[SOLVED] patch antenna bandwidth

[amntt]

how i can calculate bandwidth of patch antenna in percent? for example in the attached picture bandwidth is for example 10 mhz how i can convert it to percent because in papers they say antenna bandwidth is for example 3%:!:

 

[WimRFP]

they call it relative bandwidth, BWrel = BW/(center frequency). BW is mostly taken as the difference between the frequencies where VSWR = 2 (or Return Loss = 9.5 dB).

So antenna with a 3% VSWR=2 bandwidth at 900 MHz, has 27 MHz bandwidth where VSWR<2

 

[amntt]

many thanks

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sorry in your example the antenna has 27 mhz bandwidth at both sides? 900+27 and 900-27 then totally it has 54 mhz bandwidth?

 

[WimRFP]

BW is the difference between the frequencies where VSWR=2, so when it is 27 MHz, you may expect 13.5 MHz on each side of the center frequency.

You may know that in case of large relative bandwidth, the center frequency (frequency where VSWR is best) may not be in between the frequencies where VSWR=2.

 

[amntt]

how i can convert dbi into db ?

 

[WimRFP]

dBi has a meaning, as it is referenced to an isotropic radiatior, but dB can be anything. You may encounter dBd. Then a dipole antenna is used as a reference. As a half wave dipole has 2.14 dBi of gain, dBi = 2.14 + dBd.

So when somebody uses dB, he/she needs to mention what is used as the reference (for example input power when talking about power gain).

 

[amntt]

sorry s.o says that radiation efficiency is gain/directivity in my simulation i have gain=2.9db and directivity=3.9dbi !! so i can not devide these to different dimansion , i can?

 

[WimRFP]

Very likely the gain is also in dBi. so your radiation efficiency = 2.9dBi - 3.9dBi = -1 dB (=79%).

In the IEEE definition gain does not include the loss due to mismatch. Gain including mismatch loss is called "realized gain".

Something confusing: The EMC community uses mostly "gain" to identify realized gain.

 

[amntt]

do u know em/circuite simulation feature of cst ? i have a question regarding that.