Bandwidth increase with substrate height

[bhargav32004]

hiii
Can any one explain me how height of substrate influences the bandwidth of a patch antenna. Normally with the increase in height of substrate, bandwidth increases. How does this occur??

 

[kspalla]

When the height is increased EM field is now more confined in the air than substrate.
This means that now the losses are less due to the contribution by the substrate is less than the air.
Less loss means more bandwidth.

I hope now you understood if not PM me.

 

[bhargav32004]

thanx kspalla for the reply
But I dint understand it propely, could you please explain to me little more detailedly

 

[mauloftin]

Hi, I have this formula for bandwidth :

BW = 4 f² (t/0,794) MHz for PSV cca 2


f is central frequency [GHz]
t is height substrate [mm]

 

[shahid78]

hi kaspalla

i may not agree with your explanation of increase in BW with increase in height.

less loss means high Q which measn low BW which is total opposite to what you said

can you please mention any equation or formuation which relates low loss with increae in BW

regards

 

[kspalla]

Hi Shahid,
I agree with you and you are right. your statement is true for any systems.

In a transmission line loss means combination of dielectric, radiation, and conduction loss.

In fact radiation loss is treated as gain in antenna which is more with increased height of substrate due to field is more confined in air.

when dielectric loss is getting lower, radiation loss starts increasing in antenna. which can accommodate radiating/ capturing the nearby frequencies too.

In antenna, low loss means more radiation loss. now coming to your point , more radiation loss means more bandwidth.

I guess you got the point if not PM me.

 

[Abizazu]

Hey guys,

Q-factor is proportional to the ratio of dielectric constant/substrate height.
But, BW is inversely proportional to Q-factor. Then increasing substrate height decreases Q, implies BW will increase.

 

[cnm]

Hey guys,

Q-factor is proportional to the ratio of dielectric constant/substrate height.
But, BW is inversely proportional to Q-factor. Then increasing substrate height decreases Q, implies BW will increase.

Totally agree. A few things to add:

For patch antenna, it can be approached using a resonant cavity model. For larger substrate thickness, the dielectric loss in the cavity increases (think of the volume filled by dielectric.), while the total radiated energy from the exciting source stays the same. So the Q drops. Remember Q=omeg(reactive energy)/Loss. The Bandwidth here is the VSWR bandwidth, we should make this clear. So lower Q, means more loss, more loss means better matching. So this makes it look like a wideband device.

 

[FvM]

For larger substrate thickness, the dielectric loss in the cavity increases

Radiation loss, or in other words, coupling of the internal field to the outer world, is quite different from dielectric loss. I fear, the analogy is misleading.

P.S.: Another property of a higher substrate is the increased magnetic momentum. I assume, that it plays a major role in the patch coupling.

 

[cnm]

Radiation loss, or in other words, coupling of the internal field to the outer world, is quite different from dielectric loss. I fear, the analogy is misleading.

P.S.: Another property of a higher substrate is the increased magnetic momentum. I assume, that it plays a major role in the patch coupling.

Agree. That is not a very good analogy. But it explains the matching (VSWR) bandwidth enhancement well. Can you explain a little better for your "increased magnetic momentum" idea. You did not carry through why it is a better explanation.

I think what you referred is the equivalent magnetic current x dimension (Im*d) increase, in other words, same current but a larger equivalent radiation aperture. Correct me if I'm wrong. 8)