dear sir, i have a very common doubt as to how a feed , transmits and receives simultaneously.???
Hi Mr Prathikh,
Feed is like a microwave guide that can radiate and receive because of skin effect in wave guide principles. The effect is non interfering for various frequencies of operations and only depends on the dimensions. If you are aware of resonant theory and network analysis the distributed components of the wave guide respond to the spectrum based on the dimensions of the wave guide and the wave length. So any radiation from or to the feed are responded to by the feed and the direction (VECTOR) decides as to it is either transmit or receive.
Antenna feeds respond to wave lengths and nothing concerning transmit or receive.
During transmit it is concentrated power being given to the feed and for receive it is focussed from the reflector and so the vector is in opposite directions.
For better clarity you can read RADAR theory where one feed receives and transmits but separates the signal by a diplexers: because here the same feed works for both but in a time dependent method.
Also if you see any LNBC at the front end of DTH you can observe that the input comes from a different feed point and there is a separate port for Transmit, if the VSAT is bidirectional.