Bourns has introduced a new family of high‑Q air coil inductors covering multiple package footprints and inductance ranges for RF front‑end, tuning and amplifier stages.
The AC3028SQ, AC5037SQ, ACXX14SQ, ACXX15SQ and ACXX18SQ air coil inductor series target designers who need tight tolerance, low DCR and mechanically robust SMT inductors in high‑frequency TV, radio and RF equipment.
Key features and benefits
The new air coil inductors combine high Q, low series resistance and controlled inductance in compact SMT formats.
- Inductance range from 5.5 nH up to 82 nH, covering typical RF matching, tank and filter values in VHF/UHF front ends and low‑power RF amplifiers.
- High Q factor up to 230, helping minimize insertion loss and improve selectivity in band‑pass filters, oscillators and tuned circuits.
- Tight inductance tolerances of 2% and 5%, reducing spread in gain, center frequency and impedance matching and simplifying production trim.
- Very low DCR from 3.4 mΩ to 12 mΩ max (depending on series), which helps maintain efficiency and reduce thermal rise at RF and intermediate frequency currents.
- Rated current capability from 2.7 A to 5.6 A, allowing use in higher‑power RF stages and driver amplifiers without saturating or causing excessive temperature rise.
- Flat top and bottom terminations for good mechanical stability, reliable solder joint formation and compatibility with standard pick‑and‑place processes.
- Surface‑mount construction optimized for reflow, supporting automated assembly on standard FR‑4 RF boards and mixed‑technology PCBs.
- Operating temperature range from −25 °C to +125 °C, suitable for many industrial, broadcast and telecom environments.
- RoHS compliant construction according to the current directive and annex, facilitating use in global production without additional material exemptions.
In practice, the combination of high Q and tight tolerance makes these parts especially attractive where filter skirts, oscillator phase noise or narrowband selectivity are critical and every fraction of a dB counts.
Typical applications
The series is aimed at classic RF and tuning functions rather than power magnetics.
- High‑frequency TV and radio receivers, including RF front‑ends, tracking filters and IF stages.
- Radio transmitters in broadcast, land‑mobile and ISM bands that require stable matching networks and low‑loss output filters.
- RF amplifiers from low‑noise front‑end stages up to driver levels within the rated current envelope.
- Tuning applications such as LC resonators, VCO tanks and narrowband band‑pass filters where air core behavior and high Q are important.
Beyond the explicitly listed use cases, these series are also relevant in test and measurement RF fixtures, small signal filters in instrumentation, and where designers prefer air core inductors to avoid core material non‑linearity.
Technical highlights
| Series | Size (L × W × H, mm) | Inductance range (nH) | Q value (typ.) | Rated current (A) | Operating temperature (°C) | Notes |
|---|---|---|---|---|---|---|
| AC3028SQ | 2.67–3.30 × 2.67 × 2.79 | 27 – 47 | 200 | 4.4 – 5.5 | −25 to +125 | Medium SMT, high‑Q, higher current |
| AC5037SQ | 4.06–5.84 × 3.56 × 3.73 | 47 – 82 | 230 | 4.9 – 5.6 | −25 to +125 | Largest size, highest Q, higher L |
| ACXX14SQ | 1.30–2.59 × 1.83 × 1.40 | 5.5 – 19.4 | 60 – 90 | 2.9 | −25 to +125 | Very small, low–mid L, compact tuning |
| ACXX15SQ | 1.30–2.59 × 1.83 × 1.52 | 6.9 – 22 | 90 – 100 | 2.7 | −25 to +125 | Small, slightly higher L and Q |
| ACXX18SQ | 1.47–2.97 × 2.13 × 1.83 | 8.1 – 33 | 90 – 130 | 4.4 | −25 to +125 | Mid‑size, higher current, mid L range |
Design‑in notes for engineers
When designing with air coil inductors, Q, tolerance and parasitics are usually more critical than absolute inductance.
- Use high‑Q series (for example AC5037SQ and AC3028SQ) in places where filter insertion loss, group delay or phase noise is sensitive, such as IF filters, VCO tanks or output matching networks.
- In compact RF modules, consider ACXX14SQ or ACXX15SQ for impedance matching and tuning, but account for their somewhat lower Q at the smallest footprints when estimating total filter loss.
- Ensure that the rated current of the selected part exceeds the expected RF current, including modulation peaks and mismatch conditions; note that low DCR helps reduce self‑heating, but total temperature rise is still governed by ambient conditions and board layout.
- Board layout is critical at VHF/UHF: keep pads and connections short, maintain a controlled RF ground and consider the influence of nearby copper and components on inductance and Q.
- Because these parts are air core, they avoid saturation and core loss effects but are more susceptible to coupling and external magnetic fields; maintain adequate spacing and orientation to minimize unwanted mutual coupling in dense RF sections.
- The flat top and bottom geometry is beneficial for automated optical inspection and coplanarity, but you should still follow standard reflow profiles and land pattern recommendations from the datasheets.
For new designs or drop‑in replacements, always compare the self‑resonant frequency and Q at the operating frequency against existing components to ensure equivalent or better performance.
Source
This article is based on information provided in an official new product release from Bourns for the AC3028SQ, AC5037SQ, ACXX14SQ, ACXX15SQ and ACXX18SQ air coil inductor series, with additional independent editorial context and design considerations.