Design of Microstrip Dual-Mode Wideband Bandpass Filter with Controlled Center Frequency and Bandwidth Using Bandstop Filter Topology

ABSTRACT

This paper discusses a new method for designing a microstrip dual-mode, sharp skirt, wideband bandpass filter with controlled center frequency and bandwidth from bandstop filter topology. A meander closed loop resonator with directly connected orthogonal feed lines provides a Bandstop filter (BSF) with reduced size. A pair of L-shaped open stubs introduced along the diagonal axis D-D¹ realizes a wide passband within the rejection band (0.93–4.13 GHz) of the bandstop filter with sharp stopbands on either side of the passband. Furthermore, the effect of L-shaped open stubs susceptance on passband edges is demonstrated. A quarter wavelength stepped impedance shunt stub (SISS) connected at $\theta ={170}^{\circ }$ is proposed to achieve additional transmission zeros in the upper and lower rejection bands to improve the sharpness of filter response. Both center frequency and bandwidth of the proposed filter are controlled by the impedance ratio (R) of the SISS element. The proposed filter is simulated using ADS, fabricated and measured using Vector Network Analyzer (VNA). A good agreement is achieved between simulated and measured results.

KEYWORDS:

• Bandpass filter (BPF)
• Bandstop filter (BSF)
• Dual-mode
• Fractional bandwidth
• Meander loop
• Stepped impedance shunt stub (SISS)
• Transmission zeros

Acknowledgements

The authors would like to thank Bharath Electronics Limited (BEL), Bangalore for providing Vector Network Analyzer (VNA) for experimental measurements.

Additional information

Notes on contributors

Shobha Hugar

Shobha Hugar is currently working as assistant professor in the Department of Electronics and Communication Engineering at Sapthagiri College of Engineering, Bangalore, India. She is pursuing PhD in the area of RF and microwave passive filters in Visvevsaraya Technological University, Belagavi, India. She received the BE and MTech degrees in electronics and communication engineering and VLSI design and embedded systems from Karnataka University, Dharwad, Visvevsaraya Technological University, Belagavi ,India, in 2000 and 2008, respectively.

V.B. Mungurwadi

B M Vaishali is currently working as a professor at Visvevsaraya Technological University, Belagavi, India. She received PhD degree in 2012, from Visvevsaraya Technological University, Belagavi, India. She received the BE and ME degrees in instrumentation, electronics from Karnataka University, Dharwad, University of Pune, India in 1990 and 2003, respectively. She is working in the area of RF MEMS resonators. Email:[email protected]

J.S. Baligar

J S Baligar is currently working as associate professor in the Department of Electronics and Communication Engineering at Dr Ambedkar Institute of Technology, Bangalore, India. He received PhD degree from Bangalore University, India, in 2000. He is working in the area of RF and microwave antennas. He has published papers in IEEE Electronics Letters and Microwave and Optical Technology Letters. Email:[email protected]