Data processing: measuring – calibrating – or testing – Calibration or correction system
Reexamination Certificate
1999-09-02
2003-03-04
Hilten, John S. (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
C324S601000, C324S613000, C702S076000, C455S067700
Reexamination Certificate
active
06529844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vector network analyzer (VNA). More particularly, the present invention relates to measurement of s-parameters, third order intercept, harmonics, group delay, and noise figure using the VNA. The present invention further relates to measurement of three port devices, such as a mixer using the VNA, and calibration of the VNA.
2. Description of the Related Art
FIG. 1
shows a block diagram of components included in a conventional vector network analyzer (VNA). The VNA is configured to make vector measurements, including both magnitude and phase, of a device under test (DUT) connected across its two test ports A and B. The VNA includes a signal source which generates RF/microwave signals and can sweep over a range of frequencies. A switch selectively connects the signal source to one of two reflectometers A or B. The reflectometers A and B include couplers which couple a reference RF signal as provided from the signal source to one of test ports A and B, and a test RF signal received at one of the test ports A and B. The couplers are connected to downconverters in the reflectometers which downconvert the test and reference RF signals to intermediate frequency (IF) signals. Further components in the reflectometers then process the IF signals to provide full two port error corrected scattering parameters (S-Parameters), and other measurements such as group delay.
A conventional VNA may also include components to measure noise figure as illustrated in FIG.
2
. The noise figure is a way of specifying the noise parameters of a component, and is defined as the ratio of the signal-to-noise ratio available from the device output to the signal-to-noise ratio delivered to the input of the device, at a standard reference temperature of 290K. Noise figure measurements are made using a noise source and receiver. The noise source typically includes a noise diode connected to a power supply. The noise source provides noise over a wide bandwidth to one port of a DUT, while the other port is connected to a receiver. The receiver downconverts the noise source signal from the DUT to an intermediate frequency (IF) range, and the IF signal is processed to provide an indication of power level enabling the noise figure to be determined over the frequency range.
In
FIG. 2
, the noise source in the VNA is connectable by a switch A through a reflectometer A to the measurement port A of the VNA. The switch A normally connects the signal source of the VNA through the reflectometer A to the test port A for standard VNA measurements and is switched to the noise source when noise figure measurements are desired. Similarly, a receiver is connectable by a switch B to the test port B of the VNA. The switch B then normally connects to the signal source for standard VNA measurements and is switched to the receiver when noise figure measurements are desired.
The receiver in
FIG. 2
is separated from the reflectometers A and B, but its components are the downconverters and IF processor typically included in the reflectometers. Rather than use two separate receivers, switching is included in the receiver so that signals can be downconverted and processed from the reflectometers as well as the noise source stimulated DUT when the switches A and B are so configured.
Noise figure measurements have been performed for years with a wide variety of instruments, but the instruments have lacked flexibility. Usually the noise source and receiver must be attached directly to the DUT for all measurements, or the noise source is provided internally in a VNA, as shown in
FIG. 2
, for all measurements. The user, thus, has little choice with respect to test setup, noise source selection, or noise source traceability. With the receiver measuring power, and not operating in ratioed mode, the user cannot usually apply vector corrections using the VNA to compensate for DUT or system mismatches when the noise figure measurements are made.
Devices for measuring noise figure also do not allow a selection of frequency bandwidths for measurements which may limit the types of DUTs that can be measured using one test device. The measurement bandwidth being fixed for a given test system may also lead to either inordinately long test times or to inaccurate results.
A VNA may be used with an external automatic calibration as illustrated in FIG.
3
. The external calibration device can include calibration components include elements such as a short, open, match and a thru connection which are selectively connectable by switches to test terminals which can be connected to test ports A and B of the VNA. The automatic calibration device can also include verification lines which are connectable by switches between its terminals to verify calibration once calibration is complete. The internal components are initially characterized using actual short, open, match and thru lines which are directly connected to the ports of the VNA. During calibration using the external calibration components, calculations are performed to account for imperfections in the calibration standards of the automatic calibration device based on measurements which are made and stored when measuring the actual calibration standards.
The automatic calibration device can be provided with a separate controller, as further shown in
FIG. 3
which connects to the VNA and automatic calibration device to automatically control the calibration process. The VNA typically has a keypad which a user uses in conjunction with the external controller to type in commands to set up and run each calibration step after connecting a different standard. The controller is programmed to function as the user, and sends information to the VNA's processor to set up and run each calibration step after each calibration component is connected by internal switches in the automatic calibration device to the terminals of the VNA. The automatic calibration process is started by a user depressing a start button on the controller keypad. An automatic calibration device with components as described above, including a controller is described in U.S. Pat. No. 5,587,934 entitled “Automatic VNA Calibration Apparatus”, to Oldfield, et al. which is incorporated herein by reference.
Since a conventional VNA includes only two ports and a single signal source, measurement of components requiring two input signals, such as a mixer, and measurements of parameters where two input signals are applied, such as second and third order intercepts, cannot be performed with a conventional VNA alone.
A typical set up for measuring the frequency translation parameters of a mixer is shown in
FIG. 4. A
first of two input signals f
1
is provided to the mixer from a VNA. Since the VNA only has one signal source, apart from its local oscillator, a second signal f
2
is provided from an external signal generator. The output of the mixer is then measured using a spectrum analyzer. The output of the mixer provides a frequency translation including a sum and difference of its input signals f
1
±f
2
along with higher harmonics of those signals at its output. The spectrum analyzer is used to measure the mixer output since the reflectometers of a VNA are typically configured to measure scattering parameters rather than to provide the function of a spectrum analyzer. Using the VNA to provide the input to one port of the mixer will allow use of the VNA to characterize one port of the mixer without reconfiguration of the mixer test setup.
A typical test set up for measurement of second or third order intercept is shown in FIG.
5
. Second and third order intercept measurements are a way of characterizing distortion. Because of the increasing need for wide dynamic range at high frequencies, most wideband amplifiers, as well as other microwave and millimeter wave components, now have distortion specification. When two tones, or signals, are applied to an amplifier that is non-linear, the nonlinearity causes them to modulate one another, producing i
Kapetanic Peter
Martens Jon
Rangel David
Anritsu Company
Fliesler Dubb Meyer & Lovejoy LLP
Hilten John S.
Le John
LandOfFree
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