Research On X-band High Gain Amplification Chain

High-gain amplification chain key technologies include the following four parts : 30 dB automatic gain control(AGC), low-noise design, high gain amplification chain( greater than 75 d B), Microstrip gain equalizer.Since the analog AGC gain can be adjusted continuously, analog AGC suitable for microwave frequency, the closed-loop system is not sensitive to changes in the parameters of the system, so final choose the analog closed-loop AGC system; article is through the use of an adjustable attenuator to achieve the gain adjustment, first of output power by Wilkinson power divider into logarithmic detector detectors, detector voltage through an RC low-pass filter to filter out high frequency components, inverting amplifier output voltage to increase sensitivity, and then provide a comparison voltage threshold by a differential amplifier, and ultimately produce the appropriate voltage control adjustable attenuator to achieve gain adjustment, keep the output power constant. Design and manufacture of a closed loop to achieve the input power fluctuations 30 dB, output power is substantially constant amplitude modulation system, fill the research blank of the X-band AGC circuit. the whole link gain greater than 75 dB.To reduce the chain noise the first stage choose low noise devices, because AGC is composed attenuator, so AGC location quite critical, final choice on the deterioration of the system noise can neither avoid the saturation level of the third stage. This is the first time using a novel method to explore the circumstances under a high-gain noise figure, make up the high-gain noise noise figure analyzer test method deficiencies.Due to the high gain amplification chain, can easily lead to self-excited amplifier, so that the whole system is not working properly, even burning chips, it must avoid the generation of self-excited; herein by optimizing the design of the cavity and the entire circuit layout, interstage attenuator plus and appropriate to reduce the supply voltage of the amplifier, managed to avoid the self-excited high-gain amplifier cascade.Entire chain band flatness demanding(± 1dB), and high gain by the AGC system and constitute a plurality of cascaded amplifiers, resulting in a great fluctuation band, we use microstrip resonant unit constitutes an open notch unit, obtained by microwave network theory and equivalent circuit notch frequency and amount of attenuation, design and manufacture of microstrip minor equalizer, the equalizer input VSWR well and balanced accuracy of less than 0.5dB, ultimately the entire link with the gain flat.