Miniaturized hybrid ring coupler using fan-shaped apertures on the ground plane

A novel hybrid ring coupler is proposed for circuit miniaturization in this paper. The coupler is constructed on a substrate of high dielectric constant, and multiple open stubs are connected on the inside of the ring for the purpose of size reduction. To achieve high characteristic impedance of the main lines in limited fabrication tolerance, fan-shaped apertures are formed on the ground plane underneath the relative wide microstrip conductors in the center. The size of the ring coupler is one third of the conventional one, solving the problem that ring coupler area shrink factor can not be very small for substrate of high dielectric constant in many papers. The design method is validated by simulation results.