Compact Wide Bandwidth Balun Based on Modified Asymmetric Broadside Coupled Lines

We present the design and fabrication of a compact, wide bandwidth balun on a multilayer organic substrate. The balun is designed using asymmetrical broadside coupled lines on a patterned ground structure. The experimental results show that the balun has a measured insertion loss less than 1 dB from 0.5–9 GHz and better than 2.7 dB up to above 20 GHz. The measured phase and amplitude imbalances are less than 8 degree and 1 dB respectively from 1 GHz to above 20 GHz. The balun has a compact size of 5.5 mm $,\times,$ 3.5 mm $,\times,$ 0.3 mm.