PIFA and ceramic chip antennas

Small wireless devices such as WiFi cards, mobile phones and embedded radio modules need antennas that fit inside a thin enclosure yet still work at gigahertz frequencies. Two design families address this: the printed inverted-F antenna and the surface-mount ceramic chip antenna. Both achieve a useful electrical size in a small physical space by folding or loading the radiating structure rather than relying on a full-length resonant element.

The planar inverted-F antenna (PIFA) is a flat radiating patch held above a ground plane, fed at one point and shorted to the ground plane at another. The shorting connection lets the structure resonate at roughly a quarter wavelength instead of a half, halving its length, while the proximity to the ground plane keeps it low-profile. PIFAs can be etched directly onto a circuit board, are cheap to manufacture, and can be tuned to cover one or more bands, which made them common in portable wireless equipment.

Ceramic chip antennas take a different route to miniaturisation. A small block of high-permittivity dielectric ceramic carries a printed conductive trace; the high dielectric constant slows the wave inside the material so that a resonant structure fits in a component only a few millimetres long. Supplied as a surface-mount part, the chip antenna is placed on the board like any other component, simplifying assembly. Its small size trades away some bandwidth and efficiency compared with larger antennas, but for compact consumer devices that compromise is usually acceptable.

Frequently asked questions

Why is it called an inverted-F antenna?

The side-on shape formed by the feed line, the radiating arm and the shorting connection resembles a letter F lying on its back, giving the design its name.

How does a ceramic chip antenna stay so small?

Its high-permittivity ceramic slows the electromagnetic wave, shortening the effective wavelength so a resonant element fits within a tiny surface-mount package.

What is the main drawback of these miniature antennas?

Reducing size generally narrows bandwidth and lowers efficiency, so very small antennas accept some performance loss in exchange for fitting inside compact devices.