Improvement of outage by retrofit of antenna diversity for MIMO on a PCB M2M system

Diversity antennas are for improving the communications performance for a given signal power. The uptake of multiple-input multiple-output (MIMO) includes updating existing products, and this typically means modifying a printed circuit board (PCB) to house the updated radio chip(s), and the antennas. Modification for updated chips is relatively straightforward but adding an antenna to an already-packed PCB can be difficult because of the constraint of maintaining the existing housing and mounting arrangements. The product and design economics calls for the performance return that the retrofit diversity system will offer. Typically, the outage of the existing system is known, and the question is how much would the outage improve if a MIMO system was retrofitted. Here we present a simple solution for this problem and a design example for a machine-to-machine (M2M) system on a small PCB. The single antenna is a standard edge-mounted element. The second element of the diversity/MIMO system is a similar element mounted at a different edge - a widely-used configuration. The final design requires physical cut-and-try for matching, and the expected diversity performance evaluation includes the signal correlation, mutual coupling, and ohmic losses that inevitably occur with constrained, real-world (i.e., non-idealized) design.