Influence of Image Frequency Rejection on RF Front-End Noise Figure

In this paper, the influence of the image frequency rejection on the noise figure of the RF front-end is analyzed. The noise powers in primary down conversion system with or without image frequency rejection are calculated. It is shown that the image frequency rejection can improve the noise figure of the system by about 3 dB in the primary frequency conversion system. For the output noise power of RF front-end, the calculation shows that when the image rejection reaches 20 dB or more, the output noise is very small, almost negligible. An example of Ka-band secondary frequency conversion RF front-end is presented. The test results are consistent with the theoretical analysis.