what is VSWR ?? what role it plays in antennas???

[tender_006]

what is vswr

some plz explain abt VSWR ? how is the realtion with antennas??


thanks

 

[PaulHolland]

what is vswr?

Hi, If you feed an antenna with a signal a part of the signal may reflect from the antenna and will return back to the sender. This reflection only happens if the impedance of your antenna does not match with the impedance of your cable. So if your antenna is 50 Ohm and your coax cable is 75 Ohm, you will have a problem. The VSWR is a ratio that is telling how well your system is matched and if the energy of your transmitter is getting into your antenna. 1:1 is the optimum and it means all energy made by your transmitter is put into your antenna and nothing is reflected back to your transmitter. if Your VSWR is 1:3 it still looks OK you may think but now some 25% will return to your transmitter and only 75% is put into your antenna.

If your VSWR is low it DOES NOT mean your antenna is good !. . It only is telling its good matched. Every antenna also has an efficiency, how much of the power put into the antenna is effectively rediated by the Antenna. This is expressed in dB. Mobile phone antenna's have normally an efficiency of some -2 or -3 dB but their VSWR is 1:1.5 or below which is very good (5 % returns)

regards,

Paul.

 

[tender_006]

what is vswr

thank u very much ,, still have some confusion ????? but to some extent i understood ,, i have problem with ratio only ???? if u have plz send some more details

 

[flatulent]

what is vswr ?

This parameter comes from the early days when two wire air insulated (mostly) transmission lines were the norm. Back then directional power meters were expensive and cumbersome. The easy measurement to make was the voltage across the wires as a function of distance along the wires. When these values were graphed a repetitive pattern was formed. From the maximum and minimum values the load impedance could be calculated. You did not even have to do the graph. Just take measurements and keep the values of the highest and lowest reading.

Later on with VHF-microwave work there were coaxial measurement devices with an open slot. A probe was put into the slot and moved along the line. Similar measurements were made.

The SWR value is good for amplifier load effects.

A better parameter for some purposes is return loss. This is the fraction of power that does not get into the load.

 

[romrom]

vswr graph

hi, in the graph of VSWR against Frequency.. the part of the graph under the value VSWR=2 .. is the band width of the antenna ..

 

[flatulent]

wat is vswr

There are several definitions of bandwidth based on performance. The previous post illustrated the input impedance bandwidth. There is also the radiation pattern bandwidth where some criteria such as beamwidth, sidelobe level, or circular polarization ellipticity ratio are used.

 

[Borber]

what is the vswr

Term VSWR stays for Voltage Standing Wave Ratio. As flatulent said it is the ratio of voltage maximum to voltage minimum on standing wave along the line caused by mismatch. When line and load impedances are equal, matched, the standing wave disappears and voltage along the line is constant. That means VSWR=1:1.

 

[ravenkrofft]

how to resolve vswr problem in antenna

Hey guys.
I've been reading these comments, thx for the info!
I'm new to Ansfot and I'm still wondering how to get SWR from an antenna. Don't worry I got the model and stuff, but I still don't know how to get the SWR vs frequency graph.
Thanks for the time!

 

[menz]

antenna gain vswr

hi i need to know y return loss is minimum in magnitude at resonant frequency..plz tell me

 

[balaguru thavamani]

vswr what is

For better understanding refer the below link from microwaves101.com

**broken link removed**