Chip Antenna Layout Considerations for 802.11
This technical note is also available in PDF Format: Antenna Layout PDF (92k)
Chip Antenna matching and radiation pattern performance can be dramatically affected by the design/layout of a circuit. Antenna mounting, the antenna's position relative to circuit mismatches, the antenna position relative to adjacent components and ground planes all can affect antenna performance. Thus design engineers must use care when creating a circuit layout which includes an antenna. Johanson Technology chip antenna performance specifications are based on the chip antenna when mounted onto the associated Johanson evaluation board. These evaluation boards serve as a good starting point for designers.
Johanson Technology offers many different chip antennas that operate between 1.5GHz and 6 GHz. To view a complete list of Johanson Technology antennas with links to detailed specifications click here.
When determining the matching components needed in an individual application, begin by measuring the return loss (S11) into the matching component(s) feeding the antenna in the same configuration that is planned for the final circuit. Vary the value of the matching components until the return loss dip is centered on the specified operating band.
Some design guidelines are:
The following is an example of the Johanson Technology 2450AT45A100 Chip Antenna:
TYPICAL HORIZONTAL ORIENTATION ROUTINGFor the antenna to resonate at 2.45 GHz when mounted as shown here, the in-line matching component of 1.2 pF is required.
The matching component may be slightly different than that shown depending on distance to ground plane, dielectric constant of PCB, and PCB material thickness.
TYPICAL HORIZONTAL ORIENTATION ROUTING (ALTERNATE)
TYPICAL VERTICAL ORIENTATION ROUTING
(a) Without Matching Circuits (Moderate Bandwidth)
(b) With Matching Circuits (Wide Bandwidth)
*Line width should be designed to match 50. characteristic impedance, depending on PCB material and thickness.
(a) Return Loss Without Matching Circuits
(b) Return Loss With Matching Circuits
Listed here are the matching components needed for other common JTI antennas when mounted on JTI test boards:
The matching circuit and the component values will be different in every application, depending on PCB material, thickness, etc. The given values are for the JTI test boards, and are good starting values for finding the optimum values for an individual application.^ Back to Top