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What are inverted-F and planar inverted-F antennas?

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An inverted-F antenna (IFA) is a quarter-wave monopole bent parallel to its ground plane, with a short circuit to ground near the feed that sets the input impedance; a planar inverted-F antenna (PIFA) replaces the wire with a plate, which widens bandwidth. Both resonate when the length from the shorting point to the open end is about λ/4 and are the dominant antennas in phones and IoT devices.[1][2]

How does an IFA work?

Bending a monopole parallel to ground lowers its radiation resistance and adds capacitance; the shorting stub adds a parallel inductance, and moving the feed relative to the short acts as a tapped transformer, letting the designer reach 50 Ω without external matching. Ground-plane currents contribute much of the radiation, so the board size matters.[1]

How is a PCB IFA designed for 2.4 GHz?

Vendor reference designs give tested geometries: TI’s DN007 describes a 2.4 GHz printed IFA and AN043 a compact meandered IFA; Silicon Labs AN1088 gives IFA design guidance including ground-plane and clearance effects.[3][4][5] Copying a reference exactly, including board thickness, ground size and keep-out, gives the best first-pass result.

What sets PIFA bandwidth?

Bandwidth grows with height above ground, plate width and ground-plane size. Slots in the plate create additional resonances for multiband operation; parasitic elements and switchable or tunable matching (aperture tuning) extend cellular coverage.[1]

Frequently asked questions

What is the resonant length of a PIFA?

Roughly L + W ≈ λ/4 for the top plate, modified by height and short width.

Why do IFAs need a ground-plane clearance?

Copper under the radiating arm lowers radiation resistance and efficiency.

Can an IFA be tuned after layout?

Trimming the arm or adding a pi network on the feed is common.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

  1. “Modern Small Antennas”. K. Fujimoto and H. Morishita, Cambridge University Press. 2013.
  2. “Printed Antennas for Wireless Communications”. R. Waterhouse (ed.), Wiley. 2007.
  3. “DN007: 2.4 GHz Inverted F Antenna (SWRU120)”. Texas Instruments. design note.
  4. “AN043: Small Size 2.4 GHz PCB Antenna (SWRA117)”. A. Andersen, Texas Instruments. application note.
  5. “AN1088: Designing with an Inverted-F 2.4 GHz PCB Antenna”. Silicon Labs. application note.
Categories: Antenna types