A Compact and Low-cost RF Balun with Improved Bandwidth and Isolation

This paper presents a design for a RF balun with compact size, low-cost and improved bandwidth and isolation. It consists of a wide-band power divider and a broad-band 180° phase shifter. To achieve wide bandwidth characteristic, small reflection technique is employed for the power divider while radial stubs are used in the phase shifter. The compact size is realized by carefully designing the layout based on a low-loss material. The proposed balun works in the frequency band from 1.5 GHz to 3.2 GHz. The measured amplitude imbalance and phase imbalance between the two balanced ports are within 0.3 dB and ±5°, respectively. Measured return loss at both two balanced ports is better than −10 dB while the measured isolation is better than −20 dB.