How to design Monopole ?

How i can design monopole at for frequency range 25-110 MHz. What will be the size of ground plane? And how size of ground plane effects antenna? how i can adjust diameter of monopole on the basis of power of transmitter (e.g power is 1 W and in other case power is 100W)?

Waiting for reply with bundle of thanks in advance...

The ground size of a λ/4 vertical monopole antenna should be at least λ/4 in size.
Instead of physical ground can be used λ/4 radials.
The length and the angle (with the vertical) of the radials affect the antenna impedance and the take-off angle of the radiated waves.
The diameter of the monopole affect the antenna bandwidth (where thicker element means wider bandwidth).

Agreed but its never going to cover the 25MHz - 110MHz bandwidth required. It would improve it for a MHz or two either side of the freq the radiator was cut for. If its for receive only then design it for ~ 70MHz the approx 1/2 way point for the bandwidth you state. it will work in an OK fashion. getting very inefficient towards the band edges.

If its needed for transmit, then you are going to have to look at some form of active tuning else a plain radiator isnt going to work, other than on the freq its cut for. period.
you could look at a discone antenna, or a colinear system, that would help improve the bandwidth.
like this one.....

whatever route you take, its going to have ≦ unity gain

cheers
Dave

like this one.....

If its whip antenna, how to design it? by watching pics i can"t comprehend the dimensions. It satisfy my bandwidth requirements, so bundle of thanks for this idea.