Circuit for accurate tuning of a yittrium iron garnet (yig) filter

Claim 2

An automatic tuning circuit for a magnetically tuned broadband filter characterized by predetermined frequency span across its half power points, comprising means to apply simultaneously a plurality of spaced pairs of marker frequencies to the input of said filter, the frequency span across all of said pairs being essentially equal to said predetermined frequency span, all of said marker frequencies having essentially equal amplitudes, filter tuning means operable to vary the magnetic flux of said filter to vary the tuning of said filter so that the frequencies of its half power points are changed to the frequencies of successive marker frequency pairs and also operable to non-varying state to maintain the magnetic flux of said filter at a level such that the frequencies of the half power points are maintained at frequencies that are about the same as a selected pair of marker frequencies, means connected to the output of said filter to pass a difference beat frequency equal to said frequency span and that exceeds a predetermined threshold and to block said marker frequencies, and counting means connected to the output of said beat frequency passing means to count the number of beat frequency occurrences and operable to change operation of said filter tuning means from varying to non-varying state at a preselected count whereby the frequencies of the half power points are maintained about the same as that pair of the marker frequencies at the preselected count.

Claim 3

A circuit for tuning a broadband magnetically tunable filter that includes an ironclad electromagnet for tuning said filter over a range of the radio frequency spectrum and having a predetermined passband between the half power points of its characteristic comprising; a tuning current source for connection to the electromagnet and for providing current that varies cyclically between limits for sweeping the filter tuning over its range and controllable to stop at any current between those limits and resettable to resume cycling from the stopped current level, a marker generator for producing a pair of equal amplitude signals having frequencies within the tuning range of the filter and wherein the frequency span acrOss the signals is numerically equal to the passband of the filter, a non-linear detector, relay switch means connecting the input of the filter to a signal source or the marker generator and for connecting the output of the filter alternately to a utilization circuit or the non-linear detector, a low pass filter for passing signal energy having a frequency numerically equal to the frequency span across the pair of signals, a threshold detector connected to the output of said low pass filter, means coupled to the output of said threshold detector and coupled to said tuning current source and said relay switch means and responsive to output from said detector for setting the tuning of said broadband filter so that the frequencies of its half power points coincide with the signals from the marker generator.

Claim 4

A circuit for tuning a broadband magnetically tunable filter that includes an ironclad electromagnet for tuning said filter over a range of the radio frequency spectrum and having a predetermined passband between the half power points of its characteristic comprising; a tuning current source for connection to the electromagnet and for providing current that varies cyclically between limits for sweeping the filter tuning over its range and controllable to stop at any current between those limits and resettable to resume cycling from the stopped current level, a marker generator for producing a pair of equal amplitude signals having frequencies within the tuning range of the filter and wherein the frequency span acrOss the signals is numerically equal to the passband of the filter, a non-linear detector, relay switch means connecting the input of the filter to a signal source or the marker generator and for connecting the output of the filter alternately to a utilization circuit or the non-linear detector, a low pass filter for passing signal energy having a frequency numerically equal to the frequency span across the pair of signals, a threshold detector connected to the output of said low pass filter, means coupled to the output of said threshold detector and coupled to said tuning current source and said relay switch means and responsive to output from said detector for setting the tuning of said broadband filter so that the frequencies of its half power points coincide with the signals from the marker generator.

Claim 5

A circuit for tuning a broadband magnetically tunable filter as defined in claim 2 wherein said marker generator produces a plurality of pairs of equal amplitude signals within the tuning range of the filter and wherein the frequency difference between successive pairs is no less than the passband of the filter and the frequency span across the signals of each pair is equal to the passband of the filter, and wherein said last-mentioned means is programmable for tuning the said broadband filter to a selected one of said signal pairs.

Claim 6

A circuit for tuning a broadband magnetically tunable filter as defined in claim 3 wherein all the signals generated by said marker generator are spaced apart by equal frequency differences.