A Novel Microstrip Dual-Band Bandpass Filter Design with Harmonic-Suppression

In this article, a novel microstrip dual-band bandpass filter is designed with harmonic suppression. The design employs source loaded feeding technique to act with double role: feeding the structure and eliminating harmonics at the same time. The employed method gives a solution to suppress harmonics without introducing large extension in filter dimensions which is a great advantage. The first undesirable harmonic was cleaned from the second passband of the filter and in addition the out-of-band attenuation is improved. A prototype is fabricated to validate the design and the filter dimension is 25.8x22 mm(2). The measured out-of-band attenuation levels are better than -20dB up to 10GHz. The measured insertion losses are better than 1.5dB at both passband center frequencies 2.44 GHz and 5.75 GHz. The measured results are in good agreement with the simulated ones and the proposed filter can be used for WLAN application.