VHF harmonic impedance tuner
View Patent ↗An electro-mechanical VHF harmonic load pull tuner is made as a cascade of three independent tuning sections, each including three adjustable shunt air capacitors inter-connected using coaxial cables of appropriate length, or one section of nine shunt capacitors inter-connected using coaxial cables; each capacitor is adjustable to at least 20 values (states); the tuner creates independently controllable impedances at three (harmonic) frequencies in the frequency range between 10 and 150 MHz. An Error Function-based optimization algorithm allows impedance tuning at three frequencies independently, by optimized searching among the more than 20 9 ≈512,000,000,000 possible combined tuner states. This allows matching the output of VHF transistors and amplifiers at the fundamental and harmonic frequencies. Stepper motors, drivers and control software are used to automate, calibrate and use the harmonic tuner in an automated harmonic load pull measuring setup.
1. A calibration technique of impedance tuners comprising N≧1 tuning elements, for a number of frequencies Fi, whereby 1≦i≦M and
whereby Fi are arbitrary frequencies, including harmonic frequencies (F i+1 =(i+1)*Fi) said calibration technique comprising s-parameter measurement of said tuner using a pre-calibrated network analyzer;
said calibration comprising four steps:
a) measuring the s-parameter matrix of said tuner when all tuning elements are initialized (set to their neutral state) and saving the data in a s-parameter matrix {A};
b) measuring the s-parameters of said tuner when each element “i” is set to a number of states, all other tuning elements remaining initialized, and saving the data in an s-parameter matrix {Bi};
c) cascading the inverse matrix {A} −1 with all matrices {Bi}, except for matrix {B 1 }, resulting in matrices {Ci}={A} −1 *{Bi} and {C 1 }={B 1 };
d) numerically cascading all elements (s-parameters) of all matrices {Ci}, for i=1 to N in order to obtain the total calibration matrix {CT} of said multi-element tuner, comprising the s-parameters of said tuner for all permutations of settings of all tuning elements;
e) saving matrix {CT} in computer memory for later use.
2. A calibration method as in claim 1 for a multi-element impedance tuner;
said tuner comprising a cascade of two tuning sections;
each said section comprising an input (test) port and an output (idle) port and three variable shunt capacitors;
each said capacitor being grounded on one terminal and inter-connected on its second terminal with the previous and next capacitor by means of coaxial cable of appropriate length, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely adjusted using precise electrical motors, control electronics driving said motors and a control computer running control software.
3. A calibration method as in claim 1 for a multi-element impedance tuner;
said tuner comprising a cascade of three tuning sections;
each said section comprising an input (test) port and an output (idle) port and three variable shunt capacitors;
each said capacitor being grounded on one terminal and inter-connected on its second terminal with the previous and next capacitor by means of sections of coaxial cable of appropriate length, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely adjusted using precise electrical motors, control electronics driving said motors and a control computer running control software.
4. A calibration method as in claim 1 for a multi-element impedance tuner;
said tuner comprising an input (test) port and an output (idle) port and an assembly of variable capacitors and coaxial cables connected between said ports;
said assembly comprising a cascade of six or more variable shunt capacitors connected between them using sections of coaxial transmission cable of appropriate length;
said capacitor's one terminal being grounded and the other terminal being connected to the previous and next in series capacitor using said coaxial cable, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely controlled using precise electrical motors, control electronics driving said motors and a control computer running control software.
5. A calibration method as in claim 1 for a multi-element impedance tuner;
said tuner comprising an input (test) port and an output (idle) port and an assembly of variable capacitors and coaxial cables connected between said ports;
said assembly comprising a cascade of nine variable shunt capacitors connected between them using sections of coaxial transmission cable of appropriate length;
said capacitor's one terminal being grounded and the other terminal being connected to the previous and next in series capacitor using sections of coaxial cable, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely controlled using precise electrical motors, control electronics driving said motors and a control computer running control software.
6. A calibration method as in claim 2 or 3 or 4 or 5 for multi-element impedance tuners, whereby said electrical tuner motors are stepper motors.
7. A calibration method as in claim 2 or 3 or 5 or 5 for multi-element impedance tuners, whereby the lengths of the sections of coaxial cable between capacitors are determined such as to allow maximum coverage of the Smith chart over a maximum frequency range.
