Broadband electromagnetic field component measurement system

Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system

Reexamination Certificate

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C702S064000, C702S086000, C702S104000, C702S107000, C702S115000, C702S092000

Reexamination Certificate

active

06564158

ABSTRACT:

PURPOSE AND ADVANTAGES OF INVENTION
The purpose of this invention is to provide an improved isotropic broadband measurement of a component of an electromagnetic field. Prior art broadband field measurement system speed and accuracy were limited by existing functional partitioning and circuit architecture. The present invention establishes a faster, more flexible, and more accurate measurement method by improving the overall system functional partitioning, circuit architecture and includes a new calibration approach.
The present invention removes measurement bottlenecks allowing substantially faster field measurement.
The present invention uses data collection and compensation techniques that can be tailored to meet a large variety of measurement conditions and requirements. Measurement accuracy is improved over a very broad dynamic range.
The present invention introduces a highly efficient, accurate and flexible calibration technique. The calibration technique supports a large variety of system data compensation applications and requires very little Probe memory.
BACKGROUND OF THE INVENTION
A common method of measuring data of an electromagnetic field is based on measuring the electric field component. Referring to
FIG. 1
, a typical prior art detector-based radio frequency and microwave electric field measurement system
20
contained three primary functional subsystems: (i) a sensing subsystem
22
, (ii) a signal conditioning and processing subsystem
24
, and (iii) a control and display subsystem
26
. These subsystems and the functions performed within them as were commonly partitioned in the prior art are as shown in FIG.
1
. Physically, the sensing subsystem
22
and signal conditioning and processing subsystem
24
were often contained within an electric field probe
28
which, in operation is exposed to the environment in which the field is to be measured. The control and display subsystem
26
was contained within a system readout
30
which, in operation is preferably remote from the probe to avoid or reduce perturbation of the field to be measured.
The sensing subsystem
22
included sampling of the incident electric field using a band-limited transducer or antenna for a transducing function
32
followed by a detection function
34
using a diode or thermocouple based circuit. The sensing subsystem
22
included additional filtering components for rf band-shaping and/or noise reduction in a frequency band-shaping function
36
. The amplitude of the detection circuit output voltage was coupled into the instrumentation electronics part
24
of the system
20
.
Functions performed in the signal conditioning and processing subsystem included: analog signal conditioning such as a filtering function
38
and a level-adjust function
40
, conversion of the analog level to digital form in an A/D conversion function
42
, and a data communication function
44
to and from the control and display subsystem
26
. Measurement compensation in the signal conditioning and processing subsystem
24
included a sensor linearity correction function
46
, a temperature compensation function
52
(if required), a signal averaging or data smoothing function
50
, and calculation of the electric field amplitude in a composite field calculation function
48
. It is important to understand that the data sent from the signal conditioning and processing subsystem
24
to the control and display subsystem
28
typically contained calibrated measured data in common units such as volts per meter (V/m).
The control and display subsystem
26
typically contained a data display function
54
for visual review of instrument state and measured data, a ranging/zero control function
56
for adjusting ranging and zeroing, and sometimes included data logging function
58
along with a user interface function
60
and a data I/O interface function
62
for data exchange between the sensing and display subsystems
22
-
26
, and between the display subsystem
26
and an external data collection system (not shown here). In the operation of prior art system
20
, the user, through the system readout
30
, requested and read calibrated field intensity data from the electric field probe part, either for a single axis, or for the vector sum of the three axes readings.
Because of the functional partitioning and circuit architectures used, there were some inherent performance limitations associated with such prior art systems as follows:
1. Performing data compensation functions such as linearity and temperature correction in the probe often required additional circuitry for data compensation and added to the micro-controller processing requirements. Adding circuitry increased the physical volume of the sensing subsystem. Furthermore, additional processing slowed down the measurement response time.
2. Calculating the field intensity in the instrumentation electronics of the signal conditioning and processing subsystem also required additional processing time, again slowing down measurement response times. For 3-axis sensors, the field calculation had to be completed for each sensor axis and then the electric field was calculated as a vector sum of the individual field values.
3. Obtaining individual field readings for each of the three measurement axes usually required multiple reading requests from the system. This increased total measurement time and/or introduced inaccuracies when measuring time-varying fields since the individual axis readings were usually not simultaneous.
Common linearity correction techniques included using analog diode voltage compensation and piece-wise linear approximation lookup tables. Analog corrections offered advantages of minimal measurement time impact, but were relatively inaccurate compared to digital techniques. Also, such prior art approaches usually performed well only over relatively narrow dynamic ranges. Beyond those ranges, measurement inaccuracy increased quickly. The additional circuitry required also increased the physical volume required to contain the electronics. Increased circuit volume created a larger cross-section instrumentation electronics enclosure, which perturbed the measured field more and consequently decreased accuracy of measurement at higher frequencies.
The lookup-table method involved characterization of the detector performance at discrete electric field levels during the calibration process. A table of corrected field readings was typically stored in electronic memory. When a measurement was made the detector output voltage was compared to the available correction points and a piece-wise linear interpolation was made to find the compensated electric field reading. Accuracy was limited by the lookup table point resolution, the linear interpolation error, and the numeric precision used to store and calculate the results. The time required to perform the compensation added to the total time required for such a prior art probe to perform a measurement.
The present invention has improvements over the prior art by providing a faster and smaller probe exposed to the field, and provides faster and simpler data acquisition through the process of transmitting uncalibrated data (hereinafter “Raw Data”) from an improved probe (hereinafter “Probe”) to an improved system readout (hereinafter “Readout”), while enabling the Readout to calibrate the Raw Data by an improved method that calibrates and linearizes the electromagnetic field data with improved accuracy and reduced electronic storage requirements. The improved system has the capability of operating with a variety of Readout configurations and in one or more modes selectable by a user, giving greater flexibility than was available in the prior art.


REFERENCES:
patent: 4780910 (1988-10-01), Huddleston et al.
patent: 5085427 (1992-02-01), Finn
patent: 5300885 (1994-04-01), Bull
patent: 5357253 (1994-10-01), Van Etten et al.
patent: 5762064 (1998-06-01), Polvani
patent: 5764058 (1998-06-01), Itskovich et al.
patent: 5910905 (1999-06-01), Qian et al.
patent: 5990679 (1999-11-01), Frommer et al.
patent:

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