Anti-skewing impedance tuner calibration

1. An anti-skewing calibration method for slide screw impedance tuners at a frequency F comprising:

a scaling procedure,

a calibration procedure, and

an interpolation routine,

wherein,

the slide screw impedance tuners comprise:

a slabline having a horizontal center conductor linking a test port and an idle port, and at least one reflective tuning probe, remotely movable horizontally along the slabline and insertable vertically into the slabline between two extreme positions, a first extreme position corresponding to complete withdrawal from the slabline (vertical position Y=0) and a second extreme position closest to and immediately before mechanical contact with the center conductor (vertical position Y=YMAX),

and wherein

the scaling procedure comprises the following steps:

a) connect the tuner to a pre-calibrated vector network analyzer,

b) withdraw the reflective tuning probe from the slabline and place it at a distance X 0 smaller than half a wavelength (λ/2) at the frequency F from the test port, along the slabline,

c) in a positioning-measuring loop:

c1) gradually inserting the reflective tuning probe into the slabline to a multitude of vertical penetration positions Y and measuring a reflection factor amplitude |S 11 (Y)| and phase Φ 11 (Y) at the tuner test port, and

c2) for each penetration position Y, modifying the horizontal position of the reflective tuning probe along the slabline by a distance ΔX(Y) to keep the phase Φ 11 (Y) constant within a pre-determined tolerance, and

c3) saving scaling data |S 11 (Y)|, ΔX(Y), Y;

and wherein

the calibration procedure comprises:

d) retrieving the scaling data from the scaling procedure, and in a positioning-measuring loop:

d1) place the reflective tuning probe at the multitude of penetration positions Y and

in a nested positioning-measuring loop:

position the reflective tuning probe to a multitude of horizontal positions Z=X 0 +X+ΔX(Y) along the slabline for 0≤(X+ΔX(Y))≤λ/2+ΔX(Y), measure calibration s-parameters Sij(Z,Y) for {i,j}={1,2} of the tuner and save;

and wherein

the interpolation routine comprises:

calculating s-parameters at a target reflection factor as a linear interpolation between s-parameters associated with four adjacent calibrated reflection factor points S 11 (Z,Y) forming four corners of a trapeze including the target reflection factor.

2. The anti-skewing calibration method for slide screw impedance tuners of claim 1 , wherein

a horizontal distance X 0 of the reflective tuning probe from the test port is at least ensuring that the phase Φ 11 at the maximum penetration of the reflective tuning probe Y=YMAX is approximately equal to the phase Φ 11 at low penetration of the tuning probe.

3. The interpolation routine of the anti-skewing calibration method of claim 1 comprising: given a target position (Zt,Yt) of the reflective tuning probe, select the four adjacent calibrated points Zm, Yn), (Zm+1,Yn), (Zm,Yn+1) and (Zm+1,Yn+1) surrounding the target probe position (Zt,Yt), with Zm≤Zt<Zm+1 and Yn≤Yt<Yt+1, and calculate s-parameters Sij (Zt,Yt) as follows:

Re ( Sij ( Zt,Yt ))= Re ( Sij ( Zm,Yn ))+( Re ( Sij ( Zt,Yt )− Sij ( Zm,Yn )))/( Re ( Sij ( Zm+ 1, Yn )− Sij ( Zm,Yn )));

Im ( Sij ( Zt,Yt ))= Im ( Sij ( Zm,Yn ))+( Im ( Sij ( Zt,Yt )− Sij ( Zm,Yn )))/( Im ( Sij ( Zm+ 1, Yn )− Sij ( Zm,Yn )));

for {i,j}={1,2}.