As we all know, the circulator has a one-way transmission characteristic, the incident signal can pass smoothly (insertion loss is below 1db), and the reflected signal cannot be passed due to absorption by the absorption resistor (reflection loss can reach more than 60db). It is widely used for radio transmission, placed between the transmitter and the transmitting antenna, to prevent the antenna system from being mismatched due to the open or short circuit of the transmitting antenna, and damage to the post-power amplifier components of the transmitter due to standing waves .
Here I introduce to you a passive stepless power regulator made by using the unidirectional transmission characteristics of the circulator. In high-frequency power amplifier circuits, the reactance characteristics of PIN diodes are generally used to complete the output power adjustment. This power adjustment circuit has its shortcomings. When the power amplifier tube bias is adjusted, there is generally a certain Corresponding to the best excitation level, the output will reach the best state, if the excitation is too small, it will affect the signal-to-noise ratio; if the excitation is too large, it will cause nonlinear distortion. Passive power regulators made with circulators will not have this problem. It consists of two circulators connected in series, and an adjustable capacitor is added between the series wiring and ground, as shown in the figure. This passive power regulator is inserted between the transmitter and the transmitting antenna. The single circulator A plays the role of output power regulation, and the circulator B plays the role of isolation protection. The capacitor C is adjusted to make the circuit mismatch and the output Part of the power will become the reflected power absorbed by the resistor A. The capacity of C affects the size of the reflection, so the purpose of controlling the output power is achieved by adjusting the capacitor C. Thinking draft
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