FM mobile antenna help

[AirForces2050]

Hi
I have been searching for 2 days about FM antenna paramteres of any mobile but can't find any
I know that its the earphones acts as a dipole antenna of FM but need to get info about measured gain , bandwidth, raditation pattern ,polarization, etc.
Can you propose me any useful articles or links ?

 

[eee100]

Any antenna specifically designed for the FM frequency band would do the job. It depends on your selection or need.

 

[vfone]

In fact the earphone cable is not a dipole antenna, because dipole has the feed at the middle.
This is a simple monopole antenna, but to be more precise you can name it just a piece of wire attached to the input of the FM receiver.
Generally to measure some RF parameters of this kind of antenna is a mess. The impedance is all over the Smith chart, and very dependable by the antenna (earphone cable) position.
For testing antenna pattern and polarization you need a big antenna room, because frequency is relative low (88MHz, and if the radio supports Japan band lowest frequency is 76MHz).

 

[AirForces2050]

Thanks for the reply
Actually I am working on a research about samsung E250 antennas parameters
and I have found parameters for GSM and bluetooth but can't find any info about FM for any other mobile even.
So I just need some more detailed info about parameters or how it works
Thanks in advance

 

[E Kafeman]

Any ear cord that is used as FM antenna heavily interact with human body. Resulting antenna function depends mostly on this body and how the wire is bent.
As it not exist a detailed description on how the wire is allowed to be bent or recommended distance between a standard body and lose hanging wire, can the antenna performance be anything for any phone brand.
Best antenna function is probably if someone else is holding the phone and as this improves the dipole effect. Lets see, if the wire is held straight and is limited to 80 cm length and both person are standing bare feet in a muddy ground is best listening height then likely to be at 80 cm height as resulting antenna shape will be a full wave loop from the FM receiver view. Two persons sinking in quick sand comes on my mind... One says to the other:
- Can I borrow your headset?
- Calling for help?
- No, I want to listen at FM radio as we now have good reception.
Sorry, but as you can see, antenna parameters for a phone equipped with FM cord antenna is depending on a lot of external factors but almost nothing on the phone model.
There are few phones with embedded FM antenna and for them are the situation a bit different. I have seen simple and relative poor performing internal coil-shortened monopole antennas but also more advanced and real good working antennas from manufactures such as Ethertronics and Laird.
But still, also these internal antennas are very depending on external factors due to the long wave length compared to the phone internal ground size which never can be considered as a good working ground plane at these frequencies.

 

[kayaoo]

Any ear cord that is used as FM antenna heavily interact with human body. Resulting antenna function depends mostly on this body and how the wire is bent.
As it not exist a detailed description on how the wire is allowed to be bent or recommended distance between a standard body and lose hanging wire, can the antenna performance be anything for any phone brand.
Best antenna function is probably if someone else is holding the phone and as this improves the dipole effect. Lets see, if the wire is held straight and is limited to 80 cm length and both person are standing bare feet in a muddy ground is best listening height then likely to be at 80 cm height as resulting antenna shape will be a full wave loop from the FM receiver view. Two persons sinking in quick sand comes on my mind... One says to the other:
- Can I borrow your headset?
- Calling for help?
- No, I want to listen at FM radio as we now have good reception.
Sorry, but as you can see, antenna parameters for a phone equipped with FM cord antenna is depending on a lot of external factors but almost nothing on the phone model.
There are few phones with embedded FM antenna and for them are the situation a bit different. I have seen simple and relative poor performing internal coil-shortened monopole antennas but also more advanced and real good working antennas from manufactures such as Ethertronics and Laird.
But still, also these internal antennas are very depending on external factors due to the long wave length compared to the phone internal ground size which never can be considered as a good working ground plane at these frequencies.

That's absolutely true. But the problem is We definitely need a antenna model that can tell us whether the circuit is optimized.

 

[E Kafeman]

It have been trials to make active dynamic impedance matching but with medium and a bit expensive results. Silicon Labs have done a RF tuner designed for this kind situation, and their solution was to assume a fixed 2 kOhm impedance. That way will the reflection loss seldom be perfect, but not to bad either in most situations.

 

[ckshivaram]

Now a days the antenna is incorporated inside, these phones do not need any external antenns. if you google internal FM antenna in mobile you may get some results.

 

[lurchman]

Airforces2050,

I'm not sure why you need to model the FM receive antenna in as detailed a fashion as you apear to wish to, as most receive antenna's work acceptably provided they are "effectivly" more than 1/16th of a wavelength and the VSWR is below 75:1 and in a sufficiently strong field (which for FM is usually the case).

By "effectivly" I mean the actuall element in the transmited EM field not the actual element used to conduct the energy into the receiver front end.

That is the first thing you have to realise is what is acting as the antenna to the transmitted FM signal?

The wire? or any conductive object it is adjacent to such as the human body?

In the case of longer wavelengths such as the FM or '3meter band' adult humans when standing up are between 0.5 and 0.7 wavelengths (ie just under 5ft to just over 6.5ft). When humans are sitting down they are between 0.25 and 0.4 wavelengths (~3-4ft) in the vertical direction.

Also because humans are quite broad compared to their length (unlike a wire) they tend to be more broadband than more efficient elements.

Thus the model you are probably looking for at the receiver port is the "wire" from the electronics device acting is as a "near field gamma match to a monopole radiator" that the human body is.

As you are probably aware "near field" behaviour is at best complex to model in simple cases and virtualy impossible in complex cases (you need complex moments models).

If you want to know how the human body behaves in an RF field at those frequencies the easiest source to get hold of is likley to be from the NRPB or other Radiation Safety Body.

 

[vfone]

Hmmm. I never know that all of us (the humans) actually we are walking antennas. What about animals with four legs (and a tail)? They are better grounded, or radiates more energy (because of the tail)?