A Controllable Planar Wideband Bandpass Filters using the Combination of Microstrip and Substrate Integrated Waveguide Structure

This paper presents a planar wideband bandpass filter using a combination of microstip structure and substrate integrated waveguide (SIW). To control the bandwidth of the wideband bandpass filter, the proposed filter is designed by cascading structure between the high pass filter and low pass filter characteristic. The SIW, which is a high pass filter characteristic, is designed to determine the lower cutoff frequency. Then, the microstrip, which is a and low pass filter characteristic, is designed to determine the higher cutoff frequency. To verify the concept of the proposed filter design, three wideband bandpass filters, e.g., 2–5 GHz, 3–5 GHz and 4–5 GHz, have been simulated and achieved, resulting in fractional bandwidth of 80%, 50% and 20%, respectively. To prove the simulated results, the 4–5 GHz wideband bandpass filter is selected to fabricate on the low-cost FR-4 substrate with a thickness of 1.6 mm. The results show that measured and simulated results are agreed well in the reflection and insertion responses.