A p-HEMT 920 ps True Time Delay Line Integrated Circuit for X-Band Imaging Radars

Abstract This paper presents a novel design of an X-band (812 GHz) 4-bit monolithic microwave integrated circuit (MMIC) type true-time-delay (TTD) line for wideband high-resolution imaging radar applications. The designed TTD line circuit offers a maximum time delay of 920 picoseconds (ps) using eight 115 ps delay elements and a distributed switching network. The unit delay line is synthesized using an artificial transmission line (ATL) circuit and implemented in a compact form of 18.5 mm2 using 130 nm gallium arsenide (GaAs) pseudomorphic high-electronmobility-transistor (p-HEMT) technology. The size of the switches and characteristic impedance of the transmission lines have been optimized to minimize insertion loss variation across different delay states while maintaining a flat delay response over a wide bandwidth. A basic 115 ps delay line cell is fabricated to prototype the circuit using GaAs-based MMIC processes. The final 920 ps chip layout simulation exhibited input and output return loss of better than 10 dB, insertion loss of 28±2 dB, and group delay variation of ±10 picoseconds over a 4 GHz bandwidth.