Slide screw tuner with adjustable pitch
View Patent ↗A slide screw tuner control mechanism uses linear actuator movement with numerically controlled PITCH (number of threads per inch). The PITCH is adjustable using the concept of a differential screw, implemented by independent control of the rotation of the actuator built-in ACME screw, yielding a numerically controllable overall effective PITCH. Tuner calibration and tuning can use dynamically adjustable horizontal movement increments increasing tuning speed at low frequencies without loss of fine-tuning resolution at high frequencies.
1. A slide screw impedance tuner having mechanically adjustable horizontal movement step resolution, comprising:
a low loss slotted airline having a test port, an idle port, and a center conductor between the ports;
a rotatable lead screw extending horizontally along a length of the slotted airline;
at least one mobile carriage horizontally translatable on the lead screw along the slotted airline on a horizontal axis,
said at least one mobile carriage comprising:
a first stepper motor;
a metallic tuning probe insertable into a slot of the airline along a vertical axis perpendicular to the horizontal axis between a withdrawal position Y=0 and a maximum penetration position Y=YMAX, a position of the metallic tuning probe between the withdraw al position and the maximum penetration position controllable by the first stepper motor;
a motorized linear stepper actuator having a rotor threadingly engaged with the lead screw, the linear stepper actuator controllable to rotate the rotor relative to the lead screw to provide a per actuator-motor-step coarse displacement XC for controlling a horizontal position of the mobile carriage along the slotted airline on the horizontal axis; and
a second stepper motor, controllable independently from the linear stepper actuator, to rotate the lead screw relative to the rotor of the linear stepper actuator to provide a per actuator-motor-step fine displacement XF for controlling a horizontal position of the mobile carriage along the slotted airline on the horizontal axis.
2. The slide screw impedance tuner of claim 1 , further comprising:
a first pulley P 1 having a diameter D 1 attached to the second stepper motor;
a second pulley P 2 having a diameter D 2 attached to the lead screw; and
a timing belt rotatably linking the first pulley P 1 with the second pulley P 2 ;
wherein a first rotation of the first pulley P 1 by the second stepper motor causes a corresponding second rotation of the second pulley P 2 and the lead screw.
3. The slide screw impedance tuner of claim 2 , wherein
diameters D 1 and D 2 of the pulleys P 1 and P 2 are chosen such that the per actuator-motor-step fine displacement at a maximum frequency of operation of the slide screw impedance tuner is equal to XF=XC*D 1 /D 2 .
4. A method of moving the metallic tuning probe of the slide screw impedance tuner of claim 3 from a position X 1 , Y 1 to a position X 2 Y 2 , the method comprising:
determining a number A of coarse displacements XC and a number B of fine displacements XF for moving the metallic tuning probe a horizontal travel distance of ΔX=X 2 −X 1 , wherein A=(int)(ΔX/XC) and B=(int)((ΔX−A*XC)/XF);
moving the linear stepper actuator A steps;
moving the second stepper motor B steps; and
moving the metallic tuning probe to position Y 2 .