What is meant by the VSWR of RF Isolator or Circulator and Calculation

Author : handsun co Date : 12/15/2013 3:06:45 PM

    VSWR means voltage standing wave ratio. The Voltage Standing Wave Ratio (VSWR) is an indication of the amount of mismatch between an antenna and the feed line connecting to it. The range of values for VSWR is from 1 to ∞. A VSWR value under 2 is considered suitable for most circulator or isolator applications. The isolator or circulator can be described as having a good match.

    The reflective property of each port of a ferrite circulator or isolator is usually specified in terms of VSWR. For critical applications a Smith Chart, with an impedance plot recorded at a specified reference plane, can be provided. Typical specification for VSWR is 1.25 in Handsun Company. However, a value of 1.10 can be provided for narrow band applications.

    There have a interesting example, please think you punch in wall and one man behind wall and does he get your punch effect NO why? Now think what is reflect by wall to him nothing. So now what different in your punch and wall is impedance means wall impedance is almost 1000> to your punch so you not reflect any thing and so nothing happen with men behind wall.

The impedance matching should be equal 1:1 or vey less different and the ratio of this call VSWR.
Below is some calculation for VSWR, in mobile communication systems, the VSWR of antenna is 1.5:1 at most. Assume that:

ZA: input impedance of antenna
Z0: nominal characteristic impedance

So the reflection coefficient is calculated as below:
You can also represent the matching character of port with echo loss as below:
If the VSWR is 1.5:1, the RL is 13.98 dB.
When the input impedance of antenna is not equal to characteristic impedance, the reflected and incident waves form standing wave after overlapping on the feeder. The ratio of the maximum adjacent voltage of standing wave to the minimum adjacent voltage of standing wave is the voltage standing wave ratio (VSWR). If the VSWR is over large, the communication distance will be shortened and the reflected power will return the transmitter. As a result, the power amplifier may be burnt and the communication system will work abnormally.

When people are looking at their RF needs and trying to figure out which Microwave isolator or circulator will be right for their application. Certain basic concepts like VSWR, bandwidth, insertion loss, isolation etc are explained briefly.

We are professional supplier for RF Circulator and Isolator with competitive price, located in HK, we are focus on design and manufacture and sell coaxial isolator/circulator, drip in isolator/circulator, micro-strip and surface mount isolator/circulator), by now our products have been export to worldwide. If you have a question that is not answered here, please feel free to call us (Handsun Company) or to send us your question via the contact us page page. We will do our best to answer your question, and maybe it will appear on our list to be shared with others!