A method with clear guidelines is presented to design compact planar phase shifters; with ultra-wideband (UWB) characteristics. The proposed method exploits broadside coupling between top and bottom elliptical microstrip patches via an elliptical slot located in the mid layer, which forms the ground plane. A theoretical model is used to analyze performance of the proposed devices. The model shows that it is possible to design high-performance UWB phase shifters for the 25 degrees-48 degrees range using the proposed structure. The method is used to design 30 degrees and 45 degrees phase shifters that have compact size, i.e., 2.5 cm x 2 cm. The simulated and measured results show that the designed phase shifters achieve better than +/-3 degrees differential phase stability, less than 1-dB insertion loss, and better than 10-dB return loss across the UWB, i.e., 3.1-10.6 GHz.