A single grooved coupled line bandpass filter with improved pass band response and first harmonic suppression is described. The suppression of the first spurious harmonic was done by using rightangle triangle grooves in the middle of each of the coupled-microstrip lines that construct the bandpass filter. As the number of grooves increase as the shift in the operating frequencies increase also, so it is suitable to use less numbers of grooves as possible. A three stage bandpass filter using coupled-microstrip lines was designed, simulated, and realized to illustrate this idea. The simulated results illustrate a good performance for right-angle triangle groove over the corresponding rectangular groove. The measured S-parameters measurement of the realized bandpass filter shows the suppression of the second resonance frequency and less shift in the center frequency