Heuristic Topology for Designing Reconfigurable Balun Active Filter for Frequency, Bandwidth and Power Division Ratio

Abstract

A novel concept of balun bandpass reconfigurable active filter is proposed here. The structure is composed of a three-stage balun filter having fractional bandwidth (FBW) of 13% with matched amplifier inserted between the last two stages. This technique of incorporating active device in balun filter gives an advantage of obtaining re-configurability, while compensating for loss at the balanced ports. The modified structure is able to yield re-configurability of frequency, bandwidth, power division ratio (PDR) and wide band stop response along with reduction in size (77 mm × 42 mm). The amplifier is accommodated within the second loop and is not cascaded with the balun filter, thus saving the space. The proposed balun filter has a varying gain of approximately 4–11 dB as bias changes from Ids = 52 to Ids = 78 mA, while simulating in MWO AWR software. The active balun filter has been fabricated on RT Duroid substrate. The measured results show | S11| < −15 dB from 1.9 to 2.18 GHz, which is comparable with simulation results. The novelty of this work is to obtain bias-dependent frequency, bandwidth and PDR re-configurability with varying gain.