The designed antenna is 2X1 MIMO antenna. I want to test its return loss on VNA. How to apply input to MIMO antenna? Shall I test one antenna at one time or both antennas should be excited at the same time?
Dear Amruta,
welcome,
You measure as you define.
So, you measure the reflection proficients of every antenna, S11.,S22,S33,... SNN
with the other ports terminated at Zo, the characteristic impedance.
So, you feed one port at at a time and also measure MUTUAL coupling between the antennas by measuring the transmission coefficients S21,S31, S41 .....;
S32, S42, S52,...; S43,S53,... etc.
You assume that Sij= Sji
Best wishes
Dear Malode
You need to calibrate two ports VNA first . Then measure the S-parameters of the MIMO antenna S11 S22 S21 S12 at one time.
Thank you Raed sir for your quick response. Please tell me sir, shall I give input to both ports at the same time or test one antenna at one time?
Dear Amruta,
welcome,
You measure as you define.
So, you measure the reflection proficients of every antenna, S11.,S22,S33,... SNN
with the other ports terminated at Zo, the characteristic impedance.
So, you feed one port at at a time and also measure MUTUAL coupling between the antennas by measuring the transmission coefficients S21,S31, S41 .....;
S32, S42, S52,...; S43,S53,... etc.
You assume that Sij= Sji
Best wishes
You test the design as specified in the simulation. You said it is MIMO and 2x1 so two transmitting antennas. It results four S-parameters. Connect two ports of VNA to two inputs of the MIMO antenna and verify four S-parameters.
Thank you all of you for your valuable suggestions. I will test MIMO antenna as per your suggestions.
Hi Amruta,
Answer of Dr Abdelhalim is considered. A MIMO antenna from the name is having more than two antennas with individual ports. A VNA has got two channels commonly. This simply means you can feed two antennas at most at the same time. Then you have two scenarios:
1. if your target is to just look at S11 and S22 individually for tuning purposes then simply calibrate both of the VNA channels first, then connect channel 1 to antenna 1 and leave channel 2 of the VNA open meanwhile load antenna 2 port with a 50 Ohm load. repeat the same for Antenna 2. in this case only S11 of antenna 1 and S22 of antenna 2 are measured.
2. if you want to measure S11, S22, and S12 of both of the antennas at the same time, simply after VNA calibration, connect both the channels of the VNA to the antennas, and let trace 1 for the VNA be S11, add trace 2 for S22, and trace 3 for S12. in this case you don't need to be worry about loading the antennas, bcz you already fed both of the ports.
you keep metals away from the antennas, plus keep your body a bit away from the antennas to not interact with near field of the antennas during radiation.
*typo:
“A MIMO antenna from the name is having two or more than two antennas with individual ports.
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