An example of a heat-based power sensor is the AGILENT 8481A thermocouple-based sensor. AGILENT is a trademark of Agilent Technologies, Inc. of Santa Clara, Calif., USA. Thermal-based power sensors are true “averaging detectors” and in addition to thermocouple power sensors also include bolometer (thermistor or barretter) power sensors. They convert an unknown RF power to heat and detect that heat transfer. In other words they measure heat generated by the RF energy.
Rectification-based power sensors include diode sensors such as low-barrier Schottky diodes and PDB diodes. The electric field of the input RF signal generates an AC voltage across the diode and this AC voltage is rectified by the diode into a DC voltage. This DC voltage is related to the power of the input RF signal.
Usually the power sensor sends signals indicative of the power received by it's load to a power meter, which can be an AGILENT E4418B Power Meter.
The most important source of error in power measurements of RF and microwave signals is the mismatch of generator and sensor. Even a signal generator with low SWR of 2, for example, can still lead to an additional uncertainty of the measurement result of ±3.5% (0.15 dB) or more. Although this error can be decisive for total measurement uncertainty, it has frequently not been taken into account because it could not be specified for the sensor alone.
Due to reflections caused by the mismatch of the generator and sensor, it is not the nominal power PGZ0 of the generator 107 that is transmitted to the load 103, but rather, the power PD delivered to the load 103.
The actual value of the power PD delivered from the generator 107 to the load 103 is derived in the following.
The reflection coefficient of the load 103 is related to the incident wave and the reflected wave at the load port thus:
is the reflection coefficient at the load 103 where
Now, at the generator, bG=bS+ΓG·aG, where:
When the generator 107 is connected to the load 103 bG=aL and bL=aG.
This results in:
So the net power dissipated at the load, PD, and where PGL is the net power delivered to the arbitrary load, is
The nominal power PSZ0 of the generator 107 that would be transmitted to the load 103 if there were no reflections would be:
P
GZ0
=|b
S|2.
If the load 103 is a conjugate match for the source 101 (condition for maximum power transfer) then PAV, which is the maximum available power delivered into a conjugate matched load, is:
So the ratio of the delivered power PD to the available power PAV (sometimes called the conjugate mismatch) is:
If all the complex reflection coefficients are measured at the frequency of interest then their values can be fed into the equations above to calculate the available power PAV. The determination of the available power PAV is known as the mismatch corrected power measurement. Unfortunately the above equation is not often used for this mismatch corrected power measurement. Due to the difficulty in obtaining the complex reflection coefficients ΓG of the generator 107 the mismatch uncertainty is lived with as a fact of life.
However, during the factory calibration of sensors, complex mismatch correction is performed. This can be done because the source is a vector network analyzer, with the capability to not only provide a signal but also to measure the complex S-parameters at the port. Thus, in the above equation ΓL is known from factory calibration and ΓG is the unknown.
Determining ΓG in the above equation is not easy. Measurement of the source S-parameters or reflection coefficients is difficult when it is a live source. Reflection coefficients of 2-port linear networks are readily measured using vector network analyzers. The measurement of a live output is less readily achieved however as the network analyzer cannot introduce a signal at the generator's output frequency. Most methods make use of scalar techniques to derive the magnitude of the generator's reflection coefficients. In practice the maximum magnitude of the reflection coefficient will be all that is known.
It would be desirable to provide a compact, low loss and inexpensive module having built-in mismatch measurement and correction for measuring the power output by a generator.
The present invention provides a compact, low loss and inexpensive module having built-in mismatch measurement and correction for measuring the mismatch corrected power output of a generator.
The module determines the mismatch corrected power output of a generator. Loads within the module provide at least three different load values. At least one power sensor detects at least a portion of the power output by the generator for each of the load values. Input electrical paths transmit power from the generator to the loads. At least one output electrical path transmits signals from the at least one power sensor indicative of power received when the generator is electrically connected to the different load values.
Further preferred features of the invention will now be described for the sake of example only with reference to the following figures, in which:
The present invention allows automatic measurement of generator S-parameters or complex reflection coefficients. The measurement process combines this measurement with a basic power measurement and load complex reflex coefficients (or load S-parameters) to produce a mismatch corrected power measurement.
It is known in the art that presenting (or electrically connecting) various loads to the generator 107 can be used to determine the match of the generator. The match of the generator is based on any of the related parameters: complex voltage reflection coefficients (VRC), S-parameters or complex impedance.
