Very Low VSWR antennas

[teknikalar]

What are the advantages of Very low VSWR<1.5 antenna. as far as i understad its something related with the efficiency of the antenna.

Are there some other advantages.

 

[balaguru thavamani]

Yes.As VSWR is good the amount of reflected power towards source will be minimum hence there is increase in eff of the antenna.

 

[teknikalar]

What is itss affect on the performance/characteristics of antenna especially radiation patter and group delay.

 

[balaguru thavamani]

I think it affects gain, not Radiation pattern.

Radiation Pattern mainly depends upon the ground plane and dimensions of the antenna.

 

[farin]

That's right, it doesn't affect radiation pattern, only gain. For better understanding, VSWR could be recalculated to RL ( return loss ). RL directly represents the portion of power, that reflects back from antenna to generator in decibels, e.g. RL = 10 dB means, that antenna reflect back to generator 1/10 of incoming power, RL = 20 dB antenna reflects 1/100 of power etc. So the VSWR ( RL ) influences the efficiency of antenna. In some systems, where the transmitter and receiver share the same antenna, it could be serious problem, if antenna reflects too much power, cos that power could enter the reciver and saturate it or even burn it.

 

[teknikalar]

ITs easy to understand that if the efficiency is better then gain is improved. but i think is would also effect the pattern although a little as all these quantities are interelated to each other.

regards

 

[Azulykit]

Be careful, a low vswr does not necessarily indicate an efficient antenna. It does tell you that the reflection is low, but you see the same thing from an attenuator.

 

[balaguru thavamani]

As Azulykit said,a low vswr does not necessarily indicate an efficient antenna. But this can be resolved by checking whether Antenna is radiating r not.

 

[snkhan]

As Azulykit said,a low vswr does not necessarily indicate an efficient antenna. But this can be resolved by checking whether Antenna is radiating r not.

I think in case of an antenna, low VSWR mean higher efficient. And when one consider the efficiency then it means that low VSWR also effects the pattern not only gain.

 

[balaguru thavamani]

Hi snkhan,

How the effect will be meaning,Is there is any relation between vswr and any

pattern parameter ?

 

[jian]

For an antenna, there are different losses with regard to the input.

1. Radiation loss.
2. Return loss
3. Surface wave loss.
4. Ohmic loss

Total_Loss = Radiation_Loss + Return_Loss + Surface_Wave_Loss + Ohmic_Loss.

When you want to achive is to maximize the Radiation_Loss. Return_loss due to VSWR is just one part of the loss. When you have very low VSWR, you only eliminate the Return_Loss. You still need to reduce the Surface_Wave_Loss and Ohmic_loss. They are also critical.

Best regards,

 

[Azulykit]

Another way to think about my earlier comment: Very low VSWR is necessary for an efficient antenna, but it is not sufficient.

From the VSWR alone an efficient antenna is indistinguishable from a high attenuation pad or matched load.

Low VSWR is still something good, but it is not the whole story. It can be misleading.

 

[snkhan]

Hi snkhan,

How the effect will be meaning,Is there is any relation between vswr and any

pattern parameter ?

The answer is very well explained by jian. There is hardly any antenna for UWB providing low VSWR and only discuss effiency Vs VSWR. Have a look

http://www.worldscinet.com/cgi-bin/details.cgi?id=pii:S0219799506000442&type=html
http://www.swri.org/3pubs/IRD2001/10-9176.htm
http://www.fujitsu.com/downloads/MICRO/fcai/input/uwb_monopole_antenna.pdf
http://www.antennex.com/preview/vswr.htm
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/8636/27413/01219885.pdf

 

[jagdish sharma]

yes,vswr is related to the poewr reflected by the antenna it can be up to 5% of the forward poewr
if if there is any fault on antenna then it is related to vswr

Added after 1 minutes:

What is the difference between swr and vswr