A true-time-delay phase shifter system for ultra-wideband applications

We present the design and realization of a 4-channel 3-bit phase shifter system for ultra-wideband beam steering applications in a frequency range of 0.5-1 GHz. Design considerations leading to a small, cost-effective realization with very good phase accuracy are described employing switched-line phase shifters. An additional degree of freedom is introduced in the phase shifters by means of a constant phase delay, which leads to a 3-bit configuration for 9 beams. The ring-like structures of the phase shifter exhibit parasitic resonances, which are easily or even un-avoidably excited in ultra-wideband systems. To mitigate phase errors caused by these resonances, the switch isolation needs to be very good, typically in a range of 30 dB or better. As a consequence, high-isolation pin diode switches are employed. Overall, very good RF properties are obtained.