Measuring Unbalanced-Balanced Bandpass Filter

• Overview

• Procedure

Other Measurement Examples

Overview

This section introduces an example of actually evaluating the unbalanced and balanced SAW bandpass filter with a center frequency of 942.5 MHz. The following figure shows the measurement circuit in the condition for evaluating a DUT.

Procedure

Here, the DUT is evaluated by following the steps.

1. Connecting the DUT

Connect the DUT to the E5071C by using the instrument's three test ports.

2. Setting the Measurement Conditions

Follow the procedure below to set the measurement conditions. The measurement parameters for balanced measurements should be set after unbalanced-balanced conversion. Here, set the measurement parameters for observing the characteristics achieved during unbalanced measurements.

3. Performing Calibration

Perform a full three-port calibration for the three ports to be used.

1. Set the type and conditions of calibration.
    

   Setting Description	Key Operation
   Calibration kit to use: 85033D	Cal > Cal Kit > 85033D
   Type of calibration: Full three port calibration	Calibrate > 3-Port Cal
   Test ports to calibrate: 1, 2, 3	Select Ports > 1-2-3 (check only)

2.  Perform a reflection calibration.
    

   Setting Description	Key Operation
   Select reflection calibration	Reflection
   Perform Port 1 calibration	(With the OPEN connected) Port 1 OPEN
   	(With the SHORT connected) Port 1 SHORT
   	(With the LOAD connected) Port 1 LOAD
   Perform Port 2 calibration	(With the OPEN connected) Port 2 OPEN
   	(With the SHORT connected) Port 2 SHORT
   	(With the LOAD connected) Port 2 LOAD
   Perform Port 3 calibration	(With the OPEN connected) Port 3 OPEN
   	(With the SHORT connected) Port 3 SHORT
   	(With the LOAD connected) Port 3 LOAD

3. Perform a transmission calibration.
    

   Setting Description	Key Operation
   Select transmission calibration	Return > Reflection
   Perform a Port 1-to-Port 2 calibration	(With thru connection) Port 1-2 Thru
   Perform a Port 1-to-Port 3 calibration	(With thru connection) Port 1-3 Thru
   Perform a Port 2-to-Port 3 calibration	(With thru connection) Port 2-3 Thru

4. Finish the calibration.
    

   Setting Description	Key Operation
   Complete the calibration and then calculate and store calibration coefficients.	Return > Done (This causes Correction to turn ON.)
   Calibration property display: ON	Return > Return > Property (Turns it ON.)

4. Setting a Balance Conversion Topology

Follow the procedure below to set the balanced conversion topology.

5. Selecting Measurement Parameters

1.   Display four traces.
    

   Setting Description	Key Operation
   Number of traces: 4	Display > Number of Traces > 4
   Trace allocation: 4-part split	Allocate Traces >

2.   Set the measurement parameter (mixed mode S-parameter) and data format for trace 1.
    

   Setting Description	Key Operation
   Fixture simulator: ON	Analysis >  Fixture Simulator > Fixture Simulator (turns it ON)
   Unbalanced-balanced conversion of trace 1: ON	BalUn (turns it ON)
   Measurement parameter: Sds21	Meas > Sds21

3. Set the measurement parameter (mixed mode S-parameter) and data format for trace 2.
    

   Setting Description	Key Operation
   Unbalanced-balanced conversion of trace 2: ON	Trace next > Analysis > Fixture Simulator > BalUn (turns it ON)
   Measurement parameter: Scs21	Meas > Scs21

4. Set the measurement parameter (mixed mode S-parameter) and data format for trace 3.
    

   Setting Description	Key Operation
   Unbalanced-balanced conversion of trace 3: ON	Trace next > Analysis > Fixture Simulator > BalUn (turns it ON)
   Measurement parameter: Sss11	Meas > Sss11
   Data format: Smith chart (marker display: R+jX)	Format > Smith > R + jX

5. Set the measurement parameter (mixed mode S-parameter) and data format for trace 4.
    

   Setting Description	Key Operation
   Unbalanced-balanced conversion of trace 4: ON	Trace next > Analysis > Fixture Simulator > BalUn (turns it ON)
   Measurement parameter: Sdd22	Meas > Sdd22
   Data format: Smith chart (marker display: R+jX)	Format > Smith > R + jX

The following figure shows the setting results for each parameter.

6. Extending the Calibration Plane (removing the cause of error)

In this section you will use the port extension function to remove an electrical delay caused by cables or fixtures located between the calibration reference plane and the DUT to be evaluated. If you can provide a two-port Touchstone data file representing the characteristics of the network to be removed, the network removal function allows you to remove the network and extend the calibration reference plane.

Follow the procedure below to set port extension for each test port.

The following figure shows the results of extending the calibration reference plane.

7. Setting the Port Reference Impedances

With the reference impedances of two test ports in unbalanced measurements set to Z0, conversion of those ports into balanced ports permits the impedance of the balanced ports' common mode to be automatically set to Z0/2 and the impedance of their differential mode to be automatically set to 2Z0.

1.  Set the port reference impedance of port 1 on the DUT (unbalanced) to 50 ohm.
    

   Setting Description	Key Operation
   Reference impedance of test port 1: 50 ohm	Analysis > Fixture Simulator > Port Z conversion > Port 1 Z0 Real > 5 > 0 > x1

2. In order to set the impedance of the differential mode of port 2 on the DUT (balanced) to 200 ohm , set the impedances of two unbalanced ports before conversion each to 100 ohm.
    

   Setting Description	Key Operation
   Reference impedance of test port 2: 100 ohm	Port 2 Z0 Real > 1 > 0 > 0 > x1
   Reference impedance of test port 3: 100 ohm	Port 3 Z0 Real > 1 > 0 > 0 > x1

3. Always set the reference impedances of the two test ports before balanced conversion to the same value.

4.  Turn on the port reference impedance conversion function.
    

   Setting Description	Key Operation
   Port reference impedance conversion: ON	Port Z Conversion (turns it ON)

The reference impedance of the command mode of port 2 on the DUT is set to 50 W . The impedance of the differential mode of that port may be set and modified independently of setting the two-port reference impedances before balanced conversion. For more information, see Converting Reference Impedance of Balanced Port.

8. Adding a Matching Circuit

Here, add an inductance of 47 nH in parallel to port 2 on the DUT (balanced). It is also possible to add a matching circuit to the port before unbalanced-balanced conversion. For more information, see Determining the Characteristics that Result from Adding a Matching Circuit to a Differential Port.

• The balance matching circuit (Differential matching circuit embedding) is not applied to single-ended S-parameter results. For example, the balance matching circuit is not applied to the imbalance parameter as it is derived from single-ended S-parameters.