Analysis and Design of Compact Ultra-wideband In-phase/Out-of-phase Power Dividers

This paper presents the analysis and design of in-phase/out-of-phase power dividers with compact-size and ultra-wideband characteristics. The proposed designs are composed of a T-junction microstrip (MS)-to-slotline power divider with a shorting via and two slotline-to-MS transitions. The phase response at the outputs can be controlled by arranging the MS-line direction of the transition, i.e., the same direction results in the in-phase, whereas the opposite MS-line directions reverse the electrical field, thus resulting in the out-of-phase. Thanks to utilizing the MS-to-slotline power divider and circular slots and circular stubs at the transitions, the proposed structures achieve ultra-wide bandwidth and compact size simultaneously. The dividers are theoretically analyzed using transmission-line equivalent circuit, and then verified computationally and experimentally. Simulation and measurement indicate that the proposed power dividers yield ultra-wideband performance across 1.2-11.0 GHz (~ 160%) with magnitude difference [+ or -]0.5 dB and phase difference [+ or -]5[degrees] at the outputs. As an example of application, a differential-fed Vivaldi antenna fed by the proposed out-of-phase power divider is implemented. The antenna yields a 160% bandwidth (1.2-11.0 GHz) for 10-dB return loss and a stable end-fire radiation within the whole impedance bandwidth.