An outside source is broadcasting an RF signal at 406 MHz. I want to know if it's possible to receive this signal with one antenna, and then simply send the signal to another antenna that sends it right back out. I want this to be a simple circuit where the receiving antenna only receives and the transmitting antenna only transmits. The transmitting antenna can have a slightly different frequency but it would need to be as close to 406 MHz as possible. The intention is to reflect a signal right back at it's source, in as simple of way as possible. Will this work?
Yes, it's possible. Simply connecting two antennas with a feedline will do this.
If you want to reflect the signal right back at the source, you can more simply just omit the second antenna, and terminate the feedpoint of the first antenna in a short or leave it open. Since the short or open can't accept any power, any power received by the antenna must eventually be re-radiated by it, or lost in the resistance of the antenna, etc. Chaff works on this principle.
I can't imagine any practical application for this, however. Sometimes people construct passive reflectors this way to get a line-of-sight signal around an obstruction. But reflecting the signal directly back at the source seems rather pointless, since the field strength at the source is already strong. The minuscule power reflected back at the source is insignificant compared with the power already at the transmitter. It's like trying to burn out the sun with a mirror.