Current technology in electronics is always difficult to sustain with the rapid advancement of upcoming technologies. To address this problem, designers must implement new technologies into existing products. For instance, a current technology that is becoming more difficult to sustain is the receiver exciter (REX) in phased array radar systems. Presently, the REX systems are connectorized RF modules that are interconnected with bulky and heavy RF coaxial cable assemblies. In addition, a key attribute of REX architectures is that they utilize analog beamformers which consist of more expensive RF modules and cables. To arrive at the DREX (Digital Reciever Exciter) architecture though, a different analog solution using multilayer microwave printed wiring boards (PWBs) with surface mount technology (SMT) RF components is being proposed. Again, although the DREX solution is still analog in terms of RF downconversion, it will support an overall digital architecture by performing the beamforming through faster digital processing. As a result of this implementation, there are more benefits to be gained than just supporting a digital architecture with faster processing speeds. Tremendous gains can also be achieved with reductions in cost, size, weight, and power (CSWAP).

What improvements are to be gained with DREX technology? First is the use of commercial off-the-shelf (COTS) surface mount components that are readily available. Sustainability is secured since current technology has multiple vendors that provide such hardware. Multiple vendors versus sole source are always the preferred strategy.

Let’s examine in further detail the relation of COTS SMT components to sustainability. Many integrated circuits (ICs) typically employ standard package types. Some of the SMT package types that will be used in DREX technologies include:

• Land Grid Array (LGA)
  
• Quad Flat No-Lead (QFN)
  
• Dual Row Micro Lead Frame (DRMLF)
  
• Fine Pitch Ball Grid Array (BGA)
  
• Chip Scale Packages (CSP)
  
• Flip Chip
  
• SMTO-8
  
• 4-Pin Surface Mount (SM3)

As more and more vendors adopt identical or similar package styles, it is easier to substitute components from different vendors on the same surface mount footprint for the SMT designs. Sustainability is then gained through the use of identical package styles by competitors. The mass production of these packages will logically bring down costs for that package type.

One of the key components of a DREX or REX, is the RF amplifier or low-noise amplifier (LNA). The advancements in amplifier technology have led to smaller packages that are similar and produced across multiple vendors. An example of the LNA package (SMTO-8) can be seen in Figure 1-1. The benefit of this development is that lower volume specialized industries receive the benefits of high volume industries, like wireless communications. This high volume demand keeps RF amplifiers sustainable. In a similar fashion, intermediate frequency (IF) amplifiers will be even more readily available. Another key DREX component is the RF mixer. Vendors of mixers typically use a 6-pin SMT style package. RF filters have not migrated to being highly sustainable like the other components within the DREX. However, attempts are being made to standardize the package styles from previous through-hole package styles. RF switches are other functional blocks that come in standard 8-pin SOIC package styles which are very common in the electronics industry. The DREX assemblies are also automatic gain controlled with digital step attenuators that also come packaged in QFN package styles. Moving further to the processing side of the DREX, analog to digital (A/D) and digital to analog (D/A) converters are very commonplace in BGA package types.

While similar package styles help make products sustainable, other ideas can be applied in a comparable manner. For instance, a packaged component with leads can be replaced by its equivalent circuit on a printed wiring board (PWB). If high frequency board materials are utilized, then functions like power dividers and couplers can be etched onto the surface mount design. In this way, two key elements of a DREX can be completely removed from package dependency with the simple addition of artwork on PWB CAD files. Nonetheless, the SMT components would have resided on a high frequency board.

The EMPF is currently addressing the advancement of DREX technology in phased array radars. Lowering the CSWAP is one of the key goals of the program. A prime method at removing the CSWAP from the REX assembly is through the use of COTS SMT components. Moreover, multiple vendors will be identified as potential alternatives to the primary vendors to the DREX design. The EMPF will perform detailed packaging studies to ascertain where benefits can be achieved using different types of package styles. Also, since the packages will generally be standard to current package technology, the manufacturing and assembly processes will add sustainability to the surface mount design. The EMPF will also add value to the DREX program by designing and fabricating a set of reliability test vehicles. A layout of the DREX test vehicle that was designed at the EMPF can be seen in Figure 1-2. This test vehicle has all the significant package types of the DREX PWB. It also incorporates some of main interconnect features between various layers of the PWB. In addition, the test vehicle will undergo rigorous reliability testing including thermal cycling and vibration testing. Other areas that the EMPF can contribute to the DREX program are its manufacturing and analytical services. The expected outcome of the reliability test vehicle testing is to make a more manufacturable and sustainable product.

To conclude, sustainability requires application of common sense at the outset. If these recommendations are implemented, obsolescence can be avoided and the DREX design can be easily sustained for many years.