EXPERIMENTAL STUDY OF THE NOISE FIGURE OF THE DIGITAL RECEIVER WITH UNDERSAMPLING UP TO 18 GHZ
Due to the expansion of the frequency range and the number of emitting radio-electronic means in many scientific and technical fields, performing a wideband analysis of the signal environment becomes necessary. For this, one can use a multichannel undersampling digital receiver (USDR). Such a receiver estimates a signal carrier frequency by unfolding its spectrum in each channel from the first Nyquist zone to the subsequent zones. The unfolded spectrum components in each channel are then compared with each other. The goal is to find the frequency at which the components from all channels coincide. This frequency is assumed to be the true carrier frequency of the received signal and not its alias. In this work, we investigated the USDR prototype, which does not contain a low-noise amplifier (LNA) at its input. Therefore, the prototype’s noise figure (NF) is high and reaches 41 ... 52 dB. However, using an input LNA can significantly reduce the total NF of the device. At the same time, one should bear in mind that with an increase in the LNA’s gain above a certain value, the receiver’s dynamic range begins to rapidly narrow. The resulting frequency dependence of the NF in the 18 GHz band has significant non-uniformity (11 dB). Therefore, when creating wideband analyzers to reduce the sensitivity variation, it is advisable to use equalizers and amplifiers with compensating frequency dependences of the NF and gain. Using the USDR with characteristics similar to those obtained for the prototype, we can achieve a -125… -116 dBm sensitivity for the wideband analyzer. This sensitivity is high enough for the considered 18 GHz frequency band.