Vectorial two- or multi-port network analyzer with only one receiver

Abstract

Vectorial network analyzer with n measurement ports, where n is at least two, for measuring an n-port measurement object (315;515), with a signal generator (200;300;400) for generating an excitation signal, wherein the signal generator (200;300;400) has a mixer (202) which converts the excitation signal from an intermediate frequency plane to a measurement frequency plane, wherein only a single measuring receiver (220;320;420) is available to receive the excitation signal or the measuring signal reflected or transmitted by the object being measured (315;515), wherein the measuring receiver (220;320;420) has a first mixer (221) which converts the excitation signal from a measurement frequency plane into a first intermediate frequency plane (f IF1 ) converted, wherein the mixer (202) of the signal generator (200;300;400) and the first mixer (221) of the measuring receiver (220;320;420) are connected to a common oscillator (230;330;430) and wherein a first switching device (317,319; 519) is provided which switches the measuring receiver (220;320;420) between the signal generator (200;300;400) and the n gates of the object being measured (215;315;515).

Description

[0001] Vector network analyzers (VNAs) are primarily used to measure scattering parameters in terms of magnitude and phase. These scattering parameters are defined as ratios of wave quantities under the boundary condition that all ports of the device under test are closed with their respective reference impedances.

[0002] Previously common concepts for network analyzers with 2 or n measuring ports feature two or more parallel vectorial measuring points for measuring the numerator and denominator waveforms of the scattering parameters. Fig. Figure 1 shows an example of a two-port VNA with three measuring points. The signal generated by the signal source 101 is split into a reference and a measuring branch in the signal divider 102. The reference signal is measured by the vector measuring point 103 with respect to its magnitude and phase. In the measuring branch, the signal can be selectively routed to either port 1 or port 2 of the device under test 105 via the switch 104 and the signal isolation circuits 106 and 107. The outputs of the signal isolation circuits 106 and 107, which are typically implemented as reflection coefficient measuring bridges or line couplers, are each connected to a further vector measuring point 108 or 109, respectively.

[0003] A similar concept, but with two signal sources, is known from DE 199 26 454 A1.

[0004] Simultaneous measurement of numerator and denominator wave quantities ensures that, in successive measurements of the same scattering parameter, any rotation of the absolute phase of the generator signal or any identical phase shift of the waves caused by a change in the sampling time cancels out. Likewise, any interim amplitude changes of the signal generator are eliminated.

[0005] However, each of the three vectorial measuring points 103, 108, 109, which are generally implemented as heterodyne superheterodyne receivers with a downstream A / D converter and subsequent digital signal processing stage, requires a high degree of circuit complexity. This is usually associated with high costs.

[0006] DE 102 33 618 A1 discloses a network analyzer using time sequence measurements.

[0007] The invention is therefore based on the objective of creating a vectorial network analyzer that requires less circuitry and can therefore be manufactured more cost-effectively.

[0008] The problem is solved by the features of claim 1. The dependent claims contain advantageous embodiments of the invention.

[0009] According to the invention, only a single measuring receiver is required, which significantly reduces the circuit complexity. A switching device ensures that the measuring receiver can be switched between the signal generator and the gates of the object being measured.

[0010] According to an advantageous further development, only a single signal generator is present, with a second switching device ensuring that the signal generator can be switched between the gates of the object being measured.

[0011] Different mixers of the signal generator and the measuring receiver can advantageously be connected to a common oscillator in order to synchronize the signal generator and the measuring receiver with each other in a phase-locked manner.

[0012] Another possibility is to access a common reference oscillator during frequency processing in the signal generator and the measuring receiver, which serves, for example, as a reference for a synthesizer operating according to the PLL principle (Phase Locked Loop).

[0013] Using suitable decoupling devices, such as isolation amplifiers, the signal generator and the measuring receiver can be decoupled from the switching devices. Further decoupling devices can then be used to decouple the switching devices from the object under test.

[0014] The invention is explained below with reference to exemplary embodiments and the drawing. The drawing shows: Fig. 1 a two-port VNA with 3 vectorial measuring points according to the state of the art; Fig. 2 a one-port VNA with only one vectorial measuring point; Fig. 3 a two-port VNA according to the invention with only one vectorial measuring point; Fig. 4 the positions of the signal path switches for measuring the 4 scattering parameters of a two-port measurement object and Fig. 5 an inventive n-port VNA with only one vectorial measuring point.

