Design, development, and analysis of 1 to 4, anti-phase in-line RF power splitter for low-frequency ISM band applications

A wideband, low-loss balun-based anti-phase radio-frequency power splitter using a ferrite core is studied. The inherent impedance matching with the existing system makes it an in-line power splitter; its impedance matches at the input port without any extra impedance transformer, resulting in low insertion loss. The design approach is chosen based on the S-parameter analysis to grasp the possible implementations. The best possible implementation is analyzed based on the well-known theories, and the final S-matrix is derived. To estimate the high-frequency limitation due to the inter-winding capacitances, the implemented 1-to-4 anti-phase power splitter was tested using the vector network analyser (VNA) to find out the self-resonance of the winding coils. The practical measurements of the implemented power splitter show that the insertion loss is less than 2.1 dB, the port-to-port isolation is more than 14.5 dB, and the bandwidth is more than 23 MHz at 17 MHz.