An Extremely Compact UWB Microstrip Annular Ring Filter for Bluetooth Applications

This paper presents a novel microstrip ring filter with a center frequency (f₀) of 2.4 GHz and ultra-wideband (UWB) characteristics. It has an extremely compact size (10mm times 10mm). A Fractional Bandwidth (FBW) of around 120% and a sharp rejection greater than 40 dB have been achieved. Two transmission zeros have been introduced by adding short-circuit vias at the band edges which provide a reasonably good insertion loss. The experimental results show a good agreement with simulations. This filter can be utilized for Bluetooth applications due to its miniature size, wide bandwidth, and enhanced out-of-band rejection