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Transmission Lines
Published in Ahmad Shahid Khan, Saurabh Kumar Mukerji, Electromagnetic Fields, 2020
Ahmad Shahid Khan, Saurabh Kumar Mukerji
In coaxial cables, the field is totally confined between inner and outer conductors. In view of this confinement, their bending and twisting within some permissible limits have no negative effect on the field distribution. These can also be strapped to the conductive supports without inducing unwanted currents in them. Like parallel wire lines, these can also carry TEM modes up to a few GHz. At still higher frequencies TE and TM modes can also propagate. The TEM mode is the principal mode of propagation in coaxial cables. In case of propagation of more than one mode, any bend or irregularity in its geometry can cause intermodal power transfer. Its most common applications include television and other signals with multi-megahertz bandwidth. The characteristic impedance of a coaxial cable may be of the order of 50 to 75 ohms.
Industrial Networks of PLCs
Published in Stamatios Manesis, George Nikolakopoulos, Introduction to Industrial Automation, 2018
Stamatios Manesis, George Nikolakopoulos
Coaxial cable. The coaxial cable consists of a stiff copper wire (core) that is surrounded by an insulating material. The insulating material is covered by a woven copper braid or a metallic foil that acts both as the second wire in the circuit and as a shield for the inner conductor. The external conductor (grid) is covered by a protective plastic cover. There are two types of coaxial cables, the 50 Ω cable used for digital transmission (base band) and the 75 Ω cable used for analog transmission (wide band). The coaxial cable is characterized by a high bandwidth and a satisfactory tolerance to noise. The bandwidth varies depending on the length of the cable. For coaxial cables with a length of 1 km, the data rate can be as high as 10 Mbps. For smaller or larger distances the data rate is correspondingly higher or lower. Coaxial cables are used by many companies in commercial industrial networks for the interconnection of PLCs.
Introduction to Localarea Networks
Published in Paul J. Fortier, Handbook of Local Area Network Software, 1991
Typical of most local area networks in use today is the use of serial data transmission media and techniques. This is due to the LANs’ use in high-speed transmission, over moderately long distances, and the desire to keep wiring costs at reasonable levels. Due to this use, sophisticated line drivers and receivers (next section) have to be used, with only one driver/receiver interface unit per device. Transmission of the sequence of bits is typically strictly done digitally, using baseband or broadband signaling techniques. Baseband signaling is a technique in which the digital signal is transmitted in its original form with no changes induced by modulation techniques. Broadband signaling is a technique that provides a means to break up the transmission media into multiple channels over the same conduit by frequency division of the bandwidth [Fortier 1988]. Either of these techniques can be hosted on coaxial cable. Coaxial cable is a wire media made up of a central copper wire core encased in an insulator that is covered with a woven copper outer mesh.
Design of a 3-way wide-band in-phase power combiner for UHF applications
Published in International Journal of Electronics, 2023
In this section, a three-way power combiner has been proposed that is a modified version of the conventional three-way Wilkinson combiner. Similar to the work of Momenzadeh and Ahmadi (2020), the floating resistors have been replaced by coaxial baluns and 50-Ω terminations. The schematic of the proposed three-way power combiner has been shown in (Figure 2). As the terminations have a standard value of 50-Ω, the proposed combiner is suitable for high power applications. The power handling of this combiner depends on the loss-tangent of the substrate, the power-handling of coaxial cables, and the nominal power-rating of terminations (Naeimi & Ahmadi, 2021). In the proposed combiner, all of the branches and coaxial-cables are quarter-wavelength long at the centre frequency. The combiner has been designed for the frequency range of 470–860 MHz, which is intended for digital video broadcasting (DVB). In this work, we show that the coaxial cables have a characteristic impedance of 50-Ω. The coaxial cables and terminations are matched to ensure broadband operation. The combiner has been analysed by the even- and odd-mode methods (Pozar, 2011). In the following section, the characteristic impedances of the transmission-lines have been evaluated. To increase the bandwidth, a transmission-line is inserted behind the summing node (node-A). The proposed structure is a combination of a planar microstrip-circuit and coaxial-cables. In this structure, the cross-over for resistors has been eliminated. In a conventional three-way Wilkinson combiner, the isolation resistors are connected by a cross-over.
Design and Fabrication of a Low-Cost Mobile Antenna for Low VHF
Published in IETE Journal of Research, 2021
Mahmood Rafaei-Booket, Sina Hasibi-Taheri
The simulated result of such a radiator with optimum height (152 cm) is shown in Figure 2(b) with two different impedance ports. As seen in the same figure, the simulated radiator is a high-impedance one, and a high-impedance TL is needed to transfer its input impedance and design a matching network inside the antenna base. Therefore, a high-impedance coaxial cable is designed with characteristic impedance Z0 = 140 Ω. Such a high-impedance coaxial cable, which is depicted in Figure 1 by using label H2, composed of a straight metallic hollow cylinder with a center conductor aligned with cylinder’s center axis, and air dielectric. The optimum height of the implemented coaxial cable is 70 cm, the diameter of its center conductor is 1.8 mm, and its inner and outer diameters are 18 and 20 mm, respectively. Combination of the mentioned two parts (radiator along with high-impedance coaxial cable) is then simulated. Figure 3(a) shows the simulated smith chart in which the impedance matching is better than one reported in Figure 2(b).
Gain Enhanced Miniaturized Microstrip Patch Antenna Using Metamaterial Superstrates
Published in IETE Journal of Research, 2019
A. Bakhtiari, R. A. Sadeghzadeh, M. Naser. Moghadasi
In this section, a miniature patch antenna operating at 534 MHz has been designed using an artificial magneto-dielectric material as the antenna substrate. The (meta) material selected for the substrate can help with realizing high permittivity and permeability values and obtaining a high compression factor for the antenna. The antenna compression factor is defined as square root of relative permittivity and permeability product ). For this purpose, “2nd kind Hilbert fractal” [11] inclusions are used in substrate layer to obtain high positive permeability and permittivity at the antenna's frequency of resonance. The first step in antenna design is selecting the material for the substrate layer and using its electromagnetic parameters. Since the selected metamaterials for the substrate have complicated geometric shapes and very small dimensions, full wave electromagnetic (EM) simulations require high meshing resolution, resulting in very long simulation times. Therefore, a technique to improve simulation time would be extremely helpful for antenna design and optimization. Figure 1 shows the dimension parameters of Hilbert unit cell as the building block of the artificial magneto-electric substrate. Table 1 also lists the associated values. The parameters listed in Table 1 show an order of magnitude between dimension of the antenna and the fractals previously discussed. The proposed antenna has been fed by a coaxial feed line. Input impedance of coaxial cable is 50 Ω. As Figure 1 shows, inner section of coaxial cable is joined to patch antenna and outer section is ended and joined to ground of superstrate in its entrance.