RFResonator Types: Coaxial, Dielectric, Crystal, Ceramic, SAW & YIG
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Introduction
Resonators are vital components in RF systems, with types like coaxial, dielectric, crystal, ceramic, SAW, and YIG offering unique features. This article explains their working principles and applications, helping you understand the best use cases for each.
Ceramic Coaxial Resonator
Figure 1
The ceramic coaxial resonator is essentially a coaxial line constructed using ceramic materials. They are implemented as high-Q inductors which, when combined with a capacitor, create a resonant circuit.
Figure 1 depicts a coaxial resonator featuring a square-shaped outer conductor and a cylindrical-shaped inner conductor. There are two main forms of coaxial resonators:
- λ/4 resonator with one end shorted and the other open
- λ/2 resonator with both ends open
Applications: VCOs, Filters, Coaxial resonator oscillators.
Vendors: Integrated Microwave Corp., Trans-Tech, Tusonix, Temex Ceramics
Dielectric Resonator
Figure 2
The dielectric resonator is a disc-shaped structure with a high relative permittivity (εr). EM fields are largely confined within the dielectric resonator, which minimizes radiation losses and results in a high-Q resonator.
Dielectric resonators can operate in various modes, with the most common being the TE01 mode (transverse electric).
Frequency Range: 260 MHz to about 50 GHz.
Applications: Oscillators, microwave filters, microwave combiners, satellite equipment.
Vendors: MCV Microwave, Temex Ceramics, Trans-Tech
Crystal Resonator
Figure 3
The quartz crystal resonator is constructed by placing a slice of quartz between two electrodes. This slice is achieved by employing a variety of cuts, such as AT-Cut and SC-Cut.
Quartz crystal’s piezoelectric properties are used as frequency control elements in this type of resonator. Piezoelectric materials are used to convert mechanical energy into electrical energy, and vice versa.
Frequency Range: 1.8432 to about 250 MHz
Applications: Satellites, Mobile devices, TVs, home appliances, automotive
Vendors: IQD, Vectron, Oscilent, Murata, Abracon
Ceramic Resonator
Figure 4
The main advantage of a ceramic resonator is its shorter start-up time compared to a quartz crystal resonator. It operates based on the principle of mechanical resonance of piezoelectric ceramics.
It’s constructed using two metal electrodes on both sides of a ceramic substrate. The figure depicts the equivalent circuit of a ceramic resonator. The substrate between the electrodes vibrates when a voltage is applied. The resonant frequency here depends on the thickness of the substrate.
Applications: Automotive, medical, communications, healthcare
Vendors: Murata, Abracon, Oscilent
SAW Resonator
Figure 5
SAW stands for Surface Acoustic Wave. These waves propagate at the surface of a crystal of piezoelectric type to carry information.
SAW resonators are used to construct oscillators, much like crystal resonators.
Frequency Range: Available up to 1.1 GHz
Vendors: ECS Inc. International, Murata, Abracon, Golledge Electronics
Applications: High-Frequency Oscillators, Band Pass Filters (BPFs), security devices, door openers, keyless devices, etc.
YIG Resonator
Figure 6
YIG resonators are crystal devices that boast a high Q-factor and are thus used to develop oscillators with very low phase noise.
A YIG resonator will resonate when immersed in a DC magnetic field. The resonance is directly proportional to the magnitude of the applied magnetic field, which can be generated using magnets of various types.
Frequency Range: Up to about 50 GHz.
Applications: Filters and Oscillators
Vendors: Micro Lambda Wireless
Conclusion
Understanding the different resonator types is crucial for selecting the right component for RF designs. Each type has its strengths and weaknesses, catering to specific application needs. By carefully considering these factors, engineers can optimize their designs for performance and efficiency.
