RFIDTuning

RFID Tuning Procedure

Obzor Software Setup

• Open ObzorTR1300 from the Start Menu.

Here are the elements of the Obzor interface

• Menu Pane: All settings can be controlled through the different menus in the Menu Pane
• Status Bar: Shows the status of the Obzor TR1300. If this does NOT say "Ready", see Troubleshooting
• Graph Region: The display of the current selected graph

• Navigate the Menu Pane on the right hand side of the Obzor interface to:

System > Recall > State and Calibration and open the file titled: "S11_900M_930M.cfg"

• Navigate back to the Main Menu in the Menu Pane, then navigate to:

Response > Format > Smith > R + jX

The Graph Region should look like a circle with a little green line around the edge.

Adjusting the Delay

If you are tuning an antenna array through a Mux board (otherwise, click here):

Important: Make sure ALL the SERIES component are populated with 0 Ohm resistors and none of the antennas are connected to the mux board

• Connect the Mux Test Box to the mux board via the GPIO cable and connect the Obzor to the mux board via the coax cable.

• Navigate back to the Main Menu in the Menu Pane, then navigate to:

Scale > Electrical Delay

• Adjust the Electrical Delay so that the Marker 3 (little triangle with a 3 over it) is on the horizontal line towards the right hand side of the graph

The delay should be in ps (picoseconds). If you type 0.1 into the box, that is equivalent to 100 ps.

• Solder the antenna to the mux board.

An arc will appear on the Smith chart looking similar to the following image (the exact location of the arc will be different on every single antenna)

If you are NOT tuning an antenna array through a Mux board:

Important: Make sure the SERIES component is populated with a 0 Ohm resistor

• Navigate back to the Main Menu in the Menu Pane, then navigate to:

Scale > Electrical Delay

• Adjust the Electrical Delay so that the Marker 3 (little triangle with a 3 over it) is on the horizontal line towards the right hand side of the graph

The delay should be in ps (picoseconds). If you type 0.1 into the box, that is equivalent to 100 ps.

• Connect the antenna to the end of the Obzor cable

• Place a piece of 1/8" ABS over the antenna you are tuning and hold it down with the piece of wood at the tuning station, trying to remove any air from between the antenna and ABS.

Wood is used because it is mostly invisible to the RF system, using your hand or another piece of plastic will affect the amount of energy reflected into the system and throw your results off.

An arc will appear on the Smith chart looking similar to the following image (the exact location of the arc will be different on every single antenna)

Tuning the Antenna

This is where the art of the tuning occurs. Each antenna will react differently to the various capacitor and inductors you try. Experience has shown that inductor values greater than 12nH and capacitor values greater than 10pF are generally not viable (their impedance over powers the circuit).

Experience has also shown that the response of the system to each element inserted does not react in the way theory would suggest. If you're curious as to how the system would react in theory, open up the Smith v3.10 software from the Start Menu and play around with that.

The goal is to get the arc curved around the center point of the Smith Chart using the following circuit:

In the past, the antennas have all responded with similar general behaviors on the Smith Chart. Below is an image describing those behaviors.

The following are the steps for tuning an antenna:

• Find the impedance of the antenna with a 0 Ohm resistor in series, it should look similar to the following (this is the starting point for the tuning example):

BE VERY CAREFUL NOT TO DAMAGE ANY OF THE PADS ON THE MUX BOARD OR FR4 WHEN SOLDERING

• Leaving the 0 Ohm resistor in series, solder in a capacitor into the parallel element. Experience has shown that this capacitor value should be somewhere near 2.7pF. The following is the result on the Smith Chart:

It is possible to have a very good impedance match with only a parallel element, if the arc moved relatively close to the center point on the Smith Chart, you can try to tweak the value to get this closer.

• Remove the 0 Ohm resistor and solder in an inductor into the series element. Experience has shown that this value is around 6.8nH. The following is the result on the Smith Chart:

• Now that the whole circuit is populated, you can begin adjusting the values to move the arc around the center point in the Smith Chart. After adding in the capacitor the arc moved way below the middle horizontal line on the Smith Chart, this means that the capacitor is too large. Remove the 2.7pF capacitor and solder in a 1.0pF capacitor into the parallel element. Here is the result:

• This is exactly where the arc should be. To verify that the result is acceptable navigate to the Main Menu in the Menu Pane then:

Response > Format > Log Mag

The graph will turn into a standard 2D plot with a line across it. On the left hand axis of the graph is the amount of energy returned from the antenna in dB. For the tuning of the antenna, no part of the line should be above -10dB. That is equivalent to 90% of the energy being radiated out of the antenna and 10% being returned into the reader. The lower the line on this graph the better.

YOU MAY HAVE TO REPEAT THE GUESS-AND-CHECK STEPS MULTIPLE TIMES TO YIELD THE DESIRED RESULT

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Troubleshooting

• Status Bar showing "Not Ready"

If the Status Bar shows a message saying "Not Ready", leave Obzor open and power the device off then on again. You should see the message change to "Loading" then to "Ready" after a short period. If that does not fix the issue, make sure the USB cable is plugged into the back of the PC.