Highly Linear and Fast Phase Shifting Technology

Ghorbani, Farhad ORCID: 0000-0002-4547-3579 (2025) Highly Linear and Fast Phase Shifting Technology PhD thesis, University of Liverpool.

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Abstract

Modern communication systems are becoming increasingly complex and powerful. Many of these systems now require components that can work at high power levels while still performing accurately and reliably. One important part of these systems is the phase shifter, which controls the phase of radio signals. Phase shifters are used in technologies such as beamforming, radar, and wireless communication. Among the different types of phase shifters, digital phase shifters have become popular because they allow for precise control and easy integration with digital systems. However, the performance of digital phase shifters is often limited by the nonlinearity of the radio frequency (RF) switches used inside them. This thesis focuses on designing and testing RF switches and digital phase shifters that offer better linearity, faster switching speed, and higher power handling capability. The goal of the research is to reduce the unwanted signals that are created when the switch behave nonlinearly. These unwanted signals, called intermodulation distortion (IMD), can interfere with the normal operation of the communication system. Among them, the third-order intermodulation distortion (IMD3) is the most problematic because it falls close to the main signal and cannot be filtered out easily. Several new ideas are presented in this thesis to improve the linearity of RF switches and phase shifters. First, a detailed study of the behaviour of PIN diodes in different circuit topologies is carried out. It is shown that using the diodes in a parallel configuration (connected to ground) instead of a series configuration can reduce distortion. It is also shown that adding a quarter-wavelength transmission line in the switches with two PIN diodes helps improve the signal quality by reducing reflected distortion. A switch topology based on two PIN diodes is introduced and tested. Test results show that this topology can achieve a third-order input intercept point (IIP3) of around 98 dBm, which is much higher than many existing designs. Another switch uses multiple PIN diodes in parallel to share the current and reduce stress on each diode. By using an impedance transformer to adjust the impedance, the superior linearity behaviour is achieved. These high-linearity switches are then used to build a three-bit digital phase shifter. The performance of the phase shifter is tested and found to be better than many current V designs in terms of both linearity and insertion loss. The switching speed is kept below 300 ns, and the design can handle input powers higher than 25 watts. The thesis also investigates the use of loaded-line phase shifters, where the diodes are used to connect or disconnect stubs from the main transmission line. This configuration gives the advantage of controlling the impedance seen by the diodes, which improves the linearity further. A version of the loaded-line phase shifter is developed that uses multiple diodes in parallel at each switching point, leading to an even higher IIP3, approaching 100 dBm. To ensure the results are accurate, special care is taken in designing the measurement setups. Different calibration methods and equipment configurations are tested to avoid errors caused by test instruments. The designs proposed in this thesis are compared with other academic and commercial solutions, showing clear improvements in key performance areas. In summary, this thesis presents a complete design approach for digital phase shifters with improved linearity. The work includes new switch topologies, better use of PIN diodes, detailed simulations, and real-world measurements. These results contribute to the development of better phase shifter for next-generation communication systems.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Phase shifter, PIN diode, RF switch, Third Order Intermodulation, Third-Order Input Intercept Point
Divisions:	Faculty of Science & Engineering Faculty of Science & Engineering > School of Engineering
Depositing User:	Symplectic Admin
Date Deposited:	07 Oct 2025 10:10
Last Modified:	07 Oct 2025 10:10
DOI:	10.17638/03194375
Supervisors:	Zhou, Jiafeng Huang, Yi
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3194375
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