What is the purpose of using multiple driven elements connected through phasing lines?
Why Phasing lines set the relative amplitude and, more importantly, the relative phase of the current fed to each driven element. Because the radiated fields from the elements add in some directions and cancel in others, changing the phase relationship steers and shapes the pattern, giving broadside, end-fire, cardioid or steerable lobes. A classic example is the AM broadcast or 80/40 meter phased vertical array, where changing line lengths or switching phases rotates the null and main lobe.
Watch out Producing a low-angle pattern is only one possible result of one particular phasing arrangement, not the general purpose; phasing lines can also produce high-angle, broadside or bidirectional patterns. Phasing lines do nothing about transmitter harmonics and do not add band coverage.
Phasing lines = pattern control. Phase relationship decides where signals add and where they cancel.