length,radius and size of the ground plance effect the resonant frequency??

[vicky_45]

hi every1,
i have a question about monpole antenna on infinite ground plane...
when we change the length,radius and size of ground plane the resonant frequency varies,,,i want to know what actually happens in the wire which cause a change in resonant frequency by varing these factors..

 

[RCinFLA]

The antenna impedance is the linear progressive inductance of the monopole and the distributed capacitance from monopole to ground plane.

As you decrease the ground plane the stray capacitance from monopole to ground is reduced. As you continuously increase the size of ground plane there will be a point where the ground plane is far enough from monopole so the incremental additional capacitance diminishes.

 

[vicky_45]

hye thanks...
u mean to say that with the increase in length of monpole inductance will increase and with the increase in size of ground plane capacitance will increase....and we find that point where this inductance and capacitance are equal to each other... at this point the impedance will be minimum... and this frequency is called resonant frequency...?
if yes then is there some formulas to find the effect of radius and length on inductance and size of ground plane on capacitance????

 

[RCinFLA]

Yes, slightly, but as the monopole becomes longer then about half wavelength the distance to ground plane is so great the effects are minimal.

 

[vicky_45]

plz share if u have any relevant material which discuss the parasitic capacitance, and inductance and their effect on mopole...

 

[RCinFLA]

Book 'Antennas' by Kraus

 

[biff44]

parasitic capacitance or inductance is interesting, but you probably should spend more time researching "radiation resistance" for small ground planes. Has a much bigger effect.

 

[FvM]

you probably should spend more time researching "radiation resistance"

Right. Your usage of the terms resonance, capacitance and inductance related to antennas suggests, that you try to understand it as a circuit of lumped elements which ignores the electromagnectic phenomena involved with their operation.

 

[vicky_45]

thanks to all....
but i have a confusion about oscillation and resonance...i want to know that this resonance phenomena in antennas is same as in circuites...??