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The growing trend toward the use of smaller components in high-end microwave applications is being driven fervently by end-user demand for easier mobility and serviceability of equipment. Within the military realm especially, tactical agility in the field correlates directly to the use of certain types of equipment that are rugged and powerful, yet lightweight and compact.
Unfortunately, when it comes to performance, the design of smaller-size components oftentimes has meant that a certain amount of power and durability has been sacrificed. The challenge to microwave engineers has been to find the best balance of component size, weight and performance characteristics that will meet or exceed the required specifications for a given application.
Recognizing the critical need for more powerful, reliable and miniaturized microwave components, Dow-Key Microwave Corp. recently released its 409 Series single-pole, double-throw (SPDT) switch designed for drop-in microstrip or coplanar circuit applications.
Small Footprint, Light Weight
In response to key user demands, the 409 switch has been designed to provide extreme durability and high power handling characteristics in a highly compact footprint—0.800" × 0.600" × 0.640"—that can be mounted directly onto a microstrip or coplanar circuit assembly, as shown in Figure 1.
Weighing in at a mere 11.25 grams, the hermetically sealed 409 switch is almost seven times lighter and one-third the size of its 401 Series predecessor, which had served as the industry-standard miniature SPDT switch for many years. Where switches like Dow-Key’s 401 Series connectorized switches had in the past been used in applications required RF cables, the new compact 409 directly launches the RF signal to the microstrip or coplanar transmission lines, and provides virtually the same electrical and power handling characteristics of the venerable 401 but in a small, 310 mm2 area of the RF circuit space.
Focus on Power Handling
The design process of the 409 switch was a complex engineering task, starting with an intended military application, and working through numerous trade-offs between the power handling and size reduction of the switch.
Military applications demand much from microwave components: exposure to moisture, humidity, dirt and sand; the ability to operate reliably within extreme temperature variations between –55° to +85°C; and the capability to withstand high levels of shock and vibration. Thus, the two most critical aspects in the creation of the 409 miniature switch were to enable it to operate reliably in harsh environments while affording it the capacity to handle high levels of power.
Metal-to-metal/glass-to-metal hermetic sealing (1×10–6 atm-cc He/sec) of the housing was the obvious choice to enable the switch to perform reliably in harsh conditions. However, hermetic sealing presents certain power handling challenges to a small switch, as the properties of the glass used in the sealing process present relatively significant losses for high-frequency signals.
Additionally, as the switch miniaturization is limited by the level of power it must handle, balanced heat dissipation must be present in the design. The operating temperature of all switch components is not only impacted by the external environment but also increased as a result of the heat generated by the power transmitted through the device. Without excellent heat dissipation characteristics, any hot spots on the interface between the switch and the remainder of the assembly could be problematic for the parts inside the unit, potentially melting some of its critical dielectrics.
Dow-Key designed the 409 switch with a focus on thermal management so as to enable the miniature switch to dissipate the heat created by high-frequency RF signals. The dimensions of the 409 switch, particularly the surface areas that come into direct contact with the microstrip ground plane, were carefully designed to provide a balanced exchange of heat between the unit and the overall assembly. The company has also developed a very detailed application for the microstrip circuit design, taking full advantage of the switch power handling. The result is a switch that provides extremely low insertion loss, high-integrity routing of high-power RF signals up to 6 GHz and 100 W. Figure 2 shows the 409 switch VSWR and insertion loss performance vs. frequency.
Built to Last
In terms of materials, the 409 switch is made from aluminum and electroless nickel with kovar gold-plated contacts. An extremely robust latching drive mechanism enables the 409 to be used in high-vibration and mechanical shock applications. Rated at an operating life of one million cycles, the 409 is rated to operate at frequency ranges between DC and 6 GHz.
Ideal for redundancy, filter and amplifier switching in applications where high isolation is required, the main uses for the 409 Series switch will be primarily high-end military in nature, though it also can be used in ATE environments. From airborne, shipboard, amphibious, or land-based vehicles—or anywhere there exists a high level of vibration, shock and exposure to extreme temperatures—the 409 is suited for deployment wherever SPDT action is required.
Engineers looking for switch solutions in portable radio applications, for example, will find the 409 switch particularly useful due to its small size and low weight.
For airborne applications in which vehicles operate in high-vibration environments, the use of the 409 switch is attractive due to its ability not only to withstand high temperature variations and shock, but because it also affords high-power capability with low insertion loss. Further, at a little over 11 grams each, numerous 409 switches can be outfitted to provide redundancy and higher performance levels with a negligible addition of weight to the aircraft.
In land-based military vehicle applications, the amount of equipment that must be carried on board puts real estate at an extreme premium. Here, the 409’s small size has the potential to reduce some of the hardware requirements inside the vehicle, thus helping to maximize space while achieving the required operational benefits of the vehicle.
A high-quality alternative to solid-state devices, Dow-Key’s 409 Series switch provides microwave engineers with breakthrough performance and easy serviceability in an extremely compact unit for use in high-end, mission-critical applications. While other miniature microwave switches exist on the market, none offer the 409’s level of high-power handling capacity combined with hermetic sealing. This unique design opens up the doors for new applications that previously had been difficult or impossible to build. For more information, visit Dow-Key Microwave’s web site at www.dowkey.com.
Dow-Key Microwave Corp.,
RS No. 300
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