Agilent Technologies PN 8510-16 Guida rapida

Agilent PN 8510-16

Controlling Test Port Output

Power Flatness

Product Note

UNCORRECTED POWER

CORRECTED POWER OUTPUT POWER

Agilent 8510C Network Analyzer

Introduction

Designers and manufacturers of active devices

often need to control the power level at the test

port1of their power-sensitive devices, but find dif-

ficulty in overcoming insertion losses. The insertion

losses occur as a result of connecting components

in the measurement path between the source and

the DUT. The Agilent Technologies 8 10C is a

microwave network analyzer2capable of setting

and controlling the power level at the test port.

This product note reviews the implementation

and operational considerations of the 8 10C’s

test port power flatness-correction feature.

The 8 10C performs a flatness-correction cali-

bration by measuring the test port power level

using an Agilent power meter and creates a table

of power corrections versus frequency. The

power meter then stores the table into an Agilent

8360 series synthesized sweeper.3When the test

port flatness correction is enabled, the source

will adjust its output power to compensate for

path losses at each measurement point in the

frequency span.

1. In this document, “test port” will refer to the point in the system where the test

device is connected. This may be port 1 or port 2 of any 8510 coaxial-based test

set or the end of a cable or adapter that is attached to the DUT.

2. 8510B network analyzers with revision B.06 or later may also be used to achieve

constant test port power levels. To obtain the latest firmware revision order the

11575F upgrade kit.

3. Any 8360 synthesized sweeper with firmware revision of September 25, 1990 or

earlier must be upgraded. To upgrade your 8360 to the latest firmware revision,

order part number 08360-60167.

Power flatness correction is useful for characteriz-

ing active devices by allowing measurements of

absolute power, gain versus input power, and

swept-frequency gain compression. Swept-power

gain compression measurements are possible in

the power domain with the flatness correction

enabled.

The 8 10XF measurement system is capable of lev-

eling and controlling the test port power between

4 MHz and 110 GHz without requiring a power

calibration for each measurement. When power lev-

eling is enabled, the test port power variation is

typically less than ±1 dB over the full frequency

sweep, with 20 dB of adjustable power. For more

information regarding power leveling in the Agilent

8 10XF, refer to product note 8 10XF-1, literature

number 968- 270E.

System Configuration

The basic 8 10C measurement system configura-

tion needed for test port flatness correction is

shown in Figure 1. A single channel power meter

such as the Agilent 437B, E4418A, or E4418B is

required, along with a compatible sensor, for per-

forming the power flatness calibration. Power

meters with the 437B command set must be used

for the power level flatness correction.

Figure 1. Basic Agilent 85107B measurement system con-

figuration for test port flatness correction

The Agilent 8 11B frequency converter test

set may be used with the test port power flatness-

correction feature. The range of the test port

power is determined by the available power of

the 8360 source and the insertion loss of the com-

ponents added to the measurement system.

8517B test set

8485A

power sensor

E4418B

power meter

83651B

synthesized sweeper

8510 system bus

85107B Measurement System

8510C network analyzer

Flatness-Correction Operation

The basic setup procedure to obtain flat test port

output power is illustrated in Table 1. To simplify

the execution of the procedure, the front panel

hardkeys are enclosed in [brackets]. The softkeys

are enclosed in {braces}. Table 2 provides the pro-

cedure for setting up the power meter. The net-

work analyzer should be reset before performing

any procedures. The flatness-correction calibration

can be performed in step, ramp, or frequency list

sweep mode. Figure 2 illustrates test port power

versus frequency with and without flatness correc-

tion using an 8 107B measurement system.

When the flatness correction is enabled in an

8 10C measurement system the analyzer’s Power

Source 1 softkey controls the test port power level.

The source and test set used will determine the

available test port power range.

The maximum leveled power the source can out-

put at different frequency spans is indicated in

Table 3. Once the flatness correction is enabled,

the test port power level must be set within the

power range presented in Table 4 for common

source/test set combinations.

Figure 2. Comparison of test port power without flatness correction (channel 1)

and with flatness correction (channel 2)

Table 1. Flatness-correction calibration procedure

8510C Keystrokes Description

Set up the power meter (see Table 2)

For proper operation, the E4418B must be set up before initiating the flatness-correction routine.

See Table 2 for specific instructions.

