Short quiz on antenna arrays
Watch the lecture here, and then try out this short quiz.
In antenna arrays, what is the key physics concepts that allows us to change the location of beam maxima in space?
Controlling the phase difference between the antenna fields changes the location(s) in space where constructive/destructive interference happens thereby changing the locations of beam maxima.
What are the three design knobs available for us to change the location of a beam maxima in space?
Changing the (1) antenna spacing, (2) phase difference in current excitations, and (3) ratio of current amplitudes.
Of the three design knobs, which one is the most practical in terms of implementation?
Phase difference in current excitations.
You are given two identical antennas, each radiating 1 W power as measured at a particular point in space. Now, you array them and can change the relative phase difference between their currents. What is the maximum power (in watts) that you can achieve at the same point in space?
Four. The amplitudes are each proportional to 1, so in constructive interference, the net amplitude will be proportional to 2, and so net intensity will be 4 W.
Given an array of Hertz dipole antennas, all with axis aligned along the z-axis, what will be the array configuration that gives a beam maxima at theta=0? Hint: recall the concept of pattern multiplication.
No array configuration works. The net pattern is the product of the element pattern and array factor. The element pattern is always zero on the z-axis, so array factor has no effect and there can never be a beam maxima at theta=0.
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