decrease s11 for printed loop antenna

[randy orton]

Hello all

right now i am designing printed loop antenna with U shaped tuning element which is situated on my feeding port, and i have designed it in HFSS. and I am getting S11 of around -15dB but i want to make it more than -10dB, so what are the possible options i have?i can't increase my feeding power so what are the possible ways to achieve S11 of -10dB?instead of U shaped any other possible shape or any guess?

USUALLY I DON'T GET ANY REPLY BUT I HOPE THIS TIME I WILL GET SOME REPLY.

 

[ferdows]

hi dear i think u never response because of u questions
what u mean when u said u want to increase from -15 to -10 Db when usually other opposite of u?

 

[vfone]

I give you some hints if you want to get answers to your questions.
- Print (picture or pdf) the antenna, the measurement/simulation plots, and post them on the forum.
- Hand draw and scanned pictures are usually more explicit, than CAD pictures with many grids on the background.
- Place very clear questions and also some next steps you intend to do.

 

[randy orton]

thQs for yr advises but i really hope to get same or more reply for my questions:

ok so for you guys i have attached a full pdf so that i don't make any more confusions.

and i want S11 well above -10dB so now can you suggest me something?

 

[vfone]

You are looking for Reflection Coefficient S11 to be WELL ABOVE -10dB !? How much above? In case of antennas S11 cannot be greater than 0dB.

I think you intend to make S11 to be WELL BELOW -10dB.

Things staying like this, you forgot to mention at what frequencies you want to improve S11 (I mean, to be BELOW -10dB).
From the attached plot S11 is already BELOW -10dB between 1.8GHz and 3GHz.

 

[randy orton]

ok than i want S11 between 0 to -10db
so what are the possible ways to CHANGE IT from -15db to the range of 0 to -10dB range

 

[E Kafeman]

-10 dB results in that 10% of transmitted power is not accepted by the antenna and will reflect back into transmitter stage.
-15 dB result in that 3% of total power reflects back into transmitter.
Therefore: -15 dB makes the antenna to seem 7% more powerful then if the reflection is -10dB for same amount of TX power.
(Assume that antenna resistive losses is the same in both cases.)
One method to achieve higher reflection: reduce height above ground and re tune the antenna by shorten its length.

 

[randy orton]

from db how can you find how much power is reflected back?
10 dB results in that 10% of transmitted power is not accepted by the antenna and will reflect back into transmitter stage.
-15 dB result in that 3% of total power reflects back into transmitter.

how you can come to know that for -15db it will reflect only 3% not 15%?
what is the formula to convert db to reflected power?

if according to you -15dB is better than why every place its written that its a ideal case to have S11 of below -10dB for antennas???

 

[ferdows]

hi randy
at first i suggested u read more about antenna and propagation u can download a thesis by Johanna Paule in MIT in Google which talk clearly about antenna definition and u can see there how relation between s parameter and other like power and efficiency
and using antenna with lower S is better but it essential only in some radar and communication system in other hand we use and accept upper S or VSWR for mobile system all related to your application but u say other thing and it is unacceptable

 

[FvM]

dB is defined as 10*log10(P1/Pref). Decibel - Wikipedia, the free encyclopedia
Numerically -15 is in fact below -10.

 

[E Kafeman]

dB is unit less and is used as a relative comparison.

20 dB = 10 dB + 10 dB = (10*10) = 100
10 dB = 10
0 dB = 1
-10 dB = 0.1
-20 dB = 0.01