The invention discloses a low-
noise amplifying
system with
constant noise and a
linear phase during programmable attenuation. A first bilateral switch, an attenuating and compensating module, a second bilateral switch and a
low noise amplifier are connected in sequence between an input end and an output end of the
system. The
system also comprises an adaptive digital programmable attenuation control module, wherein the adaptive digital programmable attenuation control module is applied to digital programmed control of amplitude attenuation, and used for performing
signal channel
adaptive control according to digital attenuation at the same time in order that a programmable attenuator keeps a system
noise level constant in the presence of attenuation and keeps low
insertion loss of a
signal channel in the absence of attenuation, and the influence of the
insertion loss of a programmable attenuation radio-frequency
electronic switch on a system
noise coefficient is lowered; the attenuating and compensating module is used for attenuating a
signal amplitude, and compensating for an electric length of a signal phase during signal attenuation through the radio-frequency
electronic switch by calculation of a frequency
wavelength in order to obtain the same
phase difference under different attenuation situations and compensate for phase deviations caused by programmable attenuation; and the
low noise amplifier is used for realizing
low noise amplification of signals.