Small loop antenna types

Design Tips and Tricks for Small Loop Antenna PCBs

Thunder and lightning have frightened humans throughout history. And while thunder may not present an existential threat, lightning can be fatal. Perhaps this explains why early forays into electrical systems typically included wires or cables for safety. Today, however, many exchanges of electrical energy are wireless and require antennae.

Almost any metallic element may serve as an antenna. Yet, for accurate transmission and reception of data and communications, antennas must be designed and built to specific physical dimensions. Chief among these specifics is height or length according to signal frequency. Geometry is also important, as antenna shape will influence directivity, polarization and other signal transmission parameters. A common antenna shape with many variations is the loop antenna. For electronics, small loop antenna PCBs often are utilized, and there are guidelines that, if followed, will enhance board construction and performance.

Applications and Attributes of Small Loop Antennas

From a geometric perspective, several different structural loop antenna designs are available.  For example, these antennas may be circular, triangular, square or rectangular, as shown below.

Rectangular small loop antenna PCB
Rectangular small loop antenna PCB

Small Loop Antenna Attributes

  • ❃Direction finding
    Because nulls develop at points around the loop and when pointed in the direction of the transmitter, loop antennas are useful for direction finding.
    ❃ Lack of SNR drop at receiver
    At lower frequencies—less than 15MHz—the signal noise is lower than the internal noise. Therefore, weak signals can be amplified without SNR degradation.
    Induction coupling
    Loop inductively couple with nearby magnetic fields, enabling applications such as inductive charging of mobile phones to be performed.
    Variable radiation resistance
    Loop antennas have low radiation resistance, which results in high losses and inefficiency. However, this can be improved by rotating the antenna’s direction, increasing the number of windings and using a ferrite core.

Additionally, small loop antennas do not require grounding, as transmitted and received signals propagate in pairs. To leverage the advantages of small loop antennas, best practices should guide board design.

Best Practices for Designing Small Loop Antenna PCBs

Circuit boards can be constructed to maximize the advantages of small loop antennas. However, these boards will be used in communications systems, so issues like signal integrity—especially for high-frequency usage—are of prime importance. To achieve the best performance and ensure your PCBA's manufacturability, follow the guidelines listed below.

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Guidelines for Small Loop Antenna PCB Design

  • Use a circular geometry
    Circular loop antennas experience lower losses as compared to other shapes for the area.
  • Ensure loop trace dimensions are consistent
    For the best results, the antenna should be symmetrical. This is achieved by using a consistent material structure to form the antenna or ensuring that the copper trace parameters are consistent.
  • For transmitter boards, use large copper traces
    Small loop antennas are not commonly used as transmitters. However, if your design calls for transmission from the antenna, be sure to use high current traces.
  • Isolate board circuitry from the antenna, if possible
    As a radiator, your antenna can introduce interference to the PCBA and external circuits located nearby. One of the best ways to mitigate the effects of EMI and EMC is by isolation.
  • Perform signal analysis simulation before manufacture
    For optimal performance, antennas require tuning. Although online tunability is a beneficial feature,  determining the best antenna parameters off-line and designing your board layout accordingly may be preferable.

Working with a CM who understands these challenges can help optimize your board to get the most out of your small loop antenna application. Tempo Automation, the industry leader for building high-quality custom and complex PCBAs fast, will work with you throughout development to ensure that your design intent is maintained.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on small loop antenna PCBs, contact us.

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