Rohde & Schwarz ZVA 8, ZVA 24, ZVA 40, ZVA 50, ZVT 8, ZVT 20, ZVB 4, ZVB 8, ZVB 14, ZVB 20 Vector Network Analyzer, ZCAN Calibration Kit Application note

Product: Vector Network Analyzer R&S

®

ZVA

Measuring the S-Parameters of a 50 to 75 Ohm impedance matching device using the

Vector Network Analyzer ZVA

Application Note

This document describes how the advanced calibration techniques of the ZVA Vector

Network Analyzer can solve the challenges of measuring the S-Parameters on impedance matching devices. The document describes the concept and setup required to perform the calibration of the ZVA and making the measurement.

The procedure described in this application note applies to the ZVB and ZVT Vector

Network Analyzers as well.

Subject to change – Kenneth Rasmussen, 03.2009

Introduction

Contents

….…

2. R&S RAM, Minimum Loss Pad……...………….. 4

3. Measurement Setup for the Minimum Loss Pad. 5

4. UOSM 7

5. Measurement of R&S RAM……………………… 9

Information…………………………….

7. Ordering

1EZ59_0E 2 Schwarz

Introduction

1. Introduction

This document is designed to be a guide to help point the user in the right direction for configuring the ZVA Vector Network Analyzer to make relevant measurements on impedance matching devices like Minimum Loss Pads.

With the previous generation of Vector Network Analyzers, measurement of the

S-Parameters on impedance matching devices like Minimum Loss Pads (MLP) was impossible. This is due to the fact that MLP’s have different impedances at the Input and Output ports. Traditionally, VNA’s could not do a full 2-port calibration with different impedances on the test ports. But with the arrival of the

ZVA generation of Vector Network Analyzers and the UOSM calibration method, this is now possible.

This application will use the R&S RAM, a DC - 2.7 GHz 50C/75C Matching Pad as the Device-Under-Test (DUT).

Due to limited or no availability of calibration kits in other than 50C and 75C impedances, it is not practical to convert to other impedances.

For further information please refer to the internal help of the ZVA [HELP] or alternatively you can access the help online at the Rohde & Schwarz website, http://www.rohde-schwarz.com/webhelp/zva/start.htm

In this document:

•

Hardkeys are shown as

Softkeys are shown as

Windows buttons and tabs are shown as

Windows dialog box names are shown as

[MODE]

[PRESET] [HELP]

[Start]

Set Power…

Set Powers

1EZ59_0E 3 Schwarz

R&S RAM, Minimum Loss Pad

2. R&S RAM, Minimum Loss Pad

The Minimum Loss Pad (or L-pads) can be used to perfectly match one impedance to another, but the loss is high. In microwave engineering, this is usually not acceptable; we'd rather match two impedances with near-zero loss by using reactive components, which limits the bandwidth of the solution. In instrumentation systems however, we normally prefer a frequency-independent device like the MLP to do the impedance conversion. A typical application for the MLP is when we want to measure TV signals in a 75 Ohm system with a

50C Spectrum Analyzer. Here the MLP will provide the proper matching between the different impedances. However this comes at the expense of additional power loss.

Note that for a given input and output impedance, only one solution exists for an

L-pad where the input and output are to be perfectly matched; this is what we know as the Minimum Loss Pad.

R1

Z1 R2 Z2

Matching Pad

L-Pad matching network (Z1 > Z2)

The equations for calculating the values of R1 and R2 are simple to derive using

Ohm’s Law. For Z1 > Z2 the following applies:

R

1

=

Z

1 1

Z

2

Z

1

R

2

=

1

Z

2

Z

2

Z

1

The attenuation (or insertion power loss) is defined as (Power Out)/(Power In):

Pout

/

Pin

=

1

Z

1

Z

2

+

Z

Z

1

2 1

2

Please note, this is the linear value, not dB! The attenuation can be expressed in dB as follows:

Attenuatio n

(

dB

)

=

10

Log

10

Pout

Pin

For the R&S RAM, which converts from 75C to 50C, the following values apply:

R1 = 43.3 C

R2 = 86.6 C

Attenuation (dB) = -5.7 dB

1EZ59_0E 4 Schwarz

Measurement Setup for the Minimum Loss Pad

3. Measurement Setup for the Minimum Loss Pad

To measure the S-Parameters of a Minimum Loss Pad, the following equipment are required:

