1. A method for determining an electric voltage u(t) and/or an electric current i(t) of a RF signal on an electric cable in a calibration plane that compensates for distortions based on input signal reflections, said method comprising:electrically connecting a time domain measuring device to a device under test, said time domain measuring device having measuring inputs which distort parameters to be measured as a result of input signal reflections;

connecting the device under test electrically with the calibration plane;

electrically connecting a directional coupler to the time domain measuring device;

decoupling a first component v3(t) of a first RF signal which, starting out from a signal input, runs in the direction of the calibration plane through the directional coupler feeding said first component into the time domain measuring device at a first measuring input and measured there;

decoupling a second component v4(t) of a second RF signal which, starting out from the calibration plane, runs in the direction of the signal input through the directional coupler;

feeding said second component into the time domain measuring device at a second measuring input and measured there;

transforming the signal components v3(t), v4(t), by a first mathematical operation, into the frequency domain as wave quantities V3(f) and V4;

determining absolute wave quantities a2 and b2 in the frequency domain in the calibration plane from the wave quantities V3(f) and V4(f) using calibration parameters (e00,r, e01,r, e10,r, e11,r);

converting absolute wave quantities a2 and b2, by a second mathematical operation, into the electric voltage u(t) and/or the electric current i(t) of the RF signal in the time domain in the calibration plane;

wherein the calibration parameters link the wave quantities V3(f) and V4(f) mathematically with the absolute wave quantities a2 and b2 in the calibration plane,

wherein the first measuring input of the time domain measuring device has a reflection coefficient ?3?0 and/or the second measuring input of the time domain measuring device has a reflection coefficient ?4?0,

determining the calibration parameters (e00,r, e01,r, e10,r, e11,r are determined, with the aid of a calibration device, in relation to the frequency f and in relation to a reflection coefficient of at least one of the measuring inputs of the time domain measuring device; and

determining the wave quantities a2 and b2 in the measuring step from the wave quantities V3(f) and V4(f) using the calibration parameters (e00,r(?3, ?4), e01,r(?3, ?4), e10,r(?3, ?4), e11,r(?3, ?4));

connecting the signal input of the directional coupler during the calibration step with a first measuring port S1;

connecting the first measuring output of the directional coupler with a second measuring port S3;

connecting the second measuring output of the directional coupler with a third measuring port S4 of the calibration device; and

connecting one or more measuring standards with known reflection coefficients to a signal output of the directional coupler connected with the calibration plane S2;

wherein the calibration parameters (e00,r, e01,r, e10,r, e11,r) link the wave quantity b3 running in at the second measuring port S3 and the wave quantity b4 running in at the third measuring port S4 with the wave quantities b2, a2 running in and out in the calibration plane (14, S2) as follows:

wherein the scattering parameters Sxy (x=1-4, y=1-4) of the scattering matrix S of the four-port with the ports S1, S2, S3, S4, in particular of the directional coupler together with input cables, are determined with the aid of the calibration apparatus, wherein the calibration parameters e00,r, e01,r, e10,r, e11,r in relation to the reflection coefficients of the time domain measuring device ?3 ?4 are determined from the scattering parameters Sxy, wherein the calibration parameters are determined from the scattering parameters as follows:wherein the scattering parameters Sxy are determined through measurement of the values b1/a1, b3/a3, b4/a4, b3/a1 or b1/a3, b4/a1 or b1/a4, b4/a3 or b3/a4 at the measuring ports S1, S3, S4 of the calibration device, wherein in each case preferably the measuring standards Match (M), Open (O), Short (S) with the known reflection coefficients ?M, ?O, ?S are connected as devices under test in the calibration plane S2, where a1, a3, a4 are wave quantities running in at the respective measuring ports S1, S3, S4 and b1, b3, b4 are wave quantities running out at the respective measuring ports S1, S3, S4, and wherein the scattering parameters Sxy are determined by means of the following equations:where:?DUT is the known reflection coefficient of the calibration standard used during the measurement:

are the bx/ay measurable at the measuring ports S1, S3, S4; and

where ?O, ?S, ?M are known reflection coefficients of the calibration standards Open (O), Short (S) and Match (M), and are the bx/ay measurable at the measuring ports with connected calibration standard K.