Commercial off-the-shelf antenna element(s).
Reference design (typically supplied by radio module vendor).
Custom antenna design (usually requiring an antenna-design consultant).
Most industry experts recommend approaches 2 and 3 with the caveat that using a reference design should be considered a “semi-custom” design – meaning that while the reference design may be correct, some adjustments to the design will likely be required in a new device.
When evaluating a reference design, it is important to know exactly what the reference design represents: actual measured data from a working antenna, or perhaps just simulations from antenna-design software. Simulations are useful but often need substantial adjustments once implemented in hardware. A reference design, no matter how straightforward, should never be implemented without confirmation (by measurement) of its performance parameters. During a discussion with David Bissonette of 7 Layers, Inc., he echoed the issues above and added “For most OEMs, obtaining antenna design services at the beginning of the product design phase is critical to the product success. Although qualified design help can be expensive, the cost of a substantial product re-design – at the moment when the device should be starting volume production – is much higher.”
As briefly discussed earlier, commercial antennas often have inaccurate or misleading specifications. Remember that the antenna cannot be considered in isolation because the entire device defines the antenna impedance, bandwidth, and efficiency. Therefore, a specification or datasheet is of only limited usefulness. Off-the-shelf antennas can be excellent solutions but only if implemented as carefully as a full-custom antenna design.
Some radio module vendors and certified test labs are now offering antenna design assistance at whatever technical level is required. The expertise provided by these vendors should be used whenever possible.
4.5 Antenna System Issues
Antenna Fundamentals – Technical Brief