Doubly miniaturized rat‐race hybrid coupler

Two complementary miniaturization techniques have been applied to reduce the size of a rat‐race hybrid coupler: (i) conventional microstrip sections have been replaced with their diminished low‐impedance counterparts as the first step of size reduction and (ii) novel fractal‐shaped compact microstrip resonant cells dedicated to efficiently shorten low‐impedance transmission line segments have been implemented as the second step of circuit miniaturization.The experimental results are in excellent agreement with theoretical characteristics. Moreover, the application of the proposed complementary miniaturization methods enabled the achievement of ∼73% scale of size reduction, which illustrates the attractive possibilities of the approach.