The generator 107 can be the same as that described with reference to
Again, as in
The waves bS, bG and aG can have a frequencies in the RF range. The RF frequency range is considered to cover frequencies from approximately 150 kHz up to the IR range. In other embodiments the frequency can be in the microwave frequency range of 1 GHz and higher.
The module 201 includes a load section 203. Loads 205, 207, 209 are shown within the load section 203. In general the load section 203 should have loads with at least three different load values. Rather than three separate loads, one or two loads having variable load values can be used instead. Three or more loads with or without variable load values can also be used in the invention. At least one of the loads 205, 207, 209 is included in a power sensor (not shown). The loads 205, 207, 209 can be fixed resistors, variable resistors or distributed impedances, for example.
A single power sensor can also be used to measure the power across more than one of the loads. In such an embodiment the number of power sensors can be less than the number of loads. Also, a single power sensor can be used with a single variable load.
Input electrical paths 211 transmit power from the source 101 and generator 107 to the module 201 and loads 205, 207, 209 within the load section 203. The input electrical paths 211 and other transmission media used in the invention can be cable, waveguide, transmission line or other known transmission media. The various components of the module can be mounted on a PC board or other substrate. The housing 202 of the module 201 can include an input connector 223 for receiving the waves bS, bG and aG.
Output electrical paths 213 transmit signals 215 from one or more power sensors indicative of the amount of power received when the generator is electrically connected to any of the load values. The signals 215 can be analogue or digital. The module 201, or the load section 203 within the module 201, can include power sensors and/or power meters having analogue or digital signals to output the signals 215. Alternatively, the load section 203 or module 201 can include one or more analogue to digital (A/D) converters to output digital signals such as a digital signal 215.
A processor 217 receives the information transmitted by the signals 215 and from these signals calculates the complex voltage reflection coefficients (VRC), S-parameters or complex impedance of the generator 107. The signals 215 can also include a basic power measurement of the net power PGL delivered by the generator 107 to the load of the sensor. The processor 217 also receives, for example from a storage media 219, previously stored load complex reflex coefficients ΓL (or load S-parameters) of the sensor (the same or similar sensor used to measure the net power PGL). The processor 217 combines this data to calculate a mismatch corrected power measurement.
Once the complex voltage reflection coefficients (VRC), S-parameters or complex impedance of the generator 107 are determined, the values can be combined with the measured net power PGL delivered by the generator 107 to the load of the sensor, and the stored complex voltage reflection coefficients (VRC), S-parameters or complex impedance of the sensor, to yield a more accurate power measurement. This can be presented as source power and impedance, or s-parameter, to fully characterize the source.
The processor 217 uses the values for ΓG, PGL and ΓL to calculate the mismatch corrected power output PAV of the generator 107 using the equation:
The processor 217 can store information on a storage media 219 and can display data or results on a display 221. The processor 217, storage media 219, and display 221 can each be integral to the housing 202 of the module 201, as illustrated. In another embodiment, any of the processor 217, storage media 219, and display 221 can be external to the housing 202 of the module 201. For example, in
Again, as in
The module 201 includes the coupler 311 for distributing power from the generator 107 to sensors 305, 307, 309. The coupler can be a transmission line directional coupler, for example. The coupler 311 includes coupled output ports 313, 315, an input port 319 and a through-port 317.
Input electrical paths 211 transmit power from the source 101 and generator 107 to the module 201 and loads 205, 207, 209 within the sensors 305, 307, 309. The housing 202 of the module 201 can include an input connector 323 for receiving the waves bS, bG and aG. The input electrical paths 211 pass through the input connector 323 and the input port 319 into the coupler 311, and lead to the coupled output ports 313, 315, and the through-port 317.
Electrically connected to the through-port 317 is an electrical switch 321. The switch 321 presents, or electrically connects, a load 325, short 327, open 329 and sensor 309 connections to the generator 107.
The sensor 305 receives power output from the coupled output port 313 and the sensor 307 receives power output from the coupled output port 315, and the sensor 309 receives power output from the through-port 317 and passing through the electrical switch 321.
The three sensors 305, 307, 309 provide measurements that are combined to evaluate the quantities required.
