Electromagnetics, Transmission Lines, Waveguides and Antennas — Practice

Question 1

What is the intrinsic impedance of free space?

Accepted Answer

120 pi, about 377 ohms.

Question 2

What impedance does a half-wave section of lossless line present?

Accepted Answer

The load impedance itself.

Question 3

A 50 ohm line ends in a 100 ohm load. Find the reflection coefficient, VSWR and reflected power fraction.

Accepted Answer

Gamma = 50/150 = 1/3. VSWR = (4/3)/(2/3) = 2. Reflected power fraction = 1/9.

Question 4

Find the characteristic impedance of a quarter-wave transformer matching a 100 ohm load to a 50 ohm line.

Accepted Answer

Zt = root(50 x 100) = 70.7 ohm.

Question 5

A rectangular waveguide has a = 2.29 cm. Find the TE10 cutoff frequency.

Accepted Answer

fc = 3e8/(2 x 0.0229) = 6.55 GHz.

Question 6

For that waveguide at 10 GHz, find the guide wavelength.

Accepted Answer

Free-space wavelength 3 cm. Guide wavelength = 3/root(1 - (6.55/10)^2) = 3.97 cm.

Question 7

If the range to a radar target doubles, how does the received echo power change?

Accepted Answer

It falls to one-sixteenth, since echo power is proportional to 1/R^4.

Question 8

State the gain of a half-wave dipole in dBi.

Accepted Answer

About 2.15 dBi, or a power gain of 1.64.

Practice — Electromagnetics, Transmission Lines, Waveguides and Antennas