Four-port network analyzer and method for measuring four-port network parameters

Abstract

The invention relates to a four-port network analyzer (2) for measuring four-port network parameters, the analyzer (2) comprising: a first subsystem (4), wherein the first subsystem (4) is connected to a first port (P1) and a second port (P2); a second subsystem (6), wherein the second subsystem (6) is connected to a third port (P3) and a fourth port (P4); at least one signal source (8) and at least one receiver (10), wherein the signal source (8) and the receiver (10) each are connected and / or connectable to both subsystems (4, 6); a cross-connection switch (16), wherein the cross-connection switch (16) is configured to form a cross-connection between the first subsystem (4) and the second subsystem (6).

Description

[0001] Four-port Network Analyzer and Method for Measuring Four-port Network

[0002] Parameters

[0003] Description

[0004] The invention relates to a four-port network analyzer for measuring four-port network parameters and to a method for measuring four-port network parameters.

[0005] Four-port bench network analyzers usually comprises at least one signal source and four receivers. For example, a common network analyzer comprises two signal sources and two receivers, all independent to each other. In other words, two two-port network analyzers are combined. By combining these analyzers it is possible to measure four-port network parameters, as S-parameters, despite the lack of two remaining receivers.

[0006] However, such a configuration is complicated and the phase relation between the two receivers is not locked and not known as these are two independent systems. So, all terms of one measurement need to be captured by one single receiver.

[0007] It is therefore an object of the present invention to provide an improved and much more convenient network analyser, as well as a method for measuring four- port network parameters. The problem is solved by a four-port network analyzer according to claim 1. Furthermore, the problem is solved by a method measuring four-port network parameters according to claim 14.

[0008] In detail, within the four-port network analyzer for measuring four-port network parameters, the analyzer comprises a first subsystem, wherein the first subsystem is connected to a first port and a second port. Moreover, the network analyzer comprises a second subsystem, wherein the second subsystem is connected to a third port and a fourth port and the network analyzer comprises at least one signal source and at least one receiver, wherein the signal source and the receiver each are each independently connected and / or connectable to both subsystems.

[0009] Furthermore, the network analyzer comprises a cross-connection switch, wherein the cross-connection switch is configured to form and / or allow a cross-connection between the first subsystem and the second subsystem.

[0010] With the above-mentioned network analyser, and especially with the cross- connection switch, it is possible to measure network parameters, in particular S- parameters at four ports of a respective device under test (DUT). That means that it is possible to measure all necessary incident and reflected wave powers to gather four port S-parameters of the DUT.

[0011] In other words, the four-port network analyzer according to the invention enables a user to perform these measurements with two combined subsystems each containing a signal source and a receiver and describes the respectively necessary hardware structure and post processing methodology. In other words, with the described system, it is possible to only use one receiver and one signal source to cover the four port measurement, namely to measure a device under test which comprises up to four ports as described in more detail below. With the known setups according to the prior art, at least two subsystems each comprising a receiver and a signal source are required because none of the systems comprises more than 2 ports. The cross-connection switch makes it possible to achieve the above-mentioned advantages by combining the two subsystems. In an embodiment the analyzer may further comprise at least one RF coupler. Further, in a first setup, one RF coupler is connected to each one of the ports. This configuration - in relation to the RF coupler - is also called "frontend setup".

[0012] In an alternative embodiment, the so called "backend setup", the at least one RF coupler is connected to a signal line of the signal source. With these two RF coupler setups, it is possible to adapt the network analyzer to various DUTs or configurations.

[0013] According to an embodiment, the cross-connection switch comprises Single Pole Double Throw (SPDT) switches and RF power dividers for selecting one of the ports. That means that the signal of the signal source can be switched to a desired one of the subsystems by switching and controlling the SPDT switches. To realize such a configuration, an input of the SPDT switch is connected to the receiver and an output of the SPDT switch is connected to the RF power dividers. To receive the selected incident and reflected signals, the analyzer may further comprise Single Port Multi Throw (SPMT) switches, which lead the signals to the receiver.

[0014] Furthermore, a first SPMT switch is part of the first subsystem and wherein a second SPMT switch is part of the second subsystem. To provide a four-port network analyzer, the SPMT switches are configured as SP3T or SP4T switches.