8. A calibration method as in claim 2 or 3 or 4 or 5 for multi-element impedance tuners, whereby the lengths of the sections of coaxial cable between capacitors are determined such as to allow maximum coverage of the Smith chart over distinct frequency bands.
9. A calibration technique of impedance tuners comprising N≧1 tuning elements, for a number of frequencies Fi, whereby 1≦i≦M and
whereby Fi are arbitrary frequencies, including harmonic frequencies (F i+1 =(i+1)*Fi) said calibration technique comprising s-parameter measurement of said tuner using network analyzer in six steps as follows:
a) calibrate the network analyzer on a reference plane at the test ports of the RF cables and save the calibration in a calset- 1 ;
b) connect the test port of said tuner, with all tuning elements initialized (set to their neutral state), with port 1 of said network analyzer and calibrate said network analyzer between the idle port of said (initialized) tuner and port 2 of said network analyzer, and save the calibration in a calset- 2 ;
c) load calset- 1 in the network analyzer memory and measure the s-parameter matrix of said tuner, when all tuning elements are initialized and only the first element is activated and set to a number of states, and save the data in a s-parameter matrix {A 1 };
d) load calset- 2 in the network analyzer memory and measure the s-parameters of said tuner when each element “i”, for i=2 to N, is set to a number of states, all other tuning elements remaining initialized, and save the data in a s-parameter matrix {Ai};
e) numerically cascade all matrices {Ai}, for i=1 to N, resulting in total tuner s-parameter calibration matrix {AT} of said multi-element tuner comprising the s-parameters of said tuner for all permutations of settings of all tuning elements;
f) saving matrix {AT} in computer memory for later use.
10. A calibration method as in claim 9 for a multi-element impedance tuner;
said tuner comprising a cascade of two tuning sections, each said section comprising an input (test) port and an output (idle) port and three variable shunt capacitors;
each said capacitor being grounded on one terminal and inter-connected on its second terminal with the previous and next capacitor by means of coaxial cable of appropriate length, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely adjusted using precise electrical motors, control electronics driving said motors and a control computer running control software.
11. A calibration method as in claim 9 for a multi-element impedance tuner;
said tuner comprising a cascade of three tuning sections, each said section comprising an input (test) port and an output (idle) port and three variable shunt capacitors;
each said capacitor being grounded on one terminal and inter-connected on its second terminal with the previous and next capacitor by means of sections of coaxial cable of appropriate length, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely adjusted using precise electrical motors, control electronics driving said motors and a control computer running control software.
12. A calibration method as in claim 9 for a multi-element impedance tuner;
said tuner comprising an input (test) port and an output (idle) port and an assembly of variable capacitors and coaxial cables connected between said ports;
said assembly comprising a cascade of six or more variable shunt capacitors connected between them using sections of coaxial transmission cable of appropriate length;
said capacitor's one terminal being grounded and the other terminal being connected to the previous and next in series capacitor using said coaxial cable, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely controlled using precise electrical motors, control electronics driving said motors and a control computer running control software.
13. A calibration method as in claim 9 for a multi-element impedance tuner;
said tuner comprising an input (test) port and an output (idle) port and an assembly of variable capacitors and coaxial cables connected between said ports;
said assembly comprising a cascade of nine variable shunt capacitors connected between them using sections of coaxial transmission cable of appropriate length;
said capacitor's one terminal being grounded and the other terminal being connected to the previous and next in series capacitor using sections of coaxial cable, the first said cable connected to the test port and the last said cable connected to the idle port;
each capacitor being remotely controlled using precise electrical motors, control electronics driving said motors and a control computer running control software.
14. A calibration method as in claim 10 or 11 or 12 or 13 for multi-element impedance tuners, whereby said electrical motors are stepper motors.
15. A calibration method as in claim 10 or 11 or 12 or 13 for multi-element impedance tuners, whereby the lengths of the sections of coaxial cable between capacitors are determined such as to allow maximum coverage of the Smith chart over a maximum frequency range.
16. A calibration method as in claim 10 or 11 or 12 or 13 for multi-element impedance tuners, whereby the lengths of the sections of coaxial cable between capacitors are determined such as to allow maximum coverage of the Smith chart over distinct frequency bands.