Question

For a parallel plate transmission line, let v be the speed of propagation and Z be the characteristic impedance. Neglecting fringe effects, a reduction of the spacing between the plates by a factor of two results in

(A) halving of v and no change in Z.

(B) no changes in v and halving of Z.

(C) no change in both v and Z.

(D) halving of both v and Z

Answer 1

Correct option (B) no changes in v and halving of Z.

Explanation:

For a parallel plate transmission line shown in figure capacitance is given by,

C = εw/d

For a parallel plate transmission line shown in figure inductance is given by,

L = μ0d/w

Characteristic impedance is given by,

z = √(L/C)

z = √(μd/w x d/εw) = d/w√(μ/ε)

Hence, by reducing the spacing between the plates d by a factor of two, results in halving of Z.

Speed of propagation is given by,

v = 1/√(LC) = 1/√(μ0d/w x εw/d)

v = 1/√(μ0ε)

Hence, speed of propagation is independent from spacing between the plates.