I am currently working on a project that requires a wireless connection. Since the XBee is too big and expensive, I’ve decided to create my own wireless module. It is a AT86RF212 with an ISM 900 mhz connection. After reading around on the internet and searching around google, I am really confused about antenna design. It seems that PCB trace antennas usually outperforms the small chip antennas, and I am considering trying to design my own PCB trace antenna. The problem is that I have no idea how to. I have read the guide ere:http://colinkarpfinger.com/blog/2010/th … na-design/, but i am still very confused on how to design my antenna. All I know is that usually, antennas are designed to cover 1/4 or 1/2 wavelength of the signal, but that is apparently not the case for PCB trace antennas.
My main questions are:
What exactly is a feedline and how should I go about implementing one on the PCB?
When should I be implementing matching components? and How do I determine what exact component to use? (for example, I was considering to use the chip antenna here:http://www.digikey.com/product-detail/e … ND/2543337, but I have no idea what matching component I should be using. the datasheet doesn’t say what exact component)
I think it is easy to buy one until you have high volume requirement. Any ways if you can share the price of the pcb module, I can try to suggest you something cheaper.
And if you are still in search of antenna, then you can check on:
ebay
amazon
varia store
antenna store
To design the pcb you shuld have the schematic of the same which will guide you to design the pcb, do you have one?
Thank you for the replies. Anyways, I’ve already settled on the chip antenna and the board is already sent to the fab house
as of currently, the components for the wireless module add up to $12.35 each. It can be way much cheaper if I were to buy the components at large quantities. (especially the transceiver chip). The communication of these modules are ZigBee style and they talk to the MCU via SPI (MISO, MOSI, SCK).
The board is very small at only 2.3cm x 3.25 cm (a bit smaller than xbee). I saw someone selling XBee pros at only about $11 each in batch quantities, but I don’t trust it, since it is too good to be true. I like the XBee, only that it is too expensive (even if I buy large batches).
I will test the range of my wireless module and share my results.
tincanman:
Thank you for the replies. Anyways, I’ve already settled on the chip antenna and the board is already sent to the fab house
as of currently, the components for the wireless module add up to $12.35 each. It can be way much cheaper if I were to buy the components at large quantities. (especially the transceiver chip). The communication of these modules are ZigBee style and they talk to the MCU via SPI (MISO, MOSI, SCK).
The board is very small at only 2.3cm x 3.25 cm (a bit smaller than xbee). I saw someone selling XBee pros at only about $11 each in batch quantities, but I don’t trust it, since it is too good to be true. I like the XBee, only that it is too expensive (even if I buy large batches).
I will test the range of my wireless module and share my results.
For a 900MHz (or 868MHz) radio, rather than 2.4GHz, a chip antenna wouldn’t work very well at all. Aperture just too small. Even a 1/8 or 1/4 wave piece of loose wire would work better.
“… selling XBee pros at only about $11 each in batch?”
Pro? That’s like a 75% discount from list. The non-Pro might get to $11 with a 50% discount.
The firmware in the XBee, for low/moderate volume, warrants its price. The amortization of your NRE to develop even a subset would need huge quantities. Then there’s the little issue of life cycle support of that firmware.
Let’s not confuse ZigBee with 802.15.4. ZigBee is one of many protocols at the network layer for 802.15.4. Many apps don’t need more than basic 802.15.4, e.g., omit meshing that is the key reason for ZigBee.
Yes, I understand the difference between ZigBee and 15.4. As for my purpose, I need the mesh capability sometime in the future, so i know that I will need to use a chip that supports ZigBee protocol.
As for the cheap XBee pros, I am not lying. Just check eBay for yourself. This guy with 100% feedback are selling them and shipping them apparently from USA. They are marked used and are Series 1, but they look almost brand new. Perhaps they are just trying to clear the surplus inventory so they can stock series 2 xbees??? Here is a link: http://www.ebay.com/itm/XBee-Pro-Series … 500wt_1414
I don’t know too much about antenna design, so I did not know that ceramic chip will be bad for 900mhz. I understand the 1/4 wave antenna design, but apparently, chip antennas operate a bit differently. The main restriction is the antenna size for my application. The footprint for my overall design needs to fit into a 3.5cm cube. As of now, I’m just prototyping, so I will be testing everything close range anyways, but I just need to know how to design a antenna that will be able to give the best gain and range, but at the same time is a omnidirectional antenna.
If your design constraint is small size then you will need to sacrifice range.
As Steve implied, range is proportional to antenna capture area.
Google antennas to learn some basics so you have an idea of performance from different designs.
Basic antennas, 1/4 wave and dipoles, are not hard to design but the matching networks can get a good bit harder. PCB antennas can be hard to design and most of us would use a design published by the RF chip maker.
The ebay Xbees seem to be pulled from equipment. Maybe due to upgrading to the Series 2 Xbees.