Relationship To The Reflection Coefficient
The voltage component of a standing wave in a uniform transmission line consists of the forward wave (with amplitude ) superimposed on the reflected wave (with amplitude ).
Reflections occur as a result of discontinuities, such as an imperfection in an otherwise uniform transmission line, or when a transmission line is terminated with other than its characteristic impedance. The reflection coefficient is defined thus:
is a complex number that describes both the magnitude and the phase shift of the reflection. The simplest cases, when the imaginary part of is zero, are:
- : maximum negative reflection, when the line is short-circuited,
- : no reflection, when the line is perfectly matched,
- : maximum positive reflection, when the line is open-circuited.
For the calculation of VSWR, only the magnitude of, denoted by ρ, is of interest. Therefore, we define
- .
At some points along the line the two waves interfere constructively, and the resulting amplitude is the sum of their amplitudes:
At other points, the waves interfere destructively, and the resulting amplitude is the difference between their amplitudes:
The voltage standing wave ratio is then equal to:
As ρ, the magnitude of, always falls in the range, the VSWR is always ≥ +1.
The SWR can also be defined as the ratio of the maximum amplitude of the electric field strength to its minimum amplitude, .
Read more about this topic: Standing Wave Ratio
Famous quotes containing the words relationship to the, relationship and/or reflection:
“... the Wall became a magnet for citizens of every generation, class, race, and relationship to the war perhaps because it is the only great public monument that allows the anesthetized holes in the heart to fill with a truly national grief.”
—Adrienne Rich (b. 1929)
“But the relationship of morality and power is a very subtle one. Because ultimately power without morality is no longer power.”
—James Baldwin (1924–1987)
“What chiefly distinguishes the daily press of the United States from the press of all other countries is not its lack of truthfulness or even its lack of dignity and honor, for these deficiencies are common to the newspapers everywhere, but its incurable fear of ideas, its constant effort to evade the discussion of fundamentals by translating all issues into a few elemental fears, its incessant reduction of all reflection to mere emotion. It is, in the true sense, never well-informed.”
—H.L. (Henry Lewis)