Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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Techniques MMIC technologies to the system (Figure 2). In fact, the key this problem for the transmit portion of an X-band phasedcharacteristics of size, weight, and power consumption in a array system. Rather than utilize depletion mode pHEMT, phased-array radar system can usually be minimized by anawe turned to enhancement mode pHEMT for the HPA, a lyzing the design at the circuit, system, and technology levels. technology often relegated to other applications such as Analysis at the technology level first involves a choice high-speed logic circuitry or switches. In enhancement of semiconductor material. Modern commercial semimode, the pHEMT is normally off until a positive voltage conductor foundries typically offer a number of different is applied to the gate. Negative voltages are no longer material technologies, but a choice among these is not required, nor are voltage sequencers, since either the conalways straightforward. Components in high-frequency T/R trol or the drain voltage can be applied first; the amplifier modules typically include high-power amplifiers (HPAs) for will not turn on until both are present. In the end, we were transmit purposes, low-noise amplifiers (LNAs) for receiving able to replace the existing depletion mode PA with an purposes, mixers and oscillators for signal translation (freenhancement mode design that delivered 5 dB more gain, quency upconversion and downconversion), and attenua1 dB more power, and 2 dB improved linearity, all while tors, filters, and switches for signal conditioning. Fabricating dissipating 25 percent less DC power. In terms of SWaP-C, MMICs for all of these functions will likely require more the benefits of enhancement mode PAs are enormous, than one semiconductor technology. For example, processand offer a significant breakthrough for microwave system es based on silicon-carbide (SiC) or gallium nitride (GaN) designers in general. substrates will excel in higher-power porA second problem we considered was tions of the system such as transmit functhe receiver LNA in an X-band phasedtions, while processes using silicon germaarray system as part of a separate SBIR nium (SiGe) or gallium arsenide (GaAs) contract. Here, we also switched from a materials will exhibit lower noise for better depletion mode to an enhancement mode performance in receiver functions. process, thereby eliminating the negative Analysis at the system and circuit levels voltages and sequencers of the existing should be closely intertwined, as a system solution. The resulting design had 1 dB is only as good as the sum of its comlower noise figure, 8 dB more gain, an ponents. Unfortunately, the vast majority eight-fold reduction in DC power, and of IC and MMIC circuit suppliers do not Figure 2: Monolithic microwave integrated half the unit cost of the existing deplegive enough consideration to any specific circuit (MMIC) amplifiers are often used in tion mode solution. However, we soon phased-array radars as the active (signalsystem, opting instead to create generic gain) elements. encountered an application that called for components that can be used across widea pair of relatively well-matched LNAs, reaching applications. Such an approach, while cost-effecone for each of the two polarizations in the return signal. tive in terms of IC and MMIC development, is not always Starting with the enhancement mode LNA, we created a optimal in reducing SWaP-C, since these components candual version on one MMIC die, thereby guaranteeing a not be easily customized for use in phased-array systems. matched pair. We also worked with our packaging vendor A better approach combines technology, system, and to develop a low-cost rectangular QFN plastic package to circuit analysis to create components that aggressively best match the resulting die size. The result was a product attack SWaP-C concerns of phased-array systems. As an that combined innovation at the circuit, system, and techexample, one place where we have focused significant nological levels to deliver a component with significant development is the transmit HPA, a common component impact on SWaP-C. required in almost every application. At microwave and Moving forward, we are looking to develop components millimeter-wave frequencies, the transmit amplifier is often for phased-array radar systems using other technologies, fabricated from a depletion mode pHEMT (pseudomorphic such as high frequency GaN, or a combination of differhigh-electron-mobility transistor) process, a highly efficient ent semiconductor devices in a multichip module, espeand mature technology. However, depletion mode pHEMT cially when digital control functions must be integrated with is not without its drawbacks, most notably the need for higher frequency functions. In the meantime, we will keep negative gate voltage and a sequencing procedure to talking to and, more importantly, listening to, phased-array ensure the gate voltage is applied before the drain voltage, system developers. Ultimately, real reduction in SWaP-C lest the FET (field-effect transistor) device suffer irreparable requires cooperation between circuit, system, and technolharm. By their very nature, negative voltages and sequencogy, not just for phased arrays, but for any application ing circuits for HPAs are expensive in terms of complexity, where size, weight, power, and cost are board space, and cost of the extra components. In phased important. arrays, especially ones with thousands of elements, such Charles Trantanella, Ph.D., is VP of engineering for Custom HPAs place enormous strain on the system as a whole and MMIC. He began working in the RF/microwave industry in offer significant barriers to SWaP-C reduction. 1994 as a member of the engineering team for IC designer/ manufacturer Hittite Microwave Corp. He received a BSEE from Therefore, as part of a Small Business Innovative Tufts University and an MSEE and Ph.D. (EE) from the University of Arizona. Research (SBIR) grant from the U.S. Army, we attacked 38 Electronic Military & Defense ■ www.vertmarkets.com/electronics