[0015] Fig. Figure 2 shows a preliminary consideration of the invention for a reflectometer, i.e., a one-port network analyzer. A reflectometer typically consists of a generator 200 for the measurement frequency, a signal isolation circuit (test set) 210 for connecting the object under test 105, and the vectorial measuring receiver 220, which is also referred to as the measuring point in this application.

[0016] The measurement signal generator 200 includes a fixed-frequency generator 201, followed by a mixer 202. One output of the mixer 202 is connected to the low-pass filter 203, while a second input of the mixer 202 is connected to a sweepable local oscillator 230.

[0017] Test set 210 includes a signal divider 211, the input of which is connected to the output of the measurement signal generator 200. One output of the signal divider 211 is connected to a decoupling device 213, the output of which is connected to a signal isolation circuit 214. The second output of the signal divider 211 is connected via a decoupling device 212 to the first input of a switching device 117. The device under test 215 is bidirectionally connected to the signal isolation circuit 214. One output of the signal isolation circuit 214 is connected to a further decoupling device 216, the output of which is connected to a second input of the switching device 214.

[0018] A first mixer 221 of the measuring receiver 220 is connected to the output of the switching device 217 and is also connected to the sweepable local oscillator 230. The output of the first mixer 221 is connected via an intermediate frequency filter 222 to an input of a second mixer 223, which receives an oscillator signal from a first oscillator 224 of the measuring receiver 220. The output of the second mixer 223 is connected via an analog-to-digital converter 225 to an input of a third, digital mixer 226, which in turn is connected to a digital numeric oscillator 227. The measurement signal M can be tapped at the output of the third mixer 226.

[0019] The oscillator 201 of the signal generator 200 and the two oscillators 224 and 227 of the measuring receiver 220 are connected to a common reference oscillator 240.

[0020] In the measurement signal generator 200, the fixed frequency generator 201 generates a signal whose frequency f F1 above the measurement frequency range of the VNA. Using the wobbleable local oscillator 230, whose frequency f LO1 equal to the sum of the desired measurement frequency f M and fixed frequency f IF1 This signal is then converted to the measurement frequency f in mixer 202. M downmixed. The low-pass filter 203 suppresses the signal also generated in mixer 202 at the sum frequency f. LO1 + f IF1 .

[0021] In test set 210, the signal divider 211 splits the generator signal into a reference component, which is essentially proportional to the wave a propagating towards the object 215 and which runs directly to the complex measuring point (measuring receiver) 220 via the decoupling device 212, for example an isolation amplifier, and the switch 217. For the purposes of this application, the decoupling devices are also referred to as isolators. This signal path is hereinafter referred to as the reference channel. The other component is fed to the object 215 via the isolator (decoupling device) 213 and the signal isolation circuit 214. A signal is present at the output of the circuit 214 that is essentially proportional to the wave b reflected by the object 215. This so-called measuring channel can also be acquired by the complex measuring point (measuring receiver) 220 via the isolator 216 and the switch 217.The isolators (decoupling devices) 212 and 216 prevent the position of switch 217 from affecting the source and load reflection factors of the measuring port. This allows for the assumption of a system error model independent of the switch position. In turn, this permits the use of the well-known 3-term (OSM) method for system error correction of the VNA. The isolators 212, 216, and the optional isolator 213 can be implemented, for example, as isolation amplifiers or directional lines.

[0022] The complex measuring point 220 is typically implemented as a superheterodyne receiver. However, other reception techniques that provide vector information are also conceivable. The number of mixer stages can also vary; in the illustrated embodiment, two stages are present. First, in the mixer 221, the swept reference or measurement signal is converted back to the fixed frequency f using the same local oscillator 230 that generated the measurement frequency in the signal generator. IF1 highly mixed. f IF1 This is the first intermediate frequency of the measuring receiver 220. A bandpass filter 222 eliminates interfering mixing products at other frequencies. For further processing, the signal must be sampled and digitized. The frequency f is usually... IF1 However, it is so high that this is not immediately possible. Therefore, the additional mixer stage 223 reduces the intermediate frequency to a lower f. IP2Implemented. After sampling and analog-to-digital conversion in the analog / digital converter 225, the sampled values ​​are mixed down to a time-independent result vector M in the multiplier 226 using the numerical oscillator 227.

