Advice on S11 Curve

Thread Starter


Joined Jun 28, 2022
I have designed an Antenna for operation at 2.4 GHz in CST. I have obtained the following S11 curve and would like to know if it is suitable for a design that involves the use in Bluetooth/WiFi frequency ranges. Finally would this S11 parameter be classified as an acceptable antenna indicator to operate at 2.4GHz.



Joined Jul 21, 2022
S11 curves in antennas characterization help to find the resonance frequency of the antennas, knowing if more than 75% or more than 90% of the power that is intended to be captured/radiated would be delivered/accepted to/from the antenna's load, as well as for identifying the bandwidth. Although useful, unfortunately, analyzing the S11 curve is not enough to answer your question. Also, I would say it is mandatory to look at the radiation pattern, the gain, the radiation efficiency, dimensions and structure of the antennas (probably I am forgetting some others but this are essential) and how the integration of the antenna with the rest of the system would influence all the previous parameters.


Joined Aug 21, 2017
Divide the dB value converted to rational number by 2 and You`ll have the loss factor at the hands. Minus 40 means about 100x and 6 dB means 2x mean the figure is 200x or other words the loss factor is 1:400 what is 0.25%. Means this frequency is the best for radiating the power. However You should check the R what should be 50 or 75 Ohms depending on cable, and check the X what should be as nearer to zero as better, or it ought be externally compensated (coil, capacitor etc). Best is to activate VSWR regime on your device, then for large power it ought stand beyound the 1.2 of for small power (miliwatts) around 1.5 or extreme case 2, but never higher.

Anyway, if You see the figure about zero, thats a catastrophy. If see something -6 dB or -8 or at least -4 dB, thats rather good. Take the minimum value ant thats the range in which You should seek for resonance.
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Joined Jul 21, 2022
>>>Here you share some practic rule of thumbs but you should notice that - 40 dB will lead you to a 100x difference only if the reference is in Volts (-40dBV = 20log 0.01V/1V). If you deal with dBW or dBm, a 2x difference leads you to 3 dBm or dBW. The better is you impedance matching between the antenna and the load (equal real part or resistance and zero imaginary part or reactance) the higher the transmitted/received power.

P. S. : I should have written "these are essential" before instead of "this are". Sorry!