A Compact Meandered Monopole Antenna with Controlled Frequency Reconfiguration for LoRa IN865 and AS923-3 Bands

Abstract

The global demand for compact and low power IoT devices is rapidly increasing, particularly in countries like India and those in South Asia. Low Power Wide Area Networks (LPWANs) equipped with LoRa antennas are well-suited to address this need. Most existing LoRa antennas are multiband microstrip designs with the operating bands usually limited to one of the LoRa bands AS923-1, EU868, IN865, and RU864, along with other sub-GHz ranges. In this paper, we present a compact, low-cost, reconfigurable Meandered Monopole antenna (MMA) designed to operate only in the LoRa IN865 and AS923-3 bands. To keep the antenna compact and economical, a meandered monopole structure has been employed with an RF PIN diode on an FR-4 substrate. Unlike existing designs, the proposed antenna is accurately tuned and is dedicated solely to the LoRa frequency band. The design was simulated using CST Microwave Studio (CST-MWS) and validated through prototype measurements. Furthermore, a unique lumped equivalent circuit model was developed using Keysight ADS. The proposed antenna has shown good pattern stability and achieves a gain of 2.07 dBi. With the diode in the active (ON) state, the antenna resonates at 866.2 MHz (IN865 LoRa Band) with an S11 of -17.22 dB and Bandwidth of 19 MHz. In the inactive (OFF) state of the diode, the antenna resonates at 916.5 MHz (AS923-3 LoRa Band) with an S11 of -15.24 dB and Bandwidth of 22 MHz. The results confirm that the proposed antenna provides reliable
reconfigurability for LoRa applications in the specified bands.