In the quest for high-performance filters in frequency ranges above 3 GHz, RF system engineers have faced a number of challenges. Mini Circuits’ identified this gap in the market and has developed a series of Thin-Film Filters that meet all requirements and deliver unparalleled performance and precision in a compact form factor. These cutting-edge filters address the demands of real-world system requirements, providing repeatable performance at production volume while maintaining a small, surface-mount footprint.
Traditionally, lumped element filters using discrete wire-wound inductors and chip capacitors have been suitable for passbands below 3 GHz. However, their performance becomes sensitive to variations in physical structure and temperature at higher frequencies, making them impractical. Similarly, other filter technologies like suspended substrate stripline and cavity filters offer exceptional performance but are bulky, heavy, and expensive, limiting their suitability for integrated microwave assemblies.
The ”thin-film filter technology” addresses these design concerns. Thin film filters, fabricated through the process of Physical Vapor Deposition (PVD) or sputtering, offer high-accuracy fabrication, excellent repeatability, and rugged construction on ceramic substrates. These filters provide a wide passband width of up to 40 GHz, outstanding Q-factor, high power handling, and rejection floors deeper than -60 dB.
The fabrication process involves depositing thin layers of metal or dielectric material onto a substrate with precise control over thickness, materials, and patterns to achieve the desired filter characteristics. This technology allows for the realization of various filter topologies and implementations, making them suitable for surface-mount assembly and offering compact form factors.
Mini Circuits' ABF Series of Thin-Film Filters excels in meeting the requirements of many applications from 3 GHz through mmWave frequencies, where small device size and sharp rejection are essential. The filters offer low passband insertion loss, steep rejection skirts, wide stopband performance, and are cost-effective compared to alternative options with similar RF performance.
These RF/microwave thin-film filters find applications in wireless telecommunications (including 5G), satellite communications, radar systems, Internet of Things (IoT), and mmWave communications. They are renowned for their high performance, temperature stability, volumetric efficiency, and reliability in high-frequency environments.
The ABF-series of filters from Mini Circuits showcases stable performance over a wide temperature range of -55°C to +125°C and is compatible with surface-mount reflow soldering techniques. These filters incorporate a metal lid for shielding, confining electromagnetic fields within the filter structure to ensure accurate simulations, prevent electromagnetic interaction with other components, and provide excellent isolation.
For instance, the ABF-26G+ filter, designed for the 5G n258 band (24.25 to 27.5 GHz), demonstrates impressive performance with mid-band insertion loss measuring less than 1.5 dB and nearly 20 dB return loss across the entire band. The ABF-7R75G+ thin-film bandpass filter centered at 7.75 GHz achieves a bandwidth of approximately 50% with an insertion loss of less than 1.5 dB in a compact package footprint.
Thin-film filter technology offers RF systems engineers benefits such as low insertion loss, high rejection, good power handling, wide temperature range, excellent temperature stability, and repeatability. Their small size and surface-mount form factors make them an ideal solution for high-Q systems with limited space requirements. With the ability to realize innovative architectures at scale, thin-film filters provide an advanced filtering solution for demanding RF applications.
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