Leaky-Wave Antennas
First introduced in 1950s [86], leaky-wave antennas (LWA) are
popularly known for their beam-scanning capabilities. LWAs radiate
because of the leakage of the travelling wave as it propagates through a
guiding structure [87], [88]. LWAs generally have an inherent
property of frequency-controlled beam-scanning, which means that the
radiated beam direction changes with the change in operating frequency.
This is because all the radiating elements in an LWA are fed
sequentially, and with change in frequency, the inherent phase shift
between radiating elements changes, which directly impacts the beam
direction as shown in Figure 3.