Coupling-Parameter-Based Unequal Power Divider for On-Chip Systems

This article proposes a new kind of unequal power divider by using coupling parameters, featuring of naturally compact size, especially in on-chip systems. In the reported unequal power dividers, the unequal ratio was usually realized by selecting different characteristic impedances of quarter-wave ( $\lambda $ /4) or quasi- $\lambda $ /4 transmission lines (TLs). However, the circuit sizes were large, which are unacceptable for on-chip systems. In addition, the bandwidths of adjacent branches mismatch since the coupling coefficients change with different characteristic impedances of $\lambda $ /4 TLs. To solve this issue, this article proposes a first-time realization of unequal power division by using the coupling parameters inside each branch of filtering power divider, including the external quality factors ( $Q_{e}$ ) and coupling coefficients (k). The power division ratio is analytically derived, and the divided power in each branch increases with lower characteristic impedance of input $Q_{e}$ . In addition, by adjusting multiple coupling parameters, there will be enough design freedom to realize the desired power ratio, impedance matching, and matched or unmatched bandwidth. At last, an isolated strip line is added to improve the output isolation between adjacent branches on the chip. For demonstration, a 25-GHz 1.4:1 power divider is designed using GaAs-based integrated passive device (IPD) technology. Low loss, high isolation, small chip size, and a high-selectivity filtering response are achieved in millimeter-wave range, indicating the possible application of the proposed power divider in RF chips.