Microwave Circuits for Advanced Modulation Formats and Broadband Communication System

This PhD thesis investigates hardware solutions for next generation optical and wireless short range (SR) communication systems. More specifically, it is about microwave components that enables high efficiency and/or capacity of the system. The first part of this thesis deals with SR optical cables for high density datacenters, which are a key element of current networks.

SR cables usually employ direct detection schemes, which adopt robust and simple baseband modulations, such as non-return-to-zero (NRZ), and pulse amplitude modulation (PAM). This thesis investigates the alternative partial response (PR) modulation formats, which can significantly boost the spectral efficiency of a baseband signal by an analog low pass filter (LPF), which introduces a controlled amount of intersymbol interference (ISI).

More specifically, the target of this research are PR modulators based on microwave linear phase LPF and eventual alternatives. The motivation for having a linear phase characteristic is their low phase noise, which can significantly improve the modulated signal. Another important issue is the microwave implementation; in this thesis we investigate which technology and design in terms of spurious response and phase linearity.

The second part of this thesis is about microwave components for ultra-wideband (UWB) wireless communication systems. The targets are envelope detectors (EDs) able to operate in UWB systems. The main design challenge is the required fractional bandwidth, above 20%, for UWB systems. We proposed three EDs designed in microstrip technology and able to operate with fractional bandwidths above 30%; furthermore, they have a relatively simple and cost effective implementation.

The first two detectors are based on Schottky diodes, while the third on high electron mobility transistors (HEMTs). Experimental results of the three detectors showed outstanding results in terms of fractional bandwidth.