Design and Solutions Antenna Matching

Antennas transmit and receive radio signals by converting electromagnetic conducted waves into free space waves and free space waves into conducted waves. In the process, an antenna forms electric and magnetic fields. The generated near field is influenced by the immediate environment. The main influencing factors are metals, batteries/accumulators, casings and human bodies. The position of the chip antenna on the PCB and the PCB size/geometry also affect the near fields, since the PCB together with the chip antenna creates the structure that operates as an antenna

Due to the influencing factors, the frequency range at which the chip antenna can transmit and receive may be out of tune. With the help of RF inductors and RF capacitors, the chip antenna can be matched to the required frequency range.

The RF inductors and RF capacitors build a matching circuit that match the impedance of the chip antenna to the required frequency range under the influence of the immediate environment. Therefore, it is necessary to make an antenna match as soon as the chip antenna, the immediate environment, the required frequency range, the position of the chip antenna on the PCB or the PCB size/geometry changes. The specified antenna performance requires the correct implementation of the chip antenna for the application. More about this in our antenna design-in guidance.

When designing a radio interface, a distinction is made between an integrated chip antenna and an external rod antenna. Visit our RF & Wireless Communication App Guide to learn more about component selection.

These recommendations form the basis for implementing our chip antennas according to the specified antenna performance in the application:

• Place electrical antennas separated from the rest of the circuit and components (ANP057)
• Place magnetic antennas as centrally as possible at the edge of the longer PCB side
• Do not place any electroconductive planes, metals and batteries/accumulators in the immediate environment of the antenna (ANP057)
• Maximize the distance of the antenna to dielectric materials (e.g. casing)
• Consider the recommended PCB layout for the antenna from the antenna data sheet
• Cut out the copper in all PCB layers under the antenna
• Consider the recommended PCB layout for the matching circuit from the antenna data sheet 
• Place the matching circuit as close as possible to the antenna and connect it to the radio module ground plane
• Design the matching circuit for component size 0402
• Design the feed line of the antenna to the impedance of 50 Ohm (ANE012)
• Keep the feed line of the antenna as short as possible
• Provide the footprint for a WR-UMRF connector on the feed line of the antenna immediately after the circuit of the radio module
• Consider the recommended circuit and the PCB layout of the antenna feed line from the radio module data sheet

For more information, please refer to our Application Notes and Design Guides:

ANP057: WE-MCA Multilayer Chip Antenna Placement & Matching

ANR017 GNSS Antenna Selection

ANP074: Introduction to RF inductors

ANE012: Coaxial PCB Connector - PCB-Transmission Line Design Guide

ANR022: Radio module cross migration guide

ANR010: Range Estimation