Compact reflective microstrip phase shifter for traveling wave antenna applications

A varactor diode based microstrip phase shifter for 5.8GHz is presented. It is designed for use in microstrip traveling wave antennas where there is a strict limitation on the available space for the phase shifters. To meet all requirements, a reflective type phase shifter is chosen. Such a phase shifter includes a hybrid coupler. A compact branch line coupler is designed to make the phase shifter fit between the radiating elements in the antenna, while maintaining sufficient electrical performance. Phase shifters are designed with different types of stubs connecting the diodes to ground. A phase tuning range of 62/spl deg/ is measured for a phase shifter with parallel open stubs, and 92/spl deg/ with shorted stubs. Insertion loss is in both cases less than 0.6dB. A complete five-element array antenna is built and characterized. Measurements show beam scanning angles within /spl plusmn/32/spl deg/ from broadside.