Abstract
A microstrip lowpass filter based on transmission line elements for UWB medical applications is proposed in this paper. The filter is constructed of two symmetric shunt open-circuited stubs and three series unit elements. The filter is designed to exhibit an elliptic function response with equal ripple in the passband and the rejection band. A prototype is successfully designed, fabricated, and measured, where a good agreement is attained. The filter shows a high filtering selectivity and an ultra-wide stopband up to 20 GHz with an attenuation level of more than 20-dB. The filter is compact and has a low insertion loss and an ultra-wideband (UWB) rejection which makes it attractive for many technologies such as UWB medical applications.
Highlights
Ultra-wideband (UWB) technology has several features which makes it suitable for the application of medical monitoring such as penetrating through obstacles, high precision ranging at the centimeter level, low electromagnetic radiation, and low processing energy consumed
Lowpass planer filters with sharp roll-off, wide stopband, compact circuit size, and low insertion loss are in high demand in modern wireless communication systems and military radar receiver systems for blocking unwanted signals and suppressing spurious harmonics
Other techniques can be used to enhance the performance of the stepped-impedance filters such as stepped-impendence hairpin resonators [4, 5], folded stepped-impedance resonators [6], defected ground-plane structures (DGS) slot [7,8,9,10,11,12], and interdigital or semicircle defected ground-plane structures (DGS) [13, 14]
Summary
Ultra-wideband (UWB) technology has several features which makes it suitable for the application of medical monitoring such as penetrating through obstacles, high precision ranging at the centimeter level, low electromagnetic radiation, and low processing energy consumed. A general common microstrip structure of lowpass filter is using high and low impedance (stepped-impedance) transmission lines which is known as stepped-impedance lowpass filter [1] This type of filter has simple design methodology but it exhibits a poor skirt selectivity and a very low attenuation level at the rejection band. A cross-coupling can be introduced between the input/output feed lines to allow the filter to exhibit additional transmission zeros at the rejection band [22]. This proposed filter can be used in many technologies such as UWB medical applications [23]. The filter design, analysis, and measurement results are demonstrated in detail
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