Power splitter and combiner

Hello.
I am using 2 way 3 Db power splitter and i am using two of these splitters one each for differential input. Out of the 4 ouput ports now available I will be giving two input to LO input of my receiver board and want to transmit other two input via an antenna. Photo attached for reference

I want to order 2way 3db splitter and want to know whether I can use 3rd splitter (marked) as a power combiner? I mean are these things reversible?
I am relatively new in RF.
Thanks in advance

Most of the splitter types are reversible.
But I do not understand your block diagram. Why did you connect directly TX to RX (using differential wires), when actually both use their own antennas.

thanks vfone
actually antenna in receiver would be receiving frequency shifted signal after reflection from moving target. I am gonna subtract two frequencies to get frequency shift.
Its Doppler radar i am trying to create.
thanks