
669Planar Transmission Lines
where R
s
is the surface resistance of the conductor and was given by
Equation 2.19b.
15.3.3 Approximate Electrostatic Solution
Consider the microstrip line shown in Figure 15.11. Let Φ(x, y) be the potential
eld that is a function of x and y. This eld has to satisfy Laplace’s equation
∇
2
Φ = 0 within the space bounded by –(a/2) ≤ x ≤ a/2 and 0 ≤ y ≤ ∞, which can
be divided into two regions given as follows:
Region-I: –a/2 ≤ x ≤ a/2 and 0 ≤ y ≤ d and region-II: –a/2 ≤ x ≤ a/2 and
d ≤ y ≤ ∞. Since these two regions are dened by air/dielectric interface,
separate solutions Φ
I
(x, y) and Φ
II
(x, y) for ∇
2
Φ = 0 are