Multiple passband filter

A multiple passband filter comprising:

• a plurality of cavities, one of which comprises an input port and another of which comprises an output port, each of the cavities further comprising:
• first tuning apparatus disposed along a first axis for tuning the cavity to resonance in a first resonant mode;
• second tuning apparatus disposed along a second axis that is substantially orthogonal to the first axis for tuning the cavity to resonance in a second resonant mode;
• and
• mode coupling apparatus for adjusting the amount of energy coupled between the first and second resonant modes, wherein the mode coupling apparatus of adjacent cavities is disposed orthogonal with respect to each other;
• wherein each of the orthogonal resonant modes is independently tunable to realize a separate pole of a filter function, and wherein a plurality of poles are concentrated in a desired frequency range comprising the passband of the filter, a plurality of zeroes are located outside of the desired frequency range comprising the passband to form passband edges, and one or more zeroes are located in a central portion of the frequency range comprising the passband to form multiple passbands within the passband edges.