Design and integration of a high-order hairpin bandpass filter with a spurious suppression circuit

RF and microwave filters are an undeniable part of electronic and telecommunication systems and are widely used in receivers, tuners, up/down converters, etc. In this paper, the design procedure and results of an 11-order hairpin band pass filter, with Cauer-Chebyshev response designed at C band is presented. The filter is integrated with a harmonic suppression circuit based on quarter-wavelength short stubs. The short stubs demonstrate a good quality short circuit at harmonic frequencies. Also, because of quarter-wavelength transformer, it present open circuit at passband frequencies and had no significant impact with it. The total circuit has about 1 GHz 3dB-bandwidth at the center frequency of 4.15 GHz (3.65 GHz to 4.65 GHz) which is an ultra wide band for hairpin filters. The return loss of better than -12.3 dB and the insertion loss of 2.2 dB in pass-band are achieved. Also the rejection of filter at 5 GHz is -59.5 dB demonstrating that the stopband response of the filter is excellent. Finally with regard to short-stubs, the harmonic spurious suppression of more than 40 dB is achieved to suppress undesirable frequencies.