Patent ID: 7323955

Claim:
An absorptive bandstop filter, comprising an input port; an output port; two or more resonances, wherein said resonances have substantially the same values of unloaded Q and wherein said resonances have resonant frequencies such that the largest resonant frequency is no more than fifty percent larger than the smallest resonant frequency; one or more frequency-dependent networks, each connecting said input port to said output port, wherein said frequency-dependent networks may have portions in common to the extent that there are at least two distinct predominant signals paths that convey signal power from said input port to said output port, with at least one of said distinct predominant signal paths including no amplifier and with no more than one of said distinct predominant signal paths including one or more amplifiers, at least one of said frequency-dependent networks includes a first bandpass filter, each said frequency-dependent network has frequency-dependent signal transmission magnitude and/or phase characteristics, said frequency-dependent networks or combinations and/or portions thereof do not constitute a 3 dB hybrid coupler, some of said frequency-dependent networks may be electrically tunable, and each of said signal transmission magnitude and phase properties of each of said frequency-dependent networks are selected such that a combined signal power transferred from said input port to said output port is substantially attenuated at one or more stopband frequencies within a range of frequencies defining a stopband and such that the relative 3dB bandwidth of said stopband is substantially independent of a maximum level of attenuation within said stopband and/or the maximum level of said attenuation within said stopband is substantially independent of the unloaded Q of all said resonances.