About High-Frequency Capacitors High-frequency capacitors are marketed as such due to their ability to retain ideal capacitive behavior up to very high frequencies. Capacitors will not exhibit ideal behavior up to the intended operating frequencies in RF systems, even if they are marketed as “high-frequency” or “RF” components.
Frequency characteristics of an ideal capacitor In actual capacitors (Fig. 3), however, there is some resistance (ESR) from loss due to dielectric substances, electrodes or other components in addition to the capacity component C and some parasitic inductance (ESL) due to electrodes, leads and other components.
In the capacitive characteristic region, the larger the capacitance, the lower is the impedance. Moreover, the smaller the capacitance, the higher is the resonance frequency, and the lower is the impedance in the inductive characteristic region. Our explanation of the frequency characteristics of capacitor impedance may be summarized as follows.
1. Frequency characteristics of capacitors The impedance Z of an ideal capacitor (Fig. 1) is shown by formula (1), where ω is the angular frequency and C is the electrostatic capacitance of the capacitor.
The typical fig-ure of merit for a capacitor at high frequencies combines these two effects as effective series resistance (ESR).Figure 2 shows how the values of reactance, Q and ESR vary with frequency. This data is for a Murata 100 pF chip capacitor in an 0805 package.
In addition to the actual capacitance value, there is a short list of specifications to look at when selecting capacitors for high-frequency systems. Case size: Smaller case sizes tend to have higher self-resonance, and they can access smaller capacitance values (see below).