Efficiency
Quantifies an antenna's capability to transform a signal into a wave. It is the ratio between the far-field radiated power and the power at the antenna's input. Efficiency takes into account the input mismatch, the loss into the antenna and the loss into the surroundings. Efficiency is measured by comparing the power radiated by the antenna inside a system with the power radiatated by a free space dipole.

Isolation
Isolation or coupling can be defined as the level of power transmitted between two components. The two primary coupling mechanisms are conductive, which is created by currents induced by the antenna on the ground plane, and radiative, which is created by the antenna's near fields. By reducing the conductive antenna coupling effects with the main PCB, or another nearby antenna, the main antenna's performance characteristics are improved, and can be maintained despite subtle layout changes, which routinely occur during the development cycle.

SAR
Specific Absorption Rate (SAR) is the unit of measurement for the amount of radio frequency (RF) absorbed by the body when using a personal wireless device, such as a cellular phone. All wireless phones marketed in the United States must meet the safety limit of 1.6 W/kg (watts per kilogram) in 1 gram of tissue, set by the Federal Communications Commission (FCC). Wireless phones marketed in Europe must meet the safety limit of 2.0 W/kg in 10 grams of tissue, set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).

SAR-to-Efficiency Ratio
SAR and efficiency are both key parameters in developing high performance wireless devices. Calculating SAR independently presents an incomplete picture, since SAR can be decreased by lowering efficiency, leading to poor device performance. The SAR-to-efficiency ratio is a good metric that accounts for both performance and SAR at the same time. The key is to increase the efficiency (performance) while reducing the SAR. Ethertronics antennas have a low SAR-to-efficiency ratio, representing both low SAR and high performance.

Selectivity
Selectivity is defined as the out-of-band frequency rejection of the antenna. It can be evaluated through broad band efficiency measurements. Antennas that do not exhibit natural selectivity may require the use of Band Pass Filters to remove unwanted signals from interfering with the desired signals.