RF Inductors Selection Guide: Specs, Packages & Top Picks

The RF Inductor: Your Matching Network's Weakest Link

At DC, an inductor is a coil of wire. At 2.4 GHz, it's a complex RLC network with three parasitic elements and a resonance that might sit squarely in your operating band. RF inductors are the single most misunderstood passive in wireless design. The S-parameter plot you measured on the VNA doesn't look anything like the ideal inductor you put in the schematic — the difference is all in the parasitics.

Construction Types: The First Decision

Wirewound (Ceramic Core): A wire coil wound on a ceramic (alumina) core. Highest Q (typically 50–120 at 1–2 GHz), highest SRF for a given inductance, handles the most current. These are what you use in PA matching, filter resonators, and any circuit where loss matters. Coilcraft's 0402DC/0603DC series and Murata LQW series are the go-to choices.

Multilayer (Ferrite or Ceramic): Alternating layers of ferrite/ceramic and printed conductor, fired like an MLCC. Lower Q (10–30), lower SRF, but smaller and cheaper. Fine for decoupling, bias tees, and non-critical matching. Murata LQG, TDK MLG series dominate here.

Thin-Film: Photolithographic spiral on a substrate — the inductor equivalent of thin-film resistors. Tightest tolerance (±0.05nH or ±2%), best repeatability. Higher Q than multilayer, lower than wirewound. Ideal for precision matching in high-volume products where tuning each unit isn't practical. TDK TFS series is the standard bearer.

Air-Core (Conical/Broadband): Specialized for bias tees operating over multi-octave bandwidths. The conical shape distributes the SRF so there's no single resonance spike. Coilcraft conical and Mini-Circuits ADT series. Not something you'll spec for standard narrowband designs.

Q Factor: The Real Story

Q isn't a fixed number — it's a curve vs. frequency. An inductor rated Q=80 at 500 MHz might be Q=30 at 2 GHz. Three loss mechanisms dominate:

1. DC resistance of the coil (dominates at low frequency)
2. Skin effect — current crowds to the conductor surface as frequency increases (R_ac increases with √f)
3. Proximity effect — adjacent turns induce eddy currents in each other

Wirewound parts separate the turns (pitch winding) to reduce proximity effect. Multilayer parts can't do this, which is why their Q drops faster with frequency.

The practical tip: Always look at the Q vs. frequency plot in the datasheet. The S-parameter files (usually downloadable from Coilcraft, Murata, and Johanson websites) are even better — import into your simulator for realistic matching network performance.

SRF: The Frequency Ceiling

Self-resonant frequency is where the inductor's parasitic parallel capacitance resonates with the inductance. At SRF, the impedance peaks (the inductor looks like an open circuit). Above SRF, the impedance drops and the inductor behaves like a capacitor entirely. For a choke application, you WANT the inductor at or near SRF (maximum impedance = maximum blocking). For a matching network, keep 2–3× away from SRF. A 10nH 0402 wirewound inductor might have SRF around 6 GHz — perfectly fine for 2.4 GHz work. That same inductor in 0603 has higher SRF (less parasitic C), but larger footprint.

Tolerance: ±0.1nH vs. ±5%

For matching networks above 1 GHz, inductance tolerance starts to matter more than you'd think. A ±5% tolerance on a 1nH inductor (±0.05nH) is a ±5% impedance shift — usually acceptable. But at 0.5nH, the same percentage tolerance is only ±0.025nH, and inter-manufacturer measurement differences (Coilcraft measures at 250 MHz, Murata at 100 MHz) mean the "same value" from two vendors can produce different matching. For production, lock to one vendor's S-parameter model.

Top Picks

Sourcing Notes

Wirewound RF inductors from top manufacturers (Coilcraft, Murata) are generally well-stocked in E12/E24 values. Custom inductance values are essentially unavailable — engineers tune their matching networks to standard values, not the other way around. Thin-film parts have longer lead times (8–12 weeks) but better tolerance consistency. Multilayer parts are commodity — stock is rarely an issue.

Looking for RF inductors with specific Q and SRF requirements? Search our database or check your full BOM availability at partscubeglobal.com/bom.