assistant engineer interview questions shared by candidates
If the source impedance is 50ohms, and you have 2dB of mismatch between the source and load, on what region of the smith chart would the load impedance be found?
All the different load impedances would be on a circle of constant VSWR (related to magnitude of reflection coefficient) centered around the middle of the smith chart. The diameter of the circle determines the amount of loss. Mismatch Loss = Power delivered/Incident power = 1-|gamma|^2 10log(Pdel/Pinc) = -2dB = 10log(1-|gamma|^2) 10^-0.2 = 1-|gamma|^2 |gamma| = sqrt(1-10^-0.2)
We can determine gamma from the formula for mismatch loss. Then we can determine the Load impedance from the formula for gamma.
An antenna engineer gives you a test unit, telling you that an antenna's efficiency is -2dB when measured passively. You measure it actively and find that it is actually -3dB. What could account for the difference if there is nothing wrong with the calibration of the anechoic chamber? How could you prove it? If you measure active efficiency of an antenna as being -3dB, but you see that the TIS is 5dB worse than the conducted sensitivity for a given channel, what could be causing this if there is nothing wrong with your calibrations?