The mechanical and electrical reliability of interconnects is also important. Normal “wear and tear” can degrade the integrity of the interconnect system and produce degraded device performance and even outright device failure.
4.5.2 Self-Interference Self-interference is created when the emissions from a device's own internal circuitry enter the antenna (or the radio front end) and raise the receiver noise floor, thereby degrading the receiver sensitivity. Larry Zibrik told us that “self- interference, due to poor antenna selection or implementation, is the single biggest challenge to successful device certification”. The effect of self-interference may be just a few dB, and perhaps go unnoticed, or it can result in a sensitivity reduction of 10 to 20 dB or even higher and dramatically reduce the operating range and performance of the device. Self- interference issues may delay or even cancel a product launch. The primary noise source is the digital circuitry – usually the processor (or processors) and the system memory. Other noise sources are possible, of course, but the processor, its associated clocks, high-speed memory, and display and graphics processors are very often the highest in level and produce the widest range of frequencies. It is also critical to realize that a device that displays emissions low enough to pass the FCC regulations can still suffer from self- interference. In most cases, the receiver sensitivity is much lower than FCC test limits.
Eliminating self-interference is a complex subject and beyond the scope of this paper but the following guidelines should be followed:
1) Shield the digital electronics with PCB-mounted shield cans. Rarely is some shielding of the digital electronics not required.
Place the antenna(s) as far from the noise sources as possible.
Route the antenna interconnect(s) away from the noise sources.
Antenna Fundamentals – Technical Brief