[0015] In a further embodiment, the cross-connection switch comprises Single Pole Multi Throw (SPMT) switches and RF power dividers for selecting one of the ports. This embodiment is mainly associated with the "backend setup". Moreover, an input of the SPMT switches is connected to the receiver and an output of the SPMT switches is connected to the RF coupler.

[0016] In one embodiment, each subsystem comprises a signal source and a receiver.

[0017] In a further embodiment, the at least one signal source comprises an amplifier to improve the generated signal. In order to measure vector S-Parameters (magnitude and phase), it is necessary to either have a phase-coupled signal source and receiver or to keep a stable or known phase relation between the measurements of a (incident), b (reflected) and transmitted. The latter can be provided by capturing all terms in one single capture while keeping the signal source turned on. Therefore, the at least one signal source is configured to generate and provide such a signal.

[0018] Furthermore a method is disclosed for measuring incident and transmitted wave powers to gather four-port S-Parameters by using an analyzer as described above.

[0019] The advantages and preferred embodiments listed with regard to the analyzer are to be applied mutatis mutandis to the method and vice versa.

[0020] The above and further features and advantages of the invention will become more readily apparent from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings, in which like reference signs designate like features, and in which:

[0021] Fig. 1 shows two prior art two-port network analyzers;

[0022] Fig. 2 shows a four-port network analyzer according to a first embodiment of the invention;

[0023] Fig. 3 shows a four-port network analyzer according to a second embodiment of the invention;

[0024] Fig. 4 shows a four-port network analyzer according to a third embodiment of the invention; and

[0025] Fig. 5 shows a diagram of the amplitude of a signal according to the scheme of operation of the four-port network analyzer.

[0026] Fig. 1 shows two prior art two-port network analyzer 2 ("analyzer" in the following). The first prior art analyzer 2 comprise a first subsystem 4 and the second prior art analyzer 2 comprises a second subsystem 6. The first subsystem 4 is connected to a first port Pl and to a second port P2, wherein the second subsystem 6 is connected to a third port P3 and a fourth port P4.

[0027] Each subsystem 4, 6 comprises a signal source 8 to generate a test signal and a receiver 10 to receive the necessary measurement signals.

[0028] The analyzer 2 further comprises two switching devices 12, one switching device 12 for each subsystem 4, 6. Each signal source 8 is connected to an input of one of the switches of the respective switching device 12. Therefore, the switching devices 12 are configured to allow the user or control system to provide the ports P1-P4 with the generated signal, or test signal, of the signal source 8. For example, the generated signal of the signal source 8 of the first subsystem 4 is provided either to port Pl or to port P2 via the switching device 12 of the first subsystem 4. Accordingly, the generated signal of the signal source 8 of the second subsystem 6 is provided either to port P3 or to port P4 via the switching device 12 of the second subsystem 6. To allow such a configuration, each switching device 12 of each subsystem 4, 6 comprises a plurality of switches which are connected to each other to lead the generated signal to the respective port P1-P4.

[0029] In addition, each receiver 10 is connected to an output of the respective switching device 12. For example, the switching device 12 of the first subsystem 4 provides the test signal to the first port Pl or the second port P2. The switching device 12 of the second subsystem 6 provides the test signal to the third port P3 or the fourth port P4. The switching devices 12 are also configured to select the incident and reflected signals. An incident wave signal or power is a current or voltage wave that travels through a transmission line from the generating source towards the load. It becomes incident when it arrives at a discontinuity or another medium with different propagation characteristics. At this point, some or all of the wave will be reflected back in the opposite direction to the original, the so -called reflected wave (power). Reflections will also occur at the end of the transmission line unless it is correctly terminated with its characteristic impedance. Moreover, the analyzers 2 comprise two RF couplers 14 per subsystem 4, 6. In general, RF couplers 14 couple a defined amount of the electromagnetic power in a transmission line to a port (here: the receiver 10) enabling the signal to be used in another circuit. An essential feature of the couplers 14 is that they only couple power flowing in one direction. In the present case, the incident and reflected power waves can be measured with the help of the couplers 14. Each RF coupler 14 is connected between a port P1-P4 and the switching device 12 of each subsystem 4, 6. Therefore, this embodiment is also called a "frontend setup".

