The broadcast antenna of an AM radio station is located at the edge of town. The station owners would like to beam all the energy into town and none into the country side, however a single antenna radiates energy in radio waves equally into all directions. The station is setting up two parallel radio antennas separated with a distance L. Both antennas broadcast a signal at a frequency of 1,260 kHz, but antenna 2 can delay its broadcast to antenna 1 by a time to create a phase deference among the sources.
a) What is the time delay t needed?
b) What phase constant of antenna 2 is needed?
c) What is the smallest value of L for which you can create perfect constructive interference on the town side and perfect destructive interference on the country side?
This is a simple example of a phased array utilized to \steer" the radiation in particular directions. This is used with radio broadcasting, radars, ultrasound medical imaging and many other ends.