Calibration method for slide screw impedance tuners
View Patent ↗A new method for calibrating slide screw tuners, both using hexahedron vertically moving and disc-shaped eccentrically rotating reflective tuning probes, allows straightening the reflection factor phase response (anti-skewing); it uses a new scaling method and a new coordinate system of tuning probe control. The method is agnostic and self-regulating, it treats the tuner as a black box and depends on the test frequency. The result is improved mathematical interpolation and tuning results using reduced number of calibration points and allowing higher calibration speed.
1. An anti-skewing calibration method for slide screw impedance tuners at a frequency F comprising: a scaling step and a calibration step,
wherein,
the slide screw impedance tuners comprise:
a slabline having a test port and an idle port, and
at least one reflective tuning probe, remotely movable along and insertable into the slabline between a state of withdrawal and a state of maximum penetration,
and wherein
the scaling step comprises:
a) connect the tuner to a pre-calibrated vector network analyzer,
b) withdraw the reflective tuning probe and place it at a frequency dependent distance X0 from the test port, along the slabline,
c) gradually inserting the reflective tuning probe to a multitude of penetration positions Y and measuring a reflection factor amplitude S11(Y) and phase Φ11(Y) at the tuner test port,
d) correcting the position of the reflective tuning probe along the slabline by ΔX(Y) to keep a change of Φ11 within a tolerance,
e) saving scaling data S11(Y), ΔX(Y), Y;
and wherein
the calibration step comprises:
f) retrieving scaling data from step e),
g) placing the reflective tuning probe at penetration positions Y and at a multitude of positions along the slabline Z=X0+X+ΔX(Y) for 0≤X≤λ/2,
h) measure s-parameters Sij(Z,Y) for {i,j}={1,2} of the tuner and save.
2. The anti-skewing calibration method for slide screw impedance tuners of claim 1 , wherein
the frequency dependent distance X0 from the test port is determined as follows:
a) connect the tuner to a pre-calibrated vector network analyzer,
b) withdraw the reflective tuning probe and place at a distance at least X≈λ/2 at the frequency F from the test port, along the slabline,
c) insert the reflective tuning probe to create reflection factor S11≈0.1,
d) measure the phase Φ0=Φ11 of the reflection factor at the frequency F,
e) insert the reflective tuning probe to maximum penetration,
f) measure the phase Φ1=Φ11 of the reflection factor at the frequency F,
g) move the reflective tuning probe by ΔX along the slabline to obtain Φ1≈Φ0,
h) save X0=ΔX.