Definition

Loss tangent (tan δ) is identical to dissipation factor (Df), measuring the ratio of energy dissipated to energy stored in a dielectric per AC cycle. It's expressed as the tangent of the phase angle between voltage and current in a capacitor made from the material. Lower loss tangent means less signal attenuation at high frequencies. Standard FR-4 has tan δ around 0.02; low-loss materials like Rogers RO4003C achieve 0.0027; PTFE materials can be below 0.001. Loss tangent typically increases with frequency and temperature.