[0030] As can be taken from Fig. 1 the two subsystems 4, 6 are independent from each other. That means that phase relation between the two receivers 10 is not locked and not known. That means that the phase relation of both subsystems 4, 6 needs to be collected and provided to a further circuit for a further processing, if the signals in each of the two subsystems 4, 6 are to be meaningfully compared with each other or a known reference signal. This is done e.g. by multiple measurement channels which are connected to each other. In other words, there is a need for a further device that receives the phase relation of the first subsystem 4 and the second subsystem 6, which makes the whole system more complicated.

[0031] This disadvantage is the basis for the analyzer 2 according to a first embodiment of the invention as shown in Fig. 2. The analyzer 2 according to Fig. 2 differs from the prior art analyzer of Fig. 1 in the cross-connection switch 16, which is configured to form a cross-connection between the first subsystem 4 and the second subsystem 6. To form this cross-connection the cross-connection switch 16 comprises two Single Pole Double Throw (SPDT) switches 18, one SPDT switch 18 per subsystem 4, 6. In addition, the cross-connection switch 16 comprises two RF power dividers 20, one RF power divider 20 per subsystem 4, 6. Alternatively, the RF power dividers 20 could be replaced by switches. An input of the SPDT switch 18 is connected to the receiver 10 and an output of the SPDT switch is connected to the RF power dividers 20. The switching device 12 comprises Single Pole Multi Throw (SPMT) switches 22. The cross-connection switch 16 enables a measurement of the incident and reflected wave powers by using fewer components. For example, the measurement of the reflected wave power between a device under test, which is connected between ports Pl and P3 is as follows (for a device under test which is connected between the other ports, the measurement and connection pattern applies accordingly):

[0032] As a general remark, it should be noted that for clarity the signal trace is not shown in the figures but can be understood as described in the following. The stimulus signal is provided to port Pl via the respective SPMT switches 22 of the switching device 12 of the first subsystem 4. The incident wave as well as the reflected wave will then be provided from port Pl via the respective SPMT switches 22 of the switching device 12 of the first subsystem 4 to the receiver 10. A transmitted signal, which will be transmitted from port P3 to the receiver 8 will also be taken into account for the measurements. As port P3 is part of the second subsystem 6, which is independent from the first subsystem 4 in the prior art devices, the cross-connection switch 16 plays a special role. In general, the transmitted signal is the signal, which goes back from the device under test - which is connected between the two ports Pl and P3 in the present example - to the receiver 8. This signal is based and effected by the stimulus signal and the device-specific properties of the device under test. The transmitted signal will be transferred from port P3 through the RF coupler 14 to the SPMT switch 22 of the switching device 12 of the second subsystem 6. This switching device 12 and especially the SPMT switch 22 leads the transmitted signal to the RF power divider 20 of the "second subsystem 6"-side of the cross-connection switch 16. Then, the transmitted signal will be led to and via the SPDT switch 18 of the "first subsystem 4"-side of the cross-connection switch 16 to the receiver 10 of the first subsystem 4.

[0033] Therefore, the cross-connection switch 16 makes it possible to receive all necessary signals with the receiver 10 of the first subsystem 4. In contrast to prior art devices and systems two receivers 10 were necessary to receive signals from independent subsystems, this is no longer the case. The same applies to the signal source 8. With the above-mentioned inventive setup it is possible to provide the signals from the signal source 8 of the first subsystem 4 or the second subsystem 6. In addition to that, each receiver 10, either the one of the first subsystem 4 or the one of the second subsystem 6, can be used to receive the respective signals. This is an advantage over the prior art systems as fewer components can be used and / or the system can be adapted in a better manner to the required properties.

[0034] Fig. 3 shows the analyzer 2 according to a second - alternative - embodiment. In general, this embodiment is similar to the embodiment as shown in Fig. 2. However, the configuration of the cross-connection switch 16 is different.

[0035] According to this embodiment, the cross-connection switch 16 comprises SPMT switches 22 and RF power dividers 20. In contrast, the switching device 12 comprises SPDT switches 18. In other words, the type of switches has changed compared to the embodiment according to Fig. 2. Thereby, the output of the signal source 8 of each subsystem 4, 6 is connected to a RF coupler 14, wherein the input of the receiver 10 of each subsystem 4, 6 is connected to an output of a respective SPMT switch 22 of the cross-connection switch 16. For example, with this configuration it is possible to connect the receiver 10 of the first subsystem 4 via the SPMT switch 22 of the cross-connection switch 16 of the first subsystem 4 further via the RF power divider 20 and the switching device 12 of the second subsystem 6 to either port P3 or P4. Accordingly, it is possible to connect the receiver 10 of the second subsystem 6 to either port Pl or P2.

