# Higher side lobe levels in linear array beam pattern

I am working on beam forming of high frequency (>400 KHz) linear array for imaging sonar. I have gathered sensor data of 80 channel linear array sub merged halfway in 8 m deep water tank with a transmitting probe 6 m away from it at same depth. I recorded multiple pulses and perform offline analysis on it. The problem i am facing is very high side lobe levels in a beam pattern developed using recorded data. Can any one kindly guide me what could be possible causes of higher side lobe levels?

Thanks & Regards

Nauman

1. Array element spacing. To prevent the presence of grating lobes your element spacing needs to be less than $$\frac{\lambda}{2}$$. You haven't indicated the bandwidth of your signal, so I'll use the 400 KHz you gave and assume a speed of sound to be 1500 m/s. Then your spacing needs to be less than $$\frac{1500}{2\cdot 400\cdot10^3}=1.875$$ mm. Of course you should use the highest frequency of signal of interest for this calculation.