Design and Analytical Modeling of a Complete Transmit Receive Module (TRM) for Applications in Active Microwave Sensors

Abstract

The most advanced microwave sensors “Phased Array Radars” have received considerable importance in commercial, medical and defense applications. Lot of research has been carried out regarding development of necessary constituents such as antenna array, transmit-receive module (TRM) and back end processing units. However the cost reduction, efficiency improvement, wide bandwidth, and fabrication technology for the TRM have been pursued as key research areas. Cost reduction techniques till date have focused on the use of high tech MMIC fabrication techniques. Literature also lacks in guiding a novice design engineer working on TRM in a cost effective manner. The work aims at software modeling of the TR Module constituents and also present a mathematical analysis of signals involved to enable a design engineer understand the constraints involved in designing such a system. Commercially available, low cost Laminate FR-4 has been used for the microstrip based designing in Advanced Design Systems (ADS). Due to the low operational frequency of Fr-4and constraints on the availability of components availability, 2.0 GHz has been used as design frequency. Regarding the FR-4 frequency response, a study has been conducted to study the deviation in simulation and measured results, which indeed confirmed the low frequency operation of the laminate. The modules designed include the high gain block (HGA), low noise amplifier (LNA), transmit/ receive switch and phase shifter. Designed for maximum achievable gain, the amplification blocks are based on Class-A topology with HGA of the cascade type and LNA being a single stage amplifier. The TR switch is based on series-shunt configuration of the single pole double xv throw (SPDT) switch as this topology achieves best results both in terms of minimizing insertion loss and maximizing isolation. Varactor diode based analog phase shifter has been designed for the phase manipulation purposes. The device achieves phase variations of the order of 150 degrees. Due to control limitations of the varactor tuning, reflection type 5 bit digital phase shifter has also been designed and the simulation results fall in close agreement to some of the commercially available modules. The scope of the thesis being limited only to the software modeling and simulations, the current write-up presents this aspect only. However due to ever increasing applications of this technology, the designed modules are being pursued to the implementation stage to realize a prototype level TR module.