Functions of Main Components of Spectrometer FSEA20

    Spectrometer FSEA20 is one of the indispensable measuring instruments in microwave measurement. It can measure and analyze the harmonic component, parasitic, intermodulation and noise sideband of signals intuitively. Therefore, it is widely used in microwave communication network, radar, electronic countermeasures, space technology, satellite ground station, EMC testing and other fields.
In order to dynamically observe the spectrum of the measured signal, most modern spectrum analyzers adopt sweeping superheterodyne receiving scheme. By sweeping the first local oscillator, the measured signal is mixed to obtain a fixed IF signal. After different bandwidth filters, two signals with smaller frequency difference can be observed. In the design of broadband heterodyne spectrum analyzer, in order to eliminate the interference of mirror image and multiple response, two schemes are often adopted: the first is to use pre-selector; the second is to use up-conversion. Because the frequency of the preselector is limited by the lower limit, the broadband spectrum analyzer is always divided into two bands: high band and low band. Low band adopts the scheme of high and medium frequency. It only needs a fixed low-pass filter instead of adjustable low-pass or band-pass to suppress the image. In high band, the input signal is pre-selected by pre-selector, which can effectively suppress the image. Fig. 1 is a simplified principle block diagram of HP859X series spectrum analyzer. The microwave signal is divided into two channels after input attenuator, which are input to high and low bands respectively.
In low band, the signal with frequency of 9 kHz~2.95 GHz is switched to the fundamental mixer part of the first converter (MXR1), and the first intermediate frequency F1IF (3.9214 MHz) is obtained. The second intermediate frequency F2IF (321.4 MHz) is obtained by the second converter. In high band, the signal with frequencies of 2.75 GHz to 22 GHz is switched to the preselector (YTF). The preselected signal is input to the harmonic mixer part of the first converter (MXR2), and the second intermediate frequency F2IF is obtained. The third intermediate frequency F3IF (21.4MHz) is obtained from F2IF converted by the third frequency converter. In this IF, the signal is processed so that the signal is selected by filters with different bandwidth, and then amplified linearly and logarithmically, demodulated, quantized and displayed digitally.