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GATE 2023 BM – Question 17

Signals and Systems · Digital Filters · 1 mark · Multiple choice

A two-tap FIR filter has impulse response h[0]=h[1]=1 and all other samples zero. What is the magnitude of its DTFT for |ω|≤π?

  1. $2|\cos\omega|$
  2. $2|\sin\omega|$
  3. $2|\cos(\omega/2)|$
  4. $2|\sin(\omega/2)|$

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Correct answer: (C) $2|\cos(\omega/2)|$

Explanation

H(eʲω)=1+e⁻ʲω=e⁻ʲω/²×2cos(ω/2). The complex exponential has unit magnitude. Taking absolute values therefore gives 2|cos(ω/2)|, option C. In particular the DC gain is two and the response vanishes at π.

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