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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.
Transmission Lines
Published in G. Jagadeeswar Reddy, T. Jayachandra Prasad, Basics of Electromagnetics and Transmission Lines, 2020
G. Jagadeeswar Reddy, T. Jayachandra Prasad
When a Transmission line is not terminated with it’s characteristic impedance there will be reflected wave. We know the general equations for Transmission line V=be−γx+aeγxI=1Z0[be−γx−aeγx]
Investigation of Slow-Wave Systems Applying Versatile Electromagnetic Simulation and Design Tools
Published in Stanislovas Staras, Romanas Martavicius, Julius Skudutis, Vytautas Urbanavicius, Vladislavas Daskevicius, Wide-Band Slow-Wave Systems, 2017
Stanislovas Staras, Romanas Martavicius, Julius Skudutis, Vytautas Urbanavicius, Vladislavas Daskevicius
Reflections in the signal path with a slow-wave system (Figure 5.4b) do not exist if the internal resistance of the signal source and load resistance are the same as the characteristic impedance of the slow-wave system (at ZG = ZC = ZL). Therefore, at a selected frequency, the system characteristic impedance can be determined by changing the signal source and load resistances (ZG = ZL) until minimal reflections are obtained. Then, ZC ≅ ZG = ZL. The graph of helical system characteristic impedance versus frequency obtained on the basis of the described idea is presented in Figure 5.9. Characteristic impedance decreases with frequency.
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.
Analysis of characteristic impedance of microstrip and coplanar textile signal lines
Published in The Journal of The Textile Institute, 2021
The properties of these lines should enable the correct transmission of various types of signals. One of the most important parameters of the transmission line is its characteristic impedance. This impedance depends not only on the properties of the electro-conductive tracks but also on the properties of the substrate on which these tracks are located. Characteristic impedance is purely a function of the capacitance and inductance distributed along the line’s length. Barring dielectric ‘leakage’ and conductor resistance, the characteristic impedance of a transmission line is equal to: where L is the inductance per unit length of the line and C is the capacitance per unit length of the line.