Wideband Microstrip Filtering Power Divider Designed by Direct Synthesis Technique (DST)

In this letter, a wideband microstrip filtering power divider (FPD) with a fifth-order bandpass response is discussed. Its even- and odd-mode models are obtained, which separately determine the transmission property and the isolation of the FPD. At the first, the distributed-element to lumped-element equivalence is applied to derive its lumped-element equivalent circuit of the even-mode model, so that its physical mechanism is clearly revealed, such as how the resonances are generated and coupled. Then, the direct synthesis technique (DST) we recently proposed is applied to determine the initial electric parameters of the FPD. Further, the initial values of the isolation resistors are calculated by letting the odd- and even-mode reflection coefficients be equal. Based on these initial values, the performance of the FPD can be easily optimized. For demonstration, an FPD example was designed, fabricated, and measured, whose 3-dB fractional bandwidth is as wide as 65.4% and isolation is 22.5 dB over the passband. Compared with other ones, the FPD is featured by a wide band, good selectivity, compact size, and so on.