A 38 GHz integrated quasioptical mixer array for use in a millimeter wave imaging system.

摘要

There is great interest in developing imaging systems at millimeter-wave frequencies due to the natural atmospheric propagation windows that occur in this range and the resolution that can be achieved due to the short wavelengths. In particular, 35 GHz and 94 GHz are two frequencies of interest that provide minimums of atmospheric attenuation and allow for good imaging resolution in practical systems.; This work describes the development of a proof-of-concept 16-element imaging array designed to operate at 38 GHz. The focus of this effort was the development of a 16-element array of mixers and the integration of half-wave "bow-tie" dipole antennas with each mixer in the array. The design was aimed at proving the concept of a fully monolithic gallium-arsenide (GaAs MMIC) 94 GHz version of the same design by building a prototype at 38 GHz using a quasi-monolithic approach.; A single mixer was first developed which allowed for the characterization of the design both with and without bias to study the effects of pump power level. The data obtained from the individual mixer allows for extrapolation of the mixer performance to a future design using monolithic low barrier-height mixer diodes.; In order to characterize the mixer design, E-plane (finline) components were developed as interfaces to existing laboratory equipment. A unique E-plane balun was developed in order to provide a balanced RF input to the mixer. Surface mount devices similar to those available in existing GaAs MMIC processes were purchased and bonded to a thin, high dielectric constant circuit board to simulate the monolithic design.; The assembly was tested in an RF irradiated environment at 38 GHz and the resulting 10 GHzIF outputs from the sixteen mixers were individually measured with a spectrum analyzer, and results showed good uniformity of conversion across the length of the array. The radiation pattern of the array was measured and the sensitivity of the receiver was measured and was found to be comparable to the expected value.; The physical geometries employed will scale well to a fully monolithic version of the same design for use at 94 GHz. This work proves that a quasi-monolithic approach can be very useful in proof-of-concept prototyping work for microwave and millimeter wave circuit design.