Reference Dipole Antenna for ISM Band (868 MHz)
This short article deals with a dipole antenna for ISM (Industrial, Scientific and Medical) band. This band can be used for sensor networks which have been receiving great interest nowadays (IoT - Internet of Things). There are many applications where the sensors must have small dimensions and therefore the antennas inside such devices are highly miniaturized. The less the space available and the more components are placed nearby the antenna, the more the radiation of the antenna is affected.
This problem is probably not so critical for our home projects but it is still nice to know how your board with a temperature sensor and a small antenna performs and eventually to increase the range of the sensor by optimizing the distribution of the components etc. Therefore I made a reference dipole with an integrated balun that I can use for my tests allowing me to compare several designs.
I found an article Evaluation of Polarization Diversity Antenna for Wireless Communication Applications where my antenna came from. I changed the resonant frequency of the dipole and modified the ground plane. The results with the dimensions are as follows:
Radiation pattern - cross polarization
Dimensions - top view
Dimensions - bottom view
Radiation pattern - H plane
S11 parameter (-Return Loss)
Practical realisation, PCB is made of FR-4 - 1.6 mm