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One of the major applications for ferrite junction components is in base station amplifiers. Each amplifier module may include several isolators, which typically provide mismatch protection. In the case of the isolator placed between the power amplifier and the antenna, the primary purpose is protection against high levels of reflected power. The form factor of these isolators is a drop-in, in which the large termination chips attached to the isolator base plate are capable of absorbing up to 200 W average power. Situated after the power amplifier, the isolator must handle the full RF power of about 100 W or more. Since each base station amplifier may have several channels, nonlinear distortion will present a problem. Various linearization methods are used to limit distortion in the amplifier, but they do not help reduce distortion in the isolator (except perhaps crest factor reduction). The ferrite materials used in isolators are fairly linear up to a few watts. Above this level, the most significant nonlinear effect is third-order intermodulation distortion (IMD). This is the result of two (or more) signals of different frequencies (F₁ and F₂) interacting in a region with nonlinear transmission properties.¹ The third-order distortion products that may interfere in the receiver pass band are the difference frequencies 2F₁–F₂ and 2F₂–F₁. Higher order distortion products are usually several decibels lower in amplitude. If third-order products are reduced, the higher order products should also drop by a similar amount. IMD is measured as the ratio in power levels between the distortion signal and the input signal, in units of dBc. Typical IMD levels for isolators are approximately –80 dBc for two signal tones of 20 W each. Usually ferrite isolators obey the theoretical behavior for varying the input signals, that is, for each 1 dB change of input level, the IMD level changes by 2 dBc.