Oscillator coupled through cylindrical cavity for generating low noise microwaves

A low noise microwave reflection oscillator having a rightcircular cylindrical waveguide cavity as the frequency determining element, said oscillator comprising:

• a high gain microwave oscillator circuit having an output and a negative resistance means for providing positive internal feedback sufficient to cause oscillations at microwave frequencies;
• a right circular cylindrical resonant cavity for resonating with a cylindrical TE.sub.011 mode, said resonant cavity having two end plate portions, a cylindrical body portion of length L and diameter D where (D/L).sup.2 is greater than 1.7 and less than 2.5, and comprising:
• input coupling means located at one of said end plates for coupling a microwave signal from said oscillator circuit output to said cavity, said coupling means comprising a small circular wire loop disposed in a plane perpendicular to said end plates;
• output coupling means located at the other of said end plates for coupling a useful output microwave signal to a load connected thereto;
• and
• suppression means for suppressing within the cavity resonating modes of oscillation other than the TE.sub.011 mode and comprising:
• a single post connected to one of said end plates and disposed at a point on said plate of maximum charge concentration, said post electrically shortening the length dimension L at the point of connection to said end plate;
• and
• a continuous circular gap less than 0.10 D across separating a portion of the interior cavity surface of each plate from said cylindrical housing to restrict microwave signal current flow from the inner surface of said housing to said end plates.

A right-circular cylindrical waveguide cavity for resonating with a cylindrical TE.sub.011 mode when used as the frequency determining element in a low noise microwave oscillator, said cavity comprising:

• a right-circular cylindrical metallic housing of length L and diameter D where (D/L).sup.2 is approximately 1.92;
• two end plates enclosing said housing, each plate having a continuous circular gap approximately 0.01 D across separating a portion of the interior surface of each plate from said cylindrical housing to restrict microwave signal current flow from the inner surface of said housing to said end plates, said end plates and said housing defining a resonant cavity;
• and
• a single circular post connected to the interior surface of one of said end plates and extending therefrom into said cavity, and disposed at a point on said plate where the TM.sub.111 mode electric field Z-component into the cavity interior would be at a maximum, said post having a length and diameter, said length being adjusted so that the Q of the cavity is a maximum at the desired resonant frequency and said diameter equal to or less than its length;
• said post and said circular gaps for suppressing within the cavity resonating modes of oscillation other than the TE.sub.011 mode.