Microstrip vs Stripline vs CPW Guide
Compare microstrip, stripline, and coplanar waveguide for high-speed PCB design. Impedance calculations and use cases.
When routing high-speed signals on a PCB, choosing the right transmission line structure is critical. Microstrip, stripline, and coplanar waveguide (CPW) are the three main options, each with distinct characteristics that affect impedance, crosstalk, and signal integrity.
This guide explains the differences, shows when to use each, and provides practical impedance calculations. Whether you're designing USB, HDMI, PCIe, or RF circuits, understanding these structures is essential.
Transmission Line Overview
Microstrip
Trace on an outer layer with a ground plane below. Partially exposed to air.
Stripline
Trace sandwiched between two ground planes. Completely enclosed in dielectric.
Coplanar (CPWG)
Trace on outer layer with ground on both sides and below. Best shielding.
Quick Comparison
| Feature | Microstrip | Stripline | CPWG |
|---|---|---|---|
| Layer Position | Outer layer | Inner layer | Outer layer |
| Reference Planes | 1 (below) | 2 (above & below) | 3 (sides & below) |
| Dielectric | Air + PCB | PCB only | Air + PCB |
| EMI Shielding | Fair | Excellent | Good |
| Crosstalk | Moderate | Low | Low |
| Attenuation | Lower | Higher | Medium |
| Routing Density | High | Medium | Lower |
Microstrip: The Workhorse
Microstrip is the most common transmission line structure because it's on an outer layer, making it easy to route and debug. The trace sits on top of the dielectric with a ground plane below.
Approximate Impedance Formula
Z₀ = (87 / √(εᵣ + 1.41)) × ln(5.98h / (0.8w + t))
Where: h = dielectric height, w = trace width, t = trace thickness, εᵣ = dielectric constant
Calculate microstrip dimensions for your target impedance using your actual stackup and material properties in a suitable impedance calculator or field solver.
Advantages
- Easiest to route and manufacture
- Components can be placed directly
- Lower dielectric loss
- Easy to probe and debug
Disadvantages
- Susceptible to EMI pickup
- Higher crosstalk than stripline
- Signal radiates more
- Impedance varies with solder mask
Stripline: The Shielded Champion
Stripline places the signal trace between two ground planes, providing natural shielding. It's ideal for sensitive signals that need protection from EMI and minimal crosstalk.
Approximate Impedance Formula
Z₀ = (60 / √εᵣ) × ln(4b / (0.67π(0.8w + t)))
Where: b = distance between ground planes, w = trace width, t = trace thickness
Calculate stripline dimensions for your target impedance using your actual stackup and material properties in a suitable impedance calculator or field solver.
Note: Stripline traces are narrower than microstrip for the same impedance because the full dielectric constant applies (not reduced by air interface).
Advantages
- Excellent EMI shielding
- Very low crosstalk
- Consistent impedance
- No solder mask impact
- Better for high-frequency signals
Disadvantages
- Requires vias for component access
- Higher manufacturing cost
- More dielectric loss
- Harder to debug
- Uses inner layer routing resources
Coplanar Waveguide with Ground (CPWG)
CPWG adds ground traces on either side of the signal trace, plus a ground plane below. This provides excellent shielding while keeping the signal on an outer layer for easy component access.
When to Use CPWG
- RF/Microwave circuits where impedance control is critical
- High-density designs needing outer-layer controlled impedance
- Mixed-signal boards with analog and digital sections
- Differential pairs requiring tight coupling
Calculate CPWG dimensions for your target impedance using your actual stackup and material properties in a suitable impedance calculator or field solver.
Advantages
- Outer layer accessibility
- Good EMI shielding
- Low crosstalk
- Excellent for RF circuits
- Ground readily available
Disadvantages
- Requires space for adjacent ground conductors
- Complex impedance calculation
- Sensitive to gap width variations
- Review gap and trace-width tolerances with the fabricator
Differential Pairs: Microstrip vs Stripline
Differential signals (USB, HDMI, PCIe, Ethernet) can use either edge-coupled microstrip or edge-coupled stripline. Select dimensions using the requirements for your interface and the properties of your stackup.
Tolerance, skew and loss budgets: see the current interface specification and your device datasheet; this article does not state them.
Tip: For differential impedance (Zdiff), the traces are coupled, so: Zdiff ≈ 2 × Z₀ × (1 - k), where k is the coupling coefficient, which depends on the geometry and stackup.
Selection Guide: Which One to Use?
| Application | Structure to Evaluate | Reason |
|---|---|---|
| USB 2.0 (480 Mbps) | Microstrip | Outer-layer component access |
| USB 3.0/3.1 (5-10 Gbps) | Microstrip or Stripline | Depends on EMI requirements |
| HDMI 1.4/2.0 | Microstrip | Outer layer for connector access |
| HDMI 2.1 (48 Gbps) | Stripline | Evaluate shielding and channel loss |
| PCIe Gen3/4 | Stripline | Low crosstalk critical |
| PCIe Gen5/6 | Evaluate stripline | Check shielding and channel requirements |
| DDR4/DDR5 | Microstrip | Short traces, component access |
| Ethernet 1G | Microstrip | Simple, proven design |
| Ethernet 10G+ | Stripline | EMI and crosstalk critical |
| RF/Microwave | Evaluate CPWG/Stripline | Loss and radiation concerns |
Impedance Calculation Tools
Manual impedance calculations are tedious and error-prone. Use our free PCB Impedance Calculator to quickly determine trace width for your desired impedance. It supports:
- Microstrip (single-ended and differential)
- Stripline (symmetric and asymmetric)
- Coplanar waveguide with ground (CPWG)
- Custom dielectric constants and stackups
Manufacturing Tolerances
Compute impedance sensitivity using your own stackup in the site's impedance calculator or a field solver.
Practical Tip: Request impedance-controlled manufacturing and specify your target impedance and the tolerance required by your device documentation; agree on achievable dimensions and tolerances with the fabricator.
Summary
Use Microstrip When:
You need outer-layer routing and component access; evaluate EMI and signal integrity for the intended interface and stackup.
Use Stripline When:
You need shielding or crosstalk control for high-speed signals; evaluate the routing structure against the channel requirements for PCIe, Ethernet, or RF.
Use CPWG When:
You need shielded signals on outer layers, RF/microwave design, or tight impedance control with component access. Common in wireless and antenna circuits.
Ready to calculate your trace dimensions? Try our Impedance Calculator for quick, accurate results.
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