True-time delay structures for microwave beamforming networks in S-band phased arrays

Temir, Kaan
True time delay networks are one of the most critical structures of wideband phased-array antenna systems which are frequently used in self-protection and electronic warfare applications. In order to direct the main beam of a wideband phased-array antenna to the desired direction; phase values, which are linearly dependent to frequency, are essential. Due to the phase characteristics of the true-time delay networks, beam squint problems for broadband phased array systems are minimized. In this thesis, different types of true-time delay structures are investigated for wideband phased array applications and a tunable S-band true-time delay network having delay over 1ns with high resolution is developed, designed, fabricated and measured. Lower-cost, smaller occupied area, digital/analog control mechanism and ease of implementation are the other features of the developed network. High delay values with high resolutions for wideband operation are achieved through the combination of several techniques; therefore the desired S-band TTD network is constructed with the synthesis of switched-transmission lines, constant-R networks and periodically-loaded transmission lines. Higher delay states are realized by the switched-transmission lines technique, while the method of constant R-network is used for the intermediate delay states. To increase the tuning flexibility, smaller delay states are accomplished by analog-voltage controlled periodically loaded transmission lines. A step-by-step procedure is followed during the design process of the S-band true time delay network. Firstly, each method used in the TTD network is analyzed in detail and developed for PCB implementation and the use of COTS components. Then, the designed structures are verified via linear and EM simulations performed by ADS2011®. After that, the effects of production tolerances are examined to optimize each design for S-band operations. Moreover, the designed structures are fabricated by using PCB technology and measured. Finally, a software code is developed in MATLAB to generate the overall cascaded network with the help of measured data.