•

R&S ZVA

•

R&S ZCAN 50C

•

R&S ZCAN 75C

•

R&S RAM

•

AG 1250-0597*

•

PE 9350*

•

Test Port Cables

Vector Network Analyzer

Type-N 50C Calibration Kit, 3 GHz

Type-N 75C Calibration Kit, 3 GHz

Matching Pad, 50C/75C

Type-N(m) 50C to Type-N(f) 75C mech. Adapter

Type-N(f) 50C to Type-N(m) 75C mech. Adapter

2 required. Model depends on ZVA connectors

*) AG : Agilent Technologies PE : Pasternack Enterprices

WARNING!

At first glance, 50C and 75C Type-N connectors looks identical, but be careful.

The center pin of the 75C connectors is thinner than the center pin of the 50C connectors.

Special care should be taken when mating 75C devices. Inserting a 50C male connector into a 75C female connector can result in damage of the 75C female connector.

On the other hand, the 75C male connector cannot damage the 50C female connector due to the thinner center pin.

Please note the difference on the center pin thickness between 75C (Upper) and 50C (Lower) connectors.

1EZ59_0E 5 Schwarz

Test Port Reference Planes

Measurement Setup for the Minimum Loss Pad

Make the following setup with the ZVA as preparation for the calibration.

Please note that the Port 1 reference plane must be 50! Type-N(f) and that

Port 2 reference plane must be 75! Type-N(m).

The 75! side of the RAM is a Type-N(f), so an additional 75! Type-N(m-m) adapter are required to realize the 75! Type-N(m) reference plane on Port 2.

Calibration Setup for the Minimum Loss Pad measurement

To configure the ZVA for the measurement, press the following keys:

[PRESET]

[START CENTER] [Start] 10 MHz

[STOP SPAN] [Stop] 2.7 GHz

[PWR BW AVG] [Power] 0 dBm

[PWR BW AVG] [Meas Bandwidth] [1 kHz]

[PWR BW AVG] [Average Factor] 10, [Average On]

1EZ59_0E 6 Schwarz

4. UOSM Calibration

UOSM Calibration

An adapter represents a through standard with unknown characteristics (in particular, with unknown delay time/transmission phase). The analyzer can perform a TOSM calibration with an unknown through, provided that it is reciprocal (S21 = S12). The modified TOSM calibration is referred to as UOSM

(Unknown through – Open – Short – Match) calibration. It can be selected as follows:

1. If different connector types and/or impedances are assigned to the test ports, the analyzer automatically replaces TOSM –> UOSM.

2. If the same connector types are used but the appropriate through standard is not defined, the analyzer also replaces TOSM –> UOSM.

3. UOSM can be selected explicitly using [CAL] [Start Cal] [Other]....

After acquiring the calibration sweep data for the unknown through, the analyzer automatically determines its delay time/transmission phase.

To start the ZVA calibration using UOSM, we just select a standard two port

TOSM calibration. Since the setup applies to condition 1) above, UOSM will automatically be selected. Press the following keys:

[CAL] [Start Cal] [Two-Port P1 P2] [TOSM]

Configure Connector type and Calibration Kits as shown below:

Uncheck this

Press Next > to proceed with the calibration.

1EZ59_0E 7 Schwarz

Unknown Reciprocal Through indicates that UOSM is being used for the calibration.

UOSM Calibration

Please connect calibration standards as shown below, one by one, and click the box to measure the standard.

Press Next > to proceed when all standards are measured.

No action is required in the following window. Just press Apply to complete the calibration.

For a non-dispersive standard (Dispersive check box cleared), the Delay Time

can be determined unambiguously, provided that the transmission phase difference between two consecutive sweep points is below 90 deg. In this case

it is sufficient to press Apply in order to calculate the system error correction

data and close the calibration wizard.

1EZ59_0E 8 Schwarz

Measurement of R&S RAM, Minimum Loss Pad

5. Measurement of R&S RAM, Minimum Loss Pad

Connect the device RAM to the calibrated reference planes of the ZVA as shown below;

With the UOSM calibration performed in the previous section, we now have the

ZVA calibrated with Z

0

= 50C on Port 1 and Z

0

= 75C on Port 2. Note the marker readings in the S11 and S22 Smith Chart plots below.

