Patent ID: 8022792

Claim:
A waveguide filter comprising: at least one evanescent waveguide section; and at least one propagating dielectric filled waveguide section coupled to the at least one evanescent waveguide section, the waveguide filter utilizing at least one TM mode, the at least one evanescent waveguide section being defined using the following equations: Y e | i = - 1 j ⁢ ⁢ X 0 ⁢ coth ⁢ ⁢ γ e ⁢ l e | i ( 1 ) sinh ⁡ ( γ e ⁢ l e | i ) = - Δω 0 ω 2 - ω 1 ⁢ g i ⁢ g i + 1 ω 0 ⁢ C i ⁢ ω 0 ⁢ C i + 1 ( 2 ) ω 0 C i =coth γ e l e|i−1 +coth γ e l e|i =Y e|i−1 +Y e|i normalized (3) where Y e|i is a resultant admittance of a capacitor associated with a J inverter in the evanescent waveguide, l e is a length of the evanescent sections, γ e is a propagation constant inside the evanescent waveguide, ω 0 is associated with a center frequency of the filter, ω 1 and ω 2 are associated with a lower and upper passband edges, respectively, g i are low-pass prototype values, and Δ is a correction factor for the at least one TM mode, which corrects the steeper frequency response of the evanescent cut-off compared to lumped elements and is given by: Δ = 2 1 + 1 1 - ( λ c λ 0 ) 2 ( 4 ) where λ c is a cutoff wavelength and λ 0 is a wavelength at the center frequency.