Tx-Line Calculator

Tx-Line Calculator is an Android app for RF and microwave engineers. Enter the physical dimensions of a transmission line to get its impedance and electrical length, or enter the impedance and length you need and let it find the dimensions.

Google Play Android 11+ Source on GitHub Privacy notice

Navigation drawer listing the seven transmission line types — Seven line types

Microstrip line screen with dimensions and synthesize and analyze buttons — Microstrip

Coaxial line screen with core radius, outer radius, and core offset — Coaxial

Coupled stripline screen with width, gap, and length — Coupled stripline

Coupled microstrip line screen in the dark theme — Dark theme

7transmission line types

2ways to solve: analyze, synthesize

mil · mm · cmper-field length units

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Background

A class project that stuck around

This project started as a part-time hobby during my undergraduate studies. I was taking an RF and microwave circuits course at the time, and Android was just emerging as a mobile platform. It was a natural exercise to combine what I was learning in class, transmission line theory and microwave circuit design, with the challenge of building an Android app from scratch.

I have kept it alive and updated it now and then ever since. The most recent rounds gave it a Material 3 look with a dark theme, new line diagrams, and in 2026 a full move from Java to Kotlin on the current Android SDK.

Two Ways to Solve

Every screen works in both directions

Analyze

You enterWidth, gap, substrate height, εr, metal thickness, length, frequency

You getZ₀ and electrical length; Z_0e, Z_0o, and k for coupled lines

Use it to check a layout you already have: what impedance does this trace on this board really give at 5 GHz?

Synthesize

You enterTarget Z₀ and electrical length, or Z_0e/Z_0o or Z₀/k

You getThe dimension you picked, plus the physical length

Use it at the start of a design: a radio button marks which dimension to solve for, and everything else stays fixed.

Supported Lines

What each one can solve for

Line	Synthesize	Results	Model
Microstrip	WHL	Z0 · electrical length	Hammerstad and Jensen, with metal thickness correction and Kirschning and Jansen frequency dispersion
Coupled microstrip	WGL	Z0e · Z0o · Z0 · k · electrical length	Kirschning and Jansen even and odd modes, with dispersion
Stripline	WHL	Z0 · electrical length	Exact elliptic-integral solution for thin strips, closed-form correction for thick ones
Coupled stripline	WGL	Z0e · Z0o · Z0 · k · electrical length	Cohn, including fringing capacitance for finite thickness
Coplanar waveguide	WGHL	Z0 · electrical length	Conformal mapping (Wadell)
Grounded CPW	WGHL	Z0 · electrical length	Conformal mapping with a bottom ground plane (Wadell)
Coaxial	abcL	Z0 · electrical length	Closed form, including an off-center inner conductor (offset c)

W width · G gap · H substrate height · L length · a inner radius · b outer radius · c inner conductor offset. Lengths can be entered in mil, mm, or cm, and frequency in MHz or GHz, each field with its own unit.

Under the Hood

Closed-form models · iterative synthesis

InputsEach field converted to SI from its own unit

ModelClosed-form equations for that line type

SolverBrackets the answer, then refines it with quasi-Newton steps

ResultConverted back to your units

Analysis runs the published equations once, so it is instant. Synthesis has no closed form for most lines, so the solver runs the analysis repeatedly: it first finds a range that contains the target impedance, then narrows in with quasi-Newton iterations until it converges. Coupled lines solve for width and gap together. Everything runs on the phone, with no network access.

Hammerstad and JensenStatic microstrip impedance and effective permittivity, with thickness correction.

Kirschning and JansenFrequency dispersion for microstrip, and even and odd modes for coupled microstrip.

CohnCoupled stripline, from zero-thickness strips to fringing fields for thick ones.

WadellTransmission Line Design Handbook, for coplanar waveguide with and without a ground plane.

KotlinAndroid SDK 37Material ComponentsAndroidX NavigationView BindingGradle version catalogDependabot

Get Started

Install it, or build it yourself

Install

Free on Google Play for Android 11 (API 30) and newer.

Questions or wrong numbers? Open an issue on GitHub.

Build from source

Needs the Android SDK and JDK 17. The Gradle wrapper fetches everything else:

git clone https://github.com/rookiepeng/tx-line-calculator.git
cd tx-line-calculator
./gradlew build

On Windows, run gradlew.bat build. Or open the folder in Android Studio and run the mobile module.

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