Generally, the higher operating frequency of an antenna, means greater gain. However, the gains of my proposed antenna have the opposite characteristics in the third band . Please kindly explain the reason of this phenomenon.
The noise power is directly proportional to the frequency band of operation. Therefore, whenever the bandwidth of operation increases the noise power also increases. The increment in noise power will reduce the gain of the system as a whole. Thus, there is a strong tradeoff between the gain and the bandwidth of the system.
Sovan Mohanty Unless Dr.Yaqeen Sabah Mezaal is doing a strange measurement, the noise power will not affect the gain of the antenna. The noise power does not appear in the formula for the antenna gain.
There are lots of reasons why gain can drop as frequency increases. The gain is about 0 dB which means this is a fairly low gain antenna. The gain will depend on the match, and if it is matched at lower frequencies the match may be getting worse as the frequency increases. It may be that the direction of peak gain changes with frequency, and the gain has been measured in one direction.
Minor disagreement with Malcolm White gain (on its own, as defined by the IEEE [see 145-2013 - IEEE Standard for Definitions of Terms for Antennas]), does not depend on the input match, as it is measured with respect to power accepted by the antenna. Realized gain, on the other hand, does depend on the match, as it is measured with respect to the power at the input of the antenna.
It looks like the OP is referring to IEEE gain in the figure.
Dears
I simulated a designed antenna using CST simulator. So, the gain in the third band is just IEEE gain simulation result. I do not think noise power affect the gain result since it has no relation to general gain formula. Matching causes with respect to higher frequencies are feasible.But, at the same time, it is questionable.
For a narrow band antenna, the gain curve peaks at center frequency and trails off for higher frequencies. By shortening your structure for the 3rd band resonance, it should bring your gain back up.
A basic definition of antenna gain is:
Gain = Efficiency * Directivity
What we can say is that, directivity is proportional to frequency but not gain, as it depends on efficiency. I think, as you are increasing frequency, due to your design, the efficiency of your design is decreasing.
Efficiency mainly degrades due to poor impedance matching between feedline and the antenna, Conductor loss and Dielectric Loss.
As your design is fixed and you are checking it for a range of frequencies, it seems like one of the loss factors is getting affected. Please check from the power loss section in 2D results of CST to see whether dielectric or conductor loss is increasing. Check the impedance at those frequency ranges of the port and the feed point of the antenna to check if there is any mismatch.
Hope this helps.
Dr.Yaqeen Sabah Mezaal
Muhammad Mostafa Amir Faisal
Directivity is not always proportional to frequency. As the frequency increases extra lobes can appear, for example, and directivity drop.
Malcolm White I do agree with it, what I was trying to point out is that, gain increases with frequency is correct but we should have a look at efficiency too. I know that as frequency increases, wavelength decreases and as the antenna wavelength starts to become comparable or bigger than wavelength, side lobes do appear, resulting in reduction in directivity too. Thank you for the clarification.
Hello,
Obviously you will have this issue, because if you change the frequency range the mesh properties must be also modified, because they depend on the frequency range and implicitly to the central wavelength, and in CST MWS the used reference for gain/directivity is an ideal spherical radiator ( isotropic antenna ) which is a Lambda/2 ( at operating Frequency ) Dipole that has a gain of 2.2 dBi, and you can see, if the wavelength changes, the gain reference will also change.
So to obtain more accurate farfield results, there is so many tips and tricks to do :
1-Check Energy : The accuracy level in the T-solver should be -40dB,
2-Check boundary : you should use open (add space), and ensures that there is a LAMBDA/8 space at the center frequency for PML Boundaries,
3-Check S-Parameters Balance : Farfield values become critical, if S-Parameter balance = 1 ( which means that no power is radiated ), In this case directivity and gain are calculated from dividing 0/0, which is numerically critical,
- Badges
- Science topic