Design of a compact planar phase shifter is described that possesses ultra-wideband (UWB) performance. The proposed device is composed of 50Ω input/output microstrip-lines which are connected to a low-impedance rectangular microstrip patch, and located at close proximity to each other. The common ground-plane incorporates a slot-line terminated with two rectangular slots, which are located under the rectangular patches in order to provide effective electromagnetic coupling between the microstrip-line and slot-line. Thus a phase shifter is realized with ultra-wideband characteristics on a single substrate. The length of the slot-line and width of patch determines the desired phase shift required between the input and output ports. It is demonstrated that the design can provide phase shift anywhere between 4°- 27° across the entire UWB frequency band from 3.1 to 10.6 GHz. The simulated results show fixed phase shift 5.625°± 0.865°, 11.25°± 1.93°and 22.5°± 2.5°with insertion-loss less than 0.5 dB and return loss better than 12 dB across the ultra-wideband frequency span. The phase shifter is relatively compact in size with a dimension of 15×25 mm2. The phase shifter was fabricated and its performance measured to validate the simulation results.
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