Thank for the replies, both ideas are very interesting, and with your help i finally found what i am interested in in google.
volker@muehlhaus, using 4-port branchline coupler picture from here
**broken link removed**
If i understand right, Port 1 must be connected to LO, port 2 connected to antenna, isolated port 4 connected to mixer. Can i use port 3 output as LO for mixer?
jiripolivka, unfortunately i did not found such sensor (with directional coupler). One year ago i bought and disassembled three different door openers, two 10GHz and one 24GHz, all use similar topology with Wilkinson power divider and two antennas for TX and RX. The only difference was that 10GHz ones used DRO with ceramic resonator, and 24GHz used simple microstrip line resonator.