26nH Air Coil Inductor Low Parasitic Capacitance Air Core Choke Harsh Environment Immune

HALA1200303R 26nH Air Core Inductor Low Parasitic Capacitance Flat Pass Band RF Power Harsh Environment Immune 12T Coil

Parasitic Capacitance in Inductors: The Hidden Bandwidth Limiter

Every physical inductor is also a capacitor. The spacing between adjacent winding turns creates parasitic inter-winding capacitance that, combined with the inductance, forms a parallel LC resonator. At the self-resonant frequency (SRF), this resonator presents an open circuit — at which point the component ceases to function as an inductor. Below the SRF but within its proximity, the effective inductance rises due to the parallel resonance pulling the impedance upward, distorting the frequency response and creating a non-flat passband that corrupts wideband S-parameter performance.

The HALA1200303R 26nH ±20% 12-turn air core inductor minimizes parasitic capacitance through its single-layer air-spaced helical geometry. With 0.03mm (30µm) enameled copper wire wound on a 0.30mm mandrel, the inter-turn spacing is large relative to the conductor diameter — reversing the tight, high-capacitance geometry of multilayer chip inductors. The air dielectric between turns (εᵣ = 1.0) provides the lowest possible inter-winding capacitance for a given geometry. The result: a flat, resonance-free passband from 1.5GHz to 18GHz with no parasitic resonance notches in-band. At 18GHz — the upper operating limit — the SRF margin ensures the inductor impedance is still dominated by the inductive reactance (+j2.94kΩ at 18GHz for 26nH), not the parasitic capacitance.

Why Flat Band Pass Matters: Comparing 12-Turn Air Core to 12-Layer Chip

A 12-turn air-core helix has exactly 11 inter-turn gaps. Each gap contributes a small, well-characterized capacitance, and all gaps are effectively in series along the helical length — the total parasitic capacitance is the series combination of 11 small capacitances, resulting in a value on the order of 10-20fF. A 12-layer ferrite chip inductor has overlapping buried conductor layers where each layer pair forms a parallel-plate capacitor with thin (10-20µm) high-εᵣ (εᵣ ≈ 10-15) ceramic dielectric. The total parasitic capacitance is on the order of 100-300fF — 10-15* higher than the air-core equivalent.

This 10-15* capacitance difference has profound consequences for wideband operation. The SRF of a 26nH inductor with 200fF parasitic capacitance is approximately 2.2GHz — well within the 1.5-18GHz operating band, creating an in-band self-resonance that renders the inductor unusable above 2GHz. The HALA1200303R with 15fF parasitic capacitance has an SRF above 8GHz — providing a clean, flat passband throughout the 1.5-18GHz design range. For wideband bias tee, matching network, and filter designs where consistent impedance across a decade of bandwidth is non-negotiable, this is the difference between a working design and a non-functional one.

High RF Power Handling and Voltage Endurance

At 1.5GHz, a 26nH inductor presents j245Ω of inductive reactance. In a GaN PA bias tee carrying 200mA DC with 28V drain voltage, the RF voltage across the inductor is the vector sum of the DC bias and the RF swing. With 10W (40dBm) RF power into a 50Ω load, the peak RF voltage is approximately 31.6V — plus the 28V DC offset — for a total peak voltage of nearly 60V across the inductor terminals. The air-core HALA1200303R handles this with substantial margin because:

• No core saturation: The 200mA DC bias creates zero permeability shift. The full 26nH inductance is available for RF isolation at all bias currents, maintaining j245Ω at 1.5GHz regardless of DC operating point.
• Air dielectric breakdown: Air has a dielectric strength of approximately 3kV/mm. The inter-turn spacing of the 12-turn helix (approximately 25-30µm between adjacent turns) provides >75V breakdown voltage — comfortably exceeding the 60V peak developed in the PA scenario.
• Thermal management at 200mA: The DC resistance of the 12-turn, 0.03mm wire helix is approximately 0.8-1.2Ω. At 200mA, I²R heating is approximately 40-48mW — well within the thermal dissipation capacity of the air-core structure. There is no ferrite core to heat up and shift permeability with temperature.

