Lumped element balanced multi-band bandstop filter for ultra high frequency applications

Abstract

An ultra-compact multi-band balanced (differential) bandstop filter (BSF) topology with all lumped elements has been introduced for the first time in this study. The proposed filter is a four-port structure where each symmetrical bisection is a series cascade of K N-band cells. Each N-band cell comprises of N parallel resonant circuits connected to the same node, through capacitors. K series-coupled N-band filter sections in the symmetrical bisection exhibit a Kth order N-band BSF response in differential mode (DM) whereas common mode (CM) signal is minimally affected and maintains a high CM rejection ratio (CMRR). The advantages associated with this engineered structure can be summarised as follows: (i) it can be extrapolated to realise an arbitrary number of DM stopbands; (ii) it does not need any additional component in the symmetry plane to suppress the CM noise; and (iii) it occupies a very small area. For demonstration, a second-order dual-band differential BSF with resonant frequencies 1.15 and 1.36 GHz is designed and fabricated. It offers a rejection level of about 25 dB for each DM stopband and maintains a CMRR value of about 25 dB for both bands. Moreover, it covers an area of only 0.003[inline-formula], where [inline-formula] is the guided wavelength at the centre frequency between the two bands.

Keywords

• uhf filters
• resonator filters
• band-stop filters
• uhf integrated circuits
• lumped element
• multiband bandstop filter
• ultra high frequency applications
• ultra-compact multiband balanced bandstop filter topology
• symmetrical bisection
• k n-band cells
• parallel resonant circuits
• k series-coupled n-band filter sections
• kth order n-band bsf response
• differential mode
• common mode signal
• cm rejection ratio
• dm stopband
• dual-band differential bsf
• resonant frequency
• four-port structure
• cm noise suppression
• frequency 1.15 ghz
• frequency 1.36 ghz