Agilent 5992-0190EN Transmission Lines and Reflected Signals - Application Note c20141009 [10] free download

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Keysight Technologies Transmission Lines and Reflected Signals University Engineering Lab Series - Lab 3 Application Note Introduction Transmission lines are a very important circuit element in electrical engineering. Transmission lines are distributed elements, in contrast to lumped elements such as resistors (R), capacitors (C), and inductors (L). The electrical characteristics of a distributed element depend upon its physical geom- etry, and the electromagnetic fields which dictate its circuit behavior are distributed over a range of space. Unlike in a purely lumped element circuit, geometry matters and is a primary factor for how the circuit behaves. A transmission line cannot be described by a simple current-voltage (I-V) relation- ship like RCL elements can. Distributed elements, such as transmission lines, are more fundamentally described by the electromagnetic field distributions, which can be either static (DC), time harmonic (AC), or transient waves or pulses. Transmission lines, the subject of this laboratory, are conduits for the propagation of electromagnetic waves which carry both information and power. Travelling waves interact with inhomogeneities in their path, and these produce reflections. These reflected waves are an integral aspect of transmission line behavior which can be both useful and a challenge to manage. 03 | Keysight | Transmission Lines and Reflected Signals, University Engineering Lab Series - Lab 3 - Application Note A quick overview The characteristic impedance of a transmission line Z0 is the ratio of the voltage and current of a wave travelling along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction. The characteristic impedance is determined by the geometry and materials of the transmission line. In a lumped-element model, Z0 can be expressed in terms of RLGC parameters and the angular frequency of the electromagnetic wave: R + j L Z0 = . G + jC The phase velocity, also called the propagation velocity, is determined by the material itself: 1 v= ,