This paper presents a planar microstrip wideband dual mode Band-Pass Filter(BPF) from 2 GHz to 3.4 GHz with a notched band at 2.62 GHz.The dual mode band-pass filter consists of a ring resonator with two quarter-wavelength open-circuited stubs at =90o and =0o,respectively.A square perturbation stub has been put at the corner of the ring resonator to increase the narrow stopbands and improve the performance of selectivity.By using a parallel-coupled feed line,a narrow notched band is introduced at the required frequency and its Fractional BandWidth(FBW) is about 5%.The proposed filter has a narrow notched band and a wide pass-band with a sharp cutoff frequency characteristic,the attenuation rate for the sharp cutoff frequency responses is 297.17 dB/GHz(cal-culated from 1.959 GHz with-34.43 dB to 2.065 GHz with-2.93 dB) and 228.10 dB/GHz(calculated from 3.395 GHz with-2.873 dB to 3.507 GHz with-28.42 dB).This filter has the advantages of good insertion loss in both operating bands and two rejections of greater than 16 dB in the range of 1.59 GHz to 1.99 GHz and 3.49 GHz to 3.98 GHz.Having been presented in this article,the measurement results agree well with the simulation results,which validates our idea.
This paper presents a miniaturized microstrip branch-line coupler with good harmonic suppression performance. The proposed coupler consists of four branch-line sections, each of which is loaded by open-circuit stubs both at the center and the two ends. This type of loading can realize size reduction and harmonic suppression. As an example, a proposed branch-line coupler operating at 1.0 GHz is designed, fabricated and measured. The results show that the proposed branch-line coupler occupies 67% size of a conventional one and has better than 20 dB suppression from 1.9 to 5.8 GHz. Furthermore, the high slop of the transition band ensures good selectivity of the coupler.
