36, and the third calibration standard 38 may correspond to “open” (“O”), “short” (“S”), and “matched” (“M”) calibration standards, respectively. However, it is to be understood that the set of calibration standards may comprise other suitable types of calibration standards.

Moreover, an additional calibration standard 40 (“A”) is provided within the housing 30 in the example embodiment shown in FIG. 1. In general, the additional calibration standard 40 is a signal source with known properties or a signal sink with known properties. For example, the additional calibration standard 40 may be established as a signal generator, a comb generator, or an analog-to-digital converter.

In the example embodiment shown in FIG. 1, the calibration device 28 further comprises a switching circuit 42 that is connected to the connecting port 32 as well as to the calibration standards 34, 36, 38, 40. The switching circuit 42 is configured to selectively connect one of the calibration standards 34, 36, 38 or the additional calibration standard 40 to the connecting port 32.

FIG. 2 shows another embodiment of the calibration system 10, wherein only the differences to the system of FIG. 1 described above are explained hereinafter.

As shown in FIG. 2, the additional calibration standard 40 is provided separately from the calibration device 28. For example, the additional calibration standard 40 may be established as a signal generator, a comb generator, an oscilloscope, or an analog-to-digital converter.

In this embodiment, the calibration device 28 comprises another connecting port 44 that is connected to the switching circuit 42. The connecting port 44 is connectable to the additional calibration standard 40, such that the additional calibration standard can be connected to the connecting port 32 via the switching circuit 42 and the further connecting port 44. The switching circuit 42 is configured to selectively connect one of the calibration standards 34, 36, 38 or the further connecting port 44 to the connecting port 32.

It is noted that the calibration device 28 according to any of the embodiments described above is optional. It is also possible to connect the individual calibration standards 34, 36, 38 and/or the additional calibration standard 40 to the test instrument 12 directly, i.e. directly via a cable.

In an embodiment, the test instrument 12 may comprise more than one signal generator circuit, and/or more than one signal analysis circuit, and/or another number of ports.

In any case, each port is connected to at least one signal generator circuit, for example to exactly one signal generator circuit, and to at least one signal analysis circuit, for example to exactly one signal analysis circuit.

Hereinafter, a calibration method of calibrating the test instrument 12 is described with reference to FIG. 3.

The test instrument 12 described above is provided (step S1). Optionally, the calibration device 28 described above is provided (step S2). Hereinafter, it is assumed without restriction of generality that the calibration device 28 is provided. However, it is to be understood that the steps described hereinafter can also be performed without the calibration device 28 with appropriate adjustments.

The calibration standards 34, 36, 38 of the set of calibration standards are consecutively connected to the first port 14 of the test instrument, and a respective calibration measurement is performed by the signal generator circuit 18 and the signal analysis circuit 20 for each of the calibration standards 34, 36, 38 (step S3).

In an embodiment, a first calibration measurement is conducted with the first calibration standard 34 being connected to the first port 14. Afterwards, a second calibration measurement is conducted with the second calibration standard 36 being connected to the first port 14. Finally, a third calibration measurement is conducted with the third calibration standard 38 being connected to the first port 14.

In an embodiment, the calibration measurements conducted may be reflection measurements, i.e. a test signal is generated by the signal generator circuit 18 and forwarded to the respective calibration standard 34, 36, 38 via the first port 14, the connecting port 32, and the switching circuit 42. A signal reflected by the respective calibration standard 34, 36, 38 is forwarded to the signal analysis circuit 20 via the switching circuit 42, the connecting port 32, the first port 14, and the first directional coupler 22.

The signal analysis circuit 20 analyzes the respective reflected signals, thereby obtaining a first set of measurement data. In an embodiment, the first set of measurement data comprises measurement data on each of the calibration standards 34, 36, 38.

It is noted that starting the calibration of the test instrument 12 with the first port 14 is not necessary. Likewise, the calibration could first be performed on the second port 16 or on other ports of the test instrument 12.

A plurality of error terms of a multi-port error model are determined based on the multi-port error model and based on the first set of measurement data by the signal analysis circuit 20 (step S4).

In general, the error terms of the multi-port error model describe transmissivity and reflectivity properties of at least the respective port, i.e. of the first port 14 in the case described above. For example, the multi-port error model comprises error terms describing the transmissivity and reflectivity properties, wherein the error terms comprise one or more error parameters each.

FIG. 4 shows an example embodiment of a multi-port error model. In the embodiment of FIG. 4, the multi-port error model is a 2-port error model with four error parameters e₀₀, e₁₀, e₀₁, and e₁₁. However, it is to be understood that any other suitable multi-port error model may be used. In an embodiment, the multi-port error model may be any suitable n-term error model comprising n error parameters.

