Cheap Omni-Directional Antenna?

6 Pack Cell Phone and PDA Antenna Booster

Or, print your own.

The comments on the booster basically say it doesn't work (the ratings agree too). As for printing my own, the question implies that a folded conformation or coiled conformation will be used, but which ones? Or is there a way to do this WITHOUT folding the antenna and reducing the range?

Google Fractal Antenna.

Lots of good info on DIY antennae.

I have been interested in developing a spherical fractal antenna. Appears under sims to be Omni directional.

There is one available here, but if you want to make your own:-

Don't know whether this will assist you. It's for higher frequency than you require but you might be able to scale it up using a rule of thumb that the resonant dipole length should equal to 0.47 to 0.5 times wavelength. Still may be too large for your PCB (y = 160mm) unless you can use a double sided board, possibly with SMCs, or you may get the required range with only 1/4 wavelength (Y = 80mm). Y would be equal to Lg in the pic.

If you require more accuracy the formulas become quite complicated, taking into account the dielectric constant of the PCB substrate etc..

Hello!

Okay, so why don't I start with a more broad description of the problem: I have to design an RFID reader circuit, and I need a little bit of help. Is there anyone here who has experience with RFID circuit design and would be willing to consult/be paid for design?

Don't be a silkworm.

Use yur head and available resources,like for instance, ah,let me see,hmmm....Oh yeah! Google!

A 10 second search led me to this link,which I will provide free of charge,this time.

Next time it will cost you:

https://www.google.com/search?q=RFID+reader+circuit&ie=utf-8&oe=utf-8#q=reader+rfid+circuit+diagram:/

Sir, please assume I have that much competence. If I didn't Google the problem thoroughly enough to eventually decide I need to post here, why would I post here? My issue is that I need a particular system arrangement, the confidential details of which I would need to discuss with someone who accepted the informal job posting I made. I expect that individual would then understand the depth to which I've researched the problem, particularly for someone who has never studied engineering before.

You just lost me. I won't waste any more time on this thread.

Actually, since electromagnetic radiation is a transverse wave, no antenna can be truly omnidirectional in 3 dimensions. It can be omnidirectional in a plane (such as a dipole antenna). I assume that is what you mean.

The range would also be a function of the power of the transmitter and the sensitivity of the receiver.

Your range will be dependent on your RF link (power) budget. That budget is made up of the radiated power of your scanner's exciter, the radiated power of your excited tags, the antenna gain on the tags, the antenna(e) gains on your RFID exciter/receiver, the receiver thresholds at both ends and the free space loss.

Once you do this excercise you will know how much gain your antenna needs and then be able to design it for your frequency of operation.....a 0.25W 50Ω resister may even be enough...just saying.

Link budget first.

A piece of 1mm diameter wire, 124mm long, fits the specification.

λ = speed of light/ frequency = 300 000 000 meters/ 900 mhz.

= 0.333m

λ/ 4 = 83 mm

use a straight wire of that length.

Then tune it using printed caps and coils.

I forgot to come back and thank everyone for their help. I appreciate it, everyone who has responded, you've helped me quite a bit.

I have two more questions that you can find here if you want to help out further.