Compact wideband microstrip bandpass filter for IF stage of millimeterwave systems

This research contribution highlights the design process of a compact wideband microstrip bandpass filter for IF stage of Millimeterwave Systems. The composite BPF technique is utilized in this publication for its wideband and compact nature. The filter structure consists of series hi-low impedance microstrip transmission lines and shunt shorted high-impedance stubs. The lengths and widths of these microstrip sections are optimized to obtain the desired bandpass filter characteristics. Additionally, 50 percent size reduction is achieved by the application of meandered structure to the high-impedance lines and stubs. The bandwith of the filter is 2.3GHz with pass band of 1-3.3GHz. The insertion loss of the filter is less than 1.2dB and return loss is better than 10dB in the 1 - 3.3GHz pass band. The 3-dB fractional bandwidth of filter is 120%.The upper out-of-band rejection is 25dB at 4.5GHz. The size of the filter is 1200mil × 440mil which is extremely small at the operating frequency band.