Design of Interdigital‐Coupled Microstrip Line Bandpass Filters in the 28 and 38 GHz

This paper presents a 28‐ and 38‐GHz bandpass filter for 5G communication systems, which is implemented in an interdigital‐coupling microstrip line structure on a Rogers RT5880 substrate. The main resonator is composed of two U‐shaped units loaded with short cutoffs and stepped impedance stubs connected at the bottom of the U‐shaped structure. The design is effectively tuned to work in the 28 and 38 GHz bands of 5G NR. The LC equivalent circuit of the filter is converted to a physical size of the lumped element by using planar microstrip technology for physical implementation; the suppression in the stop band is lower than −20 dB. The proposed bandpass filter is designed as a microstrip line structure, which can be easily matched with the next level components due to its planar structure. Therefore, it is easier to apply in 5G devices and is suitable for 5G n257 and n260 applications.