how to improve the gain of antenna?

hai,
I designed a mimo antenna in HFSS v 13. In that, i reached a very good return loss and VSWR. Where as the gain of my antenna is 2dB and the directivity is about 5dB. Since the directivity is high when compared with gain, the efficiency of my antenna gets very low. Kindly, give some tips to improve the gain of my antenna.

Antenna gain is often quoted with respect to a hypothetical antenna that radiates equally in all directions, an isotropic radiator. This gain, when measured in decibels, is called dBi. Conservation of energy dictates that high gain antennas must have narrow beams. For example, if a high gain antenna makes a 1 watt transmitter look like a 100 watt transmitter, then the beam can cover at most 1/100 of the sky (otherwise the total amount of energy radiated in all directions would sum to more than the transmitter power, which is not possible). In turn this implies that high-gain antennas must be physically large, since according to the diffraction limit, the narrower the beam desired, the larger the antenna must be (measured in wavelengths).

Antenna gain can also be measured in dBd, which is gain in Decibels compared to the maximum intensity direction of a half wave dipole. In the case of Yagi type aerials this more or less equates to the gain one would expect from the aerial under test minus all its directors and reflector. It is important not to confuse dBi and dBd; the two differ by 2.15 dB, with the dBi figure being higher, since a dipole has 2.15 db of gain with respect to an isotropic antenna.

Gain is also dependent on the number of elements and the tuning of those elements. Antennas can be tuned to be resonant over a wider spread of frequencies but, all other things being equal, this will mean the gain of the aerial is lower than one tuned for a single frequency or a group of frequencies. For example, in the case of wideband TV antennas the fall off in gain is particularly large at the bottom of the TV transmitting band. In the UK this bottom third of the TV band is known as group A, see gain graph comparing grouped aerials to a wideband aerial of the same size/model.

What substrate material do you use, respectively what is the tangent loss factor of the material?
When you have a good directivity but low gain it is often because of a high loss substrate.
Also a wrong height could be responsible.


sandipm14, please don't copy text form wikipedia.

flanello said:

sandipm14, please don't copy text from wikipedia.

Click to expand...

There's nothing wrong with doing that specially if it answers the question

BUT if it came from some source like that, then the source name should have been given

Dave

flanello said:

What substrate material do you use, respectively what is the tangent loss factor of the material?
When you have a good directivity but low gain it is often because of a high loss substrate.
Also a wrong height could be responsible.


sandipm14, please don't copy text form wikipedia.

Click to expand...

Thank you for ur reply..........
I used FR-4 as a substrate material which has the loss tangent value of 0.02. The height of the substrate is 1.6mm.

I see that you mention a MIMO antenna.

I would think that there are many elements and you have some sort of feeding network.

You might want to take a closer look at the losses in those feeding elements (power dividers, couplers, ...)

I cant understand your words..............

jeeudr said:

I see that you mention a MIMO antenna.

I would think that there are many elements and you have some sort of feeding network.

You might want to take a closer look at the losses in those feeding elements (power dividers, couplers, ...)

Click to expand...

FR4 is a lossy substrate. Try a simulation with a "HF-substrate", for example a rogers. Then the gain should increase.
Another thingis the groundplane, is it large enough?

Do you have a MIMO antenna that has multiple beams? Then you should have multiple antenna ports or a feeding structure.

vishwanivi said:

I cant understand your words..............

Click to expand...

My answer is similar to the reply by flanello

flanello said:

FR4 is a lossy substrate. Try a simulation with a "HF-substrate", for example a rogers. Then the gain should increase.
Another thingis the groundplane, is it large enough?

Do you have a MIMO antenna that has multiple beams? Then you should have multiple antenna ports or a feeding structure.

Click to expand...

Since you use FR4 (which is a lossy substrate), you would have a lot of loss, non-uniform dielectric values, etc ... throughout your substrate.

In a MIMO antenna, you would generally be having some elements which distribute the power to the various radiating structures. Each of these sections of your design would have some losses in them, which add up overall and lead to a decreased efficiency when comparing the input and radiated power.