Compact Metamaterial Based 4 × 4 Butler Matrix With Improved Bandwidth for 5G Applications. - Arshad Karimbu Vallappil; Mohamad Kamal A. Rahim; Bilal A. Khawaja; Muhammad Naeem Iqbal (IEEE Access, 2020)

Butler Matrix Based Beamforming Networks for Phased Array Antenna Systems: A Comprehensive Review and Future Directions for 5G Applications. - Arshad Karimbu Vallappil; Mohamad Kamal A. Rahim; Bilal A. Khawaja; Noor Asniza Murad; Mohammed Gajibo Mustapha (IEEE Access, 2021)

A Miniaturized Metamaterial-Loaded Switched-Beam Antenna Array System With Enhanced Bandwidth for 5G Applications. - Arshad Karimbu Vallappil; Mohamad Kamal A. Rahim; Bilal A. Khawaja; Muhammad Naeem Iqbal (IEEE Access, 2024)

RFiDAR: Contactless RFID and Radar Data Fusion for Enhanced Human Activity Recognition. - Muhammad Zakir Khan; William Taylor; Muhammad Usman 003; Jawad Ahmad 001; Naeem Ramzan; Bilal A. Khawaja; Arshad Karimbu Vallappil; Muhammad Imran 008; Qammer H. Abbasi (IEEE Internet Things Mag., 2025)

Compact low-profile multiple-input multiple-output (MIMO) antenna for portable devices in next-generation 5G wireless networks. - Nathirulla Sheriff; Arshad Karimbu Vallappil; Sharul Kamal Abdul Rahim; Bilal A. Khawaja; Tan Kim Geok; Adnan Iftikhar; Muhammad Uzair (Wirel. Networks, 2025)