At RF frequencies of about 10 MHz and higher, the effective impedance of a practical ground connection is primarily dominated by which behavior?

Introduction / Context:
RF grounding is critical for stable circuits, low noise, and EMC compliance. However, a real “ground” is made of straps, vias, wires, chassis seams, and earth bonds that exhibit frequency-dependent impedance rather than an ideal zero-ohm reference.

Given Data / Assumptions:

• Frequency regime: ≥ 10 MHz (HF into VHF and above).
• Typical ground realized by wires or straps with finite length and geometry.
• Nearby conductors introduce stray capacitances.

Concept / Approach:

The impedance of a conductor with length l and inductance L behaves as Z ≈ jωL at RF, often dominating over ohmic resistance R. Even a few centimeters of wire can have tens of nanohenries; at 10–100 MHz the reactive term jωL becomes large relative to R, making the ground connection predominantly inductive.

Step-by-Step Solution:

Verification / Alternative check:

Vector network analyzer measurements of ground leads show rising inductive reactance with frequency. Using ground planes and via stitching significantly lowers impedance, confirming inductive dominance of thin leads.

Why Other Options Are Wrong:

• Resistive: True at low frequency; not dominant at tens of MHz.
• Capacitive: Stray capacitance exists, but lead inductance dominates for simple wire grounds.
• Exactly half resistive/half capacitive: Not generally true; depends on geometry and frequency.
• Ideal ground: No physical conductor is ideal at RF.

Common Pitfalls:

Using long skinny ground leads; forgetting loop area; neglecting return-current paths. Prefer ground planes, multiple vias, and short connections to minimize inductance.

Final Answer:

Inductive