580 California St., Suite 400
San Francisco, CA, 94104
Key research themes
1. How can transmission line configurations and fractal geometries be employed to design wideband and highly selective bandstop filters with improved rejection and compact size?
This research area investigates novel bandstop filter (BSF) designs that achieve wide rejection bandwidths and sharp skirt selectivity. Approaches focus on innovative transmission line configurations and geometrical techniques such as fractal shapes to enhance stopband control, frequency response, and compactness, which are crucial for suppressing broadband interferences in wireless systems.
Key finding: Introduced a modified transmission line structure allowing widening of stopband fractional bandwidth to 100% with 20 dB rejection at 1.5 GHz, surpassing previous maximum zero separations (~117.2% vs. 66.67%). The design... Read more
Key finding: Applied Minkowski fractal geometry to a conventional triangular dual-mode microstrip resonator, increasing current path length to reduce resonant frequency and thus miniaturize the filter. Achieved a compact BSF with high... Read more
Key finding: Demonstrated the use of singlets and cascaded singlets in coaxial substrate integrated waveguide (SIW) technology to realize highly compact bandpass filters with multiple transmission zeros accurately placed around the... Read more
2. What strategies leverage metamaterial-inspired structures and multiple resonator pathways to develop compact, multi-band, and dual-band bandpass filters suitable for modern wireless communication systems?
Research within this theme focuses on miniaturized bandpass filter (BPF) designs using metamaterial unit cells, split-ring resonators (SRRs), multiple transmission paths, and innovative resonator configurations. These strategies enable tunable multi-band operation, broad passbands, and high selectivity, supporting emerging wireless standards such as GPS, ISM, Wi-MAX, and WLAN while addressing the need for compact integration and broad stopband suppression.
Key finding: Designed a compact microstrip bandpass filter integrating four symmetrical split-ring resonators, achieving a 5 GHz bandwidth covering 1 to 5.2 GHz with quality factors above 1.85. The metamaterial-based SRR architecture... Read more
Key finding: Proposed a dual-path transversal-filtering DB-BPF featuring six transmission poles and four transmission zeros, yielding high selectivity with fractional bandwidths of 36.4% at 2.24 GHz and 31.2% at 7.35 GHz. Fabricated on... Read more
Key finding: Designed hairpin and interdigital bandpass filters targeting 5G frequency bands (3.7–4.2 GHz and 5.975–7.125 GHz) exhibiting wide bandwidths, low insertion losses (< −0.46 dB), and superior harmonic suppression extending... Read more
3. How can fractional-order filter designs and novel low-pass filter structures employing spur-lines improve stopband attenuation and provide electronically controllable parameters?
This theme explores fractional-order filter approximations and the integration of spur-line techniques in conventional microstrip low-pass filters to generate additional attenuation poles, improving stopband bandwidth and depth. Furthermore, electronically tunable fractional-order filters using operational transconductance amplifiers (OTAs) and adjustable current amplifiers (ACAs) enable continuous control over filter order and pole frequency, providing adaptable filtering solutions.
Key finding: Presented a 3rd-order fractional-order high-pass filter based on Follow-the-Leader Feedback topology employing OTAs and ACAs, enabling electronic tuning of filter order from 1 to 2 and pole frequency. Pspice simulations show... Read more
Key finding: Proposed two LPF configurations—serial spur-line and parallel spur-line LPFs—that utilize spur-lines to generate extra attenuation poles, achieving significant stopband bandwidth improvements (4.7× and 1.4×, respectively)... Read more