A Novel Compact Gysel Power Divider with Bandpass Filtering Responses

This study presents a novel compact design of the Gysel topology and a filtering power divider (FPD) that utilizes a coupling structure. The proposed design replaces the traditional four-quarter wavelength transmission lines of the Gysel power divider with transmission lines and lumped components, resulting in a significantly reduced circuit size. Furthermore, the introduction of this coupling structure ensures the integration of the filtering and power division functions. Two transmission zeros are created near the passband to enhance the frequency selectivity of the responses. Theoretical analysis is carried out, and closed-form equations are derived based on the even–odd-mode method. To validate the theory, a three-port equal Gysel FPD operating at 2 GHz was designed and fabricated. The simulated and measured results demonstrate that this FPD has good power splitting and filtering capability with the size of 0.15 λg × 0.25 λg (λg is the medium wavelength of the central frequency), which is a significant reduction compared to the existing Gysel FPDs. The simulated and measured results are presented to verify the theoretical derivation, demonstrating good features, such as a return loss greater than 15 dB, isolation greater than 15 dB, and an insertion loss of about 4.02 dB (3 + 1.02 dB) in the passband.