Urgent Fundamental Questions, pls help as soon as possible

Dear all,

Why 2 times of the wavelength of its centre frequency * 2 times of the wavelength of its centre frequency is chosen as the dimensions of the antenna ground plane?

Why does some antennas have rectangular ground planes. Thanks a lot.

Ho Wong

i think its a rule of thumb but im not sure, i assume you are asking about whip antennas, anyway even a wire works(and turns your whip into a dipole. in any case what you should watch is the input impedance vs ground plane.