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Questions about building FMCW radar by using ADF4158 or ADF4351

Question asked by Nathan-Hu on Oct 14, 2012
Latest reply on Oct 22, 2012 by rbrennan



I am trying to build an FMCW radar sweep from 4GHz-8GHz. I am considering two plans. or if you have any other better plan, please let me know.


First, I am considering using PLL ADF4158 with an external VCO from 2GHz-4GHz, frequency multiplier (*2)  and an external loop filter. I plan to sweep the initial 2GHz-4GHz at 400 steps (5MHz/step). The total sweep time is expected less than 100ms. Am I realistic to expect the total sweep time (100ms)? Moreover, the wide band VCO tuning voltage ranges from 0 volts to 25 volts which exceeds the ADF4158 tuning ability (0-5V). Is there a solution for this? Can the active loop filter solve this problem? If so, can you give me an example of how the active loop filter look like? 


Second, I am also considering the synthesiser ADF4351 which integrated VCO already with an external loop filter and frequency multiplier (*2). This plan solves my tuning voltage problem as mentioned above, but when I downloaded the ADF4351 evaluation board software. I tried the sweep function. The software takes about 6 seconds to finnish the sweep from 2GHz to 4GHz at 5MHz/step. It seems too long for the PLL to lock the frequency. Can someone explain why it takes so long to sweep? Is there a solution to finish that sweep less than 100ms?


Thanks very much