The two sensors 305, 307 on the coupled output ports 313, 315, respectively, provide measurements of the incident and reflected wave under all the conditions of the switch 321 for determining ΓG. As mentioned above, the switch 321 presents load, short, open and sensor connections. When the switch 321 is positioned to the load 325 position, it is preferable that a mismatch (e.g. 100 Ohm) is presented. Measurements under all the switch positions are used to ensure the source match can be found.
The load values of the load 325, short 327, and open 329, as well as the loads 205, 207, 209 can be considered to be within the load section 203 (see
The switch 321 is positioned to the sensor 309 position for use in determining PGL. Preferably the load 209 of the sensor 309 presents a matched “Z0” load (e.g. 50 Ohm). Under this condition the sensor 309 has the best sensitivity for measuring the power.
Output electrical paths 333 transmit signals 335 indicative of the amount of power received by the sensors 305, 307, 309. The signals 335 can be analogue or digital. Alternatively, the load section 203 or module 201 can include one or more analogue to digital (A/D) converters 339 to output digital signals such as a digital signal 337.
The processor 217 receives the information transmitted by the signals 335 or 337 and from these signals calculates the complex voltage reflection coefficients (VRC), S-parameters or complex impedance of the generator 107. The processor 217 calculates the mismatch corrected power output PAV of the generator 107.
The processor 217 stores information on the storage media 219 and displays data or results on a display 221′.
Again, as in
The module 201 includes the power splitter 409 for distributing power from the generator 107 to sensors 405 and 407. The power splitter 409 can be a transmission line power splitter, for example. The power splitter 409 includes an input port 411, an output arm 413 having an impedance 417 and an output arm 415 having an impedance 419.
Input electrical paths 211 transmit power from the source 101 and generator 107 (see
Electrically connected to output arm 415, as in the embodiment of
The sensor 405 receives power output from the output arm 413 and the sensor 407 receives power output from the output arm 415 and passing through the electrical switch 321.
The two sensors 405, 407 provide measurements that are combined to evaluate the quantities required.
The sensor 405 on the output arm 413 provides measurements of the power under all the conditions of the switch 321 for determining ΓG. As mentioned above, the switch 321 presents load, short, open and sensor connections. When the switch 321 is positioned to the load 325 position, it is preferable that a mismatch (e.g. 100 Ohm) is presented.
Measurements under all the switch positions are used to ensure the source match can be found.
The load values of the load 325, short 327, and open 329, as well as the loads 417, 419, 421, 423 can be considered to be within the load section 203 (see
The switch 321 is positioned to the sensor 407 position for use in determining PGL. Preferably the load 423 of the sensor 407 presents a matched “Z0” load (e.g. 50 Ohm). Under this condition the sensor 407 has the best sensitivity for measuring the power.
Output electrical paths 433 transmit signals 435 indicative of the amount of power received by the sensors 405, 407. The signals 435 can be analogue or digital. Alternatively, the load section 203 or module 201 can include one or more analogue to digital (A/D) converters 339 to output digital signals such as a digital signal 337.
The processor 217 stores information on the storage media 219 and displays data or results on a display 221′.
Again, as in
The module 201 includes the three-way power splitter 511 for distributing power from the generator 107 to sensors 505, 507, 509. The power splitter 511 can be a transmission line power splitter, for example. The power splitter 511 includes an input port 519, a first output arm 521 having an impedance 527, a second output arm 523 having an impedance 529, and a third output arm 525 having an impedance 531.
Input electrical paths 211 transmit power from the source 101 and generator 107 (see
The sensor 505 receives power output from the output arm 525 through the impedance Z2533, the sensor 507 receives power output from the output arm 523 through the impedance Z1535, and the sensor 509 receives power output from the output arm 521.
Three different power measurements of the net power delivered by the generator 107 are made by the sensors 505, 507, 509.
The load values of the impedances Z1535 and Z2533, as well as of the loads 205, 207, 209 can be considered to be within the load section 203 (see
The sensor 509 is used in determining PGL. Preferably the load 209 of the sensor 509 presents a matched “Z0” load (e.g. 50 Ohm). Under this condition the sensor 509 has the best sensitivity for measuring the power.
Output electrical paths 541 transmit signals 545 indicative of the amount of power received by the sensors 505, 507, 509. The signals 545 can be analogue or digital. Alternatively, the load section 203 or module 201 can include one or more analogue to digital (A/D) converters 339 to output digital signals such as a digital signal 337.
The processor 217 stores information on the storage media 219 and displays data or results on a display 221′.
In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.