[0023] For M to be truly independent of the sampling time, all fixed-frequency sources 201, 224, and 227 must be phase-locked to each other via a common reference oscillator 240 and continuously traversed without any phase change. The respective phase difference of sources 201, 224, and 227 relative to the reference oscillator 240 is irrelevant. It arises randomly each time the VNA is switched on. As long as the VNA remains switched on, successive measurements of the reference channel result vector M yield aThe phase remains constant at a given frequency. If the reflection coefficient of the object being measured (215) does not change, this also applies to the measurement channel result vector M. Consequently, the phase of the quotient is also constant. that is, the uncorrected raw value of the reflection factor, reproducible.

[0024] Switching the VNA off and on again results in different random phase relationships between the fixed frequency sources 201, 224 and 227, and thus also different phases of the raw individual waves. The phase difference compared to the first measurement is the same for both waves and therefore cancels out when calculating the quotient. It should be noted that the phase of the swept local oscillator 230 has no influence on the result vector, as it is eliminated by the down- and subsequent up-mixing in the converters 202 and 221. However, the amplitude and phase of the result vector M are subject to the thermal drift of the components in the signal path; this must be minimized through appropriate circuit design.

[0025] In the network analyzer according to the invention, the principle explained above is extended to the measurement of the scattering parameters of a measurement object 215 with two or more gates. Fig. Figure 3 shows an example of a VNA for two-port devices. The measurement signal generator 300 and the vector measurement receiver 320 are identical to circuits 200 and 220, respectively, from [reference missing]. Fig. 2.

[0026] The output of signal generator 300 is connected to the input of a signal divider 311, the first output of which is connected via a decoupling device 351 to a switching device 318. The other output of signal divider 311 is connected via a decoupling device 312 to the first input of a switching device 317. A first output of the switching device 318 is connected via a decoupling device 313 to a signal isolation circuit 314, which is bidirectionally connected to a first port of the device under test 315. An output of the signal isolation circuit 314 is connected via a decoupling device 316 to a first input of the signal isolation circuit 319. A second output of the switching device 318 is connected via a decoupling device 353 to a signal isolation circuit 354, which is bidirectionally connected to a second port of the device under test 355.An output of the signal isolation circuit 354 is connected via a decoupling device 356 to a second input of the switching device 319. The output of the switching device 319 is connected to a second input of the switching device 317, while the output of the switching device 317 is connected to the input of the measuring device 320. The signal generator 300 and the measuring device 320 are connected to both the common sweepable local oscillator 330 and the common reference oscillator 340.

[0027] In the two-port test set 310, signal divider 311 and switch 317 can also be adopted unchanged from the reflectometer test set 210. However, two additional signal path switches 318 and 319 are provided, one of which, namely 318, is located in the generator path and the other, namely 319, in the receiver path. A signal isolation circuit 314, 354 is provided at each of the two measuring ports.

[0028] The feedback effect of the signal path switches in the receiver path on the source and load reflection factors of the VNA measurement stores can be minimized by isolators (decoupling devices) 316 and 356 at the output of the signal isolation circuit. Similarly, isolators (decoupling devices) 312 and 351 serve to reduce interactions between the measurement and reference channels. This allows the system errors to be described using the well-known 10-term (TOSM) model. To further improve the decoupling of the measurement stores from the switches, isolators 313 and 353 can also be provided in the generator path. However, these are not strictly necessary for TOSM system error calibration, as the error model already provides independent terms for each feed direction of the device under test. With good decoupling of the generator switch 318 from the reference channel, the reference wave a only needs to be measured once per measurement point.It can then be used as the denominator for all quotients.

[0029] The Fig. Figures 4A to 4D show the positions of signal path switches 318 and 319 required to measure the 4 scattering parameters of a two-port network: Fig. 4A for measuring the reflection coefficient in the forward direction S 11 , Fig. 4B for measuring the transmission factor in the forward direction Fig. 4C for measuring the transmission factor in the reverse direction S 12 and Fig. 4D for measuring the reflection coefficient in the reverse direction S 22 .

[0030] The principle according to the invention can also be extended to the measurement of objects with any number n of gates. Fig. Figure 5 shows a corresponding measuring setup.

