# Detect incidence angle with an antenna array

Having an antenna array, how can we determine incidence angle of an incoming signal. I know it is related to the phase of the signal in each antenna but I only found information about how to send a signal in a specific direction or how to perform a spatial filter. My aim is to determine the incidence angle if it is possible.

– JRE
Commented Mar 2, 2015 at 13:37

The basic problem is that a directional antenna (one which emits in apparently one direction) will have side-lobes: -

Alternatively, shown as a 360 degree view: -

In other words, how do you determine that you are not receiving a large transmission in the direction of a side lobe compared to a lower power transmission incident on the main lobe? See this wiki article.

Other than the above, it is highly likely that the formula when transmitting will be identical for angle when receiving.

• Well then it becomes the problem of calculating the phase of each antenna right, because on emission we arange the phases so that it will take the direction we want. How can we detect the phase? Compared ro the other antennas. Square waves and logic gate? I can control the transmitter antenna too Commented Mar 2, 2015 at 14:44
• "Square waves and logic gate" - I don't follow you. Commented Mar 2, 2015 at 14:49
• A xor gate phase detector that detects the phase between square waveforms, or maybe a product detector that performs the product of two signals. Commented Mar 2, 2015 at 14:54
• Antennas work the same as receivers and transmitters. Thus the methods for steering an antenna to transmit in a given direction are the same as for steering the antenna to receive in that direction. Also sidelobes can be reduced by shading the array, i.e. adjusting the relative amplitudes of the array elements. There is a tradeoff between sidelobe level and the width of the main beam. Google Chebycheff shading for more information. Commented Mar 2, 2015 at 15:00
• @Mehdiasselman basically a 4 quadrant multiplier aka balanced mixer works at the analogue level. Commented Mar 2, 2015 at 15:05