Hi baban79,
The AD8302 requires two input signals and outputs the magnitude and phase difference between them. You would not be able to test it with a single AD9834 evaluation board and use the part to slowly sweep the phase. You'll need a second signal source such as another AD9834 board to do what you want. If using two AD9834 boards, they would have to be synchronized similar to what's described in AN-587, Synchronizing Multiple AD9850/AD9851 DDS-Based Synthesizers and AN-605, Synchronizing Multiple AD9852 DDS-Based Synthesizers. You might also want to read AN-691, Operation of RF Detector Products at Low Frequency. Page 13 specifically talks about the AD8302.