about antenna bandwidth

[Ray_Chang]

hi all
I design a small antenna about 2.4GHz.
This size is about 40mm * 20 mm.
And bandwith is about 70MHz.
How to add the bandwith of small antenna ?
can anyone give me some hints, please ?

 

[cyai]

Could you tell us which antenna configuration that you design, the antenna size of 40*20mm2 is so big that can't meet wireless product space.
As my experiences, using quarter wavelength antenna, such as PIFA or monopole antenna, the bandwidth is of more than 150MHz with fine tuning.

 

[jallem]

I assume is a p_a_t_c_h antenna. The p_a_t_c_h antenna has
that problem. For 2.4 GHz 802.11 or Bluetooth antenna
the bandwidth needed is about 73 MHz at least.
There are techniques to increase the bandwidth.
1) Lateral parasitic patches, this increase the bandwidth for
< 5 MHz, not much.
2) Matching Networks as in
H. Pues, J. Vandensande, and A.V. Capelle, Broadband microstrip
resonator antennas, IEEE Antennas Propagat Soc Int
Symp, 1978 Dig, pp. 68-69

Both of them increase the size of the antenna.
So in order to decrease the size of the antenna you coud
use shorting pins where the Electric field is zero, as in the
middle of the antenna. Even further reduction can be accomplished
if reducing the electric wall formed by the shorting pins.
Even better, if you can increase the separation of the p_a_t_c_h and the
ground plane then the bandwidth increases.

 

[firepool]

Maybe you should give us more details about this antenna you wanna design.

there are many ways to enhance the bandwidth of antennas:
you could enhance the thickness of antennas, the bandwidth can increase with the antenna becoming thicker.
you also could place a defective ground on the back of antennas, but you must know, in some case, defective ground can not meet the demand of customer, cause the back radiation from antennas often effects the circuit behind the antennas and also does hamful to brain( espacially head-wear antenna).
Furthermore, you could use some special structure to realize bandwidth of antennas, for example u-slot and some kind of thing like that. As my experience, 5% bandwidth could achive without much difficulty (working at 2.4GHz, so 5% is 120MHz).
at last, a good book for you, compact and broadbadn microstrip antenna, there are a lot good examples in this book, you should find it and download it by internet.

 

[gunajraman]

I think you can send your design .

you can go for U slot in the centre which gives very high bandwidth.
Also the feed has to be slightly offset.

Anyway can you upload your design ?

 

[flatulent]

There is a book on this topic written ten years ago. They suggest:

thick air dielectric below the p-atch

one p-atch spaced in front of the bottom p-atch, each with slightly different dimensions

slot feed from below the ground plane

enlarged areas on the end of the slot

They could get 10-20% bandwidth with these methods.

[edited part] The book is Broadband P-atch Antennas by Zurcher and Gardiol.

 

[gunajraman]

what do you think about the slot and the feed offset ?

Also planar inverted cone antennas have very high bandwidth .