Frequency response (discrete time Fourier transform) of a 3-tap boxcar filter.  To produce these plots, samples of the DTFT are obtained by computing the DFT of the zero-filled impulse response.  Alternatively, one can directly sample the closed form of the DTFT: H(ω)=13(1+e−jω+e−j2ω),{\displaystyle \scriptstyle H(\omega )={\frac {1}{3}}\left(1+e^{-j\omega }+e^{-j2\omega }\right),}  and plot the magnitude and angle of the samples.  (See File:MA2Amp_C.svg)
Note:  At the two frequencies where the magnitude goes to zero, there are phase discontinuities of π radians.  They are not artifacts of phase wrapping.  Rather, they indicate a sign inversion... multiplication by -1.  Since that is equivalent to an amplitude modification, it does not affect the filter's property of phase linearity.  An illustration of that can be viewed at File:Amplitude &amp; phase vs frequency for 3-term boxcar filter.svg.
Own work
original: Bob K vector version: Krishnavedala