Blog: 5 Critical Questions to Ask When Selecting Fixed-frequency Sources for Digitally Reprogrammable Multifunction AESA Systems

Overview

Today’s Multifunction Active Electronically Scanned Array systems are engineered and manufactured to simultaneously perform different operations, such as RADAR, electronic warfare (EW), and communications functions. One of the most critical elements of digitally reprogrammable multifunction AESA systems are the fixed-frequency sources.

In short, fixed-frequency sources take one or more precise timing reference signals as inputs, then convert and synchronize the timing references within critical AESA systems. The phase noise, stability, spectral purity, and jitter of fixed-frequency sources influences the range, resolution, and accuracy of digitally reprogrammable multifunction AESA systems. To help engineers make the right selection, we’ve outlined our top 5 questions to ask and key factors to consider when selecting fixed-frequency sources for digitally reprogrammable multifunction AESA systems.

1. What are the main types of fixed-frequency sources, and which should I select?

There is no one size fits all fixed-frequency source solution for every multifunction AESA system application. As the primary function of a fixed-frequency source is to stabilize the frequency of circuits, the frequency at which the source operates is the first and most important criteria to consider when making your selection. Fixed-frequency sources can be categorized into many different types, including:

• Direct Digital Synthesizers (DDS)
• Oven Controlled Crystal Oscillators (OCXO)
• Synthesizers with Integrated Voltage Controlled Oscillators
• Temperature Compensated Crystal Oscillators (TCXO)
• Voltage Controlled Oscillators (VCO)
• Dielectric Resonator Oscillators (DRO)
• Voltage Controlled SAW Oscillators (VCSO)

2. What specifications should I use to characterize the performance of fixed-frequency sources?

The common characteristics of fixed-frequency sources are listed below. Depending on the application, more may be required including reliability, operational life, phase locking capability, etc. A few of the key specifications that engineers should consider are:

• Frequency Accuracy– The maximum deviation of a fixed-frequency source from a given nominal frequency.
• Jitter– The stability of an oscillator in the time domain. Jitter combines all the noise sources and represents an effect with respect to time.
• Frequency Stability– The variation of output frequency due to external conditions, including temperature variation, voltage variation, output load variation, and frequency aging.
• Power-on Characteristics (Retrace)– The frequency change in a given period of time after a power cycle.
• G-sensitivity– The change in performance resulting from an acceleration force applied to an oscillator. G-sensitivity is an essential consideration for harsh environment applications.
• Aging Rate– The change in frequency over an extended period time (years).
• Short-Term Stability– The measure of the frequency variation over a short period of time.
• Spurious Content– Any non-carrier noise.
• Phase Noise– The frequency-domain representation of random fluctuations in the phase of a waveform, corresponding to time-domain deviations from perfect periodicity.

3. What custom fixed-frequency source features should I consider for my application?

To achieve the desired frequency stability and phase noise performance, engineers should consider additional features that are often required for multifunction AESA system applications. A few of these features are:

• Passive Vibration Isolation– Mitigation of vibrations by passive techniques such as shock mounting.
• Active Vibration Compensation– This system can sense incoming vibrations to fixed-frequency sources and react to them. Active vibration compensation systems employ sensors to measure vibrations and controllers with feedback loops. Compensation can also be achieved by electrically tuning internal oscillation.
• Environmental Sealing– This feature prevents contaminants and moisture from breaching the fixed-frequency source housing. Environmental sealing helps maintain the fixed-frequency source electrical performance and prevent degradation.
• Size, Weight, and Power (SWaP)– Today’s high-reliability applications often require fixed-frequency sources that are smaller, lighter, and have more powerful performance features.
• External Reference Locking– The ability to lock an output frequency to a known external frequency source.

4. What reliability factors should I consider for fixed-frequency sources?

Many standards can be applied to guarantee the delivery of high-quality solutions for fixed-frequency source applications. The common test conditions for fixed-frequency sources are:

• MIL-STD-810– This standard contains materiel acquisition program planning and engineering direction for considering the influences that environmental stresses have on materiel throughout all phases of its service life.
• MIL-PRF-55310– This specification covers the general requirements for quartz crystal oscillators used in electronic equipment.
• MIL-STD-202– This standard establishes uniform methods for testing electronic and electrical component parts, including basic environmental tests to determine resistance to deleterious effects of natural elements and conditions.
• Open Systems Standards– As the Department of Defense pushes for “open systems” engineers are now requiring fixed-frequency source solutions that closely align with the new standards. The Department of Defense has made clear its intention to enable incremental development that enhances competition, innovation, and interoperability through open system standards. The specific open standards that engineers are considering when selecting fixed-frequency sources are:
  • CMOSS– C4ISR/EW Modular Open Suite of Standards
  • FACE– Future Airborne Capability Environment
  • HOST– Hardware Open Systems Technologies
  • MORA-: Modular Open Radio Frequency Architecture
  • OMS/UCI– Open Mission Systems/Universal Command and Control Interface
  • SOSA– Sensor Open Systems Architecture
  • VICTORY– Vehicular Integration for C4ISR/EW Interoperability
  • VPX VITA 46.X– Switch fabric technologies in 3U and 6U format blades.

5. What time to market or lead time considerations should I take in account?

Program managers, procurement officers, and engineers should expect varying lead times when it comes to procuring fixed-frequency source devices for multifunction AESA systems. A common lead time in the frequency control industry is between 8 and 14 weeks. Custom fixed-frequency sources such as synthesizers have considerably longer lead-times, more than 18 weeks. Production, alignment, and test require extended lead times to meet the required performance and qualification standards. It is recommended that you get in touch with the manufacturer or supplier well in advance to gain a thorough understanding of what lead times you can expect.

Conclusion

This article presented an overview of the main types of fixed-frequency sources, required performance specifications, reliability standards, and lead time factors to take into consideration for multifunction AESA systems. For example, multifunction AESA systems require fixed-frequency sources with ultra-low phase noise performance to counter signal quality issues caused by vibration. Quantic Wenzel’s fixed-frequency sources are deployed in a broad range of multifunction AESA system applications, including clock signal generation, frequency conversion, signal modulation, and waveform synthesis. If you’d like to discuss your specific application or learn more about our capabilities, please connect with us, we’re here to help.  

References:

• Phillips, W. C., Hilterbrick, C. L., Minarick, R. W., Schmidt, K. M., Pascale, M. V., & Prill, R. S. (1997, March 6). Digitally Programmable Multifunction Radio System Architecture.
• Moo PW, DiFilippo DJ. Multifunction RF Systems for Naval Platforms. Sensors (Basel). 2018 Jun 28;18(7):2076. doi: 10.3390/s18072076. PMID: 29958465; PMCID: PMC6068503.
• Storr, W. (2022, August 4). Quartz Crystal oscillator and quartz crystals. Basic Electronics Tutorials. Retrieved October 5, 2022, from https://www.electronics-tutorials.ws/oscillator/crystal.html

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