To successfully design (or purchase) and then integrate an antenna into a wireless device, a number of measurements must be made to quantify the antenna performance in the actual product. Simply relying on a manufacturer’s datasheet, bench measurements of an antenna in isolation, or an un-verified reference design will likely result in poor performance in the device.
Impedance and Antenna Bandwidth As discussed above, antenna impedance is typically measured as return loss or VSWR. The equipment used to measure this parameter is a Network Analyzer. The impedance (and the bandwidth over which the impedance is acceptable) must be measured with the antenna installed in the device with all components installed. The impedance measurement often requires special fixtures and assemblies to allow access to the antenna terminals. It is not uncommon that the antenna requires some small tuning adjustments when the device is finally fully assembled. At this stage, if the initial design was well done, most embedded antennas are often quite easily tuned with small changes to the PCB layout or sheet metal part, and/or with the addition of passive components on the antenna or the radio PCB.
Gain and Radiation Patterns Calibrated measurements of antenna gain and radiation patterns are made in an Anechoic Chamber. The anechoic environment eliminates all reflections and allows precise and repeatable measurements to be made. The device under test is typically rotated 360 degrees in multiple orientations to determine the shape of the radiation pattern from many different directions. Reference antennas are used as calibrated gain standards.
As with impedance measurements, gain and radiation patterns should be measured using a complete product.
Efficiency Measurements As mentioned earlier, efficiency may be the single most important parameter to be measured, especially for an embedded antenna which can have degraded
Antenna Fundamentals – Technical Brief