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WLAN Technology Basics
Published in Rihai Wu, Xun Yang, Xia Zhou, Yibo Wang, Enterprise Wireless Local Area Network Architectures and Technologies, 2021
Rihai Wu, Xun Yang, Xia Zhou, Yibo Wang
The frequency range of a radio wave is known as the frequency band. WLANs operate in the 2.4 GHz (2.4–2.4835 GHz) or 5 GHz (5.15–5.35 GHz or 5.725–5.85 GHz) frequency band. Designed for Industrial, Scientific, and Medical (ISM) purposes, these frequency bands can be used without obtaining license or paying fees as long as the transmit power requirement (generally less than 1 W) is met and no interference is caused to other frequency bands. While such cost-free resources reduce WLAN deployment costs, co-channel interference can arise when multiple wireless communications technologies operate within the same frequency band. Available ISM frequency bands vary depending on country and region, and WLANs are required to use frequency bands in compliance with local laws and regulations.
Electromagnetics and Transmission Lines for Wearable Communication Systems
Published in Albert Sabban, Wearable Systems and Antennas Technologies for 5G, IOT and Medical Systems, 2020
At very low frequencies, 1 Hz–1 MHz, the wavelength is of much higher order than the size of the circuit components used in electronic circuits. At very low frequencies, voltage, current and impedance do not vary as a function of the device length. At very low frequencies, relations between voltage, current and impedance are evaluated by using Kirchhoff’s laws and Ohm’s law. Components with dimensions lower than a tenth of the wavelength are called lumped elements. At high frequencies, the wavelength is of the same order of magnitude as the circuit devices used. At high frequencies, conventional circuit analysis based on Kirchhoff’s laws and Ohm’s law could not analyze and describe the variation of fields, impedance, voltages and currents along the length of the components. Components with dimensions higher than a tenth of the wavelength are called distributed elements. Kirchhoff’s laws and Ohm’s law may be applied to lumped elements, but they cannot be applied to distributed elements. To prevent interference and to provide efficient use of the radio spectrum, similar services are allocated in bands, see [11–14]. Bands are divided at wavelengths of 10 nm, or frequencies of 3 × 10 nHz. Each of these bands has a basic band plan, which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers. In Table 2.1 the electromagnetic spectrum and applications are listed. In Table 2.2 the IEEE standard for radar frequency bands is listed.
Discrete Transforms
Published in Scott E. Umbaugh, Digital Image Processing and Analysis, 2017
The band-pass and band-reject filters are specified by two cutoff frequencies, a low cutoff and a high cutoff, shown in Figure 5.7-9. These filters can be modified into nonideal filters by making the transitions gradual at the cutoff frequencies, as was shown for the low-pass filter in Figure 5.7-3 and the high-pass in Figure 5.7-6. A special form of these filters is called a notch filter, because it only notches out, or passes, specific frequencies (see Figure 5.7-9g and h). These filters are useful for retaining, band-pass, or removing, band-reject, specific frequencies of interest that are typically application dependent. In Figure 5.7-10, specific spatial frequencies are selected by the Band-pass filter that correspond to the width of the lines in fingerprints. By removing extraneous frequency information, the noise is removed and only the information of interest is retained. In this case, it is necessary to facilitate the automatic identification of fingerprints, a computer vision problem. These three types of filters are also used in image restoration, enhancement, and compression, and more examples can be seen in Chapters 8–10.
Phase Locked Loop System with SIW-based Bandpass Filter for D-band Microwave Interferometer
Published in IETE Journal of Research, 2022
Alpesh Vala, Amit Patel, Bhargav Patel, Abhishek Sinha, Umesh Nagora, Surya Pathak, Jitendra Chaudhari, Hiren Mewada
To realize the SIW structure as a bandpass filter, waveguide metallic post coupled theory is used. Concept for the realization of bandpass filter is presented in [21]. When we insert a post or an iris in the waveguide structure, it acts as a shunt inductor or capacitor depending upon penetration of the post. If the inserted post or iris penetrates partially into the structure, then it will act as a shunt capacitor and if it penetrates in such a way that it touches both top and bottom plane then it will act as a shunt inductor. In our structure, we have placed four metallic posts to conceive it as a shunt inductor as shown in Figure 15. The distance between the posts is function of guided wavelength. The incident energy will be sloshed back and forth between these posts and will be resonant at the particular frequency. An equivalent LC circuit of the structure is shown in Figure 16. It is simulated with Advanced Design System (ADS) software. Simulated S parameter response of the circuit is as shown in Figure 17. It provides the pass band in required the range of frequency. The scattering parameters of the structure simulated in HFSS are shown in Figure 18. Here lateral distance between the posts is optimized to get the desired frequency response. A result indicates that structure provides 3 dB pass band for frequencies ranging from 6.7 to 7.2 GHz with an insertion loss of 0.6 dB and return loss greater than 15 dB.
The Internet of Things for Logistics: Perspectives, Application Review, and Challenges
Published in IETE Technical Review, 2022
Hoa Tran-Dang, Nicolas Krommenacker, Patrick Charpentier, Dong-Seong Kim
In addition, the presence of multiple networks operating under the same frequency bands probably degrades the quality of communication due to interference. For example, a majority of WSNs (e.g. Zigbee, Xbee) uses the ISM (industrial, scientific and medical) bands for enabling the wireless connectivity in the practical applications. Therefore, as the networks are located in proximity locations, the radio interference cause loss of communication links. Although, several solutions such as blocking mechanisms for the mobile phones, transmission power control techniques are proposed to reduce the impact of interference on the wireless communication the unreliability issue is still critical in the context of logistics applications because a high density of smart objects (i.e. logistics assets) is available in limited spaces like warehouses.
Novel current mode universal filter and dual-mode quadrature oscillator using VDCC and all grounded passive elements
Published in Australian Journal of Electrical and Electronics Engineering, 2019
Manish Gupta, Priyanka Dogra, Tajinder Singh Arora
Universal filter and single-resistance-controlled oscillator (SRCO) are two applications of ASP which have been discussed in detail in this manuscript. Frequency selective filters, as name implies, is the block that passes/attenuates any specific frequency or a band of frequencies. Universal filter is a type of frequency selective filter which realises all five responses, i.e., low pass (LP), high pass (HP), band pass (BP), band reject (BR) and all pass (AP), from same configuration, whereas oscillator is a circuit that generates un-damped waveform of any designed frequency. SRCO is the kind of oscillator which allows tuning of condition of oscillation (CO) and frequency of oscillation (FO) by varying a single resistance value. All the above-mentioned devices have been successfully used in designing of filters and oscillators, which is evident from the references provided and cited there in.