Radio Frequency (RF) refers to the oscillation rate of alternating current (AC) voltage, current, or electromagnetic waves in electronic devices or media. RF is a very broad term, generally referring to frequencies above 20 kHz for AC voltage. However, in the context of RF applications and RF capacitors, RF typically refers to frequencies starting from a few MHz and above. Sometimes, the terms "RF" and "high frequency" are used interchangeably when referring to high-frequency components and applications.
The RF spectrum can be divided into multiple regions (bands) based on frequency ranges and target applications. The "high-frequency" range of RF includes the "microwave band," which spans from 300 MHz to 300 GHz, and the mmWave (millimeter wave) band, which starts at 28 GHz. As frequency increases, wavelength decreases, and the name "millimeter wave" comes from the wavelength of electromagnetic waves being measured in millimeters.
RF power amplifiers (PAs), cellular base stations (4G, 5G), wireless local area networks (WLANs), telecommunications networks, global positioning systems (GPS), keyless entry systems, Bluetooth, automotive V2X, security systems, powertrains, communication systems, etc.
This refers to the resistance of the capacitor, including losses due to the dielectric and electrodes. This is important because ESR is directly related to power dissipation in the form of heat. Higher ESR can cause the capacitor to overheat, so RF capacitors must have as low an ESR as possible at high frequencies.
Q represents the efficiency of the capacitor, indicating the ratio of energy stored in the capacitor to the energy dissipated as heat due to equivalent series resistance (ESR). Q is directly related to ESR, as lower ESR means higher Q (since they are inversely proportional). Due to their low capacitance and very low ESR, RF capacitors exhibit very high Q values. Therefore, RF capacitors are often referred to as high-Q capacitors.
Since RF capacitors are commonly used in tuning and impedance matching applications, stability of capacitance with respect to temperature is critical. Any change in capacitance with temperature can cause circuit detuning or mismatching.
The SRF indicates the point where the total impedance is no longer capacitive and begins to rise. This is known as the inductive region of the impedance curve and is a direct result of the capacitor's equivalent series inductance (ESL). For certain applications, it is necessary to operate below the SRF, so RF capacitors must have as high an SRF as possible.
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