Basic Concepts of Microstrip and Stripline
Microstrip: A widely used transmission line structure in high-frequency circuits, typically composed of a metal conductor and an insulating substrate. The characteristic impedance of microstrip is influenced by its width, thickness, and dielectric constant of the substrate.
Stripline: Usually consists of two parallel conductors and is commonly used to control signal propagation and reduce interference. The characteristic impedance of stripline is also affected by the conductor width, spacing, and substrate characteristics.
Design Steps
Determine Design Parameters

Specify the required characteristic impedance (e.g., 50Ω or 75Ω).
Choose appropriate materials and thickness based on the circuit’s operating frequency.
Select Suitable Substrate

The dielectric constant (Dk) and loss tangent (Df) of the substrate significantly impact the performance of microstrip and stripline.
Select a substrate suitable for high-frequency applications (such as ROGERS or FR4) with good dielectric properties.
Calculate Width and Spacing

Use design formulas or simulation software to calculate the width and spacing of the conductors to meet the desired characteristic impedance.
Maintain appropriate widths and spacing in the design to avoid signal reflections and losses.
Layout and Routing

Arrange the microstrip or stripline position rationally in the PCB layout to avoid crossing other circuits.
Keep the routing as short as possible to reduce signal delay and interference.
Simulation and Optimization

Use electromagnetic simulation software (such as HFSS or ADS) to simulate the design, analyzing its signal integrity and reflection loss.
Make necessary optimization adjustments based on the simulation results.
Output Design Files

Ensure the generated design files meet the manufacturer’s requirements, including all parameters and dimensions for microstrip and stripline.
Considerations
Signal Integrity

In high-frequency applications, signal integrity is crucial. The design should consider impedance matching to avoid reflections and signal losses.
Environmental Factors

Consider the impact of temperature and humidity on material properties, selecting suitable materials to ensure long-term stability.
Manufacturing Tolerances

Establish reasonable manufacturing tolerances to ensure the final product’s impedance matches design requirements, avoiding performance degradation due to manufacturing errors.
PCB Layer Structure

The design of microstrip and stripline should consider the layer structure of the PCB to ensure proper placement and connection in accordance with electrical specifications.

Continued Steps and Considerations in Microstrip and Stripline Design for High-Frequency PCB Production
Common Issues and Solutions
Signal Reflection

Issue: Mismatched impedance can lead to signal reflection.
Solution: Ensure accurate calculations for trace width and spacing, employ impedance matching in circuit design, and incorporate matching networks when necessary.
Crosstalk

Issue: Signal interference between adjacent traces.
Solution: Increase spacing between traces, optimize routing to minimize interaction, and use ground layers for shielding.
Temperature Variation

Issue: Changes in temperature can affect material properties and signal transmission.
Solution: Choose materials with good thermal stability and consider the effects of thermal expansion in the design.
Manufacturing Process Limitations

Issue: Potential errors during manufacturing.
Solution: Establish reasonable design tolerances, select materials compatible with manufacturing processes, and collaborate closely with PCB manufacturers.
The design of microstrip and stripline is crucial in high-frequency PCB production. By following appropriate design steps and considerations, effective transmission of high-frequency signals can be ensured, reducing losses and interference, thus enhancing overall circuit performance. Designers should thoroughly consider material properties, environmental factors, and manufacturing constraints throughout the design process to guarantee the reliability and stability of the final product.