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FR-4 Embedded Wideband Micro-Balun with Coupled LC Resonators

In this paper, a compact wideband balun has been newly designed and fabricated by using magnetically coupled LC resonators. The proposed balun was comprised of two pairs of magnetic coupled LC resonators which share one resonator with each other. The balun was specially designed in order to obtain precise phase difference, identical magnitude, and DC isolation characteristics between two balanced ports with impedance transformation. It was fabricated by embedding high Q spiral inductors and BTO MIM capacitors into a multi-layered FR-4 packaging substrate. The fabricated balun showed excellent phase and magnitude imbalanced characteristics. The measured results were an maximum insertion loss of 1.4 dB, a minimum return loss of 10 dB, a phase imbalance of 5 degree, and magnitude imbalance of 0.7 dB at wide frequency bandwidth of 1 GHz ranged from 1.6 GHz to 2.6 GHz, respectively. The measured results were well agreed with the simulated ones.