Microstrip Line – Quasi‑TEM Mode
Common planar transmission line.
Effective permittivity: ... | λg: ...
Electric Field (E) – Cross‑section
E‑field lines from strip to ground.
Magnetic Field (H) – Cross‑section
H‑field loops around strip.
E‑field in x‑z plane (y=0)
Arrows: (Ex, Ez).
H‑field in x‑z plane (y=0)
Arrows: (Hx, Hz).
📐 Quasi‑TEM Approximation
Effective permittivity: εeff = (εr+1)/2 + (εr-1)/2 * (1+12h/w)-1/2
Characteristic impedance: Z0 = 60/√εeff * ln(8h/w + w/(4h)) for w/h ≤ 1
Characteristic impedance: Z0 = 60/√εeff * ln(8h/w + w/(4h)) for w/h ≤ 1
📝 Description & Applications
Microstrip is a planar transmission line widely used in microwave circuits. It supports a quasi‑TEM mode.
Applications: Filters, couplers, antennas, MMICs.
Advantages: Easy fabrication, integration.
Disadvantages: Dispersion, radiation losses.
💡 Interview Questions
What is the effective permittivity and why is it used?
How does the field distribution change with frequency?