A chip antenna is tantalizingly small. With its small size and reasonable performance, it would appear to provide a perfect solution for many antenna applications. However, there is a catch. Most chip antennas are not complete in and of themselves.
What is a Chip Antenna?
Most chip antennas must be used with a ground plane. In fact, the ground plane is how most chip antennas radiate. A chip antenna is a coupling device that feeds a ground plane.
The Role of the Ground Plane
As in the case of a monopole, the ground plane is a crucial part of the chip antenna. Lose the ground plane, and the monopole ceases to function properly. Lose the ground plane and a chip antenna will no longer function correctly.
The implications of this are obvious. When designing with a chip antenna, the ground plane is typically the PC board of the device using the chip. If the ground plane is the same size and shape as the demo board the chip antenna is mounted on for testing by the manufacturer, the chip should work as the specs indicate.
If the board the user intends to place the chip on is smaller than the manufacturer’s board, the performance will suffer; a crucial piece of the antenna is missing. Even a differently shaped board with the same available surface area as that used by the manufacturer can cause the chip antenna to radiate differently than what the spec sheet indicates. Not surprisingly, the PC board in a given application is not likely to resemble the board used in the data sheet for the chip antenna.
The Location of the Chip on the Board
The location of the chip antenna on the ground plane it is feeding is important as well. The chip cannot simply be placed anywhere on the board and still work as the datasheet states it should. For any given application, there will be ideal and not-so-ideal places on the board for the chip to be placed.
If the board being used is a different size or shape than the board used in the manufacturer’s specs for the chip, the chip will likely need to be placed in a different location than shown, or peak performance will not be obtained.
How Far Can You Trust the Data?
A further complication arises when it comes to testing a device that uses a chip antenna: Is the data realistic?
Again, the ground plane is a crucial component of the antenna. Anything attached to the ground plane becomes an extension of the ground plane. During testing, the coaxial cables and even the test equipment can become part of the antenna.
After optimizing the antenna’s performance during testing, the real-world performance of the device may be wildly different than what was achieved during testing. During testing, it is likely that the test setup became part of the antenna. In the real-world application, that setup is no longer part of the equation.
Ferrite can be used on test cables to help prevent them from becoming part of the antenna during testing. Unfortunately, when it comes to small devices, the relatively bulky ferrite-covered test cable somewhat overwhelms the chip antenna and its board. The smaller the device, the worse the testing effects become.
Reliably Analyzing a Chip Antenna
Fortunately, there is a feasible way to analyze a chip antenna. Thanks to the advances in modern simulation software, such as Altair FEKO, reliable simulated data is available for a wide variety of antennas and conditions, including chip antennas.
Want to see how your test setup will affect the pattern of a chip antenna? Simulate it. Programs like FEKO also provide a good starting point for working with the chip antenna. FEKO makes it easier to determine the ideal location for the chip on the ground plane to achieve peak performance. FEKO can also provide component values for tuning the antenna that come close to the ideal. This simplifies tuning the antenna as your starting point is close to what the final results will be, which makes tuning the antenna much easier than it would be otherwise. Simulation is an invaluable tool where the test setup can drastically alter a chip antenna’s performance.
ARSI 
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