HOM damping with coaxial dampers in a pillbox cavity without the fundamental mode frequency rejection filter

Coaxial dampers with E-probe and H-loop couplers are used to damp higher-order mode (HOM) in an 840 MHz cylindrical prototype cavity. The dampers are positioned to have minimum coupling at the fundamental frequency, f₀, without using any blocking circuit. The E-probe dampers are used at the equatorial plane of the cavity. The H-loop dampers are used in the end wall of the cavity. The fundamental mode decoupling can be done by positioning the loop plane in the direction of the H-field of the mode. For both dampers, the fundamental mode coupling can be better than -50 dB. The damper load resistance is varied to find the optimum loading. Measurement is made for three cases with 1) three E-probe dampers, 2) three H-loop dampers, and 3) three E-probe and three H-loop dampers