Novel and Very Compact Reconfigurable Bandpass to Lowpass/Bandpass Microstrip Filter with Wide-stopband Restriction for 5G Communications

This paper presents a novel and very compact planer reconfigurable bandpass to bandpass/lowpass filter covering the 0 to 1 GHz and 3.4 to 3.8 GHz spectrum for 5G applications. The microstrip filter employs three open-loop ring resonators with 50 Ω tapped lines for input and output ports. To achieve sharper cut-off frequencies, finite transmission zeros are successfully generated on the upper and lower edges of the 5G passbands. By utilization of the forth resonator between the input and output ports, Lowpass characteristics and reconfigurability properties are achieved. The cross-coupling coefficients between the resonators are optimized to resonate at the required frequency with proper bandwidth. The reported filter is simulated and optimized using CST software, and is designed on a Rogers RO3010 substrate with a relative dielectric constant of 10.2 and a very compact size of 10×7.9×1.27 mm3.