Abstract
Stepped impedance resonator (SIR) and its derivative resonators are widely used in the design of microwave filters. However, many spurious modes will be introduced into the stopband, resulting in lower upper stopband suppression and performance degradation. Based on the principle of slit line, a method to enhance the upper stopband suppression is proposed and verified by a miniaturized tri-notched wideband bandpass filter based on stub loaded ring resonator (SLRR) and shorted-stub loaded SIR (SSLSIR). The wideband is formed by coupling SLRR and interdigital lines, which has a rectangular DGS on the back of the substrate. Three notched bands with controllable positions in the passband can be produced by inserting two different SSLSIRs inside and outside the SLRR. Four slit lines are loaded on the low impedance stub of SSLSIR to adjust the high-order modes close to the transmission zeros (TZs). The operating frequency of the filter is 2.2–7.6 GHz, and the three notched bands are located at 2.97 GHz, 5.75 GHz and 6.46 GHz, respectively. The measurement results show that the − 20 dB enhanced upper stopband of the filter can reach 32 GHz, which proves that the filter has the characteristic of ultrawide upper stopband suppression while keeping the miniaturization.
Highlights
Stepped impedance resonator (SIR) and its derivative resonators are widely used in the design of microwave filters
The third notched band is realized by the shorted stub L3, which has an electrical length of half wavelength and is combined with the parasitic inductance of the via and the mutual inductance between stub loaded ring resonator (SLRR) and shorted-stub loaded SIR (SSLSIR) type[2]
This paper presents a miniaturized tri-notched wideband bandpass filter composed of SLRR and SSLSIR resonators
Summary
Stepped impedance resonator (SIR) and its derivative resonators are widely used in the design of microwave filters. Based on the principle of slit line, a method to enhance the upper stopband suppression is proposed and verified by a miniaturized tri-notched wideband bandpass filter based on stub loaded ring resonator (SLRR) and shorted-stub loaded SIR (SSLSIR). Four slit lines are loaded on the low impedance stub of SSLSIR to adjust the high-order modes close to the transmission zeros (TZs). A miniaturized tri-notched wideband bandpass filter based on SLRR and SSLSIR with the characteristic of ultrawide upper stopband suppression is proposed. The -20 dB enhanced upper stopband of the filter can reach 32 GHz. The novelty of this paper is that by studying the principle of slit line, the characteristics of miniaturization, ultrawide upper stopband, wide passband and independently adjustable multi-notched bands can be obtained at the same time to achieve a multi-functional high-performance microwave filter
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