High-Frequency Circuit Board: Key Features, Design Rules, and Applications

High-frequency signals propagate as electromagnetic waves and travel along transmission lines such as microstrip lines or striplines. Line width and spacing must be calculated from the signal frequency and board characteristics to keep characteristic impedance continuous.

Routing principles:

• Route critical signal lines (clock, RF) as short as possible — avoid right-angle turns and use 45° bends or curved paths instead.
• Keep differential pairs equal in length and spacing, routed in parallel, to preserve coupling and impedance balance.
• Follow the 3W/5H rules to control crosstalk: spacing between signal lines should be at least 3× the line width, and spacing between signal lines and ground planes at least 5× the line height.

Via optimization: vias are major sources of impedance discontinuity and signal loss — minimize their use in high-frequency designs. Where unavoidable, use small-diameter vias or back-drilling to remove conductive stubs from unconnected layers.

Power and ground planes: use a multilayer structure with dedicated, continuous planes, tightly coupled to form a planar capacitor for better decoupling. Place decoupling capacitor networks near the IC power pins so power impedance stays low across the target frequency range.