Constant absolute bandwidth third-order tunable bandpass filter with reconfigurable bandwidth using single λ/2 resonator

Abstract

This paper presents a third-order bandpass filter with bandwidth tuning and constant bandwidth center frequency tuning. Based on the analysis of modal voltage waveforms of a varactor-terminated half-wavelength microstrip line, a varactor is loaded at the center to control even modes, four varactors are loaded between two symmetric specific positions to tune, only, odd modes and two varactors at the ends to tune both the even and odd modes. Using these varactors, the passband is formed by bringing the first even and second, third odd modes close to each other. To keep the bandwidth of the passband constant, these three modes are controlled separately. The S-matrix has been derived to analyze and the coupling matrix has been synthesized to design the filter for a specification. An example filter has been designed and fabricated whose band can be tuned from 1.0 to 1.45  GHz (36.73$\mathrm{\%}$) with absolute bandwidth of 260 MHz and bandwidth is tunable from 130 to 490 MHz.

Keywords:

• Constant bandwidth
• half-wavelength resonator
• microstrip line
• tunable filter
• coupling matrix

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Shriman Narayana

Dr. Shriman Narayana received the B.Tech degree in electronics and communication engineering from ICFAI University Dehradun, India in 2011, M.Tech degree in Communication system and Ph.D. degree in RF and Microwave Engineering from IIT Patna, ,India in 2015 and 2021. His current research interests include RF and Microwave reconfigurable filters. He is currently working with NIT Mizoram in ECE Department.

Nagendra Kumar

Dr. Nagendra Kumar received the B.Tech. degree in electronics and communication engineering from the Siliguri Institute of Technology, Siliguri, India, in 2010, and the Ph.D. degree from the IIT Patna, India, in 2017. His current research interests include the design of tunable and reconfigurable filters, switchable filters, and multiband filters. Dr. Kumar has been a Reviewer for IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, IET Electronics Letter, IET Microwaves, Antennas & Propagation, and Progress in Electromagnetics Research.

Yatendra Kumar Singh

Dr. Yatendra Kumar Singh received the B.Tech degree (Hons.) in electronics and electrical communication engineering and M.S. and Ph.D. degrees in RF and microwave engineering from IIT Kharagpur, India, in 2001, 2004, and 2010, respectively. He is currently an Assistant Professor with IIT Patna, Patna, India. His current research interests include tunable and reconfigurable filters, power amplifiers, low-noise amplifiers, and RF oscillators. Dr. Singh was the recipient of the Young Scientist Award from the International Union of Radio Science in 2008 and the Young Engineer Award from the Institution of Engineers, India, in 2009.