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Design of Frequency Selective Surface (FSS) Printed Antennas
Published in Binod Kumar Kanaujia, Surendra Kumar Gupta, Jugul Kishor, Deepak Gangwar, Printed Antennas, 2020
Kanishka Katoch, Naveen Jaglan, Samir Dev Gupta, Binod Kumar Kanaujia
In some applications, a specific band of frequency is required where the highly directional beam is focused by the antennas. For example, for designing an ultra-wideband (UWB) antenna, some frequency ranges such as WiMAX (3.3–3.6 GHz), WLAN (5–6 GHz), and X-band satellite communication band (7.2–8.4 GHz), which are extensively used in various applications, create interference problems [75–77]. There is a need to stop these frequencies from interfering. Since these particular bands are difficult to suppress by conventional antennas, for such applications, there is a requirement of spatial filters. FSS is called spatial filter, since it modifies the wave incident on its surface by transmitting or reflecting the wave partially or fully through the surface. Spatial filtering is categorized as low-pass, high-pass, band-pass, and band-stop filtering. In low-pass FSS filters, lower frequency ranges get passed while eradicating the higher frequency band. However, for designing high-pass FSS filters, Babinet’s principle is applied, since the high-pass FSS filter operation is complementary to the low-pass FSS filter operation. Similar is the case with band-pass and band-stop filtering. Band-pass filter permits a specific frequency band to pass, while band-stop filter rejects one. Size, shape, and material of the substrate and array elements are very important parameters in the designing of the FSS filters. For a required operating band, metallic patches or apertures are embedded on the FSS substrates. Metallic patch elements act as a band-stop filter [75], whereas aperture elements act as a band-pass filter [78].
Filters
Published in Hernando Lautaro Fernandez-Canque, Analog Electronics Applications, 2016
Hernando Lautaro Fernandez-Canque
The band-stop filter is also known as notch, band-reject, or band-elimination filter. As with a band-pass filter it is possible to use a low- and a high-pass filter to create a band-stop filter. These filters can be connected in parallel as indicated in Figure 20.20.
Digital Signal Processing Backgrounds
Published in S. Sitharama Iyengar, Richard R. Brooks, Distributed Sensor Networks, 2016
Depending on the application, the frequency response of a digital filter can be characterized as all pass, band-pass, band-stop, high-pass, and low-pass. They describe which frequency band of the input sequence is allowed to pass through the filter while the remaining input signals are filtered out. All pass filters are often implemented as a MIMO system such that the input sequence is decomposed into complementary frequency bands. These components can be combined to perfectly reconstruct the original signal with a fixed delay. Hence, the overall system passes all the frequency bands and, therefore, the term all pass. With a MIMO system, the digital filter has a filter bank structure that can be exploited to implement various linear transformations, including DFT and discrete wavelet transform (DWT). Digital filter banks have found wide acceptance for applications such as data compression, multi-resolution signal processing, and orthogonal frequency division multiplexing. Low-pass filters are perhaps the most commonly encountered digital filter. They have found applications in removing high-frequency noise, extracting the low-frequency trend, and preventing alias before decimation of a digital sequence. High-pass filters are used for exposing the high-frequency content of a potential signal. They can be used for event detection. A band-stop filter will filter out unwanted interference from a frequency band that does not significantly overlap with the desired signal. For example, in a special band-stop filter, known as the notch-filter, it is possible to reject 60 Hz power-line noise without affecting the broadband signal. Band-pass digital filters are designed to pass a narrow-band signal while rejecting broadband background noise. Table 4.6 illustrates the magnitudes of that frequency responses of four types of digital filter. The corresponding transfer functions are also listed with a = 0.8 and b = 0.5. The constants are to ensure that the maximum magnitudes of the frequency responses are equal to unity. The MATLAB® program that generates these plots is given in Appendix 4.A.
Design of woven meta-materials for electronic textiles for functional applications
Published in The Journal of The Textile Institute, 2023
Hanen Zribi, Amine Hadj Taieb, Ignacio Gil, Raúl Fernández-García, Mònica Ardanuy
Metamaterials have recently received a great deal of attention because they are capable of achieving unusual electromagnetic responses, such as a negative index, not found in natural materials (Driscoll et al., 2006; Zhang et al., 2005). A metamaterial can be defined as an artificial crystal in which mesoscopic inclusion structures replace the microscopic atoms or molecular structures of natural materials (Driscoll et al., 2007). A frequency selective surface (FSS) or "spatial filter" can be integrated into the materials to obtain a metamaterial. In fact, it is a structure typically consisting of two-dimensional periodic metallic elements on a dielectric substrate (Dalkiliç, 2014). These structures provide either a band-stop filter frequency response to reject unwanted frequency bands, or a bandpass filter response by selecting a specific frequency range and allowing different signals to pass through that are not attenuated (Anwar et al., 2018).