circle (|Gamma| = 1 boundary)
+outer_circle <- data.frame(x = cos(theta), y = sin(theta))
+
+# Constant resistance circles: r/(1+r) center, 1/(1+r) radius
+r_vals <- c(0, 0.2, 0.5, 1, 2, 5)
+r_circles <- do.call(rbind, lapply(r_vals, function(r) {
+  cx  <- r / (1 + r)
+  rad <- 1 / (1 + r)
+  data.frame(
+    x   = cx + rad * cos(theta),
+    y   = rad * sin(theta),
+    grp = paste0("r", r)
+  )
+}))
+
+# Constant reactance arcs: center (1, 1/x), radius 1/|x|, clipped to unit disc
+x_vals <- c(0.2, 0.5, 1, 2, 5)
+x_arcs <- do.call(rbind, lapply(c(x_vals, -x_vals), function(x) {
+  cy  <- 1 / x
+  rad <- abs(1 / x)
+  pts_x <- 1 + rad * cos(theta)
+  pts_y <- cy  + rad * sin(theta)
+  inside <- (pts_x^2 + pts_y^2) <= 1.001
+  if (sum(inside) < 3) return(NULL)
+  data.frame(x = pts_x[inside], y = pts_y[inside], grp = paste0("x", x))
+}))
+
+# VSWR = 2 reference circle (|Gamma| = 1/3)
+vswr_circle <- data.frame(
+  x = (1 / 3) * cos(theta),
+  y = (1 / 3) * sin(theta)
+)
+
+# --- Impedance locus: RLC antenna resonant near 2 GHz ----------------------
+set.seed(42)
+Z0        <- 50
+freqs_ghz <- seq(1, 3, length.out = 80)
+omega     <- 2 * pi * freqs_ghz * 1e9
+
+R_ant <- 45
+L_ant <- 5e-9
+C_ant <- 1 / ((2 * pi * 2e9)^2 * L_ant)   # resonance exactly at 2 GHz
+
+zr <- R_ant / Z0
+zx <- (omega * L_ant - 1 / (omega * C_ant)) / Z0
+
+# Reflection coefficient Gamma = (z - 1) / (z + 1)
+denom    <- (zr + 1)^2 + zx^2
+gamma_re <- ((zr - 1) * (zr + 1) + zx^2) / denom
+gamma_im <- 2 * zx / denom
+
+locus <- data.frame(gre = gamma_re, gim = gamma_im, freq = freqs_ghz)
+
+# Labels at 1 GHz, 2 GHz, 3 GHz
+label_freqs <- c(1, 2, 3)
+label_idx   <- sapply(label_freqs, function(f) which.min(abs(locus$freq - f)))
+label_pts   <- locus[label_idx, ]
+label_pts$lbl <- c("1 GHz", "2 GHz\n(res.)", "3 GHz")
+
+# Directional arrow at 3 GHz end to show sweep direction
+n_loc <- nrow(locus)
+dx    <- locus$gre[n_loc] - locus$gre[n_loc - 5]
+dy    <- locus$gim[n_loc] - locus$gim[n_loc - 5]
+norm  <- sqrt(dx^2 + dy^2)
+arr_len <- 0.055
+arr_x0  <- locus$gre[n_loc] - (dx / norm) * arr_len
+arr_y0  <- locus$gim[n_loc] - (dy / norm) * arr_len
+
+# --- Plot -------------------------------------------------------------------
+p <- ggplot() +
+  # Grid: outer circle
+  geom_path(data = outer_circle, aes(x = x, y = y),
+            color = INK_SOFT, linewidth = 0.7) +
+  # Grid: constant-r circles
+  geom_path(data = r_circles, aes(x = x, y = y, group = grp),
+            color = INK_SOFT, linewidth = 0.22, alpha = 0.65) +
+  # Grid: constant-x arcs
+  geom_path(data = x_arcs, aes(x = x, y = y, group = grp),
+            color = INK_SOFT, linewidth = 0.22, alpha = 0.65) +
+  # Real axis
+  geom_segment(aes(x = -1, xend = 1, y = 0, yend = 0),
+               color = INK_SOFT, linewidth = 0.3) +
+  # VSWR = 2 reference circle
+  geom_path(data = vswr_circle, aes(x = x, y = y),
+            color = OKABE_ITO[3], linewidth = 0.5, linetype = "dashed") +
+  annotate("text", x = -0.38, y = 0.06,
+           label = "VSWR = 2", size = 3.0, color = OKABE_ITO[3]) +
+  # Matched-load centre marker
+  geom_point(aes(x = 0, y = 0),
+             color = INK_SOFT, size = 1.8, shape = 3) +
+  # Impedance locus
+  geom_path(data = locus, aes(x = gre, y = gim),
+            color = OKABE_ITO[1], linewidth = 1.4) +
+  # Directional arrow at 3 GHz end showing sweep direction
+  annotate("segment",
+           x = arr_x0, xend = locus$gre[n_loc],
+           y = arr_y0, yend = locus$gim[n_loc],
+           color = OKABE_ITO[1], linewidth = 1.4,
+           arrow = arrow(length = unit(0.1, "inches"), type = "closed")) +
+  # Start (1 GHz) and end (3 GHz) markers
+  geom_point(data = locus[1, ], aes(x = gre, y = gim),
+             color = OKABE_ITO[1], size = 3.5, shape = 16) +
+  geom_point(data = locus[nrow(locus), ], aes(x = gre, y = gim),
+             color = OKABE_ITO[2], size = 3.5, shape = 17) +
+  # Frequency labels
+  geom_text(data = label_pts, aes(x = gre, y = gim, label = lbl),
+            color = INK, size = 3.2, hjust = -0.15, lineheight = 0.9) +
+  # Resistance value labels along real axis
+  annotate("text",
+           x = (r_vals - 1) / (r_vals + 1),
+           y = -0.06,
+           label = as.character(r_vals),
+           size = 3.0, color = INK_SOFT, vjust = 1) +
+  coord_fixed(xlim = c(-1.15, 1.35), ylim = c(-1.15, 1.15)) +
+  labs(
+    title = "smith-chart-basic · r · ggplot2 · anyplot.ai",
+    x     = "Re(Γ)",
+    y     = "Im(Γ)"
+  ) +
+  theme_minimal(base_size = 8) +
+  theme(
+    plot.background  = element_rect(fill = PAGE_BG, color = PAGE_BG),
+    panel.background = element_rect(fill = PAGE_BG, color = NA),
+    panel.grid.major = element_blank(),
+    panel.grid.minor = element_blank(),
+    panel.border     = element_blank(),
+    axis.title       = element_text(color = INK,      size = 10),
+    axis.text        = element_text(color = INK_SOFT, size = 8),
+    plot.title       = element_text(color = INK,      size = 12),
+    axis.line        = element_blank()
+  )
+
+# --- Save -------------------------------------------------------------------
+ggsave(
+  filename = sprintf("plot-%s.png", THEME),
+  plot     = p,
+  device   = ragg::agg_png,
+  width    = 6,
+  height   = 6,
+  units    = "in",
+  dpi      = 400
+)