A Reflectionless Bandpass Filter Based on Double-Sided Parallel Striplines

Abstract

The invention relates to a non-reflection band-pass filter based on double-sided parallel strip lines, which includes a substrate, an upper metal strip and a lower metal strip that are parallel to each other and are metal grounded on the upper bottom surface and the lower bottom surface of the substrate. Both upper and lower metal strips contain a T-shaped bandpass filter and two symmetrically arranged absorption bandstop filters. An offset of distance d is formed between the quarter-wavelength open-circuit stubs of the absorption band-stop filters of the upper and lower metal strips. By offsetting the upper and lower layers of parallel striplines (a quarter-wavelength open-circuit stub), a high characteristic impedance value of more than 300Ω is easily obtained, which makes the proposed filter break through the process limit and can achieve high impedance values. And it has narrow 1dB relative bandwidth, wide 20dB relative absorption bandwidth and good passband selectivity. The band-pass filter part of the T-shaped structure introduces a half-wavelength open-circuit stub to generate two transmission zero points, which significantly enhances the selectivity.

Description

technical field [0001] The invention relates to the technical field of wireless communication, in particular to a non-reflection bandpass filter based on double-sided parallel striplines. Background technique [0002] Filters are an essential part of RF and microwave systems to mitigate interfering signals and unwanted spectral generation outside the system. Among them, the band-pass filter is a key frequency-selective component and plays a vital role in microwave / RF systems. Traditional filters reflect the energy of out-of-band signals back to the signal source, usually such reflections degrade the performance of adjacent active devices, causing unavoidable interference. For this reason, additional components such as attenuators are often used to improve performance, but this also leads to problems such as reduced dynamic range and increased circuit size. With the continuous development of 5G communication, the requirements for radio frequency circuits have also become hi...

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Problems solved by technology

However, at the same time, the width of the microstrip line with lower characteristic impedance becomes wider, and the appearance of lateral high-order modes limits its operation at high frequencies.

In previous designs, coupled microstrips are usually used to achieve high equivalent impedance, but it will inevitably lead to higher insertion loss

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