Design and simulation of a new narrow terahertz bandpass filter
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Design and simulation of a new narrow terahertz bandpass filter Hojatollah Shahounvand1 · Azim Fard1 Received: 4 May 2020 / Accepted: 15 September 2020 © Springer Nature Switzerland AG 2020
Abstract In this paper, a new THz bandpass filter, referred to as ‘a spider filter,’ is designed, simulated and analyzed. According to the study of different samples of bandpass filters in the range of 0.1–3 terahertz, the proposed filter has proved to have a very good transmission coefficient and much lower unwanted frequencies than the other bandpass filters ever made. Keywords Terahertz bandpass filter · Frequency width at half maximum (FWHM) · Unwanted frequency (output noise) · Transmission coefficient · Frequency selective surfaces (FSS)
1 Introduction Terahertz (THz) bandpass filters have wide applications in imaging, spectroscopy, molecular sensors, security systems and detection of materials [1]. One of the important parameters in such filters is the thickness of the metal film at higher frequencies (THz range) [2]. Changes in the metal film thickness have been the subject of many studies [3, 4]. Some geometric shapes such as square, circular, annular and pair of conductive rings have widely been investigated so as to determine the best structure for filters. The transmission coefficient of filters with ring-shaped arrays (patches) has been addressed in more than 70% of the research in the field [5]. This coefficient is not the same for different frequency ranges. For frequencies of 0.1–1 THz and 2–14 THz, the transmission coefficient ranges from 90% to 100% and 40% to − 70%, respectively [6]. A metal-mesh bandpass filter was designed and fabricated with a 12-um-thick copper film in the frequency range of 0.5–2.5 THz [7]. Using the CST simulation software, two same filters were placed in a row at various distances to improve the frequency bandwidth. This led to a lower frequency width at half maximum (FWHM) compared to cases with a single filter. Also, the effect of changes in the incident wave angle was investigated at several angles. In
the following, a new type of asterisk filter was proposed. In its output spectrum, it was shown to have lower noise (or unwanted frequency) than other asterisk filter samples [8]. In recent years, the use of metamaterials and frequency selective surfaces (FSS) in the terahertz field has been of great importance, which has also been used for terahertz bandpass filters. These properties as well as the use of different substrates for achieving narrower bandwidth as well as frequency spectrum tunable have been used [9–14]. In the present study, a new bandpass filter called ‘spider’ is proposed through designing and simulation. It has proved to have a very good transmission coefficient (almost 100%) and, as shown by the output spectrum, much lower output noise (or unwanted frequencies) than the other bandpass filters ever designed and made.
2 Filter structure and the results A check on the length, width and period of filter patches shows that certain changes in these dimensions lead
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