What is the VSWR?
VSWR (Voltage standing wave ratio) is the amount of reflection that comes from with impedence mismatch and is dealt in detail in transmission line theory. I forget the exact equation but its something like the raio of the mag of reflected wave to the mag of transmitted wave. The lesser the VSWR better the impedence matching and hence better transmission.
In a transmission line, the ratio of maximum to minimum voltage in a standing wave pattern. Note: The VSWR is a measure of impedance mismatch between the transmission line and its load. The higher the VSWR, the greater the mismatch. The minimum VSWR, i.e., that which corresponds to a perfect impedance match, is unity. A good online VSWR calculator is at http://www.csgnetwork.com/vswrlosscalc.html
as close to 1 is good. at market, GSM antenna are available with 1.4
It is a good idea to read almost any book of microwaves.
I will add an intuitive feeling to the VSWR definition.
If you have a long transmision line and a voltage source at one edge. Generally speaking there are two voltage waves running along thr line, one is the wave runs from the source toword the load and another that is reflected from the load toword the source.
If the load is Z0, the same as the line characteristic impedance then there in no reflection from the load. It means there is only one voltage wave running from thr source toword the load. But if the load is different from the chracteristic impedance of the line then there is reflection. Any point along the line have two waves as we understand, and each is time domain means a sine wave that runs along the line. If we add the two waves and look at the amplitood total sine we see a ripple of the "envelop". In one point the two voltage add to a high voltage and in other points they might be oposit and they substract from each other. So the sine amplitood is not constant.
(If the load is Z0, means there is no reflection, the sine amplitood is 1) .
As VSWR is high, means high reflection from the load, then the wave amplitood ripple is high.
D.J
i think you must not study the book of microwave.
vswr is the basi concept in the mw
VSWR = 1+reflection index /1-reflection index
Votage standing wave ratio
the max. amplitude of a standing wave /the min. amplitude of the one