How to Interpret Reader Antenna Radiation patterns

At Times-7 we design world class UHF RFID antennas. Being able to read radiation patterns of those antennas is paramount to set up RFID read points efficiently. Dr Prabakar Parthiban our Senior RF Engineer and Head of Engineering has published an IEEE poster to help system integrators and solution designers to interpret antenna radiation patterns in theory and in practice. This poster is a useful guide to acquire the knowledge to determine which antenna model suits your specific needs.  

The importance of selecting the correct antenna: 

An RFID antenna is a necessary part of any RFID system making antenna selection a critical part of the process. If you don’t select the correct antenna for your specific needs, you run the risk of the entire solution being unsuccessful losing time and money! We don’t want to see that happen!  Let’s take a closer look at the IEEE poster and how you can use it to help determine how many and which Times-7 antenna you might need. 

What are radiation patterns? 

The radiation pattern is a graphical representation of the antenna’s radiated power in a three-dimensional space at far-field distances. It can also be plotted in two-dimensional spherical coordinates. The examples in Fig.1 below represent the azimuth and elevation planes using a polar chart. Azimuth and elevation planes plot the 2-D radiation pattern of the antenna or array object over a specified frequency.  

Antennas follow the principle of reciprocity meaning that the radiation pattern holds true for both transmitting and receiving antennas.  

Times-7 antenna radiation pattern: 

[Fig 1] 

The antenna’s radiation angle or the width of the beam is termed as the beamwidth [Fig.2]. Half Power Beamwidth (HPBW) angle is calculated between the half-power (3dB) points of the main lobe. Wide beam antennas are low gain in nature compared to narrow beam antennas that have higher gain. The radiation pattern determines the ability to detect tags in a given area. The maximum directive gain of an antenna lies within the peak of the main lobe radiation. Side lobes are minor lobes found on the sides of the main lobe. The ratio between the magnitude of the main lobe and the back lobe is known as the antenna’s front to back ratio [Fig. 3]. 

[Fig. 3: Half Power Beamwidth (HPBW) angle is calculated between the half-power (3dB) points of the main lobe]