Method of and apparatus for filtering intermodulation products in a radiocommunication system

• US 5,862,459 A
• Filed: 08/27/1996
• Issued: 01/19/1999
• Est. Priority Date: 08/27/1996
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Charas, Philippe
• Primary Examiner(s): LE, THANH C
• Application Number:
  US08/697,279
• Time in Patent Office: 875 Days
• Field of Search: 455/63, 455/67.1, 455/69, 455/91, 455/101, 455/102, 455/103, 455/110, 455/111, 455/114, 455/115, 455/116, 455/117, 455/119, 375/296, 375/297, 330/129, 330/149, 330/151, 330/124 R, 330/52
• US Class Current: 455/114.3
• CPC Class Codes: H01Q 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 1/3235 using a pilot signal
• CPC Class Codes: H03F 2201/3212 Using a control circuit to adjust amplitude and phase of a signal in a signal path
• CPC Class Codes: H04B 7/06 at the transmitting station

Abstract

An improved feed-forward multi carrier power amplifier architecture is described along with a novel array antenna wherein the improved amplifier may be advantageously put to use. The improved amplifier provides for independent control of unwanted intermodulation products generated in the amplifier. When used in the novel array structure, a separate radiation lobe containing the unwanted intermodulation products may be steered independently from a main radiation lobe. In a cellular base station application, the radiation lobe containing the unwanted intermodulation products may be steered away from the main radiation lobe thereby providing spatial filtering of the unwanted signals. The radiation lobe containing the unwanted intermodulation products may be steered rapidly in time using, for example, a noise like function to provide statistical averaging of the interference in the direction of desired communications.

Claims

1. A feed-forward multi-carrier power amplifier, comprising:

a main amplifier for amplifying an input signal having a plurality of carrier frequencies and producing an amplified output signal including desired signals and unwanted frequency components;

means coupled to said main amplifier for generating an error signal representative of said unwanted frequency components in the amplified output signal;

synthesizer means for generating a pilot signal from a reference signal;

combiner means for combining the pilot signal with the error signal to generate a phase shifter input signal;

phase shifting means for varying, with respect to an input phase of the phase shifter input signal, the output phase of the phase shifter input signal and producing an error correction signal;

phase detector means for generating a phase offset indication of a relative difference in phase between the pilot signal and the error correction signal;

phase control processor means for comparing the phase offset indication with a phase offset value and generating a control signal;

phase control means for adjusting the phase shifting means responsive to the control signal; and

means for combining the error correction signal and the amplified output signal.

2. A feed-forward multi-carrier power amplifier according to claim 1 wherein said phase offset value is a time varying value.

3. A feed-forward multi-carrier power amplifier according to claim 1 where both the phase and amplitude of the error correction signal are varied.

4. A method for controlling the amplitude and phase of unwanted signals in a multi-carrier power amplifier, comprising the steps of:

a) amplifying an input signal having a plurality of carrier frequencies and producing an amplified output signal including a desired signal and unwanted frequency components;

b) generating an error signal representative of said unwanted frequency components in the amplified output signal;

c) generating a pilot signal from a reference signal;

d) combining the pilot signal with the error signal to generate a phase shifter input signal;

e) varying, with respect to an input phase, the output phase of the phase shifter input signal and producing an error correction signal;

f) generating a phase offset indication of the relative difference in phase between the pilot signal and the error correction signal;

g) comparing the phase offset indication with a phase offset value and generating a control signal;

h) adjusting the phase shifting means responsive to the control signal; and

i) combining the error correction signal and the amplified output signal.

5. The method according to claim 4 where both phase and amplitude of the error correction signal are varied.

6. The method according to claim 4 where the phase offset value is time varying.

7. A cellular radio base station having a phased array antenna comprising:

a plurality of feed forward multi-carrier power amplifiers, each comprising;

a main amplifier for amplifying an input signal having a plurality of carrier frequencies and producing an amplified output signal including desired signals and unwanted frequency components;

means for generating an error signal representative of the unwanted frequency components in the amplified output signal;

phase control means for adjusting a phase of said error signal and producing an error correction signal; and

means for combining the error correction signal and the amplified output signal;

a radiating element coupled to each of said plurality of feed-forward power amplifiers and spaced apart from each other along a line such that a plurality of radiating elements forms an array aperture;

means for providing a first phase taper across the radiating elements such that an array factor for the desired signal is oriented at a first angle; and

means for providing a second phase taper across the radiating elements such that an array factor for the unwanted frequency components is oriented at a second angle away from said first angle.

8. A cellular radio base station according to claim 7 wherein said second angle is time varying.

9. A cellular radio base station according to claim 7 where both phase and amplitude of the error correction signal are varied.

10. A cellular radio base station according to claim 7, further comprising:

means for providing an amplitude taper across the radiating elements such that end elements receive slightly less power than center elements.

11. A method for spatially filtering unwanted signal components in a cellular radio base station having a phased array antenna, comprising the steps of:

a) amplifying an input signal having a plurality of carrier frequencies and producing an amplified output signal including a desired signal and unwanted frequency components;

b) generating an error signal representative of the unwanted frequency components in the amplified output signal;

c) adjusting the phase of said error signal and producing an error correction signal;

d) combining the error correction signal and the amplified output signal;

e) radiating the combined error correction signal and the amplified output signal from a plurality of radiators which are spaced apart from each other along a line such that the plurality of radiating elements forms an array aperture;

f) providing a first phase taper across the radiating elements such that the array factor for the desired signal is oriented at a first angle; and

g) providing a second phase taper across the radiating elements such that the array factor for the unwanted frequency components is oriented at a second angle away from said first angle.

12. The method according to claim 11 wherein said second angle is time varying.

13. The method according to claim 11 where both phase and amplitude of the error correction signal are varied.

14. The method of claim 11 further comprising the step of:

providing an amplitude taper for an intermodulation lobe across the radiating elements such that end elements receive less power than center elements, whereby sidelobes of the intermodulation radiation pattern in the direction of the main lobe are reduced.