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The title of the thesis: Integrated mmWave transceivers and circulators 

Thesis defender: Saeed Naghavi
Opponent: Prof. Henrik Sjöland, Lund University, Sweden
Custos: Prof. Jussi Ryynänen, Aalto University School of Electrical Engineering

Solutions for delivering the growing wireless capacity demands of future 5G and 6G networks typically involve expanding available bandwidth and improving spectral efficiency. In this context, millimeter-wave (mmWave) communication has attracted significant attention as a promising technology to meet the high data rate requirements of these networks by offering multi-GHz channel bandwidths. The first prototype complementary metal-oxide semiconductor (CMOS) integrated circuit (IC) developed in this thesis explores mmWave transceiver IC design techniques through the design and implementation of a hybrid heterodyne/homodyne receiver and a wide modulation bandwidth two-step transmitter. 

At the same time, full-duplex (FD) wireless is another emerging paradigm that can theoretically double the spectral efficiency by supporting simultaneous transmission and reception of radio signals at the same frequency. Equipping mmWave systems with FD capability will further improve the network’s spectral efficiency, allowing them to address the growing capacity needs more reliably. However, the main challenge in FD mmWave systems is the self-interference (SI) signal that leaks from a radio’s transmitter into its receiver. As a result, effective multi-stage self-interference cancellation (SIC) is required across the entire signal path. This thesis primarily focuses on the antenna interface, highlighting the role of integrated circulators in FD mmWave transceivers. 

The second and third prototype CMOS ICs reflect the innovations and contributions of this thesis toward advancing the state of the art in the field of integrated circulators across the following key areas: 1) compact die area and mmWave operation, 2) high power handling, 3) new theoretical framework for integrated circulators with unequal port impedances, and 4) single-ended implementation of switched all-pass network (APN) circulators. Additionally, the research work in this thesis was conducted in close collaboration with the antenna group, leading to the introduction of the concept of a radiating circulator for the first time. In the proposed radiating circulator structure, the reciprocal phase shift cells employed in conventional structures are eliminated, and the required functionality is achieved by co-designing the antenna with the non-reciprocal branch on the IC side. As a result, this approach offers improved efficiency and a more compact die area compared to conventional, separately designed circulators. 

Key words: Integrated transceiver, mmWave, full-duplex, self-interference, circulator, co-design

Thesis available for public display 10 days prior to the defence at . 

Contact: saeed.naghavi@aalto.fi