Bandstop filter having symmetrically altered or compensated quarter wavelength transmission line sections

A bandstop filter comprising:

• a transmission line having first and second ends joined by a plurality of interconnected internal sections with each said internal section having a predetermined electrical length;
• a plurality of substantially similar resonators spaced along and coupled to selected ones of said internal sections of said transmission line with at least a selected, first internal section, increased in length a predetermined amount thereby forming a first modified section and a selected second internal section decreased in length said predetermined amount thereby forming a second modified section;
• and
• first and second impedance transformers coupled respectively to said ends.

A filter comprising:

• an elongated transmission line having a first impedance value, a first end and a second end;
• a first resonator coupled to said transmission line;
• a second resonator coupled to said transmission line on one side of said first resonator and spaced therefrom a distance corresponding to an odd number of quarter wavelengths, decreased by a predetermined amount thereby forming a decreased section;
• a third resonator coupled to said transmission line on a second side of said first resonator and spaced therefrom a distance corresponding to an odd number of quarter wavelengths increased by said predetermined amount thereby forming an increased section;
• first and second impedance transforming transmission line sections, each of said sections having a characteristic impedance with a value less than said first impedance and with one of said sections coupled to said first end and the other to said sections coupled to said second end.

A bandstop filter comprising:

• a stepped impedance transmission line having first and second ends and a plurality of quarter wavelength sections therebetween with selected ones of said sections having a characteristic impedance value in excess of a characteristic impedance value of other sections;
• and
• a plurality of substantially identical resonators spaced along and coupled to said transmission line with said plurality of resonators including
• a first resonator,
• a second resonator located on one side of said first resonator, spaced therefrom by an odd number of quarter wavelength sections of said transmission line, wherein one of said quarter wavelength sections has a length in excess of a quarter wavelength by a predetermined amount;
• a third resonator located on the other side of said first resonator, spaced therefrom by an odd number of quarter wavelength sections of said transmission line, one selected section of which has a length that is reduced from a quarter wavelength by said predetermined amount.

A bandstop filter with a center frequency f.sub.0 having an associated quarter wavelength comprising:

• a common communication line, having a first end and a second end, including a plurality of sections therebetween, wherein each said section has an electrical length corresponding to an odd number of quarter wavelengths with each said section reduced from said odd number of quarter wavelengths in electrical length by a uniform compensating amount,
• wherein said communication line includes a first, central, transmission line having a characteristic impedance of a first value, and
• wherein said communication line also includes first and second impedance transformers, each coupled to a respective end of the central transmission line, and
• a plurality of substantially identical tunable, dielectric resonators spaced along said communication line and coupled in varying degrees to said line, with selected of said resonators located adjacent to at least one of said reduced length sections;
• wherein at least some of said resonators are coupled to said central transmission line
• with selected resonators of said plurality tuned to frequencies above the center frequency and with others tuned to frequencies below the center frequency;
• and
• wherein two of said resonators have resonant frequencies of f.sub.1 and f.sub.2, respectively, wherein said resonators are tuned such that said center frequency is approximately equal to (f.sub.1 +f.sub.2)/2, and wherein one of said reduced length sections has one of said resonators coupled to one end thereof and another of said resonators is coupled to another end thereof.

A bandstop filter with a center frequency f.sub.0 having an associated quarter wavelength comprising:

• a common communication line, having a first end and a second end, including a plurality of sections therebetween, wherein each said section has an electrical length corresponding to an odd number of quarter wavelengths with each said section reduced from said odd number of quarter wavelengths in electrical length by a uniform compensating amount;
• wherein said communication line includes a first, central, transmission line having a characteristic impedance of a first value, and
• wherein said communication line also includes first and second impedance transformers, each coupled to a respective end of the central transmission line, and
• a plurality of substantially identical tunable, dielectric resonators spaced along said communication line and coupled in varying degrees to said line, with selected of said resonators located adjacent to at least one of said reduced length sections;
• wherein at least some of said resonators are coupled to said central transmission line;
• wherein each of said impedance transformers includes a transmission line impedance transformer having an electrical length on the order of an odd number of quarter wavelengths and has a characteristic impedance value different than said first impedance value;
• wherein some of said resonators are tuned to frequencies above the center frequency and others are tuned to frequencies below the center frequency;
• a conductive housing;
• a low loss, high dielectric constant, ceramic material, supported with low loss material within said housing,
• an adjustable frequency tuning mechanism carried by said housing, and
• an adjustable coupling mechanism carried by said housing.