Abstract
AbstractRealizing packaged state-of-the-art performance of monolithic microwave integrated circuits (MMICs) operating at millimeter wavelengths presents significant challenges in terms of electrical interface circuitry and physical construction. For instance, even with the aid of modern electromagnetic simulation tools, modeling the interaction between the MMIC and its package embedding circuit can lack the necessary precision to achieve optimum device performance. Physical implementation also introduces inaccuracies and requires iterative interface component substitution that can produce variable results, is invasive and risks damaging the MMIC. This paper describes a novel method for in situ optimization of packaged millimeter-wave devices using a pulsed ultraviolet laser to remove pre-selected areas of interface circuit metallization. The method was successfully demonstrated through the optimization of a 183 GHz low noise amplifier destined for use on the MetOp-SG meteorological satellite series. An improvement in amplifier output return loss from an average of 12.9 dB to 22.7 dB was achieved across an operational frequency range of 175–191 GHz and the improved circuit reproduced. We believe that our in situ tuning technique can be applied more widely to planar millimeter-wave interface circuits that are critical in achieving optimum device performance.
Highlights
Monolithic microwave integrated circuits (MMICs) often require a transition from their planar form to a waveguide in order to effectively couple input and output signals. This is usually achieved through the application of a waveguide-to-microstrip (WG-MS) transition that transforms the impedance of the waveguide channel to the optimal conjugate impedance of the MMIC input or output port
Using WG-MS transitions at frequencies higher than 100 GHz presents three particular challenges: (1) due to the uncertainties in pre-packaging on-wafer probing, it is often difficult to determine precisely the optimal impedance required by the MMIC [4, 5]; (2) simulating the interaction between the MMIC and the WG-MS transition is highly complex and prone to error; (3) once installed, the fabricated transition cannot be tuned in order to optimize the device packaged performance, i.e. to correct for the errors that may arise from 1 and 2
In order to demonstrate our in situ tuning technique, we designed and fabricated a WG-MS output transition suitable for packaging with a state-of-the-art low noise amplifier (LNA) MMIC operating at a center frequency of 183 GHz [14, 15] and destined for use in space-borne radiometers aboard the MetOp-SG meteorological satellite series [16, 17]
Summary
Monolithic microwave integrated circuits (MMICs) often require a transition from their planar form to a waveguide in order to effectively couple input and output signals. A tuning technique commonly used in planar matching networks at lower frequencies incorporates patch tuning elements to modify transmission line impedances and lengths [6,7,8] This technique cannot readily be implemented at millimeter wavelengths ranges due to the smaller feature size and assembly complexity of the related circuitry. It is often necessary to assemble (package) and test multiple design variations, and perform a subsequent device selection, or to sequentially disassemble and substitute components. These approaches are very inefficient, wasteful, and costly. The inherent variability of MMIC performance observed at millimeter wavelengths [1, 9] can affect packaged performance repeatability and often mask the effect of applied changes
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