Impedance-matching transformers for rf driven co2 gas discharge lasers

Abstract

In a CO 2 gas discharge laser energized by a radio frequency (RF) power source a transformer having selectively variable output impedance is used to match output impedance of the power source to the impedance of discharge electrodes of the laser. A similar transformer can be used to impose a selective variable phase-shift on the RF power from the source. The variable impedance transformer can also be used for impedance matching between amplifier stages in the power source.

1 . An electrical circuit for optimizing a transfer of RF-power between a source thereof having a source-frequency, and a load, the circuit comprising:
 first and second transmission-line sections each thereof having first and second opposite ends, with the first end of the first section being connected to the source, the second end of the first section being connected to the first end of the second section via a node therebetween, and the second end of the second section being connected to the load, with each of the first and second transmission-line sections having an electrical length equal to or less than about one-twelfth of a wavelength at the source-frequency; and   an electrical component having an electrical characteristic connected to the node between the first and second transmission-line sections, with the electrical characteristic of the component being selectively variable for optimizing the transfer of the RF-power between the source and the load.   
     
     
         2 . The circuit of  claim 1 , wherein the electrical component is a capacitor having a selectively variable capacitance. 
     
     
         3 . The circuit of  claim 2 , wherein the capacitor has first and second opposite plates with the first plate being connected to the node between the first and second transmission-line sections and the second plate being connected to ground. 
     
     
         4 . The circuit of  claim 2 , wherein the transformer has an output-impedance and varying the capacitance of the capacitor varies the output-impedance of the transformer. 
     
     
         5 . The circuit of  claim 1 , wherein the electrical component is a third transmission-line section having first and second opposite ends and a selectively variable electrical-length. 
     
     
         6 . The circuit of  claim 5 , wherein the first end of the third transmission-line section is connected to the node between the first and second transmission-line sections and the second end of the third transmission-line section is open. 
     
     
         7 . The circuit of  claim 6 , wherein the transformer has an output-impedance and varying the electrical-length of the third transmission line section varies the output-impedance of the transformer. 
     
     
         8 . The circuit of  claim 6 , wherein the electrical length of the third transmission line section is less than about one-twelfth of a wavelength at the source frequency. 
     
     
         9 . The circuit of  claim 1 , wherein the electrical component is an inductor having a selectively variable inductance. 
     
     
         10 . The circuit of  claim 9 , wherein the inductor has first and second opposite ends the first plate being connected to the node between the first and second transmission line sections and the second end being connected to ground. 
     
     
         11 . The circuit of  claim 9 , wherein the transformer imposes a phase-shift on the RF power delivered by the source and varying the inductance of the inductor varies the phase-shift imposed by the transformer. 
     
     
         12 . An electrical circuit for optimizing a transfer of RF-power between a source thereof having a source-frequency and a source impedance, and a load having a load impedance, the circuit having an input impedance and an output impedance and comprising:
 first and second transmission-line sections each thereof having first and second opposite ends with the first and second transmission-line sections each thereof having a characteristic impedance, the first end of the first section being connected to the source, the second end of the first section being connected to the first end of the second section via a node therebetween, and the second end of the second section being connected to the load, with each of the first and second transmission-line sections having an electrical length equal to or less than about one-twelfth of a wavelength at the source-frequency;   a capacitor connected to the node between the first and second transmission-line sections, the capacitance of the capacitor cooperative with the electric length and characteristic impedances of the transmission line sections determining the output-impedance of the circuit; and   wherein the capacitance of the capacitor is selectively variable for varying the output-impedance of the circuit to match the load-impedance thereby optimizing the transfer of the RF-power between the source and the load.   
     
     
         13 . The circuit of  claim 12 , wherein the load-impedance has a value between a maximum anticipated value and a minimum anticipated value and the capacitance of the capacitor is variable between a minimum value and a maximum value, wherein the characteristic impedance of the first transmission-line section is about equal to the maximum anticipated value of the load-impedance, the characteristic impedance of the second transmission-line section is about equal to the source-impedance, and wherein varying the capacitance of the capacitor between the minimum and maximum values thereof varies the output impedance of the circuit between the maximum and minimum values, respectively, thereof. 
     
     
         14 . The circuit of  claim 13 , wherein the source-impedance is 50 Ohms, the maximum and minimum values of load-impedance are 25 Ohms and 12 Ohms respectively, the minimum and maximum capacitance values of the capacitor are about 1.5 picofarads and about 30 picofarads respectively. 
     
     
         15 . An electrical circuit for optimizing a transfer of RF-power between a source thereof having a source-frequency and a source impedance, and a load having a load impedance, the circuit imposing a phase-shift on the RF power transferred thereby, the circuit comprising:
 first and second transmission-line sections each thereof having first and second opposite ends with the first and second transmission-line sections each thereof having a characteristic impedance, the first end of the first section being connected to the source, the second end of the first section being connected to the first end of the second section via a node therebetween, and the second end of the second section being connected to the load, with each of the first and second transmission-line sections having an electrical length equal to or less than about one-twelfth of a wavelength at the source-frequency;   an inductor connected to the node between the first and second transmission-line sections, the inductance of the inductor cooperative with the electric length and characteristic impedances of the transmission line sections determining the phase-shift imposed by the circuit on the transferred RF power; and   wherein the inductance of the inductor is selectively variable for varying the phase shift imposed by the circuit thereby optimizing the transfer of the RF-power between the source and the load.   
     
     
         16 . The circuit of  claim 15 , wherein the phase-shift has a value between a minimum desired value and a maximum desired value and the inductance of the inductor is variable between a minimum value and a maximum value, wherein the characteristic impedance of the first transmission-line section is about equal to the load-impedance, the characteristic impedance of the second transmission-line section is about equal to the source-impedance, and wherein varying the inductance of the inductor between the minimum and maximum values thereof varies the phase-shift imposed by the circuit between the minimum and maximum values, respectively, thereof. 
     
     
         17 . The circuit of  claim 16 , wherein the source-impedance is 50 Ohms, the load-impedance is 50 Ohms respectively, the minimum and maximum inductance values of the capacitor are about 40 nanohenries and 500 nanohenries, and the minimum and maximum phase-shifts are +5° and +70°.