Low frequency load pull tuner using dielectric filled spiral airline

Abstract

A new harmonic slide screw impedance tuner for VHF-UHF frequencies uses a reduced overall length spiral slabline structure and three rotating carriages allowing reducing the linear size of the tuner from originally L=3/2 to a spiral length L=2RN of a cylinder with 2R diameter and a height H made up of N floors (example: F=100 MHZ, =300 cm, R=10 cm, N=10 floors of 2 cm each, yields a 2020 cm cylinder versus a 450 cm linear slabline; a core reduction of 450/20=23). The slabline stands vertically on the bench table surface and the carriages, including the tuning probes rotate and wind up and down around a vertical axis through the center of the spiral slabline, controlled by a rack-and pinion spiral arrangement on the edge of the spiral slabline. The rotation of the carriages controls the phase of GAMMA and the insertion of the tuning probes into the channel of the slabline controls its amplitude.

Claims

1. A slide screw impedance tuner, comprising: a test port, an idle port and a spiral slabline immerged in dielectric fluid, between the ports having two conductive sidewalls forming a spiral channel and a spiral center conductor, and up to three remotely controlled mobile carriages rolling on a periphery of the sidewalls of the spiral slabline and carrying at least one reflective (tuning) probe each, remotely insertable into the spiral channel and coupled capacitively with the spiral center conductor; wherein the periphery of the sidewalls is indented forming a spiral rack; and wherein the mobile carriages include remotely controlled teethed wheels (pulleys), engaged with the indentations of the spiral rack on the sidewalls ensuring travelling of the carriages along the periphery of the sidewalls in a rack-and-pinion configuration; and wherein an available linear length of the spiral slabline is at least equal to the number of mobile carriages used, times one half of a wavelength (/2) at a lowest frequency of operation of the slide screw tuner; and wherein the spiral center conductor is centered between the sidewalls and runs at constant depth from the periphery of the sidewalls.

2. The slide screw impedance tuner of claim 1, wherein the characteristic impedance of the in dielectric fluid immerged spiral slabline is 50 Ohms.

3. The slide screw impedance tuner of claim 1, wherein the dielectric fluid, in which the spiral slabline is immerged, is a mixture of dielectric fluids of different dielectric permittivity (.sub.r).

4. The slide screw impedance tuner of claim 3, wherein the mixture of dielectric fluids is recirculated.

5. The slide screw impedance tuner of claim 3, wherein the dielectric fluid is a mixture of high dielectric permittivity (Er) fluid and low dielectric permittivity fluid.

6. The slide screw impedance tuner of claim 1, wherein the tuning probes are conductive slugs, slide-fitting into the spiral channel of the slabline and having a concave bottom surface matching the shape of the spiral center conductor of the slabline.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its mode of operation will be easier understood from the following detailed description when read with the appended drawings in which:

(2) FIG. 1 depicts prior art, a typical automated transistor load pull test system.

(3) FIG. 2 depicts prior art, a front view of an automated slide screw impedance tuner using a straight slabline, a single vertical axis and RF tuning probe (slug).

(4) FIG. 3 depicts prior art, RF probe (slug) inside a slotted airline (slabline) approaching the center conductor in a perspective view, and the relevant dimensions and parameters of the operation.

(5) FIGS. 4A through 4B depict prior art, cross section of typical probe configurations: FIG. 4A depicts a probe with galvanic ground contact to the slabline walls and spring-loaded mechanism; FIG. 4B depicts a probe with capacitive-only RF ground contact.

(6) FIG. 5 depicts a 3D view of the core of the spiral slabline.

(7) FIG. 6 depicts the spiral slabline including the center conductor.

(8) FIG. 7 depicts a detail view of a section of the spiral slabline and schematically a mobile carriage with tuning probe inserted in the channel.

(9) FIG. 8 depicts a top view of the spiral slabline and three mobile carriages on a planetary movement around the center.

(10) FIG. 9 depicts prior art, the concept of a rack-and-pinion configuration to be used in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) FIG. 5 is a perspective view of the cylindrical core of the spiral slabline. The cylinder has a center 52, a periphery lip 50 and a continuous spiral channel 51 in which is embedded a center conductor. The width of the channel and the diameter of the center conductor are dimensioned such as to create a characteristic impedance of 50 Ohms, in particular if the slabline is submerged in dielectric fluid to increase its electrical length, the thermal control of the center conductor (cooling) and increase the capacitive coupling of the tuning probes with the center conductor, allowing for smaller tuning slugs.

(12) FIG. 6 is a side view of the spiral slabline before the mounting of the mobile carriages. This embodiment includes N=8 spires on a cylinder with a radius R of 10 cm yielding a total linear length of 2RN=503 cm in air, enough for a Fo, 2Fo and 3Fo (Fo=100 MHz) harmonic tuner or, if the spiral slabline is submerged in dielectric fluid with a permittivity of 4 (like vegetal oil), to a total length of 1006 cm, enough for a Fo=50 MHz Fo to 3Fo slide screw harmonic tuner. Generally speaking, the total linear effective length of the spiral slabline must be least equal to the number of mobile carriages used, times one half of a wavelength (/2) at a lowest frequency of operation of the slide screw tuner (see ref. 4), plus, of course, the space taken by inserting the carriages, connecting the end adapters etc.

(13) Submerging the slabline in dielectric fluid also increases the capacitance between the tuning probe and the center conductor, cools the center conductor and also increases the breakdown voltage, thus also increasing the RF power handling of the tuner. Using a mixture of high permittivity dielectric fluid (example glycerine with .sub.r=40 with mineral oil of .sub.r=2.1) and adjusting the proportions will yield any desired average permittivity value, assuming the liquid is steadily recirculated to avoid separation of the fluid components. At the relatively low frequencies considered here, the dielectric RF loss of the fluids is of minor concern.

(14) FIG. 7 shows a detail of the tuning mechanism on the spiral slabline: one can see the conductive sidewalls 76, the teeth on the periphery 75, forming a spiral rack, engaged with the teeth of the pulleys 74 on the mobile carriage 72, (as shown conceptually in FIG. 9), the tuning probe (slug) 71 approaching or withdrawing radially from the center conductor 70 and the remote tuning probe control axis mechanism 73.

(15) FIG. 8 shows a top view of the VHF-UHF slide screw harmonic tuner using three mobile carriages 85 controlled remotely using small pulleys 83 engaged with the teeth (indentations) 80 of the rack-formed edge of the periphery 82 of the spiral slabline in a rack-and-pinion configuration (FIG. 9). The pulleys 83 rotate 801 and pull 803 the carriage 802 together with the tuning probe 84 along the rack 82 built into the periphery of the spiral slabline around a center axis 86 in a screw-kind angular movement from a starting point close to the input port 53 of the slabline at a radius R towards to the output port 54. The width of the channel of the slabline (item 61 in FIG. 6) and the thickness of the sidewalls are dimensioned such that the carriages can pass next to each-other without mechanical conflict. The depth and width of the channel 89 ensures that the spiral center conductor 81 forms a constant characteristic impedance over the whole length of the slabline and minimum residual reflection. To avoid magnetic coupling between the adjacent spires of the center conductor the body of the slabline cylinder could be made using magnetic material or coated with such (like Ni). Each mobile carriage includes a remotely controlled radial axis mechanism that controls a conductive tuning probe as shown in FIGS. 4A and 4B.

(16) This invention has been described in a basic preferred embodiment; obvious alternatives and configurations, to the disclosed concept of circular compact slide screw tuners using rotating carriages on a spiral slabline are possible but shall not impede on to the validity of the present invention.