Miniaturized Low Pass Filter Using Modified Unifolded Single Hairpin-Line Resonator for Microwave Communication Systems

A compact low pass filter (LPF) using single folded stepped impedance hairpin resonator is proposed. It consists of an internally coupled-line section which acts as a phi-connection capacitors, and a transmission line which act as a parallel connected inductors. Together, an elliptic low pass filter configuration is achieved. The internal coupled line´s length is tuned to adjust the cutoff frequency as well as the spurious frequency response. The length of the inductive transmission line section is maintained. Simulation investigations revealed that as the coupled line length increases, the magnitudes of the spurious frequency responses reduced and the locations were shifted to higher frequencies. Hence, wider stopband bandwidth area is achieved. It is also interesting to note that small coupled line extension introduced at the original coupled line has improved the profile further. Using electromagnetic simulation software, it is shown that a compact LPF with 2 GHz cutoff frequency and band reject of 3 GHz to 10 GHz has been successfully designed and simulated