An Ultra-Wideband Stripline Bandpass Filter with a Noise Suppression Level of More than 100 dB
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ra-Wideband Stripline Bandpass Filter with a Noise Suppression Level of More than 100 dB B. A. Belyaeva,b*, A. M. Serzhantovb, An. A. Leksikova, Ya. F. Bal’vaa, and E. O. Grushevskiia a Kirensky
Institute of Physics, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia b Siberian Federal University, Institute of Engineering Physics and Radio Electronics, Krasnoyarsk, 660041 Russia *e-mail: [email protected] Received April 27, 2019; revised April 27, 2020; accepted May 6, 2020
Abstract—An ultra-wideband bandpass filter formed by cascading of a novel high-pass filter (HPF) and a low-pass filter (LPF) on suspended substrates with a two-sided pattern of strip conductor has been investigated. The high selectivity of the HPF is ensured by the transmission zeros near the passband, the number of which is equal to the filter order. A second-order HPF has been designed on a 0.5-mm-thick substrate with a permittivity of ε = 9.8 using the numerical electrodynamic analysis of a 3D model of the filter. The experimental HPF prototype has a cutoff frequency of f b = 0.25 GHz at a level of –3 dB and a passband that extends to 5 GHz. The ultra-wideband bandpass filter formed by cascading of the LPF and the designed HPF has a fractional bandwidth of Δf/f0 = 150% with a central frequency of f0 = 1 GHz. It has the broad and deep highfrequency stopband, which extends to a frequency of 7.8f0 at a suppression level of –100 dB. Keywords: passband filter, resonator, dielectric substrate, strip conductors. DOI: 10.1134/S1063785020080179
Frequency-selective microwave devices, including bandpass filters (BPFs), are among the most important components of communication, radar, and radio navigation systems and various types of measuring and specialized radio equipment [1, 2]. In recent years, much attention of radio engineers has been paid to ultra-wideband (UWB) filters. The use of ultra-wideband signals increases the data transmission rate, which, as is known, is directly related to the working frequency bandwidth. A well-known approach to designing UWB filters is based on the enhancement of couplings between resonators via partial removal of metallization in the grounded base [3]. In addition, UWB filters based on short-circuit stubs [4] and multimode resonators [5] are widely used. The common drawbacks of these approaches are, first, the complexity of implementing filters with relative bandwidths of more than 120% and, second, a relatively narrow high-frequency stopband of these devices, which extends, at best, to a frequency of ~4f0 at an attenuation level of merely ~40 dB. It should be noted that the overwhelming majority of the available UWB filter designs cannot be screened because of the occurrence of spurious volume resonances to the housing near the passband. The unscreened filters can interfere with other components of the radio modules, which causes electromag-
netic incompatibility. The above-mentioned difficulties can be overcome, to a certain extent, by cascading of a high-pa
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