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

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.

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.

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.