Delaying antenna decisions can result in the loss of the device’s window of opportunity in the market and will end up costing hundreds of thousands of dollars in device debugging and/or redesign, not to mention additional testing and certification fees. Following are some best practices when considering RF design and integration while designing M2M products:
Plan for problems - Wireless device design is complex, especially when multi-band cellular is included, and even more so when other wireless technologies such as GPS, WiFi, and 915MHz are present. The presence of batteries and other metals close to the cellular antenna can cause issues in any system. Devices using an embedded antenna are likely to require some level of customization. (Many M2M companies are not experienced in wireless device design to debug design issues, and may not have access to the equipment and resources to acquire this expertise.)
Separate antennas - Keep the antennas as far away from each other as possible to avoid detuning issues.
Size matters. The bigger the antenna, the better the antenna - Size enables antennas to have wider bandwidth, more gain, and better efficiency. The more space allocated for a cellular antenna, the easier it will be for the antenna designer to deliver a successful solution. The same rule applies to antenna clearance.
Avoid cables and connectors - Cables and connectors should come with a warning note. They introduce loss and can bring impedance mismatches. This is unavoidable if external antennas are required, but an edge-mounted connector can be used with a transmission line to route the signals to the module. This is more effective than a cable jumper.
Target with margin - It is best to target with a 2dB margin. That way, if problems do occur, it does not affect the test plan.
Optimize shielding - Try to implement physical shielding on the printed circuit board (PCB) as much as possible. The simplest way to achieve this is to place metal cans over active circuitry.
Completely fill your ground plane - It is best to fill in all unused areas of your PCB with ground.
Test the antenna - It is important to perform proper antenna testing (return loss and efficiency) during the initial design and prototype stages. At the final stage, it is vital to measure antenna efficiency and perform OTA and RSE pre-scans.
Consult with experts - Talk to all the relevant parties regarding your application – the carrier, module provider, antenna provider, test labs and design house. A design review is also recommended before finishing hardware design.
The bottom line for ensuring quick development, speedy time to market and ease-free certification for M2M devices is planning ahead. Getting the antenna right is easy if you begin early and integrate antennas into the design as one of the first steps. The end result is that device makers will be happy because they can sell more M2M devices, and carriers will be happy because they will have more connections, all because the antenna was properly optimized for the device in question. Talk to the experts early and frequently; it will save a lot of money in the long run.
About the Author
Dermot O’Shea is co-founder and joint managing director of Taoglas. Having founded Taoglas with Ronan Quinlan in Taiwan in 2004, he is currently responsible for sales, finance and marketing and is based in Taoglas' San Diego office. Prior to founding Taoglas, Dermot worked for over ten years in the global electronics industry for companies such as Network International. He is a highly regarded source in the M2M antenna market and today advises automotive, tracking, telemedical and utility companies worldwide on antenna solutions. Dermot is an expert in the wireless antenna arena, he provides high-level counsel on device noise debugging, testing services, device certification and approval management. Dermot has a Science Degree from University College Dublin and postgraduate diplomas from Dublin Business School (Business), Griffith College Dublin (Computing) Waterford Institute of Technology (Enterprise Development).