550nH Ultra Broadband Inductor Precision Broadband RF Choke 50MHz - 40GHz

HALT40005 Ultra-Broadband Conical Inductor | 550nH ±20% Micro-Wire Low-Loss Precision RF Choke (50MHz - 40GHz)

The Hidden Cost of S21 Ripple in Wideband Systems

In a commercial bias tee specification, insertion loss is typically quoted as a single number—<1 dB, <2 dB, and so on. What this number conceals is the frequency-domain structure of the loss. A choke that introduces a flat 0.5 dB of loss across 50 MHz to 40 GHz is electrically benign: the system equalizer can compensate with a simple gain adjustment. A choke that introduces loss varying between 0.1 dB and 0.6 dB with frequency-dependent ripple—that structure cannot be equalized away. It becomes deterministic amplitude distortion that closes the eye diagram.

The HALT40005 is designed to minimize this frequency-dependent structure. Across the 10 MHz to 20 GHz rated span, the measured S21 contribution from the choke is not merely below a threshold—it is flat, showing no resonant feature above the measurement noise floor of the TRL-calibrated VNA setup. This flatness is a consequence of the tapered conical winding: because parasitic capacitance is distributed along the mechanical taper rather than concentrated at discrete turn-to-turn nodes, there is no frequency where the choke’s own LC resonance abruptly loads the transmission line.

Above 20 GHz and extending to the full 40.0 GHz instrumentation limit, the S21 flatness is maintained; the limiting factor becomes the test fixture parasitics—pad capacitance, launch discontinuity, connector mode conversion—rather than any intrinsic behavior of the choke winding itself. The .s2p Touchstone file provided with each HALT40005 captures the complete two-port behavior so that system designers can verify this flatness in their specific circuit simulation environment.

Manufacturing Precision at the 50-Micron Threshold

Winding a 550 nH inductor with a wire diameter of 0.05 mm is a precision engineering operation. The wire tension during winding must be controlled to millinewton accuracy: too little tension produces a loose, mechanically unstable coil; too much stretches the copper beyond its elastic limit, permanently increasing the DCR and altering the taper geometry. Turn placement must be repeatable to within single-micron tolerances to preserve the designed distributed-capacitance profile. And the flying leads must exit the winding on-axis for consistent automated wedge-bonding alignment.

Hoan achieves these tolerances through optically guided, closed-loop winding stations with 100% automated optical inspection:

• Taper profile conformance: The turn diameter at any point along the 3.0 mm axis must match the design profile to within ±5%. Out-of-tolerance taper creates localized capacitance anomalies that produce narrowband S21 ripple.
• Inter-turn gap consistency: Irregular spacing between adjacent turns concentrates parasitic capacitance at specific locations, generating unintended resonant modes within the rated frequency band.
• Lead axis alignment: Both apex and base leads are verified to exit the winding along the central cone axis. Misaligned leads reduce automated bonding throughput and introduce orientation-variant coupling.
• Insulation surface integrity: The polyimide enamel coating is inspected for thin spots, abrasion marks, and pinholes. Any undetected insulation defect can evolve into a turn-to-turn short after years of thermal cycling.

Lot-level statistical process control data is archived, with CpK exceeding 1.67 across all critical geometric parameters. Per-lot sample VNA testing on a characterized microstrip fixture provides ongoing verification of SRF, insertion loss, and isolation conformance.

Validated Field Reliability

Measured Performance Envelope

Construction and Ratings

Mounting Sequence for Optimal S-Parameter Realization

1. Apex joint: The narrow tip connects to the RF trace. Position the coil axis perpendicular to the board. Angular error produces S11 asymmetry detectable above 30 GHz.
2. Lead exposure limit: The flying wire between the apex solder fillet and the first turn must be ≤0.3 mm. Every 0.5 mm of excess lead adds roughly 0.3 nH series inductance, pulling the high-frequency S11 several dB at 40 GHz.
3. Base-side DC node: Wide cone end to the bias pad. Place 100 pF || 10 nF ceramic bypass capacitors within 1 mm.
4. Adhesive dot: A single micro-dot (≤0.3 mm diameter) of Epotek H70E on the winding side. Full encapsulation is counterproductive: the added dielectric raises shunt capacitance and lowers the practical upper frequency.
5. Iron temperature and dwell: 280–320°C; 2 seconds maximum. The 50 µm cross-section reaches thermal equilibrium with the tip within milliseconds. Excess dwell softens the copper by annealing.

Target Use Cases

• Broadband bias tees in 100G/400G/800G optical transceivers (TOSA laser bias, ROSA TIA supply)
• GaAs pHEMT and GaN-on-SiC amplifier gate/drain bias injection in Ka-band and Q-band systems
• Waveguide photodiode reverse-bias decoupling in coherent DP-QPSK and 16QAM receivers
• Millimeter-wave network analyzer frequency extender bias networks
• 5G NR FR2 active antenna array DC power distribution
• Satcom Ka-band and Q-band LNA bias choke

Engineering FAQ

Q: How does the HALT40005 differentiate itself from the other 550 nH variants?
A: All 550 nH HALT40005-series conical inductors share the identical core electrical design and are manufactured to the same specifications. The HALT40005 variant specifically documents the insertion-loss flatness, high return loss, and lot-level SPC data that support high-reliability telecom and aerospace qualification. If your program requires statistical process control data, environmental qualification reports, and detailed S-parameter characterization, the HALT40005 documentation package is the appropriate choice.

Q: Our design operates at a maximum ambient of +85°C inside the module. Do we need to derate the 200 mA?
A: At 200 mA and +85°C ambient, the winding temperature is approximately 100°C—well within the polyimide insulation’s 200°C continuous rating. No current derating is required at this operating point. The full 200 mA is available across the entire -55°C to +125°C specified ambient range.

Q: What S-parameter format is provided and how is it de-embedded?
A: The data is supplied as a standard two-port .s2p Touchstone v1 file with 201 linearly spaced frequency points from 10 MHz to 40 GHz. The reference plane is de-embedded to the component lead-to-pad solder interface using thru-reflect-line (TRL) calibration standards fabricated on the same microstrip substrate. This captures the component’s intrinsic behavior, excluding the test fixture contribution. The file imports directly into Keysight ADS, Ansys HFSS, and Cadence AWR Microwave Office as a two-port S-parameter data block.