how can i design double port for microstrip antenna

[hbotnik]

i am from israel, i need to design a microstrip antenna with two ports to 3Ghz one port to recieve sines siggnal and the other one to transmit modulated signal, i can use FR4 as a substrate

 

[biff44]

If they are the same frequency, you need to use a ferrite device called a circulator. You also might need some sort of PIN diode switch or limiter in front of the receiver to keep it from blowing up if the antenna is ever removed or short circuited.

If they are different frequencies, you use two bandpass filters arranged in a diplexer filter fashion. Hopefully the transmit and receive frequencies are far enough apart, and the filters are steep enough, so that broadband noise out of the transmitter does not swamp the receiver's noise figure (unless you are turning the transmitter off during receive events).

If you can control the system design, you could transmit one direction with one paolarization, and receive at that site with the opposite polarization. You then design a dual pole antenna with one port per pole.