Compact absorptive microstrip bandpass filter with adjustable bandwidth and phase

In this letter, a compact absorptive bandpass filter (ABPF) with adjustable bandwidth and phase, low group delay (GD), high absorptive ratio, and low insertion loss (IL) characteristics is proposed. The presented ABPF consists of a bandpass section that is made of a quarterwavelength coupled-line and four stubs that are basically a lumped resistor in series with a short-circuited quarter-wavelength transmission line. The stubs not only have the function of absorption, but also have the advantage of adjustable bandwidth and phase. To verify the design concept and analysis formulas, an ABPF operating at 2.4 GHz is fabricated and measured, whose simulated and measured results are in good agreement.