Second harmonic suppression band-pass filter based on a modified 1st order microstrip coupled line

This paper presents a novel band-pass microstrip filter based on a 1
^st
order parallel coupled microstrip filter with minimum fractional bandwidth. One of the main characteristic of the proposed microstrip filter is its high rejection level at the 2
^nd
harmonic of the resonance frequency (f
0
). Electromagnetic simulations based on the method of Momentum indicates that the level rejection is controlled with the adjustment of the length of a microstrip line. Experimental results of a band-pass filter with resonance frequency of 1.8 GHz (f
0
) designed with the proposed technique are compared to the response of a typical 1
^st
order coupled line filter, achieving a level rejection of 20 dB at 3.6 GHz (2f
0
).