Stripline Structure
A stripline conductor is sandwiched between two ground planes inside a multilayer PCB. Unlike microstrip (which has one ground below and air above), stripline is completely enclosed in homogeneous dielectric — giving purely TEM propagation with no dispersion.
Stripline vs Microstrip Properties
| Property | Stripline | Microstrip |
|---|---|---|
| Propagation mode | Pure TEM | Quasi-TEM (dispersive) |
| Dispersion | None (εr frequency-independent) | εe increases with frequency |
| Radiation | Zero (enclosed in metal) | Some radiation possible |
| Ground planes | Both above and below | Below only |
| PCB layer | Internal | External (top/bottom) |
| 50Ω trace width | ~40% narrower than microstrip | Standard |
Stripline Impedance Formula
Z₀_stripline ≈ (60/√εr) × ln(4b / (0.67π × (0.8W + t))) b = separation between ground planes W = trace width t = trace thickness For 50Ω on FR4 (εr=4.5, b=1.6mm, t=35µm): W ≈ 0.9 mm (narrower than microstrip!) Phase velocity: vp = c/√εr (same as bulk dielectric, unlike microstrip)
RF View: Load stripline S-parameter files from EM simulation or PCB measurements for full analysis. Stripline provides lower loss and better isolation between adjacent layers. Free on Android.