Three-port 3-dB power divider terminated by different impedances and its application to MMIC's

The three-port 3-dB power divider (T3PD) terminated by different impedances considered in this paper is very useful for a small-sized circuit design. New design equations for T3PD's are derived. They can be applied to T3PD's with both different termination impedances and, especially, a 3-dB power di vision. If a T3PD is terminated by different impedances, scattering paramet ers can not be derived with conventional even- and odd-mode methods. Under these conditions, basis-independent normalized scattering parameters are de rived. As these scattering parameters are only dependent on the ratio of R- c to R-b (where R-c and R-b are two termination impedances that are connect ed with an isolation resistor), the ratio of R-c to R-b "t" is introduced t o analyze all load conditions and the derived scattering parameters are pro ven to be correct by a commercial program. For the frequency-response chara cteristics, a T3PD terminated by 40, 50, and 60 Omega has been simulated us ing ideal transmission lines. Also, a simple method how to determine the ex act values of two indispensable elements-coplanar rectangular inductances ( C_RIND's) and coplanar metal-insulator-metal capacitors (C_MIM's)-in coplan ar monolithic-microwave integrated-circuit (C_MMIC) technology is presented using a resonator technique. As another trial, a new type of lumped-elemen t three-port 3-dB power divider (LET3PD) with low insertion loss and its de sign equations are presented. Finally, a coplanar T3PD terminated by 30, 53 , and 47 Omega was fabricated on Al2O3 substrate (epsilon(r) = 9.9 and h = 635 mu m) and it shows good agreement between experimental and theoretical results.