METHOD AND APPARATUS FOR MEASURING TRANSMISSION AND/OR REFLECTION COEFFICIENTS TO AMPLITUDE AND PHASE OF AN OBJECT I.E. MICROWAVE COMPONENTS

Abstract: Method and apparatus for measuring both magnitude and phase of reflection and/or transmission coefficient of a measurement object (3), e.g. a microwave component. The method according to the invention is provided thereby that a test signal is reflected/transmitted partly against/through an adjustable element (4) the present reflection and/or transmission coefficient of which is known, the reflected/transmitted signals are measured/detected in a detector (5) and the measurement is executed for a number of different values of reflection and/or transmission coefficients of the adjustable elements (4). Out of the measurement results obtained from the detector (5), the reflection and/or transmission coefficient of the measurement object (3) is calculated. The apparatus according to the invention is provided by that a signal unit (1) is adapted to generate a test signal which is applied partly to the measurement object (3) partly to the adjustable element (4) the current reflection and/or transmission coefficient of which is known, a detector (5) is thereby adapted to detect the reflected/transmitted signals from the measurement object (3) and the adjustable element (4) and a data processing unit (9) is adapted to handle the detected measurement results and out of these determines the reflection and/or transmission coefficient of the measurement object (3).

Description: Method and apparatus for measuring transmissiαπ- and/or reflection coefficients to amplitude and phase of an object i.e. micro wave components ' The present invention refers to a method and an apparatus for analyzing the scattering matrix of a microwave component. Background of the invention and state of the art Within the microwave field and especially within the mm-wave field there is a great need for fast and automatic measurments of reflection and/or transmission coefficients of components ( s-parameters ) as functions of some parameter, usually the frequency. On the market there are today instruments which are able to do this. One example of this is the "Network Analyzer" of Hewlett-Packard. These instruments however are complex in their design and very expensive (about 200.000 Skr. ) . They are furthermore difficult to build for the higher microwave frequencies. Recently so-called six-port systems for impedance measurements in the microwave range have been marketed. These systems, which also are disclosed in the literature, require, as the present invention. use of computers, but a more complicated microwave component with four detectors is required. This makes the six-port system more expensive and it follows that an much more complicated measuring network is required . The purpose of the invention and its most important characteristics The purpose of the invention is to eliminate the above mentioned disadvantages and to provide a method to analyze microwave components in a fast and accurate way. Furthermore the method is easy to use and comparatively cheap and simple to use. The invention also includes an apparatus for accomplishing of the method. The method according to the invention is realized thereby, that a test signal is reflected/transmitted partly against/throug the measurement object and partly against/through an adjustable element with a known reflection and/or transmission coefficient, that the reflected/transmitted signals thereafter are combined and are measured/detected in a detector, that the . measurement is executed for a number of different values of the reflection and/or transmission coefficient of the adjustable element and, that out of the different measurement results, obtained from the detector, the reflection and/or transmission coefficient of the measurement object is calculated. An apparatus for accomplishing the method is provided thereby that a signal unit is adapted to generate a test signal which is applied partly to the measurement object, partly to the adjustable element the current reflection and/or transmission coefficient of which is known, that a detector is adapted to detect the reflected/transmitted signals from/through the measuring object and the adjustable element and, that a data processing unit is adapted to handle the measurement values and out of these determines the reflection and/or transmission coefficient of the measurement object. Short description of the drawings The invention will be disclosed in an embodiment in the following with reference to the enclosed drawings. Figure 1 shows a network for reflection coefficient measurement . Figure 2 illustrates the principle of the solution in a Smith-chart . Figure 3 shows the network according to figure 1 but in a way which more clearly illustrates the mathematical description of the signal path. Figures 4 and 5 show different networks for transmission coefficient measurement. Description of an embodiment In the figures 1 , and 5 the design of the invention is schematically disclosed. The invention provides a device and a method for measuring impedance (reflection and transmission coefficients) within the micro- and mm-wave range and is in principle a measuring bridge. A test signal, generated in a signal unit (1 ) which for example can be a sweep oscillator, is split into two signals by a four-port, 3 dB, directional couper 2 whereby the one signal is reflected/transmitted against/through a measurement object 3 and the other reflected/transmitted against/ through an element 4, the reflection and/or transmission coefficient of which may be adjusted e.g. electronically. As examples of useful four-port-units hybrid-couplers , directional couplers, magic T's and hybrid rings may be mentioned. These components are commercially available in both stripline, coaxial and waveguide design. As the electronically adjustable and variable element 4, the reference load, many different, commercially available, elements may be used. Schottk -barrier diods can be used with advantage but e.g. also pin diods, ferrite-phase-changer , errite-attenuators , mechanically tunable short circuits, mechanically adjustable phase changers and mechanically adjustable attenuators may be used. The two signals are thereafter combined and detected in a detector 5, the output of which then is proportional to the square magnitude of the vector sum of the two incoming signals. The electronically adjustable element 4 is now adjusted to a new reflection alternatively transmission coefficient, a number of times and the output from the detector 5 are registered. Thereby it is possible to calculate, e.g. in a data processing unit 9, both the magnitude and the phase of the reflection (transmission) coefficient of the measurement object 3 from the value and phase. from the output of the detector 5. The networks shown in figure 4 and 5 are provided with two terminations 6, 7. The disclosed method and the apparatus may be automatized by using a computer or by using a suitable micro-computer . The cost of components will be comparatively low. In figure 5 is shown a further embodiment where an element 4 with adjustable reflection factor is used together with a " U EA . OMPI circulator 8 for the transmission measurements. The parameter values measured by the detector 5 are thereafter processed in a computer and the method may be mathematically disclosed according to the following (see figure 3) . E S a a = r b index i (different 1 ij j 2 e 2 i adjustments of the = r element ) d 4 This is an equation system with eight unknowns. The number of equations are six. b may now be solved for. 4 b = A b + 8 a 4 4 3 4 3 A and B are funct- |A | 4 4 tions of S etc. i j (A 8* + A*B ) |b a | cos Φ + 4 4 4 4 3 3 j(A*B - A B*) b a | sin Φ 4 4 4 4 3 3 Consider | b b a | cos b a sin Φ as four 3 3 3 3 unknowns (cos Φ and sin Φ are actually not independent but variables the mathematics is considerably simpler in th s way ) . Assume that we have used four different adjustments of the electronically adjustable element 4. We have in that case an equation system with four unknowns , which we may solve. = Eρ P P = K |b | i i i 4 4 i a | = Eσ P 3 i i b a I cos Φ = E x P P is the detected power, 3 3 i i i b a I s in Φ Y P 3 3 i i tions of A and B . These 4 " 4 need not to be known beforehand and we obtain the wanted quantity from The mathematics for transmission measurements will be similar. The system is calibrated for example by using a number of known impedances on the measuring port. A very simple way to realize the idea mentioned above is disclosed in the following (see figure 1 ) . The signal of the detector is composed according to The directional coupler 2 is assumed ideal and the detector 5 matched of reflections, which reduces the number of necessary measurements . = r + r = U K( 1 -K)a e m If a circle is drawn from the tip of the vector T with e radius U (the detector measures the value |U| , not the phase this circle will pass through the point of the vector - T * m P is known by calibration. Three measurements with different e r (Three circles intersect each other n one point) . Calibra- m tion can be carried out in the same way. f is than obtained e by using known values of T . m Unlike a conventional bridge this system does not require any adjustment for zero output. The output signal from a detector is measured for a number of different adjustments of the electronically adjustable element 4 and the wanted quantity is thereafter calculated. The output si nal is measured onl with respect to its magnitude and does not need to take on the value zero. Some phase measurement is accordingly not required . The costs of the system may be kept down owing to the fact that the phase maesurement is not required and that the electronically adjustable element 4 replaces in principle as many components as the number of adjustments. The accuracy of the measuring system s completely comparable to the best existing commercial systems. The time to execute a measurement is mainly limited by the speed of the frequency tuning of the signal unit 1 , the sweep oscillator which is the limiting factor also with other . systems. The manufacturing costs and the component costs of the system are low since "on line" -computer analysis will handle imperfections in the components included in the bridge. The invention is naturally not limited to the embodiments disclosed above but a number of alternative embodiments are possible within the scope of the claims.

