LNB, i.e. Low Noise Block, generally called high frequency head, is a device installed at the reflection focal point of satellite receiving antenna to amplify the satellite signal and down convert the frequency of it.
LNB now is generally designed using discrete components, including high frequency (HF) amplifier, passive band-pass filter, Dielectric Resonator Oscillator (DRO), frequency mixer, mid-frequency (MF) amplifier, voltage stabilizing unit, bias circuit, negative voltage generating circuit, 22 kHz frequency detection circuit, etc., as shown in FIGS. 1 and 2.
The shortcomings of the traditional scheme are as follows:
1. Dielectric Resonator Oscillator (DRO) has characteristic of larger temperature drift, therefore, the frequency stability of LNB is not sufficient.
2. The signal out of band, especially the signal of minor image portion, needs to be filtered with the passive band-pass filter to improve the noise performance of LNB. Band pass filter is featured with attenuation and occupies the valuable printed circuit board (PCB) area.
3. As the size of LNB is generally small, large quantity of discrete components are not convenient for repairing manufacturing and debugging.