Low cost octave directional coupler based on substrate integrated coaxial line (SICL) technique

In this paper, the design of a low cost compact octave directional coupler based on the substrate integrated coaxial line technique is presented. The proposed coupler utilized an exponential-tapered aperture to achieve desired coupling level and operational frequency band. Experimental prototype is fabricated using standard PCB process. Measured results show that the SICL coupler realizes octave coupling of -19.1±1 dB for 5.2~12.3 GHz. The return loss is more than 14.3dB, the directivity is better than 15.1dB, and the phase difference is 90±2.1 Deg for the whole operational band.