Verify the power meter's address on the 8510 system

[LOCAL] When shipped from the factory, the address of the power meter is 13. If this conflicts with another instrument on the system bus,

{POWERMETER} change the address of the conflicting instrument. The power meter must be set to address 13 in order for the firmware to func-

tion properly. Press [SYSTEM/INPUTS], {REMOTE INTERFACE} and {INTERFACE OVERVIEW} on the E4418B to ensure the

power meter’s address is set to 13. Verify that the power meter is connected to the system bus.

Set up the analyzer and measurement

Set up the start/stop frequencies and the measurement type (for example, S11, S12).

Adjust the number of analyzer trace points (if needed)

STIMULUS [MENU] When the flatness calibration is initiated, the analyzer sends the source a list of flatness-correction frequencies equal to the

{NUMBER OF POINTS} number of trace points set on the analyzer.

{POINTS}

Set the source to the maximum leveled power

STIMULUS [MENU] Set the 8360 for maximum specified power (P1) at the highest frequency in the span; see Table 3. At higher power levels, the

{POWER MENU} power meter will take less time to settle between measurement points during the calibration process.

{POWER SOURCE 1}

P1[x1]

Connect the power sensor to the active test port and begin the flatness calibration

Initiate flatness calibration

{POWER FLATNESS} Do not cycle the power on the analyzer or the source during the calibration process. The calibration may be aborted at any time by

{CALIBRATE FLATNESS} pressing any key on the analyzer’s front panel. Aborting the calibration is not recommended, since the command may cause the

system to freeze. By pressing {CALIBRATE FLATNESS} the analyzer will remind the user to zero the power meter and connect the

power sensor to the source. Press {CALIBRATE FLATNESS} again on the analyzer to initiate the calibration. Once initiated, the

analyzer retrieves the power meter measurement data and transfers it to the 8360 where it is processed and stored with the

appropriate correction frequency. During the flatness-correction calibration, the analyzer will display MEASURING DATA, xx%

DONE, PRESS ANY KEY TO ABORT. The xx% DONE indicates the percentage of the total number of correction points that have

been measured; it is not an indication of elapsed measurement time. When the flatness-correction calibration is completed, the

analyzer will automatically store the correction table into register 1 of the source. Any new calibration of the source will overwrite

the flatness-correction table.

Activate the flatness-correction

{FLATNESS ON} The source output power will now be unleveled as it attempts to output the test port power level (Power Source 1) plus the flat-

ness correction for each measurement point in the frequency span. IF Overload or Source 1 Warning—RF Unleveled may be dis-

played on the analyzer until the test power level is reduced.

Set the test port power level

STIMULUS [MENU] Set the test port power level (P2) equal to or below the maximum allowed test port power (see Table 3) for the highest frequency

{POWER MENU} in the measurement span. A constant power level equivalent to P2will now be available at the test port. The flatness-correction

{POWER SOURCE 1} calibration can be varified using the E4418B to measure the power at certain CW frequencies in the frequency range.

P2[x1]

Perform the measurement calibration

Compensate for systematic errors by performing a measurement calibration (if desired). Although a measurement calibration can

be performed before or after the flatness-correction calibration with or without correction enabled, it is recommended that the cal-

ibration be performed after the flatness correction is enabled. The calibration is no longer valid if the source power is changed

after performing the calibration.

Connect the DUT to the test port

Table 2. Agilent E4418B power meter setup

E4418B Keystrokes Description

Preset and zero the power meter

[PRESET/LOCAL] Return the power meter to a known state.

{CONFIRM}

[ZERO/CAL]

{ZERO}

Set up the 437B emulation on the power meter

[SYSTEM/INPUTS] The 437B command set must be activated in order to perform the power flatness calibration. Power meters that can be used in

{REMOTE INTERFACE} place of the E4418B are the E4418A and 437B. The E4419B dual channel power meter does not have the 437B command set and

{COMMAND SET} cannot be used to perform the calibration.

{437B}

Connect the sensor to the power reference output on the power meter and calibrate the power sensor

[ZERO/CAL] Choose a power sensor that can perform within the desired frequency span. To determine which power sensors are compatible

POWER REF {ON} with the E4418B, consult the user’s guide. Agilent E-Series power sensors cannot be used for calibration because they are incom-

{CAL} patible with the 437B command set. Additional configuration may be needed to connect the sensor to the power reference;

POWER REF {OFF} this information can also be found in the E4418B user’s guide, part number E4418-90032. After calibrating the sensor, the

power meter should display a reading of 0.0 dBm (or 1 mW) when the sensor is connected to the reference and the power

reference is activated.

