Abstract: A method of tuning the stopband attenuation of an absorptive bandstop filter having at least a first and second resonator, where the first resonator includes a first tuning element that exhibits a first resonant frequency, the second resonator includes a second tuning element that exhibits a second resonant frequency, and the tuning elements are used to adjust the corresponding resonant frequencies, includes 1) adjusting the first resonant frequency using the first tuning element; and 2) adjusting the second resonant frequency using the second tuning element, such that both resonant frequencies are coordinated to obtain a selected stopband attenuation level and to thus realize a frequency-selective variable attenuator.

Abstract: An absorptive bandstop filter includes at least two frequency-dependent networks, one of which constitutes a bandpass filter, that form at least two forward signal paths between an input port and an output port and whose transmission magnitude and phase characteristics are selected to provide a relative stopband bandwidth that is substantially independent of the maximum attenuation within the stopband and/or in which the maximum attenuation within the stopband is substantially independent of the unloaded quality factor of the resonators. The constituent network characteristics can also be selected to provide low reflection in the stopband as well as in the passband. The absorptive bandstop filter can be electrically tunable and can substantially maintain its attenuation characteristics over a broad frequency tuning range.

Abstract: An electromagnetic bandstop filter comprises a microwave circuit, at least one microwave resonator, coupling means that couples electromagnetic energy to and from the microwave resonator, and an impedance transformer coupled to, and in series with, the coupling means, wherein the transformer is coupled to the resonator only through the coupling means, and wherein the impedance transformer is shunt coupled to the microwave circuit. The impedance transformer comprises at least two series-connected transmission line sections of different impedances.

Abstract: A preferred realization of a frequency spectrum filter incorporating multiple signal paths is selected using a new design tool, a plot of resonator coupling coefficient values representing filter designs having equivalent signal transfer characteristics. The design plot is formed by first subjecting an initial matrix of resonator coupling coefficients, representing a particular filter design, to pre-multiplications by selected plane rotation matrices--which each have their respective rotation angles--and to post-multiplications by their transposes. Equations for the individual elements that form the resulting modified coupling coefficient matrix are then plotted over a range of one of the rotation angles. Examination of the result plot leads to a selection of a set of coupling values in observance of predetermined criteria. An optimum realization of the filter is then constructed by adjusting the physical resonator couplings so that they conform to the coupling values selected from the plot.

Abstract: An improved multiplexer comprises a housing, a transmission line transformer section within the housing extending in a first direction, and at least two interdigital transmission line filters adjacently disposed within the housing along the first direction. The transformer section has a first end electrically coupled to an antenna circuit connector, and a second end electrically coupled to the housing (i.e. grounded). Each filter includes several resonating elements. At least one resonating element of each filter is located in proximity with a portion of the transformer such that electrical coupling between the filter and the transformer is established. The length of each coupling portion of the transformer is approximately one-quarter electrical wavelength at the center frequency of the associated filter. The dimensions of the filter cavities are preferably selected to be as small as possible without unacceptably degrading the filter insertion loss.

Abstract: An RF filter having a housing defining a cavity with plural elongated resonators and plural resonator decouplers adjacent each of plural pairs of the resonators in the housing. The decouplers are grounded adjacent each of their ends only to the housing to provide an enhanced resonator decoupling effect. The filter may instead comprise a dielectric block with resonator holes and resonator decoupler holes each appropriately metalized with the decoupler holes being grounded at each end at external metalized block surfaces.

Abstract: A poly-band filter includes a folded metal housing which defines an interior region partitioned by a divider. First and second pluralities of resonators are provided in the housing. Alternately increasing and decreasing degrees of coupling are provided between adjacent resonators in the housing. Slot coupling is provided between first and second non-adjacent resonators displaced from input/output connectors for the filter.

Abstract: A multi-resonator notch filter incorporates a variable impedance transmission line with impedance values going from a relatively low value and increasing upward to a relatively high value then back down to a relatively low value again. A plurality of resonant cavities is coupled to the relatively high central impedance line section of the filter at odd multiples of quarter wavelength intervals. Other resonators can be coupled to lower impedance sections of the transmission line. The locations of selected resonators on the quarter wavelength intervals can be altered thereby increasing and decreasing the nominal quarter wavelength intervals of selected internal pairs by a predetermined amount thereby providing acceptable levels of performance with fewer resonators.

Abstract: A multi-resonant notch filter incorporates a stepped impedance transmission line with impedance values going from a relatively low value and increasing upward to a relatively high value then back down to a relatively low value again. A plurality of resonant cavitites is coupled to the relatively high central impedance line section of the filter. Other resonators can be coupled to lower impedance sections of the transmission line.