Miniaturized broadband rat-race hybrid for UHF biomedical and healthcare applications and TV white space systems

This paper presents the simulated and measured results for a miniaturized broadband rat-race hybrid for UHF biomedical and healthcare applications and TV white space systems. The hybrid was implemented on an FR4 substrate using spiral inductors and chip capacitors. For the frequency range of 430-710 MHz, which corresponds to the relative bandwidth of more than 49%, the rat-race hybrid exhibits power splits of -3.5 ± 0.7 dB, return losses greater than 14 dB, isolation between output ports greater than 21 dB, and errors in the desired relative-phase difference between output ports less than 4°.