Coplanar Waveguide – Quasi‑TEM Mode
Planar line with ground on same side.
Effective permittivity: ...
Electric Field (E) – Cross‑section
E‑field lines between signal and ground.
Magnetic Field (H) – Cross‑section
H‑field loops around signal.
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
Characteristic impedance: Z0 = 30π/√εeff * K(k)/K'(k) where k = s/(s+2g)
Characteristic impedance: Z0 = 30π/√εeff * K(k)/K'(k) where k = s/(s+2g)
📝 Description & Applications
CPW offers easy shunt mounting, low dispersion, and good isolation.
Applications: MMICs, antennas, high‑frequency interconnects.
Advantages: No via holes, wide bandwidth.
Disadvantages: Potential for slotline modes.
💡 Interview Questions
How does CPW differ from microstrip in terms of field confinement?
What is the advantage of using CPW over microstrip at high frequencies?