[0031] At the in Fig. In the embodiment shown in Figure 5, the signal generator 400 is connected via the signal divider 411 to the decoupling device 551, the output of which is connected to the switching device 518. Each output of the switching device 518 is connected via a decoupling device 513, 553, 560, or 561, respectively, to a signal isolation circuit 514, 554, 555, or 559, respectively, which is bidirectionally connected to a measuring port of the object being measured 515. The other output of each signal isolation circuit 514, 554, 555, or 559 is connected to an input of the switching device 519. Another input of the switching device 519 is connected via a further decoupling device 412 to the other output of the signal divider 411. The output of the switching device 519 is connected to the measuring receiver 420. As in the exemplary embodiment of the Fig. 3 A common wobbleable local oscillator 430 and a common reference oscillator 440 are connected to both the signal generator 400 and the measuring receiver 420.

[0032] Opposite Fig. In the 3rd stage, the 1-to-2 switches 318 and 319 are replaced by 1-to-n switches 518 and a 1-to-n+1 switch 519, and each of the n measuring stores has a signal isolation circuit 514 with two decoupling devices (isolation amplifiers), e.g., 513, 516 at store 1. Taking the reference channel measurement into account, there are a total of n 2 + 1 measurements are to be carried out consecutively. If switches 318 and 319 have no feedback effect, a model with n (3 + 2 (n - I)) terms can be used for system error correction, analogous to the 10-term error model of the two-port measurement.

Claims

[1] Vectorial network analyzer with n measurement ports, where n is at least two, for measuring an n-port measurement object (315;515), with a signal generator (200;300;400) for generating an excitation signal, wherein the signal generator (200;300;400) has a mixer (202) which converts the excitation signal from an intermediate frequency plane to a measurement frequency plane, wherein only a single measuring receiver (220;320;420) is available to receive the excitation signal or the measuring signal reflected or transmitted by the object being measured (315;515), wherein the measuring receiver (220;320;420) has a first mixer (221) which converts the excitation signal from a measurement frequency plane into a first intermediate frequency plane (f IF1 ) converted, wherein the mixer (202) of the signal generator (200;300;400) and the first mixer (221) of the measuring receiver (220;320;420) are connected to a common oscillator (230;330;430) and wherein a first switching device (317,319; 519) is provided which switches the measuring receiver (220;320;420) between the signal generator (200;300;400) and the n gates of the object being measured (215;315;515). [2] Vectorial network analyzer according to claim 1, characterized by , that there is only one signal generator (300;400) and that there is a second switching device (318; 518) which switches the signal generator (300;400) between the n gates of the object being measured (315;515). [3] Vectorial network analyzer according to claim 1 or 2, characterized by , that the measuring receiver (320;420) has a second mixer (223) which takes the excitation signal from the first intermediate frequency level (f IF1 ) into a second intermediate frequency plane (fIF2 ) is converted and connected to a first oscillator (224) of the measuring receiver (320;420) and that an oscillator (201) of the signal generator (200) and the first oscillator (224) of the measuring receiver (320;420) are phase-locked to a common reference oscillator (340;440). [4] Vectorial network analyzer according to claim 3, characterized by , that the measuring receiver (320;420) has a third mixer (226) which takes the excitation signal from the second intermediate frequency level (f IF2 ) is converted into a complex baseband plane and is connected to a second oscillator (227) of the measuring receiver (320;420) and that the oscillator (201) of the signal generator (200) and the second oscillator (227) of the measuring receiver (320;420) are phase-locked to the common reference oscillator (340;440). [5] Vectorial network analyzer according to claim 4, characterized by, that an analog / digital converter (225) is arranged between the second mixer (223) and the third mixer (226) of the measuring receiver (320;420), and that the third mixer (226) is a digital multiplier and the second oscillator (227) is a numerical oscillator. [6] Vectorial network analyzer according to any one of claims 1 to 5, characterized by , that the signal generator (300;400) is connected to the first switching device (317,319; 519) via a signal divider (311;411) and a decoupling device (312;412). [7] Vectorial network analyzer according to any one of claims 1 to 6, characterized by , that the first switching device (317,319; 519) is connected to the gates of the object being measured (315;515) via decoupling devices (316,356; 516,556,557,558) and signal isolating circuits (314,354; 514,554,555,559). [8] Vectorial network analyzer according to claim 2, characterized by, that the second switching device (318; 518) is connected to the gates of the object being measured (315; 515) via decoupling devices (313,353; 513,553,560,561) and signal isolation circuits (314,354; 514,554,555,559). [9] Vectorial network analyzer according to claim 2 or 8, characterized by , that the signal generator (300;400) is connected to the second switching device (318; 518) via a signal divider (311;411) and a decoupling device (351;551).

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