Ultra Wideband Conical Coils 1400nH Custom Inductor 20MHz - 40GHz

Product Overview

The HALT60005 is a broadband conical inductor for RF decoupling and bias tee applications spanning 20 MHz to 40 GHz. It delivers 1400 nH of nominal inductance through a continuously tapered conical winding wound with 0.05 mm oxygen-free copper wire, rated for 200 mA continuous DC current over an operating temperature range of -55°C to +125°C.

Complete Technical Specifications

Conical Geometry: How the Tapered Winding Eliminates Self-Resonance

Standard solenoidal inductors self-resonate at a frequency determined by the product of winding inductance and inter-turn parasitic capacitance. Above this SRF, the component transitions from inductive to capacitive behavior and ceases to provide RF isolation. In wideband systems spanning multiple octaves, this creates a transmission notch within the operating band.

The HALT60005 addresses this through its conical winding geometry:

• Apex (Narrow End, ~0.40 mm OD): Connected to the 50-Ω microstrip transmission line. The small turn diameter presents low shunt capacitance to ground, preserving signal integrity at K-band and Ka-band frequencies.
• Base (Wide End): Accumulates the full 1400 nH of blocking inductance, providing isolation down to 20 MHz.
• Tapered Transition: The continuous change in winding diameter distributes parasitic capacitance along a mechanical gradient. Rather than one discrete LC product, the capacitance is spectrally spread, yielding a flat impedance response with no sharp self-resonant peak.

Multi-Frequency Performance Characterization

Each unit is characterized on a calibrated vector network analyzer using microstrip calibration fixtures with TRL de-embedding to move the reference plane to the component leads:

0.05 mm Micro-Wire: Parasitic Capacitance Reduction

The choice of 0.05 mm wire is driven by the need to minimize inter-turn capacitance. Reducing the conductor diameter from 0.15 mm to 0.05 mm decreases the facing surface area between adjacent turns by approximately 89%. Since inter-winding capacitance scales with conductor surface area, this directly translates to proportionally lower parasitic capacitance and a higher SRF.

The polyimide enamel insulation has a low relative permittivity (εr ≈ 3.5) and is applied in a thin, uniform coating, further suppressing electric field coupling between turns. The air-core topology eliminates ferrite core losses, permeability temperature drift, and DC bias saturation effects—the SRF is governed solely by the deterministic winding geometry.

Comparative Analysis: Conical vs. Alternative Topologies

Assembly Quick Reference

1. Orientation: Small end (apex) perpendicular (≈90°) to the RF microstrip line.
2. Lead Trim: Apex flying lead ≤0.5 mm (ideally <0.3 mm) from solder fillet to first turn. Excess lead adds series parasitic inductance.
3. Base Connection: Wide end to DC bias pad. Place 100 pF || 10 nF bypass capacitors within 1 mm.
4. Fixation: Micro-dot of non-conductive, low-outgassing epoxy (Epotek H70E or H65) on winding side.
5. Soldering: 280–320°C iron tip, ≤3 seconds dwell. Compatible with SAC305, AuSn, PbSn alloys.

Primary Applications

• Broadband bias tees spanning VHF through K-band
• DC feed networks in 100G/400G/800G fiber-optic TOSA/ROSA modules
• GaAs pHEMT LNA gate bias and GaN HEMT drain bias injection
• PIN diode switch and step attenuator DC return paths
• Phased-array antenna element bias distribution
• Millimeter-wave VNA extender and test-fixture bias networks
• X/Ku/K-band radar and electronic warfare receiver front-ends

Frequently Asked Questions

Q: Why does a single 1400 nH conical inductor outperform cascading multiple inductors?
A: In standard bias networks, achieving broadband isolation requires cascading a large-value inductor (for low frequencies) with a small-value inductor (for high frequencies). The connection between them forms a parasitic LC tank circuit that resonates in-band, producing a transmission dip. The HALT60005 combines high inductance with a tapered conical architecture, achieving continuous isolation from 20 MHz to 40 GHz in a single component with no junction parasitics.

Q: Is the 0.05 mm wire durable in high-vibration environments?
A: The low mass of the air-core structure (<5 mg) reduces susceptibility to mechanical shock. When properly secured with epoxy dot-fixing, the assembly passes MIL-STD-202 Method 204 vibration and Method 213 mechanical shock tests. There is no ferrite core to crack from CTE mismatch.

Q: What is the lead time for custom inductance values?
A: Hoan maintains quick-turn conical inductor prototyping. Custom values (typically 50 nH to 2000 nH in the 0.05 mm or 0.08 mm wire series) can be sampled within 3–4 weeks. Volume production lead times are 8–12 weeks. Contact Hoan with your target inductance, frequency band, and DC current requirement.