Method for calibration and tuning with impedance tuners

An algorithm performing impedance synthesis for single probe impedance tuners for target reflection factors between approximately 0 and 0.85 using tuner calibration and interpolated s-parameter data,

• whereby said calibration data are generated by measuring two-port tuner s- parameters for a plurality of horizontal and vertical probe positions,
• and whereby said interpolated data are created using second order interpolation method for any probe position included in a grid of calibrated points,
• in two steps:
• a) searching numerically and identifying the closest calibrated point to the target reflection factor;
• b) searching numerically alternatively in horizontal and vertical direction of the probe coordinates and use interpolated data for each set of coordinates to calculate an error vector as the difference between interpolated and target reflection factors;
• the search in each direction continues until the error vector crosses a local minimum, in which case the search switches over to the other direction, until again a local minimum of the error vector is reached;
• the numeric search continues, until a change in direction does not yield any reduction of the error vector, in which case the probe's coordinates are saved as a final solution;
• all above numeric search is executed in computer memory and no tuner movement is necessary until a final position is found;
• and once a final position is found, the tuner probe is moved to it to generate the target impedance.

An algorithm performing impedance synthesis for single probe impedance tuners for target reflection factors between approximately 0.85 and 0.99 using tuner calibration and interpolated s-parameter data,

• whereby said calibration data are generated by measuring two-port tuner s-parameters for a plurality of horizontal and vertical probe positions,
• and whereby said interpolated data are created using second order interpolation method for any probe position included in a grid of calibrated points, comprises two steps:
• a) a numeric search identifies a grid of approximately 5 calibrated points closest to the target reflection factor;
• b) starting with the calibration point closest to the target reflection factor a numeric search alternatively in horizontal and vertical direction of the probe is performed and for each new position the s-parameters are calculated using interpolated data;
• an error vector is calculated as the difference between interpolated and target reflection factors;
• the search in either direction continues alternatively until the error vector either reaches a minimum or the search diverges;
• if a minimum is reached the actual probe coordinates are saved as a preliminary solution;
• then the next closest calibration point to the target reflection factor is chosen and the alternative horizontal-vertical direction search resumes until the search either diverges or yields another minimum of the error vector;
• the search continues until all points of the grid have been tried;
• finally the horizontal and vertical coordinates of the probe yielding the smallest error vector are saved as a final solution;
• and once a final position is found, the tuner probe is moved to it to generate the target impedance.

An algorithm performing s-parameter interpolation for automated slide screw tuners having a test port and an idle port, a slabline between said ports and two independently controllable RF probes, probe and probe 2 for any set of coordinates X1,Y1 of probe 1 and X2,Y2 of probe 2, and a fundamental (Fo) and a harmonic (2Fo or 3Fo) frequency as follows:

• a) the tuner is calibrated by positioning each probe individually, the other probe being withdrawn from the slabline (initialized), at a multitude of horizontal (X) and vertical (Y) positions, in order to create reflection factors (Gamma) covering the whole Smith chart (from Gamma approximately zero to maximum close to land over 360 degrees) at the fundamental frequency Fo;
• b) s-parameters of the tuner are measured at said frequencies Fo and 2Fo or 3Fo;
• c) s-parameters of probe 2 are de-embedded (cascaded with the inverse s-parameter matrix [S00]−1 of the tuner, said [S00] matrix being measured at said frequencies when both probes are withdrawn from the slabline);
• d) s-parameter for each probe and each said frequency are interpolated;
• e) s-parameters of probe and de-embedded s-parameters of probe 2, calculated in step (d), are cascadedand saved.

A calibration method for an automatic single probe slide screw tuner at a test frequency Fo, said tuner being controlled by a control processor,

• whereby said processor runs software able to interpolate s-parameters of said tuner for arbitrary probe positions,
• and whereby said processor runs software able to tune to arbitrary reflection factors inside the Smith chart, said calibration method comprises the following steps:
• a) s-parameters of said tuner are measured at a multitude of probe positions selected to generate reflection factors distributed approximately uniformly over the entire Smith chart, and saved;
• b) a number N1 of reflection factors is selected;
• c) the tuner is instructed to tune to the reflection factors of step (b) and save the associated probe positions;
• d) the tuner is directed to probe positions of step (c) and s-parameters are measured;
• e) s-parameters measured in step (d) are saved in a calibration file comprising the test frequency, the probe positions and the measured s-parameters.

