Linear Microwave Attenuator

For signal level control in microwave systems, attenuators are normally designed to improve logarithmic level variation (i.e. in dBs) in response to a control signal. For some level control applications, the logarithmic control is inadequate to provide the fine resolution needed at low attenuation levels. Examples of such requirements include: weighted loading of antenna arrays, alignment of mono-pulse receivers, antenna nulling, and digital modulation (e.g. QAM) for communications. In most of these applications, it is highly desirable to have independent means of control for amplitude and phase. This proposal describes several alternate circuit designs to attain the attenuation/level control requirements, and outlines an approach to select the optimum design for MMIC implementation. Design options include: active gain controlled amplifiers vs. attenuators, and digital vs. analog control of attenuation/gain. Methods of phase compensation and linearization, applicable to various design options, are also presented to show that the level control function can be accomplished with negligible phase variations. Hittite proposes to implement an MMIC design of the attenuator/level control circuit. The MMIC design will lead to miniaturization and provide the flexibility of integrating additional microwave circuit functions on-chip with the attenuator. Hittite also proposes a laboratory demonstration of the selected approach using available assets.