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Microwave Tuners Show OpenRFM Flexibility

Aug. 3, 2015
This “building block” approach to an open-system test instrument architecture provides a great deal of measurement capability and flexibility across the traditional 2-to-18-GHz EW bandwidth.
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Microwave systems and test solutions rarely have enjoyed the benefits of any form of standards to govern the design and manufacture of integrated microwave assemblies (IMAs). As a result, an IMA from one manufacturer will invariably be different in size, interfaces, and many other aspects from an IMA supplied by another manufacturer. Nor has there been any seamless integration between RF and digital subsystems in a common form factor.

The RFM-1R1S18K-L1-VXS downconverter/tuner separates its 1.5-GHz bandwidth into four IF outputs, each with 375-MHz bandwidth centered at 745 MHz.

To rectify this, Mercury Systems last year proposed a standardized open-system architecture based on a “building block” approach. Called OpenRFM, the approach brings RF and microwave technology into the realm of systems-level standards such as OpenVPX, VME, and VXS commonly used by digital embedded systems for electronic-warfare (EW) and other defense electronics applications. In its continuing support of the proposed standard, the company has introduced the Ensemble RFM-1RS18 tuner available in four configurations that cover the 2-to-18-GHz frequency range commonly associated with electronic-warfare (EW) applications.

The four configurations include the single-channel models RFM-1R1S18K-L1-VXS and RFM-1R1S18K-1875-L1-VXS downconverter/tuners and the RFM-1T18K-1875-L1-VXS and RFM-1T1S18K-1875-L1-VXS transmit upconverter/tuners (see photo). The downconverter/tuners convert signals from 2 to18 GHz to a lower-frequency intermediate frequency (IF) for processing. The complementary transmit upconverter/tuners accept an IF which is converted to a user-selectable frequency in the 2-to-18-GHz range.

All four units are composed of as many as three OpenRFM modules—a wideband front-end, an IF converter, and, in three of the models, a fast-switching direct-digital synthesizer (DDS) for maintaining precise signal coherence. Each instrument packs broadband capabilities into a single-slot 6U VXS form factor. Whether employed as standalone units or paired together, these new models offer excellent performance and flexible capabilities to meet EW needs.

Model RFM-1R1S18K-L1-VXS offers 1.5-GHz instantaneous bandwidth, which is three times the industry standard. The 1.5-GHz instantaneous bandwidth split into four IF outputs each with a 375-MHz bandwidth centered at 745 MHz. By dividing the full 1.5-GHz instantaneous bandwidth into narrower swaths of bandwidth, the instrument is capable of very high signal fidelity in the digital conversion process, as the highest resolution (that is, greater effective number bits) and dynamic range are afforded by analog-to-digital converters (ADCs) with lower sampling rates and bandwidths. Consequently, the 375-MHz segments of bandwidth at each of the four outputs can be much more precisely processed than if the entire 1.5-GHz bandwidth was digitized and processed as a whole.

Dramatically reducing bandwidth also results in less data to be processed at each output and can thus be searched more rapidly for signals of interest and analyzed with less formidable processors or signal processing workstations. The Ensemble RFM-1R1S18K-1875-L1-VXS unit differs from the model RFM-1R1S18K-L1-VXS since it has a single output with 1 GHz of instantaneous bandwidth centered at 1.875 GHz. This unit is designed to take advantage of higher sampling ADCs and is well suited for applications working with digital RF memories (DRFMs) when paired with either of the transmit tuners.

Models RFM-1T18K-1875-L1-VXS and RFM-1T1S18K-1875-L1-VXS are both single-channel, single-output tuner/upconverters that accept 1 GHz of instantaneous bandwidth centered at 1.875 GHz. The 1T1S18K contains a DDS, while the 1T18K does not. The RFM-1T18K-1875-L1-VXS can be paired with the RFM-1R1S18K-1875-L1-VXS, sharing the DDS capabilities of the receive unit and ensuring locked tune frequencies.

Click table to enlarge.

The RFM-1T1S18K-1875-L1-VXS can be used as a standalone transmitter tuner or can also be paired with the RFM-1R1S18K-1875-L1-VXS to provide an RF transmit/receive solution with independent tuning capabilities in both transmit and receive path. All of the units provide manual gain control to optimize noise figure and other performance parameters. The table provides a brief summary of the major performance specifications for all four subsystems.

OpenRFM offers the flexibility to provide customer specific products quickly. For instance, the RF transmit and receive capabilities described could easily be integrated with the DDS synthesizer module to provide an RF only product. Likewise, any of the four products described could quickly be migrated to an OpenVPX form factor to offer the advantages that OpenVPX has to offer.

This is typical of what can be achieved by the OpenRFM approach. It illustrates how subsystems can be built to meet specific customer requirements in a small fraction of the time and at much less cost when compared to current microwave industry practice. Modules can simply be interchanged and as OpenRFM’s control plane, interfaces, and other features remain the same regardless of the modules used, only minor adjustments are required to accommodate new hardware.

OpenRFM also allows “technology refresh” to be achieved easily over multiple platforms as components with greater performance—such as ADCs and digital-to-analog converters (DACs)—become available. As Mercury and (hopefully) other manufacturers adopt the OpenRFM approach, the result will be a large library of single and multiple-function blocks that can be interchanged regardless of the manufacturer to dramatically reduce the amount of time required to build a subsystem or modify it later.

Mercury Systems, Inc., 201 Riverneck Rd., Chelmsford, MA 01824; (866) 627-6951, (978) 256-1300

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This file type includes high resolution graphics and schematics when applicable.

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