Tunable bandpass filter with constant absolute bandwidth using single tuning element

1) A tunable bandpass filter to provide a constant absolute bandwidth across a tuning range, comprising:

• a) a pair of resonators to determine a filter center frequency, each said resonator has a rectangular waveguide cavity, wherein said filter center frequency depends on the dimensions of said rectangular waveguide cavity;
• b) a pair of side walls attached to said pair of resonators to form a filter housing;
• c) a tuning element movably attached to at least one of said pair of side walls and extending in said filter housing and movable orthogonally to said pair of resonators, and wherein said dimensions of said rectangular waveguide cavity change by moving said tuning element, thereby said filter center frequency is changed;
• d) a plurality of inter-resonator coupling structures to provide a filter bandwidth, each said inter-resonator coupling structure located at a predefined location between said pair of resonators to couple an energy from one rectangular waveguide cavity to another rectangular waveguide cavity, thereby providing a band-pass frequency behavior and to ensure that the filter bandwidth remains constant even when the dimensions of the rectangular waveguide cavity are changed by moving the tuning element, and
• e) a pair of input/output couplings to provide a reflection co-efficient of the tunable bandpass filter, and to cause an input power entering the filter with minimum reflections.