Dover Technologies carries a great deal of "microwave firepower." By acquiring Voltronics Corp. (www.voltronicscorp. com), for example, Dielectric Laboratories (www.dilabs.com) (DLI) added major market share in precision trimmer capacitors to its already formidable capabilities in ceramic capacitors, filters, and application-specific components. Microwave Products Group recently acquired Pole/Zero to go along with K&L Microwave (www.klmicrowave.com) and Dow- Key Microwave (www.dowkey.com). Vectron International (www.vectron.com) acquired the Corning Frequency Control business three years ago, again adding to their "microwave firepower." These companies have long been dominant developers and suppliers of microwave filters, switches, and high-performance clock oscillators, respectively. Yet for all this microwave capability, Dover's microwave companies have seldom collaborated. That is about to change for DLI, K&L Microwave, and Vectron. Growing demand for higher-level integrated assemblies, such as sophisticated switch-filter banks for high-vibration applications and small temperature-stable voltage-controlled oscillators (VCOs) at higher frequencies, have the three Dover companies pooling their resources and teaming up for the first time—for the benefit of their customers.
Not surprisingly, it was the needs of their customers that brought the companies together, with a bit of corporate encouragement. DLI has long been known for the stability of its ceramic capabilities and thin-film products. Several years ago, the company began applying its ceramic materials expertise to the development of high-quality-factor (high-Q) resonators as well as filters based on those resonators (visit the Microwaves & RF website at www.mwrf.com for copies of two White Papers on Dielectric Laboratories' "Disruptive Technology"). Given the outstanding temperature stability of the ceramic materials, which are produced from the ground up at Dielectric Laboratories' facility in Cazenovia, NY, the firm's customers quickly recognized the benefits of filters formed on the ceramic substrates.
One of the companies taking notice was another Dover company, Vectron. A long-time leader in stable clock oscillators for military and commercial telecommunications applications, Vectron had reached an approximate frequency ceiling of about 2 GHz with its own surface-acoustic-wave (SAW) oscillator technologies. When presented with resonators from DLI, the potential for higher-frequency sources was apparent, especially to Jeff Mink, Vectron's engineering director for VCSO/SO Development: "The big benefit of the DLI technology for our oscillators is temperature stability. Their materials enable us to create an oscillator that is just like a SAW device in terms of stability, but at the direct frequency of 10 GHz. Another benefit that is apparent is vibration insensitivity. In the past, other companies have improved their oscillators by using ceramic stiffeners in their circuits. The DLI materials enable us to adopt a similar approach, but in a significantly scaled-down footprint."
DLI's president, Brian DuPell, confirms that Vectron was one of the first companies, Dover or otherwise, to seize upon the possibilities of the stable ceramic materials. "The collaboration with Vectron actually started more than two years ago, when we began taking our new resonator technologies to market. Vectron wanted to make higher fundamental-frequency oscillators, and we had a technology that supported that. We had a business case where it made sense for the two companies to work together."
Working with Vectron on higher-frequency oscillators actually brought in a third, non-Dover company to the team in the form of semiconductor supplier Mimix Broadband (www.mimixbroadband.com). Earlier this year at the MTT-S Symposium and Exhibition in Honolulu, HI, Vectron, Mimix Broadband, and DLI shared the stage for a technical presentation on how the three companies' contributions resulted in a high-performance, narrowband 10-GHz VCO. DLI provided the resonator and bypass capacitors, Mimix Broadband provided a custom MMIC, and Vectron provided the assembly and evaluation. The result is a low-noise source, which breaks the 2-GHz barrier for Vectron and hints at the possibilities of future teamwork.
Mink explains that the temperature-stable materials arm the 10-GHz oscillator with temperature stability that is a dramatic improvement over existing oscillators at that frequency: "We are going up against oscillators with frequency drifts in the neighborhood of 1 percent at 10 GHz. With our device, because of the temperature performance of the ceramic resonator, we are seeing about +20, –180 PPM stability, which is considerably better than what is currently possible with other oscillators at this frequency." Measured results over a temperature range of –40° to +100°C show the excellent stability of the 10-GHz ceramic-based oscillator (Fig. 1). Mink also explains that since no multiplying is required from lower frequencies,
which is typically done with crystal or SAW-based VCOs, the phase-noise performance is not degraded by 10logN, where N is the multiplication factor. For example, when a 622.08-MHz voltage-controlled SAW oscillator (VCXO) is multiplied by 16 to achieve a SONET system rate of 9953.28 MHz, 12 dB is lost in the phase-noise performance, which is significant to the jitter performance. (Note: Next month, this three-part series on the collaboration of Dover companies continues with a closer look at Vectron's 10-GHz oscillator.)
Shrinking Filters
DLI caught the attention of K&L Microwave (also a Dover company) sometime later, as the result of further involvement with higher-level assemblies. One of these involved several miniature switch-filter banks for a customer fighting for available space in a densely packed system. The project includes both high and low-band assemblies covering the UHF though KU band. The estimated size of the high-band module, for example, is only 2.2 2.0 0.180 in. (Fig. 2). To save size, it employs grounded coplanar waveguides rather than coaxial connectors to mate with a higher-level assembly.
For miniaturization, the filters are fabricated with DLI's CF ceramic material, with a dielectric constant of 23. The material provides significant size reduction compared to cavity filters or designs formed on standard alumina substrates (with dielectric constant of 9.8). In addition, the temperature stability of the CF material and the filters is outstanding at better than ±15 PPM over the full military temperature range. Other features include vibration insensitivity, no out-gassing, and Rad-Hardening capabilities.
Although DLI fabricates the ceramic materials from scratch and designed the filters, they selected a commercial microwave switch for routing signals within the compact assembly. The switches, a 2-to-20-GHz single-pole, two-throw (SP2T) and a SP3T monolithic IC from M/A-COM (www.macom.com), are based on HMIC PIN diode technology for fast switching speed and high isolation. The typical switching speed is 10 ns. It should be noted that all assemblies within the switch-filter module are not based on DLI's ceramic materials. Interconnections from the switch to the filters are based on grounded coplanar-waveguide (CPW) transmission lines fabricated with thin-film technology on 10-mil-thick alumina. The module, which mounts control circuitry based on commercial ICs and lower-cost substrate material (such as Kapton) to the underside of the switch-filter circuitry, is protected by an aluminum/silicon-composite housing with similar thermal expansion as the printed-circuit boards (PCBs) contained within the housing.
Part of this customer's project includes a low-band module within the same band, although this one is based on DLI's CG material with dielectric constant of 68 for miniaturization at the lower frequencies. The design actually consists of upper and lower cavities within a single module, each with a seven-filter bank and switching. The CG material provides better than ±30 PPM temperature stability over the full temperature range. (Note: For more details on the high- and low-band switch-filter assemblies, don't miss the third part of this series in the November issue of Microwaves & RF.)