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I am trying to determine the thermal noise for a Frequency modulated continuous wave radar. The radar is the TI IWR6843 chip. Currently, I am using the radar to transmit a chirp with a bandwidth of 4 GHz.

I want to calculate the thermal noise power. For the IWR6843 chip, the noise figure is stated as 12 dB. The only other information I need to calculate the noise power is the bandwidth of the receiver. Attached below is an image of the receive subsystem Receive Subsystem

According to the IWR6843 manual, the IF bandpass filter supports bandwidths up to 10 MHz. My question is, which bandwidth should I use for the noise calculation, 4 GHz or 10 MHz? I believe that 10 MHz is correct, but I wanted to double-check. My main concern is that at the output of the mixer, there should be many frequencies present, which are harmonics from multiple frequencies being mixed together, including the noise. Many of these harmonics will be filtered out, but I wasn't sure if it was possible for the mixing process to increase my noise density.

Thank You

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The 10 MHz bandwidth is correct. The bandwidth of 4 GHz is the instantaneous bandwidth that is being put into the chirp in order to achieve a fine range resolution. Since this is FMCW, all of the returns are dechirped into sinusoids, which have a bandwidth requirement much less than the waveform's, but still achieve the same range resolution.

I have an answer "proving" how the range resolution is maintained in FMCW here.

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