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Which PCB substrate is best for antennas?

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The substrate of a printed antenna sets its size (through relative permittivity εr), bandwidth (through εr and thickness) and efficiency (through loss tangent tan δ). Common choices are FR-4 (εr roughly 4.2–4.7, tan δ around 0.02, inexpensive), hydrocarbon-ceramic laminates such as RO4003C (design εr about 3.55, tan δ about 0.0027 at 10 GHz) and PTFE laminates such as RT/duroid 5880 (εr 2.20, tan δ about 0.0009 at 10 GHz).[1][2][3]

How do permittivity and thickness affect a patch?

Higher εr shrinks the patch roughly as 1/√εeff but increases stored energy, lowering bandwidth and efficiency and encouraging surface waves. Thicker substrates widen bandwidth but also raise surface-wave loss and probe inductance. Low-εr, thick substrates give the best bandwidth and efficiency where size allows.[4][3]

When is FR-4 good enough?

For many 2.4 GHz and sub-GHz printed IFAs and monopoles, FR-4 works well because the antenna fields are mostly in air and the loss is moderate. FR-4 permittivity varies with glass-resin ratio and frequency, so resonance tolerance is wider. For patches, arrays with long feed networks and frequencies above a few GHz, low-loss laminates are preferred.[5][3]

What about mmWave and LTCC?

At mmWave, loss tangent, copper roughness and thickness tolerance become critical. Low-temperature co-fired ceramic (LTCC) and organic package substrates allow multilayer antenna-in-package designs with fine features and embedded feed networks.[6][7]

Frequently asked questions

What is loss tangent?

The ratio of the imaginary to real permittivity, tan δ = ε″/ε′; it sets dielectric loss.

Why use the design εr rather than the process εr?

Manufacturers publish a design value from circuit measurements that better predicts in-circuit behavior.

Does copper roughness matter?

Yes at high frequencies, where it raises conductor loss.

References

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

  1. “RO4000 Series High Frequency Circuit Materials data sheet”. Rogers Corporation. current revision.
  2. “RT/duroid 5870/5880 High Frequency Laminates data sheet”. Rogers Corporation. current revision.
  3. “Microstrip Antenna Design Handbook”. R. Garg, P. Bhartia, I. Bahl and A. Ittipiboon, Artech House. 2001.
  4. “Microstrip Antennas”. D. M. Pozar, Proceedings of the IEEE, vol. 80, no. 1, pp. 79-91. January 1992.
  5. “AN043: Small Size 2.4 GHz PCB Antenna (SWRA117)”. A. Andersen, Texas Instruments. application note.
  6. “Millimeter Wave Mobile Communications for 5G Cellular: It Will Work!”. T. S. Rappaport et al., IEEE Access, vol. 1, pp. 335-349. 2013.
  7. “Antenna Engineering Handbook, 4th ed.”. J. L. Volakis (ed.), McGraw-Hill. 2007.
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