Need help with small antenna design (80MHz-110MHz)

[Pacotam]

I need to build a small anntenna with 80MHz-110MHz with the size is less than 6cm x 2cm. As there are a Large LCM surround beside the antenna, there happen a big effect of EMI.

Please advice some antenna design.

Thank for your help

 

[VisiGoth]

How big is your third dimentsion? Will you be consideing magnetic pick up, coils, ferrites?

Did you mention EMI because you have a directivity requirement?

I must show my ignorance. What is large LCM surround?

 

[Pacotam]

Thank for your help.
1. the dimentsion is 6cm x 2 cm X 1 cm. I have design a loop antenna with the maximum circumference is 19cm and 1cm width, which the profromance is not so good. So I want to get some news design. I will consider any type antenna. For the ferrities, I will consider with the cost. As some meterial of the ferrites is too experience.

I need to design with a small antenna with high performance.

I know the ferrities loaded loop antenna may be usfull in this antenna. But I am not so sure can apply in my project or not.

2. As the large LCD module generate a EM Field which made the Antenna recvice not well.

3. sorry for my words. The LCD Module which is not

 

[VEBill]

80 - 110 MHz (or 88-108 MHz) is the FM broadcast band (in all regions I believe...[?]).

I assume the application is receive only. Hmmmm... is this for the Sony PSP ?

EMI shouldn't be too much of a problem if the radio is an FM radio (as opposed to AM). Making sure that the detector is AM-immume would be the easiest way to deal with the noise (at least most of it).

Ferrites are not normally employed for antennas at these sorts of frequencies. Not saying it isn't possible, but you don't normally see ferrite in an FM radio antenna system.

Most applications employ the headphone cord as the antenna.

 

[Pacotam]

Thank for your information.
In our product applied with FM broadcast to receive signla.

Actually is not for PSP.

I have use some equirement to test that the LCD have generate EMI to effect the proformance.

As there is no headphone. so I cannot employ the headphone cord as the antenna.

 

[VisiGoth]

For a similar requirement a group looked at putting a loop aroung the LCD. This really picked up large noise spikes, but the actual energy in the FM band was low. However, the idea was rejected because of the cost. This design had several turns, but maybe there are fewer turn alternatives.

They also looked at sharing a structure with other antenna elements. The problem there was repeatability of using the battery as the ground plane. If you control your vendor this might be an option for you. If it is possible that your custormers will buy cheap third party repacement batteries you will be in trouble. That ended up to be the main problem with the application that used the batery as the main part of the structure.

 

[Higgler]

This is very challenging to perform over that large of bandwidth.
Do you have any specific gain requirements? -10 dBi, -20 dBi, -30 dBi???

You're fighting the laws of physics going that small.
Using Ur or Er and trying for a quarter wave antenna, you need values of 200. That'll limit your bandwidth severely, so it's a one frequency antenna.

If you have any mounting base that the unit plugs into, or can add a connection to a human being either a neck strap or wrist strap that's metal, that will help performance alot.

kch

 

[Pacotam]

Thank for your help.

I have try to use the wire antenna round the the LCD. I discover that the LCD have effect the antenna.
Meanwhile I apply the loop antenna arrnound the LCD which the L value is too large for the Chip tuning. meanwhile EMI effect the antenna

So we need to apply a antenna with a small space which is far away the LCD.

For the gain, our target only want to get low as we can. we cannot apply with 1/8 wavelength wire antenna. But as this is too big, so we need to apply loop antenna for solve this problem.

 

[VEBill]

For HF (shortwave), one trick is called the 'Active Antenna' where a short whip is basically fed into the gate of a FET (very Hi-Z). The whip is a very small fraction of a wavelength and they work like gang busters for receive applications. The possibility emerges that the same approach could be scaled to the higher FM broadcast band frequencies (including selection of a suitable FET).

The noise issue would need to be addressed by taking advantage of the inherent noise rejection of a good (carefully designed) FM discriminator. You're not going to be able to reject the noise with a tiny (basically isotropic) antenna.