| A monolithic microwave integrated circuit (MMIC) is a microwave circuit in which the active and passive components are fabricated on the same semiconductor substrate. MMIC, having advantages of small size, light mass, high reliability and excellent reproducibility, finds use in a variety of microwave system, especially in airborne radar and space applications. The phase shifter, as a important component in transmit/receive (T/R) module of phased array radar, steer the electronic beam for inertialess scanning. With the rapid development in MMIC technology, T/R module is mostly realized in monolithic circuit. For phased array radar's significant usage in military field, the developed countries make intense research and development activity in monolithic circuits and compete hard with each other, while making rigid limitation on export of MMIC technology and circuits to our country, especially of MMICs that can be used in T/R module. Although we made great efforts on research and development of various MMIC circuit chips including phase shifter in the past decade of years, the performance of phase shifter couldn't meet application requirement yet. So it has great practical significance to research on phase shift mechanism, develop MMIC technology and do research and development works on monolithic phase shifter.In this paper, firstly we analyzed the basic phase shift mechanism and various basic phase shifter circuit forms, specially devoted to the circuit analysis and design aspects. It provides the theoretical basis for circuit topology selection, design and optimization of the phase shifter. On the basis of theory analysis of phase shifter, we designed and fabricated the X-band 5-bit monolithic phase shifter circuit on the GaAs MMIC product line.The phase shifter circuit use GaAs MESFET switches as control devices. We analyzed the dependence of equivalent circuit parameters of MESFET switch on material and device structure. For modeling, we designed and fabricated six set of MESFET switches with different gate width, then measured their performance and extracted switch model parameters. MESFET switch database corresponding to the MMIC product line is then established, and using the dependence of switch model parameters on gate peripheral we can attain the MESFET switch performance with any gate width through parameters scaling.The phase shifter circuit consists of five digital bits corresponding to differential phase shifts of 180, 90, 45, 22.5 and 11.25 cascaded in a linear arrangement. The three lowerphase shift circuits are of loaded-line type, in which the 11.25 phase shift bit use a single loaded-line configuration. The 90 and 180 phase shift bits are of reflection type, using Lange coupler to realize the separation between the incident and reflection signals. According to process rules of the GaAs MMIC product line, we properly designed the circuit layout. In order to reduce the overall chip size, the transmission lines are folded with sufficient spacing to avoid interline coupling. The Lange couplers are also folded to keep the 90 and 180 bits' sizes similar to other phase shift bits' sizes. All the individual circuits are designed to interface to 50. Using process control monitor (PCM) to control process parameters, we fabricated the monolithic phase shift circuit chip. With HP 8510 vector network analyzer (VNA) we measured the phase shifter' microwave performance. Over the 9-10GHz frequency band, the fabricated phase shifter's insertion loss (IL) is 7.3+ 1dB and the input/output voltage standing wave ratio (VSWR) less than 1.6, while its worst root mean square (RMS) phase error is 5?in the working frequency bandwidth. By analyzing the phase shifter performance, it can be found that reflective type phase shifter could be used in wide bandwidth application and the performance has met the design specification.
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