Background
Microwave filters are used in a wide range of applications and forms including lumped element filters, planar distributed filters, and quasi-optical filters. Most optical filters for laboratory use or use in cameras are made from multiple coatings of different dielectric materials where the difference in the index of refraction of the materials causes multiple internal reflections, and the thicknesses of the layers are carefully designed as patterned planar structures on a chip or circuit board. These long wavelength filters require a way of collecting radio waves traveling through the air, such as an antenna onto the circuit board or chip.
Quasi-optical metal mesh filters using equivalent capacitive and inductive grids have been used for free space millimeter-wave to far-IR (THz) filtering applications. Examples of these filters are low-pass filters using free space capacitive shunts which are realized as arrays of square metal grids. However, the grids in these filters are not ideal capacitors because they exhibit diffraction approximately 2x above their resonant frequency and have high frequency leaks. Other types of filters can be realized in quasi-optical metal mesh using artificial dielectrics. Stepped impedance filters are the most common type of filter for optical wavelengths, which are manufactured using multilayer dielectric films.
Invention Description
Researchers at Arizona State University have developed a novel design for free space coupled quasi-optical filters based on stepped impedance designs. In this design, the dielectric layers are realized as metamaterials using metal mesh patterns. At long wavelengths, this invention provides a method for making custom dielectric materials by embedding periodic metallic grids in a dielectric substrate. This allows the creation of filters that are highly efficient, low loss and can be used in long wavelength applications.
Potential Applications
- Long wavelength (radio to far-IR) astronomical instruments on ground-based and space-based telescopes
- High-end radio and millimeter-wave communications downlink receivers
- Laboratory test systems
Benefits & Advantages
- Improved filter performance (larger range of dielectric constants possible)
- Allows use of stepped impedance filters for microwaves or millimeter waves in a free space coupled design
- High efficiency & low frequency loss