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Latest Solid-State Tech Revolutionizing Radar Applications

AESAs (active electronically scanned arrays) are being increasingly utilized in evolving radar systems for receiving and radiating functionality. These resources offer a variety of desirable features in comparison to other radar implementations. These solutions include frequency agility, jam resistance, grateful degradation and deployment with other solutions like electronic self protection devices, electronic attack protocols or communication channels.

Though OpenVPX is still the standout practice for EW applications throughout the United States, companies in Africa and Europe continue to find ways to leverage the standard procedures in regard to EW signal processing.

Systems engineered prior to the AESA latest evolution usually required a single transmitter or several high powered transmitters that fed antenna, or semi-active or passive array structures. The transmitters utilized were VEDs (vacuum electronic devices) that included traveling magnetrons, klystrons, wave tube amplifiers or cross field amplifiers. These options were the only available options at the time based on then current technology if one wanted to reach required levels of microwave or RF power in order to generate sufficiently high operating efficiency.

In current environments, the newest tech operates in conjunction with greater broadband. Another notable feature is low-loss power that offers sound alternatives to higher powered vacuum devices. Advancements in GaN (gallium nitride) and MMIC (monolithic microwave integrated circuit) have made it possible to implement an amplifying platform that achieves power levels in the thousands of watts. In some cases, the modules can be combined and creating a configuration that incorporates command and control circuity, power supplies and thermal management with the capacity to generate tens of kilowatts. These features replace legacy VED transmission with solid state opportunities. This means incidental improvement of radar system characteristics and noticeable improvement in availability and reliability of these systems.

VEDs offer better versions of high voltage resources that usually suffer short lifespans. In contrast, GaN semiconductor MMICs provide mean-time-to-failure of greater than 10 million hours with junction temps of 200 degrees centigrade. Besides shorter life periods, VEDs are also prone to gassing up and requiring periodic operation to maintain functionality. The newer options remain effective in non-powered states and are ready for operation immediately.

The high powered modules combine several devices for composite power output. Usually with a single amplifier of this kind, failure resulted in less than 0.7 dB power loss with somewhere in the vicinity of 0.7 additional dB reduction for every subsequent device taken out of service. This is opposed to extremely high powered applications in which several GaN MMIC amplifiers are in place. In this operation, we tend to find transmitter performance to be similar to an AESA. In that single device, failure generally has an inconsequential effect on overall power and performance.

Solid state transmission is also available where there is less spurious signals and thermal noise via a vacuum device. Broadband TWTAs have an exceptional ability to output substantial power compared to alternatives. When operating at full capacity, they return a high harmonic content, capable of putting out as much or more return at the second harmonic. This is better than realized at fundamental frequencies of interest.

Often, the intermodulation characteristics are found to be disappointing. The comparatively typical solid state harmonic content is generally more than 15 dB below primary signals. This is considered a dynamically better performance. It enables meeting output filtering requirements as well as produces better and reduced power handling requirements with associated performance and cost advantages.

Typically, VEDs can be depended on to operate via very high voltage power supplies. This is starting at a minimum of several hundred volts and maxing out at up to 10 kilovolts. That operating range does represent challenges to the implementation of a power supply. It also demonstrates a possible personnel safety hazard if there is the need to explore the supply voltages.

While the community is relatively impressed with these operations, there are still those that express doubt. When it comes to these solid state solutions, critics usually focus on alleged deficiencies in tech with respect to effectiveness when compared to a VED. This has the capacity to actually correct the assertion that with some deployments, VED-based power amplifiers can achieve efficiency of up to 70 percent.

Normally, high power, rugged solid-state (military SSD) amplification are only achievable through circuit combination with large numbers of GsAs (gallium arsenide) based amplification. These methods that use circuit combining usually result in diminishing returns due to amplitude and phase matched paths over increased device numbers and bandwidth. This leads to returning higher losses following the amplifiers. Directly, those losses degrade effective operating efficiency and output power availability of the amplification. In turn, high efficiency GaN units are capable of greater than 100 watt power levels from single devices. These can be applied with low loss combined structures that generate less than 0.5 dB of loss.

Despite the application’s parametric performance being a requirement for either technology to meet standards for accepted use, the chance for cost reduction and volume manufacturing capacity alongside design reuse, there is no more compelling reason to replace legacy VED transmitters. These devices are structured for inherent broadband and can be populated with devices across a range of frequency coverage. This means leverage of a myriad of GaN MMIC models which are available commercially.

While not necessarily ready to replace all applications where vacuum devices prevail, the solid state alternatives in transmitters discussed here should be considered where one needs increasingly high powered microwave signal amplification.

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