Antenna in metal container
Antenna in metal container
(OP)
Hi! Can an antenna work properly inside a metal container ? The antenna must work at 860 MHz /2.4 GHz and it must be placed inside the container. Is it possible and what kind of antenna can be used?
RE: Antenna in metal container
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Antenna in metal container
One assumes you want to radiate out of the sealed container.
Describe your container more if possible.
kch
RE: Antenna in metal container
About the container. It will be roughly something like this
h
In the worst case the container will be metallic with no special openings except the doors. Some containers might have a ventilation system in the four upper corners, something like four holes.
Considering this, can I succeed a range of about 300-500m using a dipole-like antenna?
RE: Antenna in metal container
The radiated signal is going to have a unusual pattern, or gain in different directions from the container - probably will radiate better in the directions of the doors.
I assume you're trying to get 300-500meters range regardless of the orientation of the container to the opposite end of the link. Now, ignoring other 'complex system' factors, how much transmitted power you begins to become a factor of how reilably you must communicate, and whats the worst signal gain you might have from the container. Most ISM band devices have somewhat similar receiver sensitivity and noise figures (I won't get into processing gain of digital modulation systems). What it gets to on your link budget is that you have a lot of unpredictable and variable unknowns.
The major factor for success in such a unpredictable link is to depend upon what I called 'complex system' factors. Use of diversity antennas at both ends of the link help to avoid radiation pattern nulls, frequency hopping helps only a slight bit, using major frequency differences (i.e. both 860 and 2.4 GHz) could improve the communication, repeating data packets could help, but a packet based system with handshaking and other complex network system tricks are your best bet. Such systems are usually organized around standards such as 802.15.4, z-wave, zigbee, etc.
Radio systems for shipping containers are already made -some using the techniques indicated above. However, I would not use the 860 Mhz band for a transportable radio as the 868 MHz ISM band is not universal world-wide. In north America and some other countries, this frequency range is used for some cellular services, and the ISM band is at 902-925 Mhz. The 2.4 GHz band is used for ISM use around the world with only minor restrictions in some areas (transmit power must be lower in Europe, some minor restrictions in Japan, etc.
RE: Antenna in metal container
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Antenna in metal container
RE: Antenna in metal container
What's the experiment used for? Real shipping containers on ships? or some dry land experiment?
kch
RE: Antenna in metal container
For a zigbee communication protocol between two containers for example, what should I look at first to maximize the possibility to make them communicate.
I think that an omni directional antenna could give better chances than a directive one.
RE: Antenna in metal container
Find a patch antenna which uses a metal ground plane, or a pair of patch antennas and place them on the door (inside) if possible. Find the point where the gap might be maximum on the doors (center of doors? edge?). If you want energy to come out of the top of the door, orient the antennas vertically polarized. If the energy comes out the vertical edges of the door, orient the antenna horizontally polarized. Current on the door surface will leak out the door. If there isn't a gap in the doors, make one with a thin dielectric, i.e. glue a sheet of bare FR4 in the door seam.
We've proposed similar antennas for sensors inside thermal chambers.
kch
RE: Antenna in metal container
Another thing I wanted to ask: Is every antenna compatible with zigbee standars? (the only thing that should I care is the operation freq 868 and 2.4 GHz or is there smthing else to consider before I choose an antenna)
Thanks again!
RE: Antenna in metal container
In a reflective environment, it might be advisable to use two antennas in a spatial diversity arrangement. At two bands, that becomes a wee bit more complicated.
An alternative would be to provide the spatial diversity at the other end of the link.
RE: Antenna in metal container
Only UWB (Ultra Wide Bandwidth) antennas need some constant phase versus frequency control. Those are very specialized.
If these antennas get condensation/ice on them, often times they'll shift frequency, so be cautious about that. i.e. your system goes bad on a cold or moist day and is ok on a hot dry day.
Your task is not a simple one, good luck
kch
RE: Antenna in metal container
RE: Antenna in metal container
You will probably get a lot longer range by adding a hole and putting the antenna outside. I realize that wouldn't be considered unless it's absolutely needed.
An alternative to a hole is a flex cable antenna, electronics inside, co-planar coax. (or stripline) flex line through the door edge (if possible), and antenna outside. The antena could be a simple notch antenna etched right into the flex line.
Extreme multipath environments can limit range.
kch
RE: Antenna in metal container