Abstract
In this paper, a lowpass filter is designed using half elliptical resonators with a wide stopband. New formulas are presented to achieve a circuit model for the half elliptical resonators used in this work. Additionally, the transfer function and transmission zero equations are used to adjust the frequency of the transmission zeros of the filter. The cut-off frequency of the lowpass filter is 1.26 GHz with a sufficiently large stopband, extending from 1.48 GHz to 20 GHz. The proposed filter’s figure of merit is 62,520, demonstrating its outperformance compared to the state of the art. The filter is implemented on a RT-5880 substrate with a constant dielectric of 2.2, thickness of 31 mil and loss tangent of 0.0009. The LPF was fabricated and tested, showing good agreement between the simulated and measured results.
Highlights
Lowpass filters (LPFs) are one of the highly demanded devices in the modern communication circuit
In [1], a compact LPF is proposed with distinguishing features, such as sharp roll-off and low insertion loss
A compact LPF is presented in [4] based on defected ground structure; this method has a complex fabrication process, which could be restrictive in many applications [5]
Summary
Lowpass filters (LPFs) are one of the highly demanded devices in the modern communication circuit. Stepped-impedance structures, open tubs and radial-shaped resonators have widely been used in designing microstrip filters, lowpass filters with a large stopband [7,8,9]. Square split-ring resonators are used to shape a small microstrip LPF with a new structure in [10], but this filter suffers from high insertion loss in pass-band. An electromagnetic band-gap structure has improved the efficiency of the applied lowpass filter in [11] This method has a complex fabrication process. T-shaped and circular-shaped resonators are used in [13] to design a lowpass filter to achieve a sharp roll-off and extended stopband, where work, equivalent circuits and equations of transmission zeros (TZs) were presented; the size of the paper is undesirably large. The proposed LPF correctly passes the sub 1 GHz signals and suppresses unwanted harmonics at higher frequency bands
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