It sometimes happens that after incorporating a known-to-be-good antenna into a device, the device fails to perform as hoped. Perhaps the coverage becomes spotty, or perhaps the antenna simply fails to work. Assuming there are no obvious problems (broken connections, wrong impedance for the device in question, etc.), what would cause a good antenna to fail to function as expected?
Environment
One thing to keep in mind is that an antenna can be seriously affected by its environment. Putting a dipole next to a large chunk of metal will almost certainly adversely affect the performance of the antenna.
We often find this principle at work in many devices we encounter. A small antenna in a smart device that is placed underneath the battery, for example, will be greatly inhibited from performing at its peak. For one thing, the battery will tend to block RF energy from passing through it. For another thing, these large conductive objects have the potential to detune the antenna.
Proximity of a Person
The human body can affect antenna performance.
A person is mostly water, and water (especially at Bluetooth frequencies) tends to absorb RF energy. This means that a smart device carried around on someone’s person can suffer from spotty coverage.
A person can detune an antenna, as well.
Ground Plane
Another difficulty is the ground plane. Some antennas must have a ground plane of a certain minimum size to operate. It follows that if the ground plane on the device in question is too small, the antenna will not perform properly.
This is especially true for chip antennas that essentially use the ground plane to radiate. The spec sheets for a chip antenna show the ideal performance of the antenna — but to achieve the chip manufacturer’s exact results, you must follow the datasheet exactly. This means that not only you can not skimp on the ground plane, but that the ground plane must be the exact shape as shown by the manufacturer. The antenna must be placed in the same location on the ground plane that the manufacturer recommends.
If the device differs from these specs (which tends to be highly probable), the odds are that the antenna will not perform as well as expected.
The Solution
Simulation software is invaluable in cases like these. It allows the designer to see how the new environment will affect the antenna performance before actually going into production with it.
Furthermore, antenna simulation software provides an easy method of determining where to find the peak performance of the antenna. This ballpark estimate can then be tested and fine-tuned.
It is usually better to design an antenna with the final device environment in mind, rather than try to adapt the antenna to the environment.
ARSI 