Select or create the calibration factor table that applies to the power sensor in use (if needed)

[SYSTEM/INPUTS] The factory enters nine tables of typical calibration factors for nine different sensors in the E4418B. Use the up and down

{TABLES} arrows on the display to highlight the desired table. If tables 2 through 9 are cleared, the data previously stored in those tables

{SENSOR CAL TABLES} cannot be restored. See the E4418B user’s guide, part number E4418-90032, for information on entering custom calibration

HIGHLIGHT TABLE factor tables.

TABLE {ON}

{DONE}

Table 3. Agilent 8360 series synthesized sweeper maximum leveled power (in dBm)

Maximum Frequency 83620B 83621B 83623B 83623L 83631B 83651B

20 GHz 13 10 17 15 10 10

26.5 GHz N/A N/A N/A N/A 4 4

40 GHz N/A N/A N/A N/A N/A 3

50 GHz N/A N/A N/A N/A N/A 0

Table 4. Settable test port power ranges (assuming no test set step attenuation)

RF Source 83620B/83621B 83631B 83651B

8510 Test Set with 8514B with 8515A with 8515A with 8517B with 8517B, Option 007

Frequency Test Port Power Levels [Pmax to Pmin] (in dBm)

0.05 GHz 2.5 to –20.5 –3.5 to –26 –3.5 to –26 –1.5 to –21.5 5 to –21

2 GHz 1 to –22 –6 to –29 –6 to –29 0.5 to –23.5 5 to –21

20 GHz –7.5 to –27 –13.5 to –30 –13.5 to –30 –7.5 to –30 2 to –23

26.5 GHz N/A N/A 25 to –30 13.5 to –30 1 to –24

40 GHz N/A N/A N/A –20 to –30 – 3 to –21.5

50 GHz N/A N/A N/A –27 to –30 –13 to –29

The following error messages may occur while

attempting to enable the flatness correction and/or

reducing the test port power level:

• If flatness correction is enabled before reducing

the test port power level, IF Overload or Source

1 Warning—RF Unleveled may be displayed on

the analyzer as the source becomes unleveled.

Unleveling occurs when the source attempts to

output its maximum specified power plus the

flatness correction.

• If the output power is reduced to a suitable test

port power level before turning flatness correc-

tion on, No IF Found may be displayed. There

may not be sufficient output power from the

source for the 8 10C to phase lock to the signal.

These error messages should disappear when flat-

ness correction is enabled with the appropriate

test port power level setting. If the test port power

level is not correctly reduced, the source will

become unleveled and try to output maximum

power. Although flatness correction will be applied

to the unleveled signal, the measurement for the

unleveled portion of the frequency span will not be

valid because the flatness-correction feature can-

not compensate for the inconsistent power varia-

tions that occur.

Power control with flatness correction

The ability to compensate for power variations

across the entire measurement span of the source

will depend on the highest leveled output power

the source can produce and the amount of power

compensation required. The test port power may

be adjusted over the entire Pmax to Pmin range with-

out degrading the flatness-correction calibration.

Table 4 shows test port power ranges for various

source/test set combinations. To determine the test

port power levels for a particular frequency span,

choose a power level between Pmax of the highest

frequency in the measurement span and Pmin of the

lowest frequency in the measurement span. For

example, the power range for a 0 MHz to 20 GHz

span with an 83621B/8 1 A system is –13. dBm

to –26 dBm. A high-power Agilent 83623B adds

7 dBm to Pmax of the 83621B. If a user sets up a

0 MHz to 20 GHz measurement with an 83623B

and an 8 1 A, the test port power range is

–6. dBm to –26 dBm.

Operational Considerations

Calibration time

The user may choose to speed up the calibration process by reducing the number of trace points on the

analyzer. Table provides some typical calibration times for flatness correction over the full frequency

span of the source for different source/test set combinations. Calibration times may be slightly reduced by

increasing the stepped measurement speed with the quick step feature on the Agilent 8 10C.

Table 5. Typical calibration times (in minutes) versus number of calibration points with maximum leveled source power

Number of Points 83620B/83621B 83631B 83651B

with 8514B with 8515A with 8515A with 8517B

801 30 32 40 60

401 15 16 20 30

201 8 8 10 15

101 4 4 5 8

512224

Verifying a flatness-correction calibration

To verify the flatness-correction calibration, the

power sensor should be reconnected to the test

port to measure the test port power at individual

frequencies. Since the measurement system is

calibrated in 0W, inaccuracies will occur when

a device is not well matched. Since the flatness-

correction calibration is not a real-time power

leveling feature, it cannot correct for mismatches

that occur between the test port and the DUT.

