Antenna design

duck-antenna

Duck antenna included with the APC220 radio modules

The antenna that is included with the APC220 radio is a 433MHz Rubber Duck antenna. This antenna is robust and great for testing, but won’t usually fit inside a soda can.

A good alternative is the simple thread antennas that can be attached to a SMA-Connector or alternatively soldered directly on to the transmitter output. Normally such antennas will be a quarter-wavelength. The thickness is not critical; the most important is the flexibility and durability.

thread-antenna

Quarter wave thread antenna.

Antenna length can be calculated from equation below when the frequency (f), and velocity of light (c) is known:

If we have a frequency f of 434 MHz, then the equation for calculating the length of a quarter wavelength is:

L = \frac{c}{4\cdot f} = \frac{3\cdot 10^8 m/s}{4\cdot 434\cdot 10^6 Hz} = 0.173 m

By this calculation we find that the antenna should be 17.3 cm long.

CanSat with a quarter ware thread antenna

CanSat with a quarter ware thread antenna

We can build this antenna by using a coaxial cable. Remove 17.3 cm of the plastic jacket and the metallic shield from the cable, leaving the centre core and dielectric insulator. Make sure that the shielded part of the cable reaches all the way out of the can before it is stripped.