A Compact Planar Branch-Line Hybrid Coupler for Wireless Applications

This paper presents a planar branch-line hybrid coupler with the characteristic of broadband. The frequency range for operating is improved by making consecutive resonators through using two sections. In addition, the compactness is achieved thanks to using zigzag lines. Based on RogerRT/Duroid 5870 substrate layer <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{h}=0.7874$</tex> mm, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon_{\mathrm{r}}=2.33$</tex>, tanδ = 0.0012), the final design witnesses a total dimension of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.37 \lambda_0 \times 10.34 \lambda_0 \times x 0.0057\lambda_0$</tex>, in which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda_0$</tex> is the free-space wavelength at the lowest operating frequency of 2.2 GHz and the bandwidth percentage of 49% at S11 under -10 dB and the isolation of more than 15 dB.