Immunity to Harsh Environments and Radiation

The HALA1200303R is inherently immune to environmental degradation mechanisms that affect ferrite-core and semiconductor-based passive components:

• Radiation hardness: The air core operates on the fundamental constant μ₀ = 4π*10⁻⁷ H/m. There is no semiconductor junction to accumulate total ionizing dose (TID) damage, no crystal lattice to suffer displacement damage, and no magnetic domain structure to be disrupted by single-event effects. The inductance is a geometric and free-space constant — it does not change in any radiation environment.
• Condensing humidity: The 30µm enameled copper wire is protected by a continuous polyurethane insulation coating. The air core itself cannot absorb moisture (there is no porous ferrite to saturate). Post-assembly conformal coating extends moisture protection to the solder joints.
• Thermal shock (-55°C to +125°C): The air core has zero CTE mismatch between core and winding — because there is no core. The 0.03mm copper helix expands and contracts freely with temperature. After 1000 thermal shock cycles, inductance, Q, and SRF remain within initial tolerance.
• Salt fog and corrosion: The pre-stripped and tinned leads resist oxidation. Stored at 20-25°C and 40-60% RH, solderability is maintained for 1 year. For extended corrosion protection in marine environments, post-assembly conformal coating is recommended.

Key Specifications

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Assembly Guidelines for 30µm Wire

• Microscope Handling: The 0.03mm wire is comparable to a human hair (50-70µm). All manual assembly must be performed under ≥20* stereomicroscope using anti-static fine-point ceramic tweezers. Handle exclusively by the leads — never grasp the 12-turn coil body.
• Perpendicular Mounting: Position coil axis strictly at 90° to the microstrip RF trace. Parallel alignment creates parasitic mutual inductance that distorts S-parameters and degrades channel isolation.
• Minimum Lead Length: Trim leads to absolute minimum after soldering. Each excess millimeter adds ~0.8-1.0nH parasitic series inductance — significant relative to a 26nH target value.
• Solder Profile: SAC305 lead-free or Sn63/Pb37. Tip temperature ≤260°C, maximum 3-second dwell. The 30µm wire has minimal thermal mass — it heats rapidly and the enamel insulation degrades above ~300°C.
• Post-Solder Cleaning: Clean with ≥99% isopropyl alcohol under microscope. Verify no flux residue between turns — residual flux conductivity degrades Q factor above 10GHz.
• Fixation: After RF tuning, apply a micro-droplet of low-dielectric RF adhesive (Epotek H20E, εᵣ <3.0) to encapsulate 2-3 center turns. Verify S-parameters post-cure.

Applications

• SATCOM L/S/C/X/Ku-Band Receivers: The HALA1200303R covers all major SATCOM downlink bands from a single part number: L-band (1-2GHz, j163-j327Ω), S-band (2-4GHz, j327-j654Ω), C-band (4-8GHz, j654Ω-j1.31kΩ), X-band (8-12GHz, j1.31kΩ-j1.96kΩ), and Ku-band (12-18GHz, j1.96kΩ-j2.94kΩ). This decade-plus impedance range enables a single bias tee design to serve multi-band SATCOM terminals without inductor value changes between bands. Radiation-immune air-core construction ensures consistent performance in LEO, MEO, and GEO orbital environments where total ionizing dose accumulation occurs over multi-year mission lifetimes.
• GaAs/GaN RF Power Amplifier Bias Networks: 200mA DC handling with zero saturation supports gate and drain bias injection. Flat passband ensures consistent bias tee impedance across multi-band PA designs.
• High-Resonant Microwave Filters: 12-turn precision-wound geometry with minimal parasitic capacitance enables high-Q resonator elements in Chebyshev and elliptic filter topologies from 1.5-18GHz.
• Broadband Fiber Optic Interconnects: 26nH bias choke for laser driver and TIA bias injection in 25-56Gbaud optical transceivers. Flat passband ensures no parasitic resonances within the signal bandwidth.
• Wideband Test and Measurement: S2P Touchstone data per lot supports accurate de-embedding of inductor response from VNA measurements across 10MHz-20GHz.

Contact us for evaluation samples, S2P characterization data, or to discuss custom inductance values on the HALA120 platform.