A Tetra-Band Microstrip Branch-Line Coupler Using Equivalent Quarter-Wavelength Transmission Lines

The tetra-band branch-line coupler (BLC) using equivalent quarter-wavelength transmission lines (EQTLs) is proposed. Moreover, the design equations of the tetra-band BLC are provided in this paper. The presented EQTL is comprised of a section of arbitrary-length transmission line (TL) and a coupled-lines (CLs). A desired tetra-band operation can be achieved by proper design of the coupling level for those coupled-line sections. A 3-dB tetra-band microstrip BLC located at the frequencies of 0.9/2.5/4.0/5.6 GHz is designed, fabricated and measured for verification. The measurements agree well with the simulations, and validate good performance over all the four passbands.