Conical inductors for broadband applications

Inductors are an integral component in radio-frequency (RF) and microwave circuit design and are typically used as either impedance-matching elements or bias chokes. There are a wide variety of inductors designed to meet today's diverse applications. Using an inductor in a given application requires understanding its capabilities and limitations. One of the main limitations of an inductor is its self-resonance frequency or first parallel-resonance frequency (PRF), which affects the usable bandwidth. This application note presents a commercially available, very high performance inductor that can be used for very broadband UHF to millimeter-wave choking or bias feed applications. Conical inductors are capable of extremely broadband, resonance-free inductance in the microhenry range that can be used for low-loss RF choking and bias feeding. The conical shape combined with careful assembly to low capacitance attach pads allows usable bandwidth of these inductors from 10 MHz to 40 GHz. The conical inductor overcomes the limited bandwidth seen in standard SMT inductors by virtue of its conical design and careful assembly.