Patent ID: 7495528

Claim:
A triplexer circuit for separating an input signal into signals in three frequency bands which are different from each other, comprising: a first filter module that passes signals in a first frequency band; a second filter module that passes signals in a second frequency band; and a third filter module that passes signals in a third frequency band, wherein the first, second, and third filter modules are connected in parallel with each other, the second and third filter modules form a parallel resonant circuit for signals in the first frequency band, the first and third filter modules form a parallel resonant circuit for signals in the second frequency band, and the first and second filter modules form a parallel resonant circuit for signals in the third frequency band, wherein when a pass frequency of the first filter module is f 1 , a pass frequency of the second filter module is f 2 , and a pass frequency of the third filter module is f 3 , phase components of reflection coefficients at the pass frequencies f 1 , f 2 , and f 3 in the filter modules satisfy the following conditions: θ 2 ( f 1)+θ 3 ( f 1)=2 n 1 π and θ 2 ( f 1)≠(2 p 1 −1)π, θ 3 ( f 1)≠(2 m 1 −1)π (A1) θ 3 ( f 2)+θ 1 ( f 2)=2 n 2 π and θ 3 ( f 2)≠(2 p 2 −1)π, θ 1 ( f 2)≠(2 m 2 −1)π (A2) θ 1 ( f 3)+θ 2 ( f 3)=2 n 3 π and θ 1 ( f 3)≠(2 p 3 −1)π, θ 2 ( f 3)≠(2 m 3 −1) (A3) where θ i (f 1 ): phase of a reflection coefficient at the frequency f 1 in the i-th (=1, 2, 3) filter module, θ i (f 2 ): phase of a reflection coefficient at the frequency f 2 in the i-th filter module, θ i (f 3 ): phase of a reflection coefficient at the frequency f 3 in the i-th filter module, n 1 , n 2 , n 3 , m 1 , m 2 , m 3 , p 1 , p 2 , p 3 : arbitrary integers.