Meaning
Printed circuit board trace geometries where a conductor is routed on an outer layer and separated from a parallel ground plane by a dielectric substrate control the transmission of high-frequency signals. Implementing a microstrip layout is the standard method for routing RF paths between a wireless transceiver chip and its antenna. This structure allows the designer to achieve the precise characteristic impedance needed to prevent signal loss.
Impedance Matching
Trace width and the thickness of the dielectric layer are the primary factors that determine the characteristic impedance of the transmission line. In a microstrip layout, these dimensions must be carefully calculated using the dielectric constant of the board material to hit the target impedance, which is typically fifty ohms. If the board manufacturer uses a different material thickness, the impedance will change, causing signal reflections and reduced range.
This requirement is verified by adding a test coupon on the board panel to measure the impedance after fabrication.
Crosstalk and Shielding
RF signals running along a microstrip trace can radiate electromagnetic energy and interfere with nearby analog or digital signals. To prevent this, designers place ground guard traces or routing vias along both sides of the RF path to provide shielding. This isolation is particularly important when the high-frequency line runs close to sensitive sensor inputs or power supply traces.
Proper spacing and grounding of adjacent copper planes prevent unwanted signal coupling and maintain overall system stability.
Mechanical Placement
Components like matching capacitors and inductors must be placed as close to the trace as possible to avoid discontinuities. This dense routing prevents the transmission line from acting as an unintentional radiator.
