Directional Full-Duplex RF Booster for 2450 MHz ISM Band
A directional repeater system with simple architecture composed of wideband receive and transmit antennas, a high gain low-power amplifier, and a bandpass filter is proposed for the 2450-MHz ISM band. The repeater system does not require down-conversion and up-conversion with frequency translation and does not rely on any operational protocol to manage users. As a result, the repeater (RF booster) can support all users, channels, modulation themes, and devices simultaneously. Close to 70 dB of isolation between the Tx and Rx antennas over the entire band (~100 MHz) is achieved for a compact structure with lateral dimensions of 8 cm $\times $ 12 cm and thickness of 1 cm. The isolation between the Tx and Rx antennas is achieved using polarization mismatch between orthogonal double-stack patch antennas and a novel two-element Rx antenna whose elements are appropriately located with respect to the Tx antenna to cancel the signal leakage from the Tx antenna to the Rx antennas. Two types of repeaters, one utilizing only the ground plane and polarization mismatch, and the second using the two-element Rx antenna in addition to polarization mismatch, are fabricated and tested in different environments. It is shown that more than 30 dB improvement in coverage can be achieved.