usx
Member level 2
I've been working on a transceiver system with BGT24LTR11 chips at it's core and I was unable to achieve necessary signal to noise ratio. I want to know whether it's theoretically possible and for that I need to understand how the terms in the title all intertwined.
The following parameters/figure of merit I'm familiar with: Minimum detectable signal MDS = -84 dBm, Tangential Signal Sensitivity (MDS with SNR of 12 dB) = -72 dBm, peak radiated power = +30 dBm, receiver antenna = +30 dB
When I do link budget at 100 ft, with 24 GHz carrier frequency, I get the following:
+30 dBm -90 dB (FSL) - 90 dB (FSL) + 30 dB (receiver antenna) = -120 dBm into receiver (1 femto Watt)
Computed TSS/MDS above requires -72 dBm at the very least and I have -120 dBm only. This is where I can't quite connect non-linear mixer to power into receiver. I've refreshed my memory with nonlinear heterodyne detection but how do I relate it to power into the receiver/mixer?
Measurement I've made today only adds to the confusion: I've measured SNR for a single-hit non-fluctuating target (1 m^2 cross section) in dB as Vtarget_rms/Vnoise_rms
SNR: 13.6 dB at 50 ft, 10.8 dB at 100 ft, 7.9 dB at 200 ft
The results are perplexing because radar range equation tells that doubling of distance should decrease SNR by 12 dB, instead I observe 3 dB with each doubling, indicating that I'm not understanding something or there are crucial parameters I'm ignoring.
I realize that there are dozens of parameters I haven't indicated here, ADC, filtering, test conditions, analog circuitry, IF noise spectrum, etc. but the fundamental thing I want to know is if I have enough power to achieve required SNR, so I can start addressing the rest.
The following parameters/figure of merit I'm familiar with: Minimum detectable signal MDS = -84 dBm, Tangential Signal Sensitivity (MDS with SNR of 12 dB) = -72 dBm, peak radiated power = +30 dBm, receiver antenna = +30 dB
When I do link budget at 100 ft, with 24 GHz carrier frequency, I get the following:
+30 dBm -90 dB (FSL) - 90 dB (FSL) + 30 dB (receiver antenna) = -120 dBm into receiver (1 femto Watt)
Computed TSS/MDS above requires -72 dBm at the very least and I have -120 dBm only. This is where I can't quite connect non-linear mixer to power into receiver. I've refreshed my memory with nonlinear heterodyne detection but how do I relate it to power into the receiver/mixer?
Measurement I've made today only adds to the confusion: I've measured SNR for a single-hit non-fluctuating target (1 m^2 cross section) in dB as Vtarget_rms/Vnoise_rms
SNR: 13.6 dB at 50 ft, 10.8 dB at 100 ft, 7.9 dB at 200 ft
The results are perplexing because radar range equation tells that doubling of distance should decrease SNR by 12 dB, instead I observe 3 dB with each doubling, indicating that I'm not understanding something or there are crucial parameters I'm ignoring.
I realize that there are dozens of parameters I haven't indicated here, ADC, filtering, test conditions, analog circuitry, IF noise spectrum, etc. but the fundamental thing I want to know is if I have enough power to achieve required SNR, so I can start addressing the rest.