Abstract
A slide screw tuner uses a tuning probe that penetrates into the slot of the slabline inclined towards the test port, in order to compensate for the capacitive skewing of the angle of the reflection factor Γ. This anti-skewing effect is done by splitting the mobile combo carriage into a fixed and a rotating section, held together by a center pin that allows an adjustable inclination. The linearized trajectory of Γ improves the accuracy of interpolation between calibration points.
Claims
1. A slide screw impedance tuner comprising, a low loss slotted transmission airline (slabline) having a test port, an idle port and a center conductor between the test and idle ports, and at least one remotely controlled mobile combo carriage sliding horizontally along the slabline, controlled by an Acme lead screw, and an electronic motor control board; said at least one remotely controlled mobile combo carriage comprising one fixed section and one section rotating against the fixed section on a plan parallel to the center conductor of the slabline, wherein a horizontal position of the one fixed section is controlled by the Acme lead screw, and wherein the one rotating section holds a vertical axis and is linked with the one fixed section using a center pin; and wherein the vertical axis holds a metallic tuning probe having a stem held by the vertical axis and a bottom section insertable into a slot of the slabline.
2. The slide screw impedance tuner of claim 1 wherein a rotation angle between the one fixed section and the one rotating section is adjustable.
3. The slide screw impedance tuner of claim 1 wherein the bottom section of the tuning probe has a concave periphery with semi-circular profile, and wherein a channel of the concave bottom section is parallel to the center conductor.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention and its mode of operation will be better understood from the following detailed description when read with the appended drawings in which:
(2) FIG. 1 depicts prior art, a block diagram of a load pull measurement setup, in which electro-mechanical impedance tuners are used to manipulate the source and load impedances presented to the DUT.
(3) FIG. 2 depicts prior art, a front view of a slide screw tuner and associated components and definitions.
(4) FIG. 3A through 3B depict prior art: FIG. 3A depicts schematically the tuning probe and its movement relative to the center conductor; FIG. 3B depicts the trajectory and skewing of the reflection factor as the tuning probe approaches the center conductor.
(5) FIG. 4 depicts the inclined movement of the tuning probe to create anti-skewing effect.
(6) FIG. 6 depicts movement of mobile combo carriage and inclined tuning probe.
(7) FIG. 7 depicts cross section of mobile combo carriage with fixed section and rotating section holding the tuning probe.
(8) FIG. 8 depicts de-skewing effect of the inclined tuning probe.
DETAILED DESCRIPTION OF THE INVENTION
(9) Beyond field deformation by the insertion of the tuning probe 30 (FIG. 3A) the major portion of skewing 33 is due to the hyperbolic increase of the capacitance between the tuning probe 30 and the center conductor 31 (area 701 in FIG. 7). The capacitance changes with the inverse of the gap S between center conductor and tuning probe: C=ε.sub.0*A/S, wherein A is the effective surface between the probe and the center conductor (FIG. 5). Starting at the center of the Smith chart 32 and as the probe moves towards the center conductor the gap S shrinks and the capacitance C increases. The nonlinear change causes the 33 trajectory (FIG. 3B) to skew and not to follow the circles 34, 36 for linear change of the parallel susceptance Im(Y)=jωC as a function of either frequency (ω=2*π*F) or capacitance C. The skewing creates a negative phase change (ΔΦ) between the linear extrapolation 35 and the actual trajectory 33. The skew also creates a far from orthogonal response 37 of the Γ trajectory as a function the cartesian controlling stimuli X and Y of the tuning probe. This stretches the Lagrange interpolation used for interpolating between calibration points (see ref. 3, col. 5, lines 64-67 and col. 6, lines 1-3), resulting in inaccuracies at very high skewed r. If during vertical movement of the tuning probe it also moves towards the test port 44, then the phase will increase (turn anti-clock-wise) 80 and compensate the skewing effect 81 as shown in FIG. 8.
(10) The mechanism is implemented as shown in FIGS. 4, 6 and 8. FIG. 4 shows the principle of anti-skewing: the tuning probe 40 is inclined by the angle Θ against the prior art vertical direction 42. In order to avoid mechanical conflict with the center conductor 41 when coming in close proximity, the tip of the tuning probe is rounded in a semi-circular form profile, but keeps the basic concave bottom form of prior art probes, as can be seen in area S of FIG. 7. As the probe 40 moves along the axis 45 (V) its closest point to the center conductor also moves towards the test port 44. Following the relation Φ(rad)=4*π*X/λ, or Φ(°)=2.4*X(mm)*F (GHz) this means that for a vertical movement ΔV=0.5 mm and an angle Θ=30°, at F=10 GHz the anti-skewing phase increase is ΔΦ=2.4*(0.5 mm*sin(30°)*10 (GHz=6°). Anti-skewing increases with the angle Θ and the frequency F. The dimensions ΔV and ΔX between limits 42 and 43 shown in FIG. 4 are drawn exaggerated only for understanding the concept. In reality the movements are differentially small but in the same proportions, as shown in the calculations.
(11) The anti-skewing structure is shown in FIG. 6. The mobile combo carriage includes two sections, a fixed section 61 and a rotating section 62 inclined by the angle Θ against the vertical. The rotation plan of the inclined section is parallel to the slot of the slabline and the center conductor 63. Both sections are attached to each-other using a center pin 73 (shown in FIG. 7). The angle between the sections is held normally by surface friction or by adding a (not shown) fixation screw on the pin. The vertical axis 65, that holds the tuning probe 64, moves along the angle Θ towards the center conductor 63. The fixed portion 61 of the combo carriage includes an internal thread that is engaged with the ACME lead screw 60, which controls its horizontal position X along the slabline 78 and the center conductor 63.
(12) The combo carriage and control are shown in FIG. 7 in a cross section. The fixed section 74 slides on rollers 76 along the slabline 78 on block 77 controlled by the ACME lead screw 75. The rotating section 70, which carries the vertical axis 71, the vertical motor 72 and the tuning probe 79 are anchored against the fixed section 74 using the pin 73, and can be rotated on a plan parallel to the center conductor. The pin 73 allows section 70 to be inclined (0) against section 74 and is held in position by surface friction between the blocks 70 and 74. If needed, a set screw may be added against the pin 73 to better secure the inclination.
(13) The slide screw tuner with anti-skewing capacity has been disclosed using a preferred embodiment. Obvious alternatives, though imaginable, shall not impede on the validity of the present invention.
