Stub loaded hexagonal open loop band pass filter with improved selectivity

A stub loaded hexagonal open loop band pass filter is presented in this paper. The filter operates in the 850 MHz - 950 MHz band and shows good skirt selectivity. A detailed theoretical analysis of the even and odd modes of excitation of the resonator is performed. The prototype of the filter is fabricated on substrate C-MET LK4.3 with dielectric constant 4.3 and loss tangent 0.0018. The measured results exhibit good agreement with the simulation. The electrical size of the resonator is 0.18 λ
_g
x 0.303 λ
_g
; when λ
_g
= 187.5 mm.