Vswr in log periodic dipoole array antenna

[enamshah]

i am developing lpda of 1-3 ghz and i am using tau=0.942 for gain=10 dbi but when i simulate it in hfss i get a very high vswr....also the gain is low in 1-1.5 ghz(about 3-4db) and from 2.75-3ghz(about 7-8 db)......how can i reduce vswr and increase gain.......furthermore i am using n-type female connector ....does location of connector also have an affect on vswr........

 

[davenn]

as a rule of thumb with a log periodic antenna you will have 3 elements resonant on any given freq within the bandwidth range of the antenna

the books generally agree that 3 elements = ~ 6dBd gain. I would imagine it would be difficult to get much more than that without severely sacrificing other parameters of the antenna.

here's an example of a 2 - 11GHz log-periodic antenna I make use of.

cheers
Dave

 

[enamshah]

thnxs dave
but the prob of vswr still persists and i am not making planar lpda rather i am using structure based lpda(2 booms)
so how can i reduce vswr .......does location of connector also have an affect on vswr.

 

[plasma]

you can buy it in ebay and learn how to do it for your developing. 6$ to 40$

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[FvM]

You should check Zi versus frequency for a systematic mismatch and correct the antenna geometry if appropriate.

If you have an asymmetric feed connection, as the above shown PCB antenna, then the cable position will affect the antenna characteristic. You can use ferrite tubes to suppress the cable common mode waves.