Design and analyze of a highly compact directional coupler based on microwave planar circuit

In this article, an extremely miniaturized branch-line coupler (BLC) operating at 0.9 GHz is analyzed, designed and introduced to enhance the bandwidth accompanied by highly size reduction without via-holes, multilayered technique and air-bridged. A combination of a simple low-pass and band-stop filters is proposed to increase isolation between BLC's ports. This model is equaled by a quarter wavelength line and necessary equations are obtained using even and odd modes analysis. A compact BLC is designed and analyzed using this technique. It is shown that the proposed BLC works as well as conventional ones though with size reduction of about 74% and 4.5% enhancement in bandwidth in analogy with recent branch-line coupler.