Voltage current sensor with high matching directivity

• US 20030046013A1
• Filed: 07/12/2002
• Published: 03/06/2003
• Est. Priority Date: 02/27/1998
• Status: Active Grant

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: Kevin S. Gerrish
• Inventors: Gerrish, Kevin S.
• Granted Patent: US 6,708,123 B2
• Time in Patent Office: Days
• US Class Current: 702/60
• CPC Class Codes: H01J 37/32082 Radio frequency generated discharge H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01J 37/3299 Feedback systems

Abstract

A technique for measuring the current, voltage and phase of an RF power wave to an RF load, accounts for the finite length of the voltage and current pickups, and corrects for effects of standing wave components of voltage and current. Voltage and current are computed as complex functions of the voltage pickup signal and the current pickup signal, based on coefficients precalibrated for said-predetermined radio frequency. Alternatively, a corrected current value can based on the corrected voltage value and complex load impedance. The correction coefficients can be obtained, for each of a plurality of calibrating radio frequencies within an RF range, from voltage and current pickup signals under conditions of (a) open circuit load, (b) short circuit load, (c) fixed known impedance load; and (d) one of voltage and current being applied at a precise input level to a known load from an RF calibration source. The voltage and current probe can comprise a metal housing having a cylindrical bore therethrough, and first and second recesses, a center conductor and cylindrical insulator within said bore and voltage and current sensor boards mounted in the recesses.

Claims

1. A method of deriving current, voltage and phase information for current and voltage components of an RF power wave that is applied at a predetermined radio frequency (RF) to an RF load, and in which a voltage/current probe having a voltage pickup of finite length and a current pickup of finite length applies a voltage pickup signal V_v and a current pickup signal V_i to a signal processor which processes said voltage and current pickup signals to produce values of voltage, current and phase appearing at said load and corrected for effects of standing wave components of voltage and current, comprising:

computing said voltage as a complex function of the voltage pickup signal and the current pickup signal, based on coefficients precalibrated for said predetermined radio frequency, and

computing said current as a complex function of the voltage and current pickup signals based on coefficients pre-calibrated for said radio frequency.

2. A method of deriving current, voltage and phase information for current and voltage components of an RF power wave that is applied at a predetermined radio frequency (RF) to an RF load, and in which a voltage/current probe having a voltage pickup of finite length and a current pickup of finite length applies a voltage pickup signal V_v and a current pickup signal V_i to a signal processor which processes said voltage and current pickup signals to produce values of voltage, current and phase appearing at said load and corrected for effects of standing wave components of voltage and current, comprising:

computing a corrected voltage value as a complex function of the voltage pickup signal and the current pickup signal, based on coefficients precalibrated for said predetermined radio frequency,

computing a complex impedance of said load at said predetermined radio frequency on the basis of said voltage and current pickup signals, and

computing a corrected current value based on said corrected voltage value and said complex impedance.

3. A method of deriving current, voltage and phase information for current and voltage components of an RF power wave, at a selected operating frequency selected within a range of radio frequencies, which power wave is applied to an RF load, and in which a voltage/current probe having a voltage pickup of a finite length and a current pickup of a finite length applies a voltage pickup signal V_v and a current pickup signal V_i to a signal processor which processes said voltage and current pickup signals to produce values of voltage, current, and phase appearing at said load, and corrected for effects of standing wave components of voltage and current;

comprising,

for each of a plurality of calibrating radio frequencies within said range,

obtaining voltage and current pickup signals under conditions of (a) open circuit load, (b) short circuit load, (c) fixed known impedance load; and

(d) one of voltage and current being applied at a precise input level to a known load from an RF calibration source; and

computing and storing correction coefficients based on the voltage and current signal values obtained under said conditions (a) to (d); and

at said selected operating frequency, applying stored correction coefficients to said voltage and current pickup signals to obtain one or more of a corrected voltage value, a corrected current value, and a corrected load impedance value.

4. The method of claim 3 wherein, for a selected operating frequency between successive calibrating radio frequencies for which said correction coefficients are stored, said step of applying stored correction coefficients includes interpolating between stored values for each said correction coefficient for the calibration frequencies above and below said selected operating frequency.

5. The method of claim 3, wherein said fixed known impedance is a 50 ohm resistive load.

6. The method of claim 3, wherein said radio frequencies are in the range of about 0.2 megahertz to about a hundred megahertz.

7. Voltage and current probe for detecting voltage and current values of an RF power wave that is applied therethrough to an RF load, comprising:

a metal housing having a cylindrical bore therethrough, and first and second recesses, the recesses each opening to said bore for an axial distance;

a center conductor extending along the axis of said bore;

a cylindrical insulator within said bore surrounding said center conductor and extending radially between said conductor and said housing;

a voltage sensor board mounted in the first recess and having a capacitive pickup plate facing radially towards the axis of the bore; and

a current sensor board mounted in the second recess and having an elongated inductive pickup conductor facing radially towards the axis of the bore and extending axially for said axial distance.

8. The voltage and current sensor as in claim 7, wherein said first and second recesses are positioned opposite one another on said metal housing across the axis of said bore.

9. The voltage and current sensor as in claim 7, wherein said voltage sensor board includes, in order radially outward, said capacitive plate, an insulator layer, a ground plate completion conductive layer, and a circuit board carrying voltage pickup components, with at least one electrical conductor passing from said capacitive plate through openings in said insulator layer and said ground plate completion conductive layer to said voltage pickup components.

10. The voltage and current sensor as in claim 9 wherein said voltage pickup components are symmetrically distributed upon said board so as to create an electrical symmetry in both axial and transverse directions.

11. The voltage and current sensor as in claim 7, wherein said current sensor board includes, in order radially outward, said inductive pickup conductor, an insulator layer, a ground plate completion conductive layer, and a circuit board carrying current pickup components, with at least one electrical conductor passing from each end of said inductive pickup conductor through openings in said insulator layer and said ground plate completion conductive layer to said current pickup components.

12. The voltage and current sensor as in claim 11, wherein said current pickup components are symmetrically distributed on said board so as to create an electrical symmetry both in axial and transverse directions.