Question

Why radiation pattern of long wire is affected by change in length?

Answer 1

A random wire antenna is a radio antennaconsisting of a long wire suspended above the ground, whose length does not bear a relation to the wavelength of the radio waves used, but is typically chosen more for convenience. The wire may be straight or it may be strung back and forth between trees or walls just to get enough wire into the air; this type of antenna sometimes is called a zig-zag antenna. Such antennas are usually not as effective as antennas whose length is adjusted to resonate at the wavelength to be used. Random wire antennas are a type of monopole antenna and the other side of the receiver or transmitter antenna terminal must be connected to an earth ground.