Stripline
Understanding Stripline
Stripline is the enclosed counterpart to microstrip. Because the signal conductor is completely surrounded by ground planes and dielectric, stripline has several advantages: no radiation loss, pure TEM propagation (no dispersion), and excellent isolation between adjacent lines. The trade-off is that it is an internal layer with no access for surface-mount components.
Stripline Advantages
- No radiation: Enclosed structure prevents radiation, critical for filter and power divider networks.
- TEM mode: Pure TEM propagation with no dispersion. Phase velocity independent of frequency.
- High isolation: Ground planes above and below shield adjacent traces from coupling.
Design Considerations
- Impedance: Determined by strip width, ground plane spacing, and dielectric constant. Narrower strip and wider spacing increase impedance.
- Manufacturing: Internal layer construction requires precise lamination and via drilling.
- Component placement: Cannot place surface-mount components on an internal stripline layer; requires via transitions to access microstrip on outer layers.
Z0 = (60/sqrt(er)) x ln(4b/(pi d W_eff))
where b = ground plane spacing, W = strip width
Propagation velocity:
v = c / sqrt(er) (no dispersion)
Effective wavelength:
lambda = lambda0 / sqrt(er)
Frequently Asked Questions
What is stripline?
Stripline is a PCB transmission line where a signal conductor is sandwiched between two ground planes with dielectric between them. It is completely enclosed, supporting pure TEM mode propagation with no radiation or dispersion.
What is the difference between microstrip and stripline?
Microstrip has the signal trace on the surface with one ground plane below; it is partially open (fields in both substrate and air). Stripline is sandwiched between two ground planes; it is fully enclosed. Stripline has no radiation but cannot directly mount components.
When should I use stripline instead of microstrip?
Use stripline when radiation must be minimized (filter networks, power dividers), when high isolation between traces is needed, or when non-dispersive propagation is required. Use microstrip when surface-mount components need to be placed on the transmission line.