Modern wideband microwave systems often require a flat overall gain response with respect to frequency. However, this performance can be difficult to achieve since the gain of most wideband microwave components decreases as the frequency increases. In the tech brief, “Realizing the SWaP-C Benefits of Designing with Positive Gain Slope MMIC Amplifiers,” Custom MMIC explains how distributed-amplifier monolithic microwave integrated circuits (MMICs) that exhibit a positive gain slope can be advantageous for system designs.
The tech brief illustrates the response of a typical wideband distributed amplifier, revealing a negative gain slope of around 3 dB from dc to 20 GHz. A wideband system typically incorporates multiple amplifiers, as well as passive elements and transmission lines. Thus, a cascaded system design that includes amplifiers, passive elements, and transmission lines can result in a system with a significant negative gain slope.
As an example, a frequency response is shown of a cascaded lineup that consists of five typical wideband microwave amplifiers along with passive components and transmission lines. The lineup results in approximately 20 dB of negative gain slope from dc to 20 GHz, demonstrating how negative gain slopes must be taken into account.
Passive equalization is a common approach to compensate for a negative gain slope. However, the document explains some of its drawbacks, such as the addition of components that will increase the size and cost of the overall system. Another concern is additional loss, which affects system sensitivity and noise.
The tech brief explains how a distributed-amplifier MMIC with a positive gain slope can aid system designers. By using these amplifier MMICs to design a system, the system’s gain can be equalized without needing additional components. A wideband system performance analysis is presented to demonstrate the benefit of using distributed-amplifier MMICs with a positive gain slope. The brief lays out the performance of typical lineups both with and without equalization. On top of that, it illustrates the performance of two other lineups: one with five amplifier MMICs with positive gain slopes and another with only four.
Custom MMIC, 300 Apollo Dr., Chelmsford, MA 01824; (978) 467-4290
