Microstrip vs Stripline
Microstrip and stripline are the two dominant transmission line structures in PCB design. Microstrip is easier to fabricate and probe, while stripline offers better shielding and lower radiation loss — the right choice depends on frequency, isolation requirements, and PCB layer budget.
Microstrip
Microstrip is a conductor on the outer layer of a PCB with a ground plane below, separated by the substrate dielectric. Part of the field extends into air above the trace, giving an effective dielectric constant lower than the substrate.
Advantages
- Easy to access for probing and rework
- Lower fabrication cost — outer layer, no buried vias needed
- Lower dielectric loss at high frequencies due to partial air field
- Easy to match with end-launch connectors
Disadvantages
- Radiates more than stripline — not shielded on top
- Susceptible to coupling and interference from external fields
- Effective dielectric constant varies with frequency (dispersion)
- Higher impedance sensitivity to solder mask thickness
When to use
Use microstrip for RF traces on outer layers where probing access is needed, connectors land on the outer layer, and EMI shielding is handled at board or enclosure level.
Stripline
Stripline is a conductor buried between two ground planes inside the PCB stackup. The field is fully contained in the dielectric, giving a well-defined, frequency-stable characteristic impedance.
Advantages
- Fully shielded — minimal radiation and coupling to adjacent layers
- Stable impedance — no air-dielectric interface, no dispersion
- Better for high-density designs with sensitive RF signals
- Lower crosstalk between adjacent lines
Disadvantages
- Requires at least 4-layer PCB — increases cost
- Cannot be directly probed — requires test vias
- Higher dielectric loss than microstrip at same frequency
- Via transitions add parasitic inductance and reflections
When to use
Use stripline for high-frequency signals requiring isolation (PLLs, clocks, RF distribution), sensitive differential pairs, and any trace that must not radiate or pick up interference.
Key Differences
- ▸Microstrip is on outer PCB layers; stripline is buried between ground planes
- ▸Stripline provides full EM shielding; microstrip is open on top and radiates
- ▸Microstrip has lower dielectric loss due to partial air interface; stripline has stable εr
- ▸Stripline requires a 4+ layer PCB; microstrip works on a 2-layer board
- ▸Microstrip is accessible for probing; stripline requires test vias
Summary
Choose microstrip for cost-sensitive designs, outer-layer connectors, and when probing access is needed. Choose stripline for high-frequency isolation, sensitive signals, and dense multilayer boards where EMI and crosstalk must be controlled. Many RF PCB designs use both — microstrip to connectors, stripline for internal routing.
Frequently Asked Questions
Which has lower loss at 10 GHz — microstrip or stripline?
Microstrip typically has lower total loss at high frequencies because part of the field travels in air (lower εr), reducing dielectric loss. However, radiation loss increases with frequency for microstrip. Stripline loss is dominated by dielectric loss in the PCB material.
Can I use microstrip at 77 GHz?
Yes, but with careful attention to surface roughness, solder mask removal, and connector transitions. Above ~20 GHz, surface roughness of copper becomes a significant loss factor. Low-loss laminates (Rogers, Isola) are typically required above 10 GHz for microstrip.
What is a coplanar waveguide (CPW)?
CPW adds ground planes on each side of a microstrip trace on the same layer. This provides better shielding than microstrip while remaining on the outer layer — a hybrid approach used in RF ICs, antenna feeds, and high-frequency PCBs.
How do I transition between microstrip and stripline?
Use a via to transition between layers. The via diameter, drill, and pad size must be carefully designed to minimize parasitic capacitance and inductance. Back-drilling (removing the via stub) is often needed above 10 GHz to avoid resonances.