Issue link: https://read.uberflip.com/i/1423190
LoRa Alliance ® Whitepaper Page 47 of 49 LoRaWAN ® Gateways Radio Coexistence Issues and Solutions Copyright ©2021 LoRa Alliance, Inc. All rights reserved. www.lora-alliance.org 10 GATEWAY ENCLOSURE AND SHIELDS In the previous chapters, we demonstrated that RF filtering is a key factor to ensure that a LoRaWAN gateway will not suffer from desensitization due to colocated emitters. The following filtering performance is expected: • 70dB to 100dB attenuation in the channel filters of the transceiver and LoRa demodulator • 60dB attenuation in the RF filters • 40dB attenuation in an external or embedded cavity filter Adding all the above attenuations, we can expect a significant amount of attenuation in the receiver path! The LoRaWAN gateway, when colocated with other emitters, is surrounded by electromagnetic fields. The strength of these fields depends obviously on the proximity to these emitters and to their radiated power. These electromagnetic fields may leak directly into the electronic components of the LoRaWAN receiver. For example, we may experience direct electromagnetic field leakage between LTE BS transmitter and the LoRa transceiver. In this case, the effects of RF filters and cavity filters are reduced to null! Electromagnetic interference (EMI) effects, therefore, must be carefully considered when designing an outdoor gateway. In Europe, as part of the CE marking, LoRaWAN gateways must be compliant with ETSI EN 301 489-1 (see [10]), ensuring EMC compliance. Electromagnetic field immunity of the gateways is tested according to the EN 61000-4-3 procedure. A 3 V/m field is applied from 80MHz to 6GHz. This test may guarantee a good EMI performance of the gateway, but in the case of colocation with high-power emitters, this test is not sufficient, as stronger fields can be reached. To optimize the EMC performance of the LoRaWAN gateway, effective shielding is required in colocated sites. The shields can be used at different levels: • Enclosure: Using a metal enclosure is an easy and efficient way to improve EMC performance. However, some precautions must be considered to avoid degradation of performance: o Avoid or reduce aperture size o Use EMI gaskets o Connect all metal parts together (cover, frame, etc.) A plastic enclosure (ABS, polycarbonate) could be also envisaged, but internal shielding should be reinforced in this case. • Module: A modular conception is especially convenient when using a plastic enclosure. Each module is inserted in a metal box, providing the required EMC protection. • PCB: Effective PCB cans must be used to cover radio chipsets to avoid internal coupling inside the gateway and protect them from external interference. • Cables: Efficiently shielded cables must be used to interconnect PCB. Finally, the enclosure and the associated mounting kit, antenna brackets, etc., must be connected to the installation site's grounding system for effective EMI protection.