Wideband out-of-phase power divider using microstrip to slotline transitions, coupled lines, and shunt open-ended stubs

The design of a planar out-of-phase power divider with broadband behavior is presented. The proposed device uses broadside coupled microstrip-slotline-microstrip transitions at the input port and coupled microstrip lines with shunt open-ended stubs at the output ports to extend the impedance matching bandwidth at three ports of the device. Moreover, a dumbbell-shaped slot is located underneath the coupled lines and shunted with a proper chip resistor to improve the isolation between the output ports. The utilized structure is suitable for single layer integration as both the input and output ports are located at the same layer. Following a proper theoretical method based on the even-odd mode approach and slotline design guidelines, a prototype of the presented device aiming to operate across the band 1-3 GHz is designed, built, and tested. The developed device has overall dimensions of 30 mm x 60 mm using the substrate Rogers RO4003 (dielectric constant=3.38 and thickness=0.406 mm). While the device can be used for any wideband application, the developed prototype is designed to operate within the band 1-3 GHz, which is used in most microwave-based medical imaging applications. The achieved simulated and experimental results show 100% fractional bandwidth (1.1-3.3 GHz) assuming 15 dB of isolation as the reference. The proposed device has equal power division between the two output ports with less than 0.2 dB amplitude imbalance. Moreover, the phase difference between the signals at the two output ports is 180 degrees +/- 1 degrees across the frequency band 1-3.5 GHz. (c) 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2216-2218, 2015