Bladerf micro phase coherency for 4 channel coherent reception

[venky0108]

Hi,

I am trying to setup 4 channel phase coherent receiver with two Bladerf A4 SDR boards for Angle of Arrival(AoA) estimation setup. In the setup process following setup are performed:

1)Clock In of Board 1 & Clock out of Board 2 are connected for sharing the clock
2)Sample synchronization through Trigger functionality.Board 1 is made trigger master and Board 2 is made Trigger slave, J51-1 & J51-3 of both boards are connected
3)Four RX channels of SDR boards is fed with same signal through power divider.

Observations:

1)Frequency offset of the four channels are measured and they are same

Channel Mean Standard Deviation Min value Max Value range
Freq offset ch1 -478.7109375 38.80481412 -585.9375 -366.2109375 219.7265625
Freq offset ch2 -475.78125 38.89318775 -585.9375 -366.2109375 219.7265625
Freq offset ch3 -478.7109375 38.80481412 -585.9375 -366.2109375 219.7265625
Freq offset ch4 -475.78125 38.89318775 -585.9375 -366.2109375 219.7265625
Freq offset ch1 -476.953125 42.06525257 -585.9375 -366.2109375 219.7265625
Freq offset ch2 -472.8515625 38.76055174 -512.6953125 -366.2109375 146.484375
Freq offset ch3 -476.953125 42.06525257 -585.9375 -366.2109375 219.7265625
Freq offset ch4 -472.8515625 38.76055174 -512.6953125 -366.2109375 146.484375
Freq offset ch1 -472.8515625 39.8523658 -512.6953125 -366.2109375 146.484375
Freq offset ch2 -472.8515625 41.95083356 -512.6953125 -366.2109375 146.484375
Freq offset ch3 -472.8515625 39.8523658 -512.6953125 -366.2109375 146.484375
Freq offset ch4 -472.8515625 41.95083356 -512.6953125 -366.2109375 146.484375


2)Phase offset between channel 1 & 2, 1&3 , 1& 4, 3 & 4 are measured. Phase offset is not same with respect to channel .

Channel Mean Standard Deviation Min value Max Value range
phase offset ch1 & ch2 -138.96 2.144388025 -141 -128 13
phase offset ch1 & ch3 145.888 891.5005617 -4040 4011 8051
phase offset ch1 & ch4 119.64 901.8573759 -4002 4049 8051
phase offset ch3 & ch4 33.856 1.129275874 25 34 9
phase offset ch1 & ch2 -138.392 2.18319399 -140 -128 12
phase offset ch1 & ch3 8.896 684.6637694 -3582 3904 7486
phase offset ch1 & ch4 74.288 682.0492629 -635 3944 4579
phase offset ch3 & ch4 34.016 0.85775521 25 35 10
phase offset ch1 & ch2 -136.304 3.427474872 -140 -127 13
phase offset ch1 & ch3 -70.096 791.8313702 -4096 4197 8293
phase offset ch1 & ch4 -149.824 774.8225094 -4192 603 4795
phase offset ch3 & ch4 34.096 0.294591242 34 35 1

ch1 & Ch3 , Ch1 & Ch4 phase offset are random with huge standard deviation