The marker readings for S21 and S12 also show expected measurement results close to -5.7 dB power insertion loss in both directions.

-10

-20

-30

-40

-50

-60

-70

Trc1

S11

S11 Smith Ref 1 U Cal

0.5

2

1 j214.34

25.176

C mC pH

Trc2 S21 dB Mag 10 dB / Ref 0 dB Cal

M1 1.355000 GHz -5.8041 dB

M1

0 0.2

0.5

M1

2

5

-5

-10

-20

-30

-40

-50

-60

-70

-0.5

-2

Ch1 Start 10 MHz

-1

Pwr 0 dBm Stop 2.7 GHz

Trc3 S12 dB Mag 10 dB / Ref 0 dB Cal

S12

10

3

•M1 1.355000 GHz -5.8160 dB

M 1

Ch1 Start 10 MHz Pwr 0 dBm

Trc4 S22 Smith Ref 1 U Cal

S22

0.5

2

2

Stop 2.7 GHz

5

4

-j117.95

995.85

C mC pF

0 0.2

-0.5

0.5

M1

2

-2

-5

Ch1 Start 10 MHz Pwr 0 dBm Stop 2.7 GHz Ch1 Start 10 MHz

-1

Pwr 0 dBm Stop 2.7 GHz

1EZ59_0E 9 Schwarz

Additional Information

6. Additional Information

This Application Note is updated from time to time. Please visit the website

www.rohde-schwarz.com

to download the latest versions

Please send any comments or suggestions about this application note to

[email protected]

.

7. Ordering Information

Listed are all R&S ZVA, R&S ZVB and R&S ZVT network analyzers. Of course, accessories like test cables, or manual and automatic calibration kits are available in addition. For details, please contact your local R&S sales office, or the R&S web site.

Order No. Type

1145.1110.08

R&S ZVA8

1145.1110.10

R&S ZVA8

1145.1110.24

R&S ZVA24

1145.1110.26

R&S ZVA24

1145.1110.40

R&S ZVA40

1145.1110.42

R&S ZVA40

1145.1110.50

R&S ZVA50

1145.1110.52

R&S ZVA50

1300.0000.08

R&S ZVT8

1300.0000.20

R&S ZVT20

1145.1010.04

R&S ZVB4

1145.1010.06

R&S ZVB4

1145.1010.08

R&S ZVB8

1145.1010.10

R&S ZVB8

1145.1010.14

R&S ZVB14

1145.1010.19

R&S ZVB14

1145.1010.20

R&S ZVB20

1145.1010.25

R&S ZVB20

0800.8515.52 R&S ZCAN

0800.8515.72 R&S ZCAN

Designation

Vector Network Analyzer, 2 Ports, 8 GHz

Vector Network Analyzer, 4 Ports, 8 GHz

Vector Network Analyzer, 2 Ports, 24 GHz

Vector Network Analyzer, 4 Ports, 24 GHz

Vector Network Analyzer, 2 Ports, 40 GHz

Vector Network Analyzer, 4 Ports, 40 GHz

Vector Network Analyzer, 2 Ports, 50 GHz

Vector Network Analyzer, 4 Ports, 50 GHz

Vector Network Analyzer, 2 - 8 Ports, 8 GHz

Vector Network Analyzer, 2 - 6 Ports, 20 GHz

Vector Network Analyzer, 2 Ports, 4 GHz

Vector Network Analyzer, 4 Ports, 4 GHz

Vector Network Analyzer, 2 Ports, 8 GHz

Vector Network Analyzer, 4 Ports, 8 GHz

Vector Network Analyzer, 2 Ports, 14 GHz

Vector Network Analyzer, 4 Ports, 14 GHz

Vector Network Analyzer, 2 Ports, 20 GHz

Vector Network Analyzer, 4 Ports, 20 GHz

0 Hz to 3 GHz, 50@ Calibration Kit

0 Hz to 3 GHz, 75@ Calibration Kit

ROHDE & SCHWARZ DENMARK A/S Ejby Industrivej 40, DK-2600 Glostrup, Denmark

Telephone +45 43436699 Fax +45 43437744 Internet: www.rohde-schwarz.dk

This application note and the supplied programs may only be used subject to the conditions of use set forth in the download area of the Rohde & Schwarz website.

1EZ59_0E 10 Schwarz