PCB Fabricated Passive RF Balun for 3 T MRI Applications

In this article, a passive balun for 3 T magnetic resonance imaging (MRI) scanners operating at 128 MHz was designed and analyzed to successfully convert a balanced input signal from a dipole/loop antenna into an unbalanced output signal connected to preamplifiers or transmission line. The lumped circuit element, mathematical modeling and simulations and measurement results for the balun performance are shown. The proposed balun is intended to be integrated in electric and magnetic field probes for time domain monitoring of the time-varying RF signals during medical device testing. The implemented balun is fabricated on a low-cost, copper cladded, four-layer FR4 printed circuit board (PCB) with overall footprint of 13.4 mm $\times 14$ mm. A comparison among the ADS momentum simulations and the measured results indicates good agreement with the measured insertion and return losses of better than -1.5 dB and -15 dB, respectively.