A compact substrate integrated coaxial line bandpass filter with extended rejection bandwidth

In this article, a compact bandpass filter is proposed using substrate integrated coaxial line technology. An extended rejection bandwidth performance is achieved by introducing partially coupled λ/4-stepped impedance resonators. Based on the multilayer PCB process, a prototype has been fabricated in a 5.8 × 20 × 1.13 mm³ planar module, which is about 0.045 λ₀ × 0.16 λ₀ × 0.009 λ₀. Measurements confirm that the proposed filter centered at 2.35 GHz is realized with a very low insertion loss of 0.96 dB, and a 27-dB rejection bandwidth up to 5.82f₀. The filter features compact size, low crosstalk, low loss, and high density integration ability.