[0036] In addition, the analyzer 2 according to Fig. 3 only comprises two RF couplers 14, which are connected to a signal line 24 between the respective signal source 8 and the respective switching device 12 of each subsystem 4, 6.

[0037] The third embodiment according to Fig. 4 is based on the embodiment according to Fig. 2. The difference is that the third embodiment only comprises one signal source 8 and one receiver 10 for both subsystems 4, 6 and therefore for all four ports P1-P4. That means that the one signal source 8 can be connected over a switch (switch next to the signal source 8) to either the first subsystem 4 or the second subsystem 6. In more detail, the signal source 8 can be connected to either the switching device 12 of the first subsystem 4 or the switching device 12 of the second subsystem 6. The SPMT switches 22 of each switching device 12 then connects the signal source 8 to one of the ports P1-P4. Vice versa, the receiver 10 can be connected to the ports P1-P4 accordingly via the switching devices 12 to receive the necessary signals, e.g. the reflected signal.

[0038] Fig. 5 shows a diagram of the amplitude of the received signal during one operation mode of the analyzer 2 for a four port device under test. In order to measure all vector S-Parameters (magnitude and phase), it is necessary to either have a phase-coupled signal source and receiver or to keep a stable or known phase relation between the measurements of a (incident), b (reflected) and transmitted. The latter, namely the phase-coupling, can be provided by capturing all terms in one single capture while keeping the signal source turned on and controlling the switching of connections between the source 8, required probe Pl - P4 and receiver 10, the result of this time capture being shown in Fig. 5.

[0039] To us the above circuitry to perform measurements is described in the following. As a preliminary remark, the signal source 8 should ideally, or indeed will be, kept turned on during the whole measuring process, e.g. during the whole capture. If not, namely if the signal source 8 were to be turned off during the capture, the phase relation gets lost which makes calculation of parameters difficult if not impossible. Maintaining the phase relation is, therefore, of significant benefit in the operation of the system.

[0040] By keeping the signal source 8 turned on and in this time performing frame the shifting of the switches 18, 22 the different connections described above can be obtained. The measurements which are made are the measurement of the three waveforms: incident waveform, reflected waveform and transmitted waveform. The order in which the measurements are taken, meaning which waveform is measured first, second and third, does not matter. For example it is possible to measure the incident waveform first, the reflected waveform second and the transmitted waveform third. What is important is to know which waveforms were measured during each section and, ideally, that the signal source 8 is kept on. This means that the capture over a period of time will relate to each of the different switch combinations desired to generate the respective measurements, the relevant measurements will then be temporally separated in the final capture information.

[0041] While providing a signal from the signal source 8 and performing the relevant switching operations to allow different measurements to be made, the aforementioned waveforms will be measured based on this applied signal. Once the complete sample has been taken, with the measurements taken in the aforementioned and chosen order, the resultant capture can be cut into three temporally separated parts, and the intermediate sections of the trace ignored or the samples containing the switching period actively scrapped. The resulting captures will then provide the desired measurements upon which further signal processing can be performed to obtain data about the DUT.

[0042] In detail, and by way of example, it would be possible and even desirable to keep the exact number of samples taken for each of the measurements of the respective waveforms the same. The phase relation between the three parts would then be stable, e.g. samples 1 to 100 could be for the incident waveform, samples 120 to 220 could be for the reflected waveform and samples 240 to 340 could be for the transmitted waveform.

[0043] After obtaining the samples, removing from the entire trace the measurements which relate to the switching periods and then recording each of the waveforms, these parts can be analyzed with a Fast Fourier Transform (FFT) to receive a complex number for the parts. From this, the reflected Sil and transmitted S21 S-Parameters can be calculated in a straightforward manner. As highlighted, this is provides as straightforward method of obtaining all of the relevant data, without concerns of mismatched phase relationships, in a single capture and then calculating the desired S-parameters from the relevant sections of the trace.

[0044] That means in other words, that by keeping the signal source turned on, e.g. the incident wave power can be measured first by setting the respective captures. Then measuring the reflected wave power after a switching period to other respective captures. Therefore, there is no need for shutting the signal source down or complex adjustments to the signal source. As already mentioned the inventive system allows the measurement of full vector scattering parameters of devices that have up to four ports, e.g. amplifiers, power dividers, circulators, couplers and / or switches.

