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.
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.
DFM for High-Speed Digital PCBs
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.
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