Compact Wideband Marchand Balun with Amplitude and Phase Compensation Shield

In this paper, a compact wideband Marchand balun with the amplitude and phase compensation is presented. The proposed three-layer balun consists of two sections using folded slot-coupled microstrip lines on the top and bottom metal-layers. To improve the in-band amplitude- and phase-balances, a ground-shield is introduced to embed in the central ground patch on the middle metal-layer. Based on the structures mentioned above, a wideband balun operating from 2.28 to 5.41 GHz is implemented and fabricated. The measurement exhibits the in-band amplitude-and phase-imbalances of ±0.42 dB and ±1.81°, respectively. Moreover, the core circuit-size of the balun is about 0.22 λg × 0.22 λg, where λg is the microstrip guided wavelength at the center frequency of 3.845 GHz.