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radiation from a more omni-directional antenna would be wasted in the direction of the building.

4.3 Common Implementation Mistakes

The following discussion is on typical antenna implementation problems and mistakes. This is not a comprehensive list but simply a discussion of the most common issues.

Dipole or Monopole Parallel to Ground Plane

As discussed earlier, a commercial dipole or monopole style antenna is often mounted close to and parallel to a ground plane. These antennas must be mounted perpendicular (or within about 25 deg of perpendicular) to the local ground plane. It makes little difference if the edge of the ground plane or a surface of the plane is used. Both impedance and efficiency can suffer dramatically from improper mounting.

Antenna in Conductive "Window"

Sometimes a product is housed in a metal enclosure, for functional and/or aesthetic reasons. If the antenna is not external to the enclosure, the typical solution is to open up a "window" in the metal enclosure. This idea appears simple and straightforward but this approach is usually disastrous. An antenna in a conductive window, even if tuned correctly for this situation, will have seriously degraded efficiency. Efficiency degradation of up to 15 dB has been measured on otherwise efficient antennas that have been exposed in a window within a conducting surface. In general, windows for antennas should be avoided completely.

Printed Antenna Surrounded by Ground Plane

Printed antennas should be placed on the periphery of the PCB under consideration. Ideally, the antenna should have three edges exposed (at one end

Antenna Fundamentals Technical Brief


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