Triple probe automatic slide screw load pull tuner and method
An automatic, electromechanical microwave tuner, used for load pull transistor testing, employs three horizontally and vertically adjustable RF probes; the tuner creates very low mechanical vibrations, because it is capable of generating all microwave reflection factors required for complete load pull and noise measurement operations, using only vertical probe movement; it also provides high tuning dynamic range, large frequency bandwidth and continuous choice of tuning target areas.
1. An electromechanical, microwave load pull tuner comprising an input (test) and an output (idle) port, a horizontal transmission airline in form of a slotted coaxial or parallel plate airline (slabline), three carriages movable parallel to the airline, which hold one vertically adjustable capacitive probe each and mechanisms for separate remote control of each horizontal and vertical movement of the carriages and probes.
2. An electromechanical tuner as in claim 1 , where the adjustable capacitive probes can be independently inserted vertically and positioned at variable distance from the central conductor of the slabline, in order to create an adjustable capacitive load, said position control of the probes being made using stepper motors, which are remotely controlled by a control computer and associated software.
3. An electromechanical tuner as in claim 2 , where the adjustable probes can be positioned horizontally fully independently using a horizontal lead screw or belt drive or rack and pinion drive, linked to stepper motors, which are remotely controlled by a control computer and associated software.
4. An electromechanical tuner as in claim 2 , where the horizontal position of the probes can be modified in such a way, that the distance between the probes and the test port of the said tuner can be adjusted and allow controlling the phase of the reflection factor presented at the test port of the tuner.
5. An electromechanical tuner as in claim 2 , including three independently operating sections, each of which includes one mobile carriage carrying one probe each and associated electric remote motion control.
6. A calibration method for said electromechanical tuner of claim 2 , in which scattering parameters (S-parameters) are measured using a calibrated vector network analyzer (VNA) between the test and idle ports of the tuner at a given fundamental frequency of operation and its two harmonics, as a function of a selected number of horizontal and vertical positions of each RF probe, the horizontal positions selected such as to cover 360° of phase at the fundamental frequency and the vertical positions chosen such as to cover from minimum to maximum amplitude of the reflection factor at the test port in five steps, step 1 consisting of measuring S-parameters of the tuner as a function of the positions of probe 1 , probes 2 and 3 being initialized, step 2 consisting of measuring S-parameters of the tuner as a function of the positions of probe 2 , probes 1 and 3 being initialized, step 3 consisting of measuring S-parameters of the tuner as a function of the positions of probe 3 , probes 1 and 2 being initialized, step 4 consisting of cascading the S-parameters measured in steps 2 and 3 with the inverse S-parameter matrix of the tuner, measured when all probes are initialized, and step 5 consisting of saving the S-parameters collected and calculated in steps 1 to 4 in a total of 3 calibration data files, one for each of 3 harmonic frequencies, ready for retrieval.