25MHz - 40GHz Broadband Inductors 1.0uH RF Choke Coil HALT50005

HALT50005 Ultra-Broadband Conical Inductor | 1000nH (1.0µH) ±20% Micro-Wire Ultra-Wideband RF Choke (25MHz - 40GHz)

One Millihenry at 40 Gigahertz: The Physics of the Impossible

A designer looking at the number 1.0 µH and then scanning across to 40 GHz has every right to be skeptical. Conventionally, an inductor delivering a full microhenry of inductance requires enough turns that the aggregate inter-winding capacitance produces a self-resonance somewhere in the low hundreds of megahertz. At 40 GHz, that same component has long since transitioned from inductive to capacitive behavior and offers essentially zero RF isolation.

The HALT50005 achieves this seemingly contradictory combination of specifications by employing a continuously tapered conical winding wound from 0.05 mm (50 µm) oxygen-free copper wire. The key insight is not to eliminate parasitic capacitance—that is physically impossible in any multi-turn winding—but to distribute it across a geometric gradient so that no single LC product dominates. At the narrow apex, the microscopic turn diameter presents negligible shunt loading to the 50-Ω microstrip, allowing K-band and millimeter-wave signals to pass unimpeded. At the wide base, the accumulated 1.0 µH of inductance blocks signals with a low-frequency corner of just 25 MHz. Between these two extremes lies a continuous impedance spectrum with no discrete self-resonant peak.

The HALT50005 is rated for 250 mA of continuous DC current with a temperature rise constrained to 15°C or less. An optional 0.08 mm heavy-wire variant is available on custom order for applications that prioritize current handling over the last few gigahertz of upper bandwidth.

Three-Band VNA Performance Validation

Each HALT50005 undergoes production VNA testing on a TRL-calibrated microstrip fixture. The measured behavior across the operating spectrum is summarized below:

Specification Reference

Why 25 MHz Matters for Low-Frequency Isolation

Many conical inductors in this product family start their rated blocking at 50 MHz or even 100 MHz. The HALT50005 extends the low-frequency corner down to 25 MHz—a 50% improvement over the 550 nH series—because the higher inductance (1.0 µH versus 0.55 µH) generates proportionally more inductive reactance at any given frequency. For systems that carry low-frequency telemetry tones, supervisory channel modulation, or slow control signals on the bias line, this additional octave of low-end blocking margin eliminates the need for a separate large-value choke in the bias network.

The 250 mA current rating—25% higher than the 550 nH series at 200 mA—reflects the slightly thicker wire gauge used in the available turns, which also marginally reduces the DC resistance and the associated I²R self-heating. This makes the HALT50005 particularly well-suited for bias tees in GaN power amplifier drain bias networks, where the combination of high bias current and wide operating bandwidth places simultaneous demands on both the current capacity and the frequency response of the choke element.

Assembly Protocol

1. Apex to RF trace: Solder the narrow cone tip to the 50-Ω microstrip line. Coil axis must be perpendicular to the board. Off-perpendicular mounting degrades S11 above 30 GHz.
2. Lead exposure limit: The flying lead between the apex solder fillet and the first winding turn must not exceed 0.3 mm. Excess lead contributes series inductance that pulls the apparent input match.
3. Base to DC node: Wide cone end to the bias input pad. Place 100 pF and 10 nF MLCC bypass capacitors within 1 mm.
4. Epoxy dot: Single micro-dot (≤0.3 mm) of Epotek H70E on the winding side. Arrests microphonic modulation without the capacitive penalty of full encapsulation.
5. Soldering thermal profile: 280–320°C tip; 2 seconds maximum dwell per joint.

Applications

• Broadband bias tees in 100G/400G/800G optical transceiver modules
• GaN-on-SiC SSPA drain bias feed in X-band through Ka-band radar transmitters
• GaAs pHEMT LNA gate bias in Ka-band satellite receivers
• High-speed photodiode reverse-bias networks in coherent receivers
• 5G NR FR2 active antenna array DC distribution
• Millimeter-wave VNA extender bias networks for on-wafer characterization

FAQ

Q: How is this variant different from the HALT40005 series?
A: The HALT50005 provides 1000 nH (1.0 µH) of inductance versus 550 nH for the HALT40005 series. This higher inductance extends the low-frequency blocking corner from 50 MHz down to 25 MHz and increases the RF isolation to >1.8 kΩ (versus >1.5 kΩ). The current rating is also higher at 250 mA (versus 200 mA). All three variants share the same 0.05 mm wire, conical geometry, and 40 GHz upper frequency limit.

Q: Our bias tee must pass signals down to 30 MHz. Is 25 MHz start sufficient?
A: The 25 MHz rating represents the -3 dB corner of the choke’s inductive reactance curve. At 30 MHz, the HALT50005 provides approximately 1.2× the reactance available at the corner frequency, delivering robust blocking with comfortable margin. If your application requires blocking below 25 MHz, contact Hoan for custom higher-inductance conical inductor options.