PREDISTORTION COMPENSATION FOR A MICROWAVE AMPLIFIER

• US 3,755,754 A
• Filed: 02/04/1972
• Issued: 08/28/1973
• Est. Priority Date: 02/04/1972
• Status: Expired due to Term

• Current Assignee: John L. Putz
• Original Assignee: John L. Putz
• Inventors: Putz, John L.
• Primary Examiner(s): Lake, Roy
• Assistant Examiner(s): Mullins, James B.
• Application Number:
  US05/223,598
• Time in Patent Office: 571 Days
• Field of Search: 330/124,149,151 332/18,37R 328/163 325/46
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3252 using multiple parallel paths between input and output H03F1/3258, H03F1/3282, H03F1/3294 take precedence

Abstract

A predistortion circuit for compensating distortion in a final amplifier includes a first directional coupler for separating a portion of the input modulated microwave signal into first and second channels having first and second signal components therein, respectively. The second signal component is fed to a distortion amplifier having a distortion transfer characteristic substantially similar to that of the final amplifier to be corrected. The distorted output of the distortion amplifier is proportioned in amplitude by a variable attenuator and combined in phase opposition with the larger undistorted first microwave signal in a second directional coupler to form a composite predistortion microwave signal having distortion components inverted in phase relative to thephase of the undistorted components. The distortion components in the composite predistorted input signal to the amplifier cancel the distortion components introduced by the final amplifier to produce an output signal in the final amplifier having substantially reduced distortion components.

Claims

1. In a distortion corrective input circuit for a microwave amplifier of the type which introduces distortion components of a predetermined character into an input signal supplied thereto, means for separating a modulated microwave signal to be amplified into first and second modulated microwave signal components in first and second microwave channels, respectfully, distortion means for distorting said second microwave signal component in a non-linear manner to produce a distorted second modulated microwave signal component containing both an original signal subcomponent and distortion subcomponents of a character similar to those introduced by said microwave amplifier, and means for combining in substantial phase opposition said first microwave signal component with said distorted second microwave signal component to obtain a predistorted composite modulated input microwave signal to the amplifier, whereby such predistorted composite input signal will compensate the distortion introduced by said microwave amplifier.

2. The apparatus of claim 1 wherein said microwave amplifier is a microwave electron tube.

3. The apparatus of claim 1 wherein said means for combining said modulated first and second microwave signal components in substantial phase opposition includes phase shifter means for shifting the phase of one of said first and second microwave signal components into substantial phase opposition relative to the other.

4. The apparatus of claim 1 wherein said means for combining said first and second microwave signal components in substantial phase opposition includes directional coupler means for adding phase opposed first and second microwave signals to obtain said composite predistorted microwave signal.

5. The apparatus of claim 1 including means for adjusting the relative amplitudes of said first and second microwave signal components such that said first microwave signal component as combined with said distorted second microwave signal component has a substantially higher voltage than that of said distorted second microwave signal component, whereby the undistorted signal components in the combined predistorted composite signal are inverted in phase relative to the distorted signal componeNts of the combined composite signal to be amplified.

6. The apparatus of claim 1 wherein said distortion means and said microwave amplifier to be corrected each include a velocity modulation tube having similar transfer characteristics.

7. The apparatus of claim 3 wherein said phase shifting means is disposed in said first microwave channel.

8. The apparatus of claim 1 wherein said distortion means includes a distortion amplifier having a distortion transfer characteristic similar to that of said microwave amplifier.

9. In a method for predistorting a microwave signal for reducing distortion in an amplified output microwave signal where such distortion is introduced by a microwave amplifier, the steps of:

separating an input modulated microwave signal into first and second modulated microwave signal components in separate microwave channels, distorting said second microwave signal component to produce a distorted second microwave signal component having both original and distortion subcomponents, said distortion subcomponents being similar to those introduced by said microwave amplifier, and combining said first microwave signal component with said distorted second microwave signal component in phase opposition to provide a composite predistorted microwave input signal to he amplifier to be corrected, whereby said composite predistorted microwave input signal will compensate the distortion introduced by said microwave amplifier.

10. The method of claim 9 including the step of proportioning the amplitudes of said combined first and distorted second microwave signals relative to each other such that said first signal as combined with said second signal has a microwave voltage substantially greater than that of said second signal, whereby the phase of the distortion components in said composite predistorted signal will be inverted relative to the phase of the undistorted microwave signal components in said composite predistorted signal.