mikrostrip

A microstrip is a planar microwave transmission line consisting of a conducting strip on a dielectric substrate with a continuous ground plane on the opposite side.

Dimensions—strip width W, substrate height H, and relative permittivity ε_r—determine the characteristic impedance Z0 and the field distribution, which is mainly confined near the strip.

The line supports a quasi-TEM mode; the effective dielectric constant ε_eff lies between that of the substrate and air, influencing impedance and losses.

Impedance is commonly estimated with ε_eff ≈ (ε_r+1)/2 + (ε_r−1)/2 × 1/√(1+12H/W). For W/H ≤ 1, Z0 ≈ (60/√ε_eff) ln(8H/W + 0.25 W/H); for W/H ≥ 1, Z0 ≈ (120π)/(√ε_eff [W/H + 1.393 + 0.667 ln(W/H + 1.444)]).

Materials include FR-4, PTFE-based laminates, and low-loss ceramics such as Rogers RT/duroid; fabrication is via photolithography or screen printing on the substrate with a bottom ground plane.

Advantages are a low profile, ease of fabrication, and good integration with other planar circuits; drawbacks include conductor and dielectric losses, dispersion at high frequencies, and sensitivity to substrate tolerances and environment.

Applications include patch antennas, filters, couplers, and impedance-matching networks in RF and microwave systems.

Microstrip was developed in the mid-20th century to enable planar microwave circuits on a single substrate.