Adjusting the frequency span after calibration

Once a flatness-correction calibration with the

maximum number of points (801 points) has been

completed, adjustments can be made to reduce the

number of trace points on the analyzer. The user

may also change the measurement frequency span

to a subset of the original calibration span without

invalidating the calibration. The source will output

corrected power at the appropriate measurement

points.

This capability is particularly useful for users who

are testing a number of devices with different

frequency spans at the same test station. In this

case, the user may choose to perform the flatness-

correction calibration with the maximum number

of calibration points across the full frequency

range. Subsets of the original calibration frequency

range can then be used to meet the specific testing

requirements of the individual devices.

When to recalibrate

The flatness-correction calibration does not need

to be repeated unless: (1) the user wants to cali-

brate over a wider frequency range, (2) the meas-

urement path between the source and the test

device changes, (3) the RF source power changes,

(4) the user wants to increase the number of meas-

urement points, or ( ) the environmental condi-

tions under which the original calibration was per-

formed changes dramatically.

Keep in mind that the flatness-correction table

is automatically saved into register 1 of the RF

source. Any new calibration of the source will

overwrite the flatness-correction table. If multiple

flatness-correction calibrations are performed,

only the most recent calibration will be saved for

the DUT.

Using test set step attenuators with flatness correction

If lower test port power levels are desired, test

set step attenuators may be used. The frequency

response of the step attenuators can be eliminated

from the measurement by performing the flatness-

correction calibration with the appropriate atten-

uation enabled. High sensitivity power sensors

(848 D to 26. GHz and 8487D to 0 GHz) are

available for power measurements from –20 dBm

to –70 dBm. The limitation of making power meter

measurements at these low power levels is that the

actual calibration process takes considerably more

time since the power meter takes much longer to

settle at each correction frequency.

Using test port 1 calibrations on test port 2

In most cases, port 1 will be the input port of the

DUT. When port 2 must be used as the input port

to the device, the user may choose to use a port 1

flatness-correction calibration on port 2 since the

port 1 and port 2 signal paths are symmetrical.1

Figure 3 illustrates the use of port 1 flatness cor-

rection on both ports 1 and 2. The port 2 measure-

ment with port 1 flatness-correction calibration is

optimized for measurements below 30 GHz.

1. Test sets with option 003 (high forward dynamic range) cannot be used because

the reverse transmission dynamic range is degraded.

Flatness corrections in fixture or wafer-probing

environments

Test port flatness correction may be applied

with any other power function. Power slope may

be used to compensate for the path loss in non-

coaxial environments such as microstrip and

coplanar waveguide measurement systems. The

maximum test port power for any particular fre-

quency span cannot exceed the maximum test port

power level for the highest frequency in the span

(see Table 3) minus the maximum power slope

compensation required.

Figure 3. Corrected test port power using port 1 flatness correction on port 1

(channel 1) and port 2 (channel 2)

Practical Application Examples

Absolute output power measurements with

flatness correction

One benefit of the flatness-correction capability is

the ability to measure the absolute output power of

active devices. Since the input power level to the

DUT is kept constant, the magnitude offset feature

of the Agilent 8 10 can be used to display absolute

output power across the entire frequency span of

the device. Table 6 shows the procedure for

absolute output power versus frequency measure-

ments with test port flatness correction.

Table 6. Absolute output power measurements with flatness correction

8510C Keystrokes Description

Set up the source and power meter as illustrated in Figure 2

Set up the measurement

PARAMETER [MENU] Set up the analyzer for a b2measurement.

{USER 2 b2}

Activate the test port power flatness-correction

Perform the flatness correction calibration. Set the test port power level and enable the flatness

correction as explained in Table 1.

Connect a thru

Perform a thru calibration with the flatness correction enabled

[CAL] Perform a thru calibration to eliminate the frequency response errors of the port 2 path in the measurement. Be sure to

{CAL#…} include any attenuators and/or adapters which are part of the measurement in the thru calibration. It may be necessary to

{CALIBRATE:RESPONSE} swap adapters for the thru connection. Any cal set may be selected to access the response calibration in the calibration

{THRU} menu structure

{DONE RESPONSE}

{CAL SET #}

Connect the DUT

Measure the absolute output power

RESPONSE [MENU] When the device is reconnected, the gain will be displayed. Enter a magnitude offset equivalent to the test port power level

{MORE} (P2). Measure the absolute output power at any point in the measurement span.

{MAGNITUDE OFFSET}

P2[x1]

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