Claims: AMENDED CLAIMS (received, by the International Bureau on 05 January 1984 (05.01.84)) 1. A method for measuring of value and. phase of the transmission and/or reflection coefficient of a measuring object (3) , e.g. a microwave component, c h a r a c t e r i z e d t h e r e b y, that a test signal is brought to reflect/transmit partly against/through the measuring object (3) and partly against/through an adjustable element (4) the present reflection and/or transmission coefficient of which is known, that the re lected/ ransmitted signals thereafter are combined and are measured/detected in a detector (5) , that the measurement is executed for a number of different values of the reflection and/or transmission coefficient of the adjustable element (4) and, that out of the different measurement results, obtained from the detector (5) , the reflection and/or transmission coefficient of the measuring object (3) is calculated. 2. An apparatus according to the method in claim 1 for measuring of value and phase of the reflection and/or transmission coefficient of a measuring object (3) , e.g. of a microwave component c h a r a c t e r i z e d t h e r e b y, that an adjustable element (4) is adapted to reflect a test signal transmitted from a signal unit (1 ) , that this is repeated for a number of different values of the adjustable element (4) , that a detector (5) is adapted to detect the reflected/transmitted signals from/through a measuring ob.ect (3) and the adjustable element (4) , and that a calculating unit (9) is adapted to handle the detected measurement results and from these determine the reflection and/or transmission coefficient of the measuring object (3) . 3. An apparatus according to claim 2, c h a r a c t e r i z e d t h e r e b y, that the signal unit (1 ) consists of a scanning oscillator. 4. An apparatus according to claim 1 or 2, c h a r a c t e r i z e d t h e r e y, that a directional coupler (2) is adapted to guide the test signal from the signal unit (1) to/from the measuring object (3) and the adjustable element (4) respectively. 5. An apparatus according to any of the claims 2 -4, c h a r a c t e r i z e d t h e r e b y, that the directional coupler (2) is of four-port type.

Inventors: HAGSTROEM CLAES, KOLLBERG ERIK, HAGSTROEM, CLAES, KOLLBERG, ERIK
Applicants: HAGSTROEM CLAES, KOLLBERG ERIK, HAGSTROEM, CLAES, KOLLBERG, ERIK
Application year: 1983
Main classification: G01R27
IPC codes: G01R27