Using Vias and Slots for Miniaturization of the Directional Couplers

Abstract

The possibility of increasing the effectiveness of miniaturization of the planar directional coupler by applying vias along the edge of the printed capacitor is studied. The substrate material is the well-known FR4 with the following substrate parameters - dielectric permeability 4.4, thickness 1 mm and dielectric loss tangent 0.02. The standard and compact (using the low-pass filters replacing the transmission lines segments) designs of the 3-dB branch-line microstrip directional coupler were synthesized and simulated having the central operational frequency of 1800 MHz. The layout of a more compact coupler was obtained, which area is less than 75.8% than that of the design in the traditional version and has bandwidth defined by the 20-dB isolation level of 170 MHz. It was found that the addition of the metallized slots or vias can be very helpful in getting the better miniaturization performance with the use of low-pass filters instead of the transmission line segments.