RF Antennas - 433MHz

Wireless & IoT
1

Hi All,

I’m new to the forum but not so new to Sparkfun or Electronics. However I am new to RF communication. I currently am working with PICAXEs and could do with some help about RF Antennas, specifically 433MHz RF. I use the Quasar TX1 and RX4.

I have been looking for antennas and have narrowed down my choices down to these 3:

[Chip Antenna

[SPLATCH Planar Antenna

[Coil Antenna

But I have a few questions before I buy.

  1. What is the issue with mounting the chip and planar antenna on a ground plane area of a pcb?

  2. If I have a transmitter (TX1) and Receiver (RX4) on the same board, can they share on antenna or do they require seperate ones?

  3. Does the length between the antenna pin on the rf modules and the antennas make a big difference?

  4. I have already made the pcbs and have changed plans for the antennas, now the entire board has a ground plane, can I put a layer between the pcb and pcb with the antenna on to stop whatever problems the ground plane may cause?

  5. What is with 1/4 and 1/2 wavelengths? How are these different from whole wavelengths (aside from the obvious)?

Thanks for your, sorry if im being a bit dim here.

Sephers.](http://www.simplesolutions-uk.com/index.php?do=products&sub=showdetails&pid=43)](http://www.simplesolutions-uk.com/index.php?do=products&sub=showdetails&pid=30)](http://www.simplesolutions-uk.com/index.php?do=products&sub=showdetails&pid=150)

2

433MHz.

I’ve not seen a chip antenna for this low freq.

Coil - I’ve used them at 2.4GHz and they are terrible. Large negative gain.

Perhaps best small/cheap for 433MHz is simply a 1/4 wavelength of wire.

3

You should use 50 ohm microstrip between the radio module and the antenna connector. It can be as long as you like, within reason, as losses will increase.

A 1/4 wave antenna over a ground plane isn’t a very good match, but it’s often used. Four radials at 45 degrees will give close to 50 ohms.

A 1/2 wave antenna (basically an end-fed dipole) has a very high impedance at the feed point and will need a complex matching circuit. A 5/8 wave antenna can be useful, as it doesn’t need a ground plane.

Don’t put a Tx and Rx on the same board and don’t use the same antenna, unless you design a switching arrangement.

Leon

4

Any of the antennas in the link will work as they are designed for 433MHz.

However, if you need range these would not be best. If you need a very compact solution then these antennas would work. Note that the Planar antenna has a gain in the vertical polarization of -8.6dB and -13dB in the horizontally. The data sheets have minimal information but there is enough to design the PCB.

Note the distance from the ground plane in the data sheets. These will not work if placed over a ground plane. I’ll guess that they will need at least a 1/2 wave separation from a ground plane.

Google antennas for descriptions of 1/4 & 1/2 wave antennas.