With the endless array of applications and form factors for M2M devices, it’s very common that the device under test really shouldn’t or can’t be tested in the standard way.
If you plan a M2M device with external cellular antenna, then you will find a supplier for common antennas easy. If you plan a small device with integrated antenna, then you will run in trouble easy as soon the size of the PCB is smaller than 40 mm x 100mm. Some designs accept 40mm x 90mm. I am working on a book how to design a M2M device. Chapter 1 is talking about embedded antennas. By comparing more than 10 “out of the shelf antennas” I have seen that all reference PCBs have a size of close to 40 mm x 100 mm ground plane. They all have an antenna efficiency of 50% to 70%. Some customized PIFAs are listed with up to 90%. Just measures the size of your mobile phone and the phone of your friend and you will see that the size is close the same.
The two main questions at hand are how should these devices be tested, and what parameters should be used to quantify their performance (i.e. other than TRP & TIS)?
TRP is related to the antenna efficiency. If the antenna you select has from beginning to less efficiency, then you have no chance to pass. The matching circuit on first PCB should hold the components mentioned at the reference PCB. The final tuning of the matching circuit makes sense only if you have the final plastic enclosure. An enclosure made by rapid prototyping has maybe another Epsilon R. The Epsilon R of the plastic will interfere with your antenna.
The TIS of your device can be damaged by display or microcontroller easy. By selecting a microcontroller with internal Flash-ROM, RAM and oscillator you minimize the risk of “digital noise” on your PCB. As lower the power consumption of your uC is as lower the chance on noise. See also:
Microchip microcontrollers for M2M and Smart Home
http://www.gsm-modem.de/M2M/m2m-faq/microchip-microcontrollers-m2m-smart-home/
Best will be to try to get the wireless modules, the antennas, the micro controllers, the power supply, battery and charger from one hand. If you like, I can help with resources for developing a prototype up to final product. Just drop an email to harald.naumann at gsm-modem.de or use the form here.