Ceramic Technology Yields Stable Resonators

Sept. 20, 2005
This high-performance ceramic resonator technology supports frequency-stable components from 500 MHz to >67 GHz with frequency tolerances as low as 0.1 percent.

Frequency stability is critical in many applications that can require tight spectral tolerances. For those components subject to frequency variations, Dielectric Laboratories (Cazenovia, NY) has developed a customizable ceramic process for resonant circuits, such as resonators, diplexers, and filters. Applicable for components from 500 MHz to >67 GHz, the process offers, for example, a 10-GHz resonator with typical temperature coefficient of frequency of –2.3 PPM/°C (1 MHz drift @ 10 GHz) from –20 to +120°C.

Dielectric Laboratories refers to its new ceramic process as a "disruptive technology," perhaps for what its components do to engineering preconceptions. The company's patent-pending XTREME-Q™ line of single-frequency cavity resonators is one example of the types of components that can benefit from the stable ceramic process. Resonators have been fabricated at frequencies of 3.20, 8.20, 9.95, various frequencies around 10 GHz, 12.80, and 18.65 GHz with typical temperature coefficient of frequency of –2.3 PPM/°C at the five lower frequencies and typical temperature coefficient of frequency of –7.3 PPM/°C at 18.65 GHz (Fig. 1). These values hold for temperatures from –20 to +120°C. The typical loaded Q at 50 Ω for these resonators ranges from 250 at 8.20 GHz to 400 at 18.65 GHz. The typical return loss is 25 dB at 8.20 GHz and just under 25 dB at 18.65 GHz.

These single-frequency microwave and millimeter-wave resonators are completely self-contained and fully shielded. This allows accurate measurements to be made with coplanar wafer-probe technology with minimum effects on resonator performance due to probe loading. Because of the accuracy of these measurements, Dielectric Laboratories' engineers have developed a reliable set of computer-aided-engineering models to simulating resonator frequency, Q, return loss, and other parameters. Typically, simulations are within about 0.1 percent of measured data on fabricated resonators.

The resonators are available in surface-mount and microstrip-mount (using wire bonds) versions (Fig. 2). Both employ gold metallization, with nickel/gold backside metallization in the surface-mount resonators and gold backside metallization in the microstrip-mount components. These components are a fraction of the size of dielectric resonators (DRs). For example, a 10-GHz XTREME-Q™ resonator measures 0.17 × 0.2 × 0.06 in. compared to a shielded 10-GHz DR at the same frequency measuring 1 × 1 × 0.5 in.

In addition to the single-frequency resonators, the firm uses the temperature-stable ceramic process to manufacture standard and custom miniature filters, duplexers, diplexers, and gain equalizers from 500 MHz to >67 GHz. XTREME-Q™ filters, for example, can be produced in a variety of configurations, including Chebyshev, Bessel, edge-coupled, end-coupled, hair-pin, and interdigitated types and DLI's newly developed Symmetrical Dual Mode Resonator Filters with passbands of 25 percent or less. Typical specifications include passband insertion losses of 0.5 to 3.0 dB, rejection of 45 dB minimum, and return loss of 15 dB.

The technology also lends itself to high-performance ceramic duplexers and diplexers a frequencies from 1 GHz to beyond 67 GHz. The duplexers and diplexers are three-port components that are used to separate or combine different frequencies. The insertion loss for these more complex filter types is stil less than 3 dB, with better than 20 dB return loss for most designs. These compact ceramic duplexers and diplexers achieve better than 50 dB isolation, and can be supplied in large volumes with excellent unit-to-unit repeatability.

One final example of the ceramic technology is a bias filter network that serves to filter noise and RF energy from an active device's power supply. Ideal for GaAs FET devices and monolithic microwave integrated circuits (MMICs), this single component can be used to replace many separate circuit elements in a discrete-component bias network.

For more information on this "disruptive technology" and how it can be used to make resonators, filters, and equalizers, don't miss the special Microwave Design Basics insert in the next issue of Microwaves & RF. Dielectric Laboratories, Inc., 2777 Route 20 East, Cazenovia, NY 13035-9433; (315) 655-8710, FAX: (315) 655-0445, Internet: www.dilabs.com.

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