Highly‐tunable and wide stopband microstrip bandpass filters

Abstract

This paper presents the design of a highly‐tunable single‐ended and balanced filter with improved upper stopband performance. The proposed filters are designed using a spurline and a U‐shaped stepped impedance resonator (SIR) with a varactor diode connected to the open‐circuited end. A spurline is introduced in both designs to achieve wide stopband performance by suppressing the higher‐order modes. The proposed filters have high tunable ranges (single‐ended: 2.35‐3.99 GHz; balanced: 2.39‐4 GHz), low insertion losses (IL) (single‐ended: 0.07‐0.2 dB; balanced: 0.21 to 1.1 dB) and wide upper stopband performance (single‐ended: 3.79f1 with a rejection level higher than 20 dB; balanced: 3.79f1 with a rejection level higher than 20 dB). Performance of both filters are experimentally validated by comparing the experimental results with the simulated ones. Both filters can cover most of the fifth‐generation (5G) wireless communication bands with different biasing voltages (capacitance). When both filters are compared with state‐of‐the‐art filters, the proposed filters are found to achieve high tunable ranges with low IL and wide upper stopband performance.

Miniaturized, Wide Stopband Filter Based on Shielded Capacitively Loaded SIW Resonators

“…The equation (1) illustrates how the size and operating mode of the square SIW cavity resonator determine the resonance frequency [22].…”

Tunable microwave amplitude equalizer based on spurline and tunable resonant cavities

“…The spurline is a simple, compact and coplanar microstrip defect structure planted in the traditional microstrip line, which is often used in filter and antenna design for harmonic suppression. 12,13 Figure 1A shows the structure of a spurline with an L-shaped slot. And it can be analyzed with the parallel-coupled transmission line network (as shown in Figure 1B).…”

A fully tunable filter based on the improved tubular structure

“…Filter was the key component of the wireless communication systems. [1][2][3][4][5][6][7][8] With the increasing application of wireless devices, the interference problems in receivers were becoming more and more serious. The tunable bandpass filters were widely used to suppress variable highlevel interference signals outside the pass band.…”