Broadband phase shifter using an RF transformer-based resonator

In this paper, we propose a new wideband microstrip phase shifter based on an RF transformer. The structure consists of two main components: a mainline and a reference line. The mainline is a bandpass filter that incorporates the coupling characteristics of the RF transformer to achieve the required bandwidth. The reference line is a uniform transmission line, and its electrical length is adjusted to control the phase shift. Compared to traditional phase shifters, this design offers several advantages, including a wide bandwidth, compact size, simple structure, and a large phase shift range. To demonstrate the effectiveness of the design, a phase shifter with a 90°-225° phase shift range was both designed and simulated. Additionally, a 90° phase shifter was fabricated and measured. The measurement results show that the phase shifter achieves a phase shift of 90° ± 2.1°, with an S11 of less than -10dB and a fractional bandwidth (FWB) of 63.25%.