How it works
An RF inductor supplies controlled reactance to a matching network, resonator or bias feed. At GHz frequencies the winding capacitance, pad and return path become part of the component. Ceramic/multilayer, wirewound and air-core parts solve different size, Q and tolerance problems; the same nH marking does not make them interchangeable.
Below self-resonance, an ideal inductor has reactance XL = 2πfL. The actual RF part must be evaluated at the frequency where it will work.
Parameters that matter
- Q at the working band
- Q describes reactance relative to loss at a stated frequency. Compare Q at your band, not the best number anywhere on the curve.
- Self-resonance
- SRF is where parasitic capacitance resonates with L. Matching networks need a well-behaved inductive region; a narrowband RF choke may deliberately use the impedance peak.
- Tolerance and models
- Tolerance in nH can matter more than a percentage for very small values. S-parameters need the correct reference plane and pad de-embedding.
- Bias-feed current
- Current and DCR limit a DC bias feed; they do not establish RF power handling or linearity.
A worked selection example
Illustrative calculation · not a product guarantee
Check a 3.3 nH part at 2.4 GHz
First-pass matching calculation: an ideal 3.3 nH series inductor at 2.4 GHz, with ±0.2 nH tolerance. Q = 40 is used only as a hypothetical loss example; it is not a supplier specification.
- Calculate inductive reactance: XL = 2πfL ≈ 49.8 Ω.
- The ±0.2 nH tolerance alone changes reactance by approximately ±3.0 Ω at this frequency.
- If Q at 2.4 GHz were 40, equivalent series resistance would be XL/Q ≈ 1.24 Ω.
- Replace the ideal model with each candidate’s frequency-dependent S-parameters and the actual PCB. Verify return loss and delivered power with a VNA/RF bench.
The same nominal nH value can produce a different match. Decide from band-specific loss, parasitics and board measurements.
Where it fits
Suitable starting points
- Antenna matching; RF PA/LNA bias feeds; band-select filters and resonators.
Where to take extra care
- Not a switch-mode energy-storage substitute. A ferrite bead chosen for loss can degrade a high-Q matching network.
Series directions to investigate
Sunlord SDCL and HQ/UHQ are documented ceramic/high-Q directions. Compare the exact series with wirewound alternatives in the allowed package. Record both metric dimensions and EIA inch code to avoid a “0402” size mismatch.
What Chinese suppliers can offer
Where the opportunity lies
The opportunity is access to ceramic and high-Q families in nearby assembly ecosystems, making a small-value tuning kit and repeat sample builds feasible. Confirm model files and tolerance availability first; proximity does not guarantee RF equivalence.
What still needs evidence
Confirm the exact manufacturing source, current datasheet, sample results and commercial terms before placing an order. Series availability does not establish qualification for your application.
Questions for the supplier
- 01
S-parameters covering the band and harmonics, with fixture/de-embedding notes.
- 02
Q/L/SRF curves and test frequency for the exact ordering code.
- 03
Tolerance distribution, reel orientation and repeatability across sample lots.
Technical references
These references support the principles and catalogue directions discussed here. Public documentation is a different evidence level from a supplier reply, a lot document or an independent test. This guide does not claim those later stages have been completed.
- 1. Key Parameters for Selecting RF Inductors
- 2. Measuring Self Resonant Frequency
- 3. RF PA module application guide
- 4. Declaration of conformity: product platforms and series
These guides explain selection principles. Final decisions require the current datasheet for the exact ordering code, operating conditions and appropriate application testing.