QUESTION

Question

I have an application for a small,battery-powered, LoRa asset tracker for the US market using the 915MHz ISM band (902-928MHz).  The LoRa module used is the Murata CMWX1ZZABZ-093 which does not include an antenna.  The asset tracker only transmits and the other part of the system, the asset tracker monitor, only receives.  The monitor is not size constrained and can have more options for the antenna.

a)  Which antenna would perform better -- the Latona SR4C033-R or Grandis SR42I010-R?  The Grandis is smaller, but which one has better performance?

b)   For optimum antenna performance, what is the recommended minimum size of ground plane (your eval boards are 11.5cm x 3.5cm =  40.25 sq cm or ~6.2 sq in)?
c)  Why are the matching circuits for the 2 antennas (in their data sheets) different circuits and not just different component values?
d)  The form factor of the application requires the asset tracker to have a small antenna and height above the PCB is limited.  We would like the LoRa range to be at least 3 miles.  Are the two antennas above suitable for this application or should we be looking at something else?

Answer 1

Hello Murdock,

I appreciate your inquiry and can provide feedback below.

a) The performance between the two are comparable for your application. The Grandis has a smaller form factor because it's not designed to cover as large of bandwidth as the Latona.

b) Both the Grandis and Latona utilize the host PCB ground plane to radiate effectively. Optimum antenna performance would recommend using a ground plane at least the size of the evaluation board and one can expect to deviate from that maximum performance the smaller your device gets.

c) When tuning antennas, the goal is to match the impedance in as few components as possible. There are many matching network topologies that can be utilized in conjunction with the variable component values to allow maximum flexibility in achieving this goal.

d) The range of the LoRa device will depend on many factors including its intended use case (i.e Line-of-sight vs. Non-Line-of sight attenuation), the output power of your transmitter, the receive sensitivity of your device, as well as the efficiency of the antenna. While we can't guarantee specific performance without first verifying the application in a real-world environment, there are several tests showing people online achieving that distance with antennas of comparable efficiencies. So given the above, I'd conclude yes our antennas would work for your desired application.

Thanks,

Dan Dobransky