Here's some. http://www.google.co.uk/search?sourceid=navclient-menuext&ie=UTF-8&q=satellite+Transponder 1,910,000 hist in 0.19 sec.

I searched like that but my requirements are like this:

Polarization : LHCP and RHCP (Switchable in field)

Gain : minimum 11 db or better

Center Frequency : 402.75 MHz ± 200 KHz

3dB Beam width : 40^o

VSWR : 1.2 : 1

Impedance : 50 ohm

Axial Ratio : TBS

Operating wind speed : 100 KMPH

Wind Survival : 175 KMPH

Connector : TBS

Temperature : -40°C to +55°C

Humidity : 0 to 100% RH

Weight : TBS

Size : TBS

now suggest me a transponder I searched somany sites but I didn't find plz specify the name of the company of that antenna

Well, try using the telephone and talk to their sales offices instead!

I did using telephone link but now i need to transmit via Satellite

Oi! You two! Stop SHOUTING! Some of us are trying to get some sleep!

So why didn't you say that in the first place? Try different search engines! Something will pop up I'm sure!

Try google for LHCP+RHCP+402.75 (+TRANSPONDER) you may get what you are looking for (you may need to register at the site)

I have no idea how "transponder" comes into this, but what you are describing is specs on a satellite antenna.

Left hand or Right hand circular polarization (switchable)

Gain 11 dBi I will assume. (gain relative to isotropic)

Frequency 402.75 MHz +/- 200 KHz (no problem there)

3dB beamwidth 40 degrees... Is this a minimum beamwidth or max? It is also tied in with the gain figure.

VSWR 1.2-1 (I assume this is over the 400 KHz bandwidth).

For connectors, I would use type "N".

If I were designing it, I would use two yagi antennas on the same boom. One vertical polarized and one horizontally polarized. They are fed 90 degrees out of phase to attain circular polarization, and also to attain switchable left or right handed circular polarization.

Assuming you know nothing, Yagi's are like TV antennas.

Size for such a critter would be approximately 1.3 meters long, and 35 cm wide.

Wind loading would depend on the design of the final antenna.

Basically, if this is the info you want, forget transponder, and look at antennas.

The American "Amateur Radio Relay League" has an antenna book which gets into sat antennas You might find it helpful.

Sincerely

Bill

ps what you do when the signal gets to the ground is up to you (AKA transponder).