Design of X-band substrate integrated coaxial line type 6.2 ns true-time delay line

Wideband phased arrays for Radar, EW, and Communication system utilizes true-time delay (TTD) lines to overcome beam squint issues associated with conventional phased arrays steered over large scan volume. A long-range X-band high-resolution (10 cm) imaging radar for squint-free-beam scanning over $ \pm 60^0 $ ±600 in both the planes of array need long-time delay of few nanoseconds. Design of such long-time delay lines to fit within multiples of inter-element spacing of an array or at the transmit–receive module (TRM) level is quite challenging. A novel design of a 5-bit programmable time delay line using substrate integrated coaxial line (SICL) structure to offer a 6.2 ns maximum delay in step of 0.2 ns over 8–12 GHz is presented in this paper. The designed multi-layer RF PCB based TTD line has demonstrated delay flatness within 1 $ \% $ % of an average delay for each state in a compact size of $ 45.5 \times 34.5\,{\rm mm}^2 $ 45.5×34.5mm2 over 4 GHz bandwidth.