A calibration method for an automatic slide screw tuner, having two independent probes 1and 2, at test frequencies Fo and 2Fo,

• said tuner being controlled by a control processor,
• whereby said processor runs software able to interpolate s-parameters of said tuner for arbitrary positions of each probe,
• and whereby said processor runs software able to tune to arbitrary reflection factors inside the Smith chart for each frequency independently,
• said calibration method comprises the following steps:
• a) s-parameters of said tuner are measured at Fo and 2Fo at a multitude of positions of each probe selected to generate reflection factors at Fo distributed approximately uniformly over the entire Smith chart, and saved;
• b) s-parameters of probe 2 are de-embedded at Fo and 2Fo using the tuner initialization matrix, measured when all probes are withdrawn;
• c) s-parameters of probes 1and 2 are cascaded for all permutations of probe positions;
• d) a number N2, of reflection factors is selected at Fo and 2Fo;
• e) the tuner is instructed to tune to the reflection factors of step (d) and save the associated probe positions;
• f) the tuner is directed to probe positions of step (e) and s-parameters are measured;
• g) s-parameters measured in step (f) are saved in a calibration file comprising the test frequencies, the probe positions and the measured s-parameters.

A calibration method for an automatic slide screw tuner, having three independent probes 1,2 and 3, at test frequencies Fo, 2Fo and 3Fo, said tuner being controlled by a control processor,

• whereby said processor runs software able to interpolate s-parameters of said tuner for arbitrary positions of each probe,
• and whereby said processor runs software able to tune to arbitrary reflection factors inside the Smith chart for each frequency independently,
• said calibration method comprises the following steps:
• a) s-parameters of said tuner are measured at Fo, 2Fo and 3Fo at a multitude of positions of each probe selected to generate reflection factors at Fo distributed approximately uniformly over the entire Smith chart, and saved;
• b) s-parameters of probes 2 and 3 are de-embedded at Foto 3Fo using the tuner initialization matrix, measured when all probes are withdrawn;
• c) s-parameters of probes 1to 3 are cascaded for all permutations of probe positions;
• d) a number N3 of reflection factors is selected at Fo, 2Fo and 3Fo;
• e) the tuner is instructed to tune to the reflection factors of step (d) and save the associated probe positions;
• f) the tuner is directed to probe positions of step (e) and s-parameters are measured;
• g) s-parameters measured in step (f) are saved in a calibration file comprising the test frequencies, the probe positions and the measured s-parameters.

An algorithm performing s-parameter interpolation for multi-probe automatic slide screw impedance tuners at a fundamental and two harmonic frequencies (Fo, 2Fo, 3Fo), said tuners having a test port and an idle port, a slabline between said ports and three wideband RF probes 1, 2 and 3 placed at horizontal and vertical positions (Xt1,Yt1) of probe 1, (Xt2,Yt2) of probe 2 and (Xt3,Yt3) of probe 3, said probes being independently controllable, insertable and movable into the slot of the slabline, said algorithm comprising the following steps:

• a) generate calibration data as follows:
• i. initialize all probes by withdrawing from the slabline and moving probe 1 closest to said test port, probe 2 at least one half of a wavelength away and probe 3 at least one wavelength away from probe 1, at Fo;
• ii. measure the s-parameters of said tuner and save in matrix [S00] at Fo, 2Fo, 3Fo;
• iii. move probe to vertical and horizontal positions allowing generation of reflection factors (S11) covering the Smith chart approximately equidistantly at Fo, measure and save s-parameters at Fo, 2Fo, 3Fo;
• iv. move probe 2 to vertical and horizontal positions allowing generation of reflection factors (S11) covering the Smith chart approximately equidistantly at Fo, measure s-parameters at Fo, 2Fo, 3Fo, cascade the inverse matrix [S00]−1 with said s-parameters and save;
• v. move probe 3 to vertical and horizontal positions allowing generation of reflection factors (S11) covering the Smith chart approximately equidistantly at Fo, measure s-parameters at Fo, 2Fo, 3Fo, cascade the inverse matrix [S00]−1 with said s-parameters and save;
• vi. cascade all permutations of s-parameters in steps (a.iii) to (a.v) and save;
• b) interpolate s-parameter for probe coordinates (Xt1,Yt1) to (Xt3,Yt3) and for each frequency Fo, 2Fo and 3Fo, using data saved for each probe in steps (a.iii), (a.iv) and (a.v) correspondingly, and save;
• c) cascade s-parameters of probes 1, 2 and 3 generated in step (b) at all frequencies for the above probe coordinates (Xt1,Yt1) to (Xt3,Yt3).