433 MHz flat antenna design

[dteich]

Our product (

http://www.designatedparking.com)

is a 20" aluminum partially spherical housing 3" tall with a 4" plastic canopy under which the antenna lies. We use a spiral antenna with estimated gain of -14dbD, and the range is only 40 feet with a -112 db receiver. We need at least twice that range.

We are looking for an improved antenna concept. Thanks for any help.

 

[VEBill]

Hmmm... There's nobody driving the Audi A4. Very strange... ;-)

Where are you aiming your current "14dBd" antenna? If it really does have that much gain (that's a lot by the way), then is it aimed in the general direction of the car?

How did you decide where the car would be ? 40 or 80 feet away, the client could be over there or over here. This application calls out for a low gain antenna to provide better coverage.

Why not put the antenna, a better antenna, into the nice yellow and black plastic gate?

Does the driver need to see the gate?

 

[debodine]

Move the antenna to the yellow cross bar for better propagation characteristics, at least during the approach phase. Just one option...

 

[VEBill]

I'm guessing that the antenna (the one with 14 dBd gain) is aimed straight up - ideal for passing helicopters. If so, then the systems might work better with a simple 6" wire antenna.

IR R/C might be a better choice.

Why 80' ? Is the motor too slow ?

 

[dteich]

Thanks guys for the fast response.

The range requirement is 25 feet from inside the car. That cuts 6 to 10 db off the power, so we are now in the 45-80 feet line of sight range. Any closer and you can not see the barrier over the nose of your car.

We can not put out a vertical antenna due to vandalism. Placing the antenna in the horizontal barrier will not do much good when the barrier is down, and anyways it will be surrounded by metal.

 

[VEBill]

I just reread your OP and I just notice the MINUS in front of the "-14dBd" (sorry I missed it the first time). Yikes, that's not good. You should be able to do better than that without even trying.

Garage door openers can typically do at least 100' and they often use a cheap superregeneratiev receiver and a dangling wire antenna.

 

[dteich]

V1BLL -- I AM in the Garage door business, and we get 300 feet open air using a 1/4" whip with a -105db receiver.

You are right -- the antenna stinks. So... what can you suggest?

dori@dp-corp.com

 

[VEBill]

If I were you, I would put aside the packaging issue for the moment and get the system working to maximum range using a simple vertical antenna. Make sure that the system is working correctly and that you get the expected range using a known antenna (perhaps a simple 1/4 lambda whip - don't drive over it).

Once you get the system working to maximum range, then you'll see how much margin you have.

One would think that you could use a simple bit of wire bent into the plastic part of the housing.

 

[Comcokid]

Questions-
1) At what frequency is your product?
2) What is the "package" and transmit antenna on the user end? - A Garage Door Opener package?
3) Could your your link-margin problem on the transmitter end? (I find it hard to believe your antenna is as bad as -14 dBm
4) Don't you have some additional problems locating the antenna in the base when it rains and water may cover it by an inch or two?

Suggestions-
Yes, you can put your antenna inside the aluminum cross-bar depending upon the frequency. I assume your cross-bar is extruded, therefore hollow. If the antenna is put in the crossbar, and a slot 1/4 wavelength long is milled through the bar, it will radiate. The slot can be coverved by a tough plastic. At this point, it depends upon: frequency, location inside the bar, spacing, etc. Some cleaver mechanical design to feed a coax from your receiver up through the hinge joints to the antenna will be needed.

Alternate antenna suggestion - create a larger slot in the crossbar plugged with plastic, and mount the antenna in the middle of the plastic flush with the outside. You can color the plastic and make it look like it is part of the styling.

 

[Higgler]

Why don't you use a simple patch antenna with solid FR4 dielectric.
Size is approx. 7" long, 3" wide, and 0.063" thick. It gives wide beamwidth and will have about 15 dB more gain than your present antenna and it's vertically polarized (even though it's flat). Material cost is $1.17 per antenna from McMaster Carr ($35 for a 24x36 inch piece). Assembly is simple.
It's also tough enough to drive over it.
What's your signal frequency bandwidth (and source frequency stability/drift) and temperature range?

kch
Antenna Engineer)
Toyon Research Corporation).
Feel free to call me with questions, (805)685-1482.

 

[jimeagle]

My experience with FR4 Patch antennas on this frequency is that they have significant loss... probably -8dBi gain (-10dBd), due mainly to the loss tangent of 0.01.

Teflon works better with about -1 to -3dBi gain, depending on whether you use a full sized patch (1/2-wavelength in the dielectric) or a half-patch (1/4-wavelength in the dielectric).

If you can afford exotic materials, TMM4 (Rogers) or Arlon are also well suited to patch antennas in this band. Loss tangents for these materials are 10 times better than for FR4 or about 0.001 but the reduced size due to the higher dielectric constant reduces antenna gain by another 1-2dB compared to Teflon.

Tuning tends to be fairly narrow at 434MHz as well so that detuning effects due to dirt, oil, rain or other items on the antenna will further reduce gain due to the off tuned condition.

The patch should be made of 0.125" thick material to provide maximum performance (i.e., >0.01-wavelength thick).

The best performance would be an Air dielectric patch but the size would increase significantly to about 14" diameter (or per side) and spacing of 1/2-inch or more would be required. There would be mechanical design issues, as well, such as keeping water out of the structure, having a struture strong enough to drive over, and support of the radiating plate over the ground plane.

 

[Higgler]

Jimeagle,
I made an antenna for Dori using FR4. The gain was alot higher than -8 dBi, closer to zero dBi. I can't discuss the details of the antenna design other than saying that FR4 varies alot and is not a well controlled/tested dielectric.
It's in production now.
kch

 

[Virginaflyboy]

Do you know who is making automotive antennas now? Especially those used in all the new electronics on board. Thanks Ed

 

[victorira]

To Vriginaflyboy:

I think that our company can help you. We are designing different kind of antennas including remote keyless entry hidden planar antennas for automotive applications (passive and active). Antenna is printed on circuit board with or without amplifier.

 

[AndyKayll]

This could now be a defunct post but I have only just found , this site (very impressed by the way) and thought... what the heck. Looked at your site link and yes, can see the vandalism problem (along with driver error (I thought it was MY Parking space)) so the cheaper and simpler the moving part the better.
I assume (see fave quote) that the device gets power from someware... Do a central or distributed receiver system from the power distro point.

Fave Quote... Never Assume, You make an Ass out of U and Me

 

[Higgler]

The antenna goes into hardware found at

http://www.designatedparking.com

website. Take a look there for info. Pretty good product for people who get their parking spaces stolen regularly.

kch

 

[dteich]

Hi Guys -- Thanks for the compliments on the product. The planar antenna that we use works well -- Kevin did a super job.

Dori

 

[Higgler]

Dori,
Good to hear it's what you needed. I've been thinking of starting my own company "

http://www.FastAntennas.com",

but haven't done it yet. There are alot of designs such as yours that take very little effort.

kch