BMW cars !!!!!! its Antenna ?

hi all


i guess all of use notice the radio antenna in the bmw cars , it is so short less than 5 cm i guess ?

does any one have idea about such antenna how it works & does it need a certain radio ?


thx all

ahmed osama,

Isn't the the antenna you're refering to the external 900/1800 MHz GSM antenna used by car kits (hands free)? For those frequencies, it is not particularly short. Typically, I think the FM radio antenna is integrated in the rear window (combined with de-frost functionality).

Regards,
Peter

I have heard that BMW and others use the metal film on the rear window for both removing condensation and radio reception.

well i don't know i just saw many cars bmw & others have a very small antenna in top ,i don't know it used for that

but about GSM i really didn't understand that , hands free means that u leaving ur moible a part from u using a certain wired headphone or bluetooth it has no relation with the mobile RF at all ,every mobile has its own antenna (on its pcb or just a short one)

Added after 40 minutes:

I guess i found it !


but some antennas i don't know how it work? like the TV one , the car body shields its reception?

does anyone can explain that?

Dear osama,

if you have access to IEE Journals, here is something which is very similar to what you are looking for.

I attach also the abstract:

Multiband PCB antenna
IEE Proceedings - Microwaves, Antennas and Propagation -- December 2005 -- Volume 152, Issue 6, p. 471-475
A reduced height automotive antenna covering the three mobile telephone bands used around the world is described. The antenna is much more compact than a conventional monopole and is printed on a PCB for low-cost production. Circuit components are used to tune the antenna to cover the regional band variations for mobile telephone systems, enabling one design to cover them all. A voltage standing-wave ratio of better than 2 : 1 is achieved. Performance when used as a roof mount automotive antenna is close to that of a quarter-wave monopole antenna.

There are two such antennas in the bigger shark fin looking antenna and only 1 in the thinner version. I think for the bigger shartk fin there is the possibility of attaching a GPS antenna between the two mobile phone antenna.

The TV antennas normally make use of the car body for reception (E.g. monopole type systems hidden underneath plastic cover). There should be an array of antennas to reduce multipath. I've seen an early Japaness system that rotates mechanically to obtain optimal TV reception.

Regards,
Element7k

Here is the antenna of BMW car, extracted from "antenna engineering handbook" 4ed.

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