A 23:1 bandwidth ratio balun on multilayer organic substrate

We present the design and development of a novel, super wide bandwidth balun on a multilayer organic Liquid Crystal Polymer (LCP) substrate. The balun has a measured bandwidth ratio of 23:1, from 80 MHz to 1860 MHz. Within the operating bandwidth, the balun achieves an input return loss of better than 10 dB, an insertion loss of better than 1 dB, an amplitude imbalance of better than 0.4 dB and a phase imbalance of better than 10 degree. The size of the balun is 40.64 mm × 40.64 mm or 0.22 λ_g × 0.22 λ_g, where λ_g is guided-wavelength at the center frequency of 970 MHz. This balun achieves the largest bandwidth ratio reported to date on a multi-layered printed circuit board.