Variable capacitors for high accuracy tuning

1. Rotary blade variable capacitors for impedance tuners,

said tuners comprising three or more said capacitors interconnected using lengths of coaxial cable,

whereby said capacitors comprise a grounding contact, sliding on the rotating blades;

and damping resistors between the sliding contact and ground.

2. Rotary capacitors as in claim 1 , having a floating fixed and a grounded rotating set of interdigital blades,

and a conductive contact sliding on the edges of the rotating mobile blades;

and having damping resistors attached to the sliding contact and leading to ground terminal.

3. Rotary capacitors as in claim 2 having damping resistors connected at both ends of said sliding contact leading to the ground terminal.

4. Rotary capacitors as in claim 2 having an array of multiple damping resistors distributed over the length of said sliding contact.

5. A tuner as in claim 1 , whereby the lengths of said interconnecting cables are optimized using a network simulation and optimization software algorithm,

whereby said algorithm calculates the reflection factor of a cascade of variable shunt capacitors interconnected using numerically adjustable lengths of coaxial cable, as a function of capacitance value and frequency,

whereby said capacitors are represented by sets of measured s-parameters for a number of capacitance settings between the minimum and maximum values, and

whereby the lengths of interconnecting cables and capacitor s-parameter sets are optimized in order to reach a maximum Smith chart coverage over a given frequency band.

6. A calibration method for tuner as in claim 5 ,

whereby the tuner two-port s-parameters are measured at a given frequency using a pre-calibrated vector network analyzer for a multitude of settings of each capacitor, between the minimum and maximum capacitance value and for all possible permutations of capacitor settings of all capacitors,

and whereby all sets of s-parameters and associated capacitor settings are saved in tuner calibration file ready for retrieval.

7. A calibration method for a tuner as in claim 5 ,

whereby the tuner two-port s-parameters are measured at a given frequency using a pre-calibrated vector network analyzer as follows:

a) measure two-port s-parameters matrices for a number of settings “j” of each capacitor Ci (i=1, 2, 3 . . . ) individually, between the minimum and maximum capacitance value, all other capacitors being set to their minimum capacitance setting (neutral state), and save in file [Sij],

b) measure the s-parameter matrix of the tuner two-port with all capacitors in their neutral state and save in file [S0],

c) de-embed all s-parameter matrices [Sij] for i>1, by cascading with the inverse matrix [S0] −1 and save in matrices [Sij′], whereby [S1j′]=[S1j], [Sij′]=[S0] −1 ×[Sij];

d) cascade s-parameters of all permutations of all capacitor settings of all matrices [Sij′] and save in a tuner calibration file ready for retrieval.

8. An interpolation algorithm for calculating the s-parameters of tuners calibrated as in claim 5 or 6 , for any capacitor setting (cs) between calibrated points k, as follows:

a) calculate the four sets of s-parameters [Si·mn], {m,n}={1,2}) of each tuning section “i” (i=1, 2, 3 . . . ) between two successive calibrated capacitor settings (k, k+1), whereby k<cs<k+1, using linear interpolation for the real and imaginary part of each set of s-parameters [Si·mn(k)] and [Si·mn(k+1)],

whereby k is the index of the calibrated point k=1, 2, 3, 4 . . . N,

and N is the number of capacitor settings used in the calibration,

b) cascade the interpolated s-parameter matrices of all tuning sections.