[0045] List of reference numerals

[0046] 2 four-port network analyzer

[0047] 4 first subsystem

[0048] 6 second subsystem

[0049] 8 signal source

[0050] 10 receiver

[0051] 12 switching device

[0052] 14 RF coupler

[0053] 16 cross-connection switch

[0054] 18 Single Pole Double Throw (SPDT) switch

[0055] 20 RF power divider

[0056] 22 Single Pole Multi Throw (SPMT) switch

[0057] 24 signal line

[0058] Pl first port

[0059] P2 second port

[0060] P3 third port

[0061] P4 fourth port

Claims

Four-port Network Analyzer and Method for Measuring Four-port Network ParametersClaims1. A four-port network analyzer (2) for measuring four-port network parameters, the analyzer (2) comprising: a first subsystem (4), wherein the first subsystem (4) is connected to a first port (Pl) and a second port (P2); a second subsystem (6), wherein the second subsystem (6) is connected to a third port (P3) and a fourth port (P4); at least one signal source (8) and at least one receiver (10), wherein the signal source (8) and the receiver (10) each are connected and / or connectable to both subsystems (4, 6); a cross-connection switch (16), wherein the cross-connection switch (16) is configured to form a cross-connection between the first subsystem (4) and the second subsystem (6).

2. Analyzer (2) according to claim 1, wherein the analyzer (2) further comprises at least one RF coupler (14).

3. Analyzer (2) according to claim 2, wherein one RF coupler (14) is connected to each one of the ports (P1-P4).

4. Analyzer (2) according to either claim 2 or claim 3, wherein the at least one RF coupler (14) is connected to a respective signal line (24) of the respective signal source (8) of the subsystems (4, 6).

5. Analyzer (2) according to one of claims 1 to 3, wherein the cross- connection switch (16) comprises Single Pole Double Throw (SPDT)switches (18) and RF power dividers (20) for selecting one of the ports (P1-P4).

6. Analyzer (2) according to one of claims 1 to 4, wherein the cross- connection switch (16) comprises Single Pole Multi Throw (SPMT) switches (22) and RF power dividers (20) for selecting one of the ports (P1-P4).

7. Analyzer (2) according to claim 5, wherein an input of the SPDT switch (18) is connected to the receiver (10) and an output of the SPDT switch (18) is connected to each of the RF power dividers (20).

8. Analyzer (2) according to claim 6, wherein an input of the SPMT switches (22) is connected to the receiver (10) and an output of the SPMT switches (22) is connected to the RF coupler (14).

9. Analyzer (2) according to claim 5, wherein the analyzer (2) further comprises Single Port Multi Throw (SPMT) switches (22) for selecting the incident and reflected signals.

10. Analyzer (2) according to claim 9, wherein a first SPMT switch (22) is part of the first subsystem (4) and wherein a second SPMT switch (22) is part of the second subsystem (6).

11. Analyzer (2) according to one of claims 1 to 10, wherein the network parameters are at least one of incident, transmitted and reflected wave powers.

12. Analyzer (2) according to one of claims 1 to 11, wherein each subsystem (4, 6) comprises a signal source (8) and a receiver (10).

13. Analyzer (2) according to one of claims 1 to 12, wherein the at least one signal source (8) comprises an amplifier.

14. Method for measuring at least one of incident, transmitted and reflected wave powers to gather four-port S-Parameters by using an analyzer (2) according to one of claims 1 to 13.

15. Method according to claim 14, further comprising the step: keeping the signal source turned on during the complete measurement process, in particular while recording a signal to be analyzed.

16. Method according to claim 14 or 15, further comprising the step: measuring the incident waveform, the transmitted waveform and reflected waveform based on the recorded signal by cutting the recorded signal into three parts while scrapping the samples containing the switching period of the switches (18, 22), in particular whilst keeping the phase relation between the three parts stable.

17. Method according to one of claims 14 to 16, further comprising the step: analyzing the measured incident waveform, reflected waveform and transmitted waveform with a Fast Fourier Transform to receive a complex value of each the incident waveform, the reflected waveform and the transmitted waveform; and calculating the reflected and transmitted S-Parameters based on the complex value of each the incident waveform, the reflected waveform and the transmitted waveform.

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