On Tue, 14 Dec 2010 06:19:35 +0000, frankieNrosie
wrote:

i use the diode as the switch to reconfigure the freq..later on i will
upload the figure of proposed antenna-

I have not the vaguest idea what that is about. "The diode"?

diode is use as a switch to vary the length of the driven element..
so, if i got many length of the driven element, thus i'll have many
freq..
do u understand me?

I understand what you write, but not why you choose this arrangement.
I can guess many configurations, but your goal is obscure.

Inventive to say the least.

Conventional antenna design already has passive solutions for your
active element requirement and they stand the chance of reducing the
risks inherent in putting a diode into an antenna structure for
switching its length.

73's
Richard Clark, KB7QHC