[A] C- and X-Band Substrate Integrated Waveguide (SIW) in PCB Technology

This research focuses on designing miniaturized high-Q SIW-based filter designs and implementing these filters to design various low-phase noise oscillator designs. We have worked on designing miniaturized filters for C-band and X-band frequency ranges in PCB technology. Also, this research studies the effects of sub-modes SIW designs, various loadings like CSRR resonators, and DGS resonators in the sub-modes SIW structures.

[B] Millimeter Wave SIW Design

For on-chip millimeter-wave SIW designs, the main issue associated is the size and the performance limitation of the used technology. So, this research in this area explores the feasibility and performance of implementing SIW structures directly on commercial CMOS technology. This involves developing fabrication techniques and design methodologies to integrate SIW transmission lines with active devices such as amplifiers, oscillators, and mixers. The focus is on enabling on-chip millimeter-wave circuits with enhanced performance, reduced footprint, and improved integration for applications such as 5G communications, automotive radar, and high-speed data communication.

[C] Sub-THz Band SIW Design

Sub-THz band design for on-chip applications with SIW involves pushing the frequency boundaries even further. This research aims to develop SIW-based structures capable of operating in the sub-THz frequency range, typically in the hundreds of gigahertz to several terahertz. This entails exploring innovative design approaches to enable efficient sub-THz signal transmission, filtering, and radiation. The objective is to unlock the potential of commercial CMOS technology to achieve on-chip sub-THz SIW-based transmission lines, filters, resonators, and antennas for emerging applications such as terahertz imaging, wireless communication, and sensing.

Defected Ground Structure (DGS) based on-chip filter design involves creating compact and high-performance filters for integrated circuits in RF and microwave frequencies. By introducing patterns or defects in the conventional ground plane, desired filtering characteristics are achieved. These patterns modify electromagnetic wave propagation to create passband or stopband responses. DGS filters can be customized for various filter types like low-pass, high-pass, band-pass, or band-stop. They offer advantages such as compactness, integration capability, and improved performance compared to lumped-element filters. Much research has been reported in PCB and other technologies to effectively design filters using DGS structure.

On-chip design DGS-based filters enable to achieve easy integration with other on-chip active designs with circuit miniaturization and enhanced system performance. With tailored patterns on the ground plane, DGS-based filters can be exploited to achieve desired filtering characteristics with advantages in size, integration, and performance for various applications for higher frequencies like K-bands, millimeter waves, etc. The area of this research includes studying and verifying the low-loss high-Q standalone filter design using various DGS patterns and implementing it for applications like filters and oscillator designs.

Often for the measurement of RF/Microwave structures, measuring pads and the measurement setups adds unwanted parasitic elements and transmission line effects. This gives the measurement measured result benchmark far more than we expected. Such effects are more pronounced in higher frequency ranges above K-bands like millimeter waves, sub-THz, and THz bands. Common methods for using well-characterized calibration standards on time-domain relfectometers (TDRs) or vector network analyzers (VNAs) are well-suited for lower frequency ranges. An accurate de-embedding ensures reliable performance and signal integrity in RF and microwave circuits.
We study and perform the various on-wafer de-embedding methods that involve removing the effects of unwanted parasitic elements and transmission line effects between measurement points from lower frequencies up to the sub-THz band. The steps consist of measuring the S-parameters using the normal measurement setup for on-wafer designs along with the de-embedding structures. Then, the de-embedded results of DUTs i.e., the measurement result of DUT after the reference structure, which is obtained by removing unwanted parasitic elements and the transmission line effects, is compared with the exact intrinsic design simulated. We use various de-embedding methods for different frequency ranges:

• Open-short De-embedding

• Thru only De-embedding

• Open-short-thru De-embedding

• L-2L De-embedding

• multi-TRL (mTRL) De-embedding