What is null steering in an antenna array, and how does it help mitigate interference?

• A. Rotating the array to find a signal peak
• B. Adjusting relative phases and amplitudes to place a null opposite a jammer's direction
• C. Shifting to a different frequency band
• D. Increasing the transmitter power

Answer: (B)

Null steering is a beamforming technique used with antenna arrays to shape the pattern so there’s a deep minimum, or null, in the direction of an interference source. By adjusting the relative phases and amplitudes of each array element, the signals combine destructively toward the jammer while remaining constructive toward the desired signal. This virtual “null” reduces the received energy from the interference, improving the signal-to-interference ratio without needing to move the antenna or change frequency. It’s an adaptive method that relies on estimating the jammer’s direction and updating the element weights to maintain the null as conditions change. Other options don’t address the interference direction directly: rotating the array peaks a signal in some direction but doesn’t suppress interference; changing frequency sidesteps the problem but isn’t null steering; increasing power typically worsens interference.