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Derivation of Reflection Coefficient vs SWR
Keith Dysart wrote:
When the generator is matched to the line so that the reflected wave does not encounter an impedance discontinuity when it arrives back at the generator (and therefore is not reflected), ... On the contrary, it is redistributed back toward the load in the process of destructive interference and becomes constructive interference associated with the forward wave. Whether you call that a reflection or not, the fact that the forward power equals the source power plus the reflected power tells us that reflected power being dissipated in the source would violate the conservation of energy principle. where does the reflected power go? Power doesn't flow so reflected power doesn't "go" anywhere. It is the reflected energy that is flowing, i.e. going somewhere. If the power were flowing, its dimensions would be joules/sec/sec. Maybe you would like to try to explain the physical meaning of those dimensions? Does it enter the generator? forward power = source power + reflected power A component of the forward energy is equal in magnitude to the reflected energy so no, it doesn't enter the source. Is it dissipated somewhere? Not during steady-state. During steady-state it is being used for impedance transformation. After steady-state, it is dissipated either in the source or in the load as a traveling wave. Answers to these questions will quickly lead to doubts about the *reality* of "reflected power". Reflected power is the Poynting vector associated with the reflected wave. It exists at a point. It's average magnitude (indirectly measured by a Bird) is Re(ExH*)/2. It's direction is the direction of the flow of reflected energy. If you don't believe in reflected energy, let your fingers become the circulator load resistor for an open-circuit stub being driven by a KW source. -- 73, Cecil http://www.w5dxp.com |
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