Antenna tuning system for operation over a predetermined frequency range

A tunable antenna system for operation over a predetermined frequency range comprising,

• an antenna having a length and width each significantly less than a quarter wavelength within said predetermined frequency range,
• a controllable reactive element coupled to said antenna having a variable reactance for tuning said antenna in a resonant circuit to the frequency of a desired signal in said frequency range, and
• an antenna-tuning circuit responsive to the frequency to which said antenna is tuned for providing an antenna-tuning signal to said controllable reactive element, to control the reactance of the reactive element so that the antenna remains tuned to the frequency of said desired signal, said antenna-tuning signal comprising,
• a dither component of dither frequency for varying the tuning of said antenna around the frequency of said desired signal,
• said antenna tuning circuit including a level detector for producing a level signal representative of a signal transduced by said antenna,
• said level signal including a deviation signal representative of the difference between the frequency to which said antenna is then tuned and said desired frequency,
• and a deviation detector responsive to said deviation signal for providing a dither amplitude control signal that reduces the amplitude of said dither component with decreasing value of said difference.

A tunable antenna system for operation over a predetermined frequency range comprising,

• first and second antennas each having a length and width each significantly less than a quarter wavelength within said predetermined frequency range with mutual coupling therebetween,
• first and second controllable reactive elements coupled to said first and second antennas respectively each having a variable reactance for tuning said first and second antennas respectively in first and second resonant circuits respectively to the frequency of a desired signal in said frequency range,
• first and second antenna-tuning circuits responsive to the frequency to which the associated one of said first and second antennas is tuned for providing first and second antenna-tuning signals to said first and second controllable reactive elements respectively to control the reactance of said first and second reactive elements respectively so that said first and second antennas remain tuned to the frequency of said desired signal,
• said first and second antenna-tuning circuits including first and second level detectors respectively for providing first and second level signals respectively representative of signals transduced by said first and second antennas respectively,
• said first and second level signals including first and second deviation signals representative of the difference between said desired frequency and the frequencies to which said first and second antennas are then tuned respectively,
• and circuit structure for using said first and second deviation signals to independently control said first and second antenna-tuning signals respectively.