Pretty small low-cost bandpass filter using a single square open-loop resonator with a centered stub for WLAN/Bluetooth/ZigBee/RFID and ISM band applications

In recent years, microwave filtering technologies have known great advancement and wide employment in wireless communication systems, necessitating the development of miniaturization techniques to respect the size limitation in wireless communication devices and reduce the cost, in order to satisfy the consumer and be more competitive. Accordingly, the design of a microwave filter is chosen based on its electrical performance, size, and manufacturing price. Therefore, it is necessary to make a good compromise between the mentioned criteria to satisfy the industrial requirements. This paper proposes a small and inexpensive bandpass filter (BPF), where the proposed structure is carefully constructed over a low-price FR4 Epoxy substrate with a full dimension of (17.6 × 9 × 1.6) mm³. The proposed filter offers good electrical performance in terms of reflection coefficient (S₁₁), insertion loss (S₂₁), Voltage Standing Wave Ratio (VSWR), and selectivity. A filter prototype is fabricated and tested to affirm the simulation results. Consequently, the measured results show a good agreement with the simulation, proving the suitability of the proposed filter for different wireless applications, including WLAN, Bluetooth, ZigBee, RFID, and ISM bands.