Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With waveguide or long line
Reexamination Certificate
2002-09-03
2004-10-12
Lair, Donald M. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With waveguide or long line
C324S132000
Reexamination Certificate
active
06803754
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a power sensor for measuring the average power of modulated or unmodulated radio-frequency or microwave signals over a large dynamic range.
BACKGROUND OF THE INVENTION
A very wide variety of embodiments of power sensors are known. The most common versions contain either a single thermal sensor, which produces an electrical measurement quantity proportional to the electrical power absorbed, or contain a single diode rectifier in a one- or two-way circuit, which delivers an electrical output quantity equivalent to the voltage across the terminating resistor, from which the power to be measured can then be determined. Whereas power sensors with diodes can measure accurately the power of CW signals (unmodulated sine-wave signals) over a range of from −70 dBm to +20 dBm, their use in relation to envelope-modulated signals is restricted to the diode's so-called quadratic characteristic-response region from −70 dBm to approximately −20 dBm. The dynamic range of about 50 dBm which can be achieved here is significantly smaller than in the case of CW signals, and is roughly the same size as in the case of thermal sensors.
In particular, the requirements of the communication standard for the second and third generations of digital mobile telephony have led to the development of a new group of power sensors with a substantially larger dynamic range for modulated signals. In one of these known power sensors, two sensor branches are provided and, specifically, a first sensor branch for measuring in a low power measurement range is provided directly at an input, and a second sensor branch for measuring in a high power measurement range is connected to the input via a special resistor network which serves both as a characteristic impedance-matched termination for the first sensor branch and also to provide the power feed for the second sensor branch (U.S. Pat. No. 4,943,764). In the practical embodiment of this known power sensor, the sensitive input-side sensor branch needs to be turned off when the other sensor branch for the high powers is being used (Hogan, R.: Wide-Range Sensor Gauges Power Of Complex Signals. Microwaves & RF, September 1999, pp. 128-137). The measurement range of the power sensor which is produced is specified as from −60 dBm to +20 dBm, which means that the sensitivity is 10 dB less than is achievable with known power sensors for CW signals (datasheet “EPM Series Power Meters, E-Series and 8480 Series Power Sensors”, literature number 5965-6382E from Agilent Technologies). The sensor is available in a 6 GHz version and in an 18 GHz version.
A power sensor with two sensor branches is also already known, which feeds the signal power to be measured via a power splitter into two sensor branches, respectively with different sizes of attenuators, in order to measure the signal power in a lower power range and in a high power range (U.S. Pat. No. 4,873,484). The power splitter used in this case is designed as a so-called three-resistor power splitter (Russel A. Johnson: Understanding Microwave Power Splitters, Microwave Journal Vol. 18, December 1975, pp. 49-56). In such sensors which operate with power splitters, it is also already known to arrange two such three-resistor power splitters (also referred to as resistive power dividers) in cascade, and hence to provide a total of three sensor branches for different power measurement ranges (Anritsu Co.: A Universal Power Sensor. Microwave Journal, March 2000, pp. 130-134). The measurement range specified by the manufacturer for this power sensor is likewise only from J−60 dBm to +20 dBm. The sensor is available only in a 6 GHz version.
Lastly, in the case of power sensors with diodes, it is also already known to use a plurality of diodes connected in series in the same direction as a rectifying element, either in order to reduce the effect of the junction capacitance, which depends on the drive level, on the linearity of the sensor in the case of sensors which are used exclusively for CW signals (U.S. Pat. No. 5,204,613) or, in the case of sensors for modulated signals, in order increase the measurement range of a sensor branch (Hogan, R.: Wide-Range Sensor Gauges Power Of Complex Signals. Microwaves & RF, September 1999, pp. 128-137).
SUMMARY OF THE INVENTION
There is a need to provide a power sensor for measuring the power average value of modulated signals in the frequency range up to 18 GHz or higher, whose sensitivity and dynamic range are greater than in the case of the known solutions and are comparable with the properties of power sensors for CW signals.
This and other needs are addressed by the invention, in which at least three mutually independent sensor branches with correspondingly different power measurement ranges are provided, in order to divide up the required dynamic range of 90 dB so finely that the perturbing effects due to noise or errors, which occur at the measurement-range limits of the individual sensor branches during the RMS value rectification, can be kept sufficiently small. The individual sensor branches preferably contain diode detectors which, in a manner that is known per se, are constructed using a single rectifier diode (one-way rectifier) or two rectifier diodes with different polarities (two-way rectifier) and an associated charging capacitor. In order to achieve the high sensitivity, as in the case of a power sensor for CW signals, a first sensor branch is arranged directly at the input, whereas the other sensor branches are fed with correspondingly divided powers via power splitters and attenuators. The synchronization of the sensor branches as a function of frequency is particularly important in this case, since only with minor frequency-response differences is unproblematic changeover from the measurement results of one branch to those of another branch possible. This is not guaranteed in the case of the known solutions.
According to the invention, the synchronization problem is solved by the fact that the measurement quantity, that is, the wave impinging on the sensor, is sent with the least possible perturbation through the first sensor branch and subsequently is divided between the two other sensor branches by means of a power splitter, with substantially load-independent synchronous response (tracking), and the measurement device in the first sensor branch is to be configured in such a way that its measurement value is representative of the level of the power of the incident wave, irrespective of the matching of the power splitter. To that end, in the first sensor branch, a plurality of voltage taps, each with an allocated detector, are provided at suitable intervals on the feed line to the power splitter, and the sum of the output voltages of the detectors, or of the apparent powers which can be determined therefrom, is formed in a suitable way. The summation reduces the positional dependency of the measurement results, which is due to standing waves on the feed line, so that the power of the incident wave can be measured very accurately because it is being measured substantially independently of the matching of the power splitter and hence frequency-independently (Sucher, M.: Final Report on High Power Measuring Techniques; Microwave Research Institute, Report R-718-59, PIB-646, March 1959). A further advantage of such an arrangement with distributed measurement points is that the perturbations which are generated by the individual detectors partially cancel out one another and hence improve the input-side matching of the power sensor. Although the advantages of the described measurement arrangement are restricted to a frequency band of the order of one to two octaves, it is also expedient to use it in a broadband power sensor with a frequency band extending over several octaves, because perturbations due to mismatching of individual modules do not usually become relevant until the upper two thirds of the specified frequency range.
For symmetrical division of the measurement signal, i
Bratfisch Toralf
Diestelhorst Arnd
Katzer Michael
Reichel Thomas
Ditthavong & Carlson P.C.
Lair Donald M.
Rohde & Schwarz GmbH & Co. KG
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