The disclosed radio frequency (RF) bandpass filter may include an RF transmission medium that defines (1) a plurality of cavities aligned parallel to each other along a major axis, where (a) each cavity includes planar surfaces that define (i) a first dimension aligned with the major axis and (ii) second and third dimensions aligned perpendicular to the major axis and each other, where the first dimension is shorter than the second and third dimensions and (b) each adjacent pair of cavities is coupled by an inter-cavity slot, (2) an RF inlet that couples a received RF signal to a first cavity at a first end of the plurality of cavities, and (3) an RF outlet that couples a filtered RF signal from a second cavity at a second end of the plurality of cavities externally to the filter. Various other filters and manufacturing methods thereof are also disclosed.