In early 2012, engineers at a prime aerospace manufacturer were assigned the task of replacing several existing integrated test adapters (ITAs) used to test multiple line replaceable units (LRUs) belonging to an Air Force program. One goal was to replace the existing ITAs with as much commercial off-the-shelf (COTS) technology as possible.
These ITAs were to be used in combination with a common core ATE system as well as embedded complex microwave switching matrices that were customized to LRU specific requirements. The engineers recognized that the ITA designs were prone to failures and were compromising system up-time. In order to satisfy the test requirements of the LRUs, the engineers had to incorporate the use of an RF Interface Unit (RFIU) within each ITA. The RFIU provided attenuation, filters and switching that routed and conditioned test instrumentation signals and allowed them to be placed as close as possible to the device under test.
The high frequency signals being routed made the design difficult. Engineers had to pay particular attention to isolation, insertion loss, and VSWR, and had to incorporate LRU specific/custom designs in order to minimize the effects the insertion of an RFIU between the signal path has on signal integrity.
Although the number of RF components and configurations of each ITA was unique, the engineers found it more efficient to develop a common infrastructure to contain the RF components and a common communications interface back to the host called the Internal Integrated RF Interface System (IRIS). The aerospace manufacturer’s engineers selected the LXI-compliant EX7000-OEM communications and control interface as the COTS core for all IRIS assemblies.
The EX7000 family is the industry’s first series of scalable microwave subsystems built on an open-architecture Ethernet/LXI platform.
In addition to supplying the EX7000 switching systems, VTI Instruments was asked to design and build the IRIS assemblies. By collaborating closely with the aerospace manufacturer's engineers, the team was able to develop a flexible ITA infrastructure that included nearly 100% RF COTS components and a COTS LXI-based communications and control interface.
Maximizing Common Components
Each of the six IRIS assemblies interfaced to the same test station through its ITA and therefore shared the same station resources. The IRIS assemblies within each ITA derived power through the mass interconnect, therefore it was easy to design each IRIS such that it used the same station power resources. The six IRIS assemblies had unique signal distribution topologies, and the superset of components included splitters, filters and switches. A decision was made to design a common component housing tray that could be integrated into the IRIS assemblies even though not all IRIS assemblies made use of every component. While none of the IRIS assemblies required a fully populated tray, designing one assembly lowered assembly costs by minimizing the number of unique sheet metal parts as well as reducing the number of drawings needed for the project.
In a similar vein, relays and components were selected to reduce the number of unique components. The relay topologies chosen were limited to SPDT and SP6T to provide opportunity to achieve cost benefits through volume purchase while also simplifying the spares resource pool.
Microwave and RF test applications often drive the need for custom interface units; however, this does not imply that a solution must be based on a proprietary or non-standard infrastructure. By incorporating an LXI-based communications and control interface into each ITA, VTI was able to meet the goal of providing a solution using COTS components, as well as reducing the documentation and software development efforts.