Smith Matcher Tutorial — Analog Intuition

Interactive tool walkthrough

Match a load on a live Smith chart

This page is a scrollable tutorial for the Smith Chart Impedance Matcher. Read top to bottom, or jump from the sidebar. Figures below are simplified maps of the real UI — open the tool in another tab and follow along.

No video · no install · works offline once the site is loaded

What this tool does

You pick a load (fixed R+jX, a Z(f) table, or measured S-parameters), build a matching network (L, C, R, transmission lines, stubs), and watch the match move on a Smith chart while a frequency-response plot shows return loss across a band.

Load

Fixed Z Z(f) S-param

Z₀RX

Network

+ Element Build Auto-tune

Smith

Frequency response

Mental map of the workspace: Load (what you match to) · Network (parts) · Smith (Γ at design F) · Frequency response (how good the match is across band).

Tip. The short “How to use” list at the bottom of the tool is a cheat sheet. This page is the full walkthrough.

1 · Choose a load

Top-left card. Everything else exists to match this impedance (or S-parameter port) toward Z₀ at the design frequency.

Load

Z₀ (Ω)50 Load R (Ω)100 Load X (Ω)25

Fixed Z Z(f) table S-param

Three ways to define the load. Pick one radio, then fill in the data that mode needs.

Fixed Z — constant R + jX at every frequency. Best for learning L-section matching and dragging arcs.
Z(f) table — datasheet-style R(f), X(f). Import JSON or edit the blank table. Design F picks the row used for the Smith match.
S-param — match to S11 or S22 from imported Touchstone files (next section).

Try it. Open the tool → leave Fixed Z on → set R=100, X=25, Z₀=50. You should see a red load marker off the center of the chart. Open tool →

2 · S-parameter files

Switch load mode to S-param. Import one or many .s1p / .s2p files (or a whole folder in Chrome/Edge). The tool converts the selected port’s reflection into Z(f) for matching.

S-parameter files

Import Folder

ADL7075_25C.s2p S11 S22 Smith Mag

ADL7075_85C.s2p S11 S22

Multi-file library: pick the active file, choose S11 or S22 as the match target, and optionally overlay raw Γ on the Smith chart or magnitude on the |S| plot.

Parses GHZ / MHZ / … and DB / MA / RI formats; Z₀ from the # line.
On import, the sweep band often snaps to the file’s min/max frequency, with design F near the middle.
S21 / S12 can appear on the magnitude chart when useful — matching still uses reflection (S11/S22).

Try it. Mode = S-param → Import a vendor .s2p → select the file → S11 or S22 → watch the load marker and the frequency-response curve update.

3 · Design frequency & sweep band

Matching is optimized / visualized at Design at F. The dual-ended Sweep band controls the frequency axis of the response plot (and optional Γ(f) trail on the Smith chart).

Frequency ⚙ Limits

Design at F

1.00 GHz

0.50

3.00 GHz

Drag ends for bandwidth below / above design F

Green mark = design F inside the band. ⚙ Limits sets how far the sliders can go (handy after importing wideband S-params).

Tip. Narrow the band around your channel when judging match bandwidth; widen it when you want to see out-of-band behavior.

4 · Match on the Smith chart

The chart is the Γ plane. Center = perfect match to Z₀. Gold circles = constant resistance; teal arcs = constant reactance (switch to the Y grid to see constant conductance / susceptance instead).

Load Γ After each element Z₀ center Optional Γ(f) band sweep

Drag an endpoint (when enabled) to tune along the proper arc. Hover the chart for Z, Γ, VSWR, and RL without covering the plot.

Z / Y — impedance vs admittance grid (same Γ plane).
VSWR — constant-|\Gamma| circle; stay inside for a return-loss budget.
Q — constant-|X|/R “football”; useful when thinking about matching Q.
Drag endpoints — grab a node on the match path and slide along the element’s arc.

5 · Network, Build, and Auto-tune

The schematic runs from Z₀ (left) to the load (right). Series parts sit on the bus; shunts drop to ground. Click a value to type; hover + scroll to nudge.

Network

Z₀ L 4.7 nH C 2.2 pF Z_L

+ Element Build Auto-tune ⚙

Build snaps L/C/R to preferred E-series values for the set tolerances (⚙). Auto-tune optimizes continuous values for the current topology at design F.

+ Element — picker with smart defaults at design F (series/shunt L, C, R, TL, open/shorted stubs).
Typical flow: sketch topology → Auto-tune → Build → tweak by drag or wheel.
TL / stub lengths quantize to 0.5° on Build (not E-series).

Try it. Load an example (e.g. L-section match) → Auto-tune → Build → compare Matched vs Raw S₁₁.

6 · Frequency response

Below the Smith workspace, the response chart shows how good the match is vs frequency. This is where “looks matched at design F” becomes “good enough across my band.”

Frequency response

Matched S₁₁ Raw S₁₁ RL guide Γ(f) on Smith

RL ≥ 15 dB Match BW: 180 MHz · 0.91–1.09 GHz

Matched = with your network. Raw = load alone (no matching network) — they coincide if the chain is empty. RL guide draws the threshold and can shade pass bands; match bandwidth is reported under the controls.

7 · Save & load a project

Use Save / Load on the Smith toolbar to snapshot the whole project: load mode, network, band, tolerances, and S-param library references where applicable.

PNG — export a chart snapshot for notes or slides.
Debug — dumps state when something looks off (handy for bug reports).
Example buttons on the left load teaching presets (L-section, broadband, device Z(f), …).

Quick recipes

Learn L-section matching

Fixed Z · R=100 · X=25 · Z₀=50
Load example “L-section match” (or add series L + shunt C)
Auto-tune → watch the path to center
Toggle Z/Y grid while you drag

Device from datasheet S2P

S-param mode → Import .s2p
Pick S11 or S22
Set design F to your channel
Build a short match → Build → check match BW

Stock parts only

Get a continuous solution (Auto-tune)
⚙ set L/C/R tolerances
Build → re-check S₁₁ vs band
Nudge with wheel if a part is off-grid