The error model of FIG. 4 describes a portion of the calibration system 10 between the signal generator circuit 18 and a reference plane 46. As is illustrated in FIG. 4, the reference plane 46 is located at the point where a device under test (DUT) 48 is to be connected to the first port 14.

During the calibration, the calibration device 28 is connected to the first port 14 at the reference plane 46. Thus, the reference plane 46 may be at an end of a cable connecting the first port 14 and the calibration device 28, namely at the end of the cable facing away from the first port 14.

The four error parameters e₀₀, e₁₀, e₀₁, and e₁₁describe a transmission between the signal generator circuit 18 and the signal analysis circuit 20, a transmission between the signal generator circuit 18 and the reference plane 46, a transmission between the reference plane 46 and the signal analysis circuit 20, and a reflection at the reference plane 46, respectively.

The multi-port error model can be expressed as a matrix

E
1

=

(

e
00

e
01

e
10

e
11

)

.

In this example, the error terms e₀₀, e₁₁, and e₀₁·e₁₀can be determined based on the first set of measurement data, i.e. one of the determined error terms comprises a product of two error parameters that cannot be determined individually based on the first set of measurement data.

In an embodiment, the additional calibration standard 40 is connected to the first port 14, and an additional calibration measurement is performed with the additional calibration standard 40 connected to the first port 14 by the signal generator circuit 18 and the signal analysis circuit 20, thereby obtaining a second set of measurement data (step S5).

In an embodiment, a mismatch of the additional calibration standard 40 may be corrected based on the first set of measurement data for determining the second set of measurement data. For example, an impedance mismatch between the additional calibration standard 40 and the reference plane 46 may be corrected based on the first set of measurement data for determining the second set of measurement data.

The error parameters comprised in the product of error parameters are determined based on the second set of measurement data by the signal analysis circuit 20 (step S6). For example, one of the two error parameters comprised in the product of error parameters is determined directly based on the second set of measurement data, i.e. one of the two error parameters is measured directly.

The other one of the two error parameters can then be calculated based on the determined product and based on the measured error parameter of the product.

In the example multi-port error model described above, if the additional calibration standard is a signal source, the error parameter e₀₁can be measured directly, and the error parameter e₁₀can then be calculated.

If the additional calibration standard is a signal sink, the error parameter e₁₀can be measured directly, and the error parameter e₀₁can then be calculated.

Thus, all error parameters of the multi-port error model are determined based on measurements performed with respect to the first port 14 only.

Operational parameters of the test instrument 12, for example of the signal generator circuit 18 and/or of the signal analysis circuit 20, are adapted based on the determined error parameters by the control circuit 26 (step S7).

Accordingly, the test instrument 12 is calibrated with respect to the first port 14 based on the determined error parameters.

In an embodiment, the calibration may be performed in time domain or in frequency domain.

Steps S3 to S7 described above are then repeated for the second port 16 (step S8).

The multi-port error model for calibrating the second port 16 is shown in FIG. 5, and is established similarly to the multi-port error model for calibrating the first port 14 described above.

The four error parameters e₀₀, e₁₀, e₀₁, and e₁₁describe a transmission between the signal generator circuit 18 and the signal analysis circuit 20, a transmission between the reference plane 46 and the signal analysis circuit 20, a transmission between the signal generator circuit 18 and the reference plane 46, and a reflection at the reference plane 46, respectively.

The multi-port error model can be expressed as a matrix

E
2

=

(

e
00

e
01

e
10

e
11

)

.

If the test instrument 12 comprises further ports, the further ports can be calibrated consecutively, i.e. one port may be fully calibrated at a time.

Thus, the calibration method described above enables a full calibration of all ports of the test instrument 12, wherein each port can be calibrated independent of any other ports.

Certain embodiments disclosed herein include systems, apparatus, modules, units, devices, components, etc., that utilize circuitry (e.g., one or more circuits) in order to implement standards, protocols, methodologies or technologies disclosed herein, operably couple two or more components, generate information, process information, analyze information, generate signals, encode/decode signals, convert signals, transmit and/or receive signals, control other devices, etc. Circuitry of any type can be used. It will be appreciated that the term “information” can be use synonymously with the term “signals” in this paragraph. It will be further appreciated that the terms “circuitry,” “circuit,” “one or more circuits,” etc., can be used synonymously herein.

In an embodiment, circuitry includes, among other things, one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a system on a chip (SoC), or the like, or any combinations thereof, and can include discrete digital or analog circuit elements or electronics, or combinations thereof. In an embodiment, circuitry includes hardware circuit implementations (e.g., implementations in analog circuitry, implementations in digital circuitry, and the like, and combinations thereof).