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feat(ggplot2): implement smith-chart-basic (#7453)
## Implementation: `smith-chart-basic` - r/ggplot2 Implements the **r/ggplot2** version of `smith-chart-basic`. **File:** `plots/smith-chart-basic/implementations/r/ggplot2.R` **Parent Issue:** #3792 --- :robot: *[impl-generate workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/26135676591)* --------- Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com> Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com> Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>
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‎plots/smith-chart-basic/implementations/r/ggplot2.R‎

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

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