Microstrip filter technology was first released in 1952, since then, numerous advancements in both dielectric material manufacturing and thin film processing techniques have led to the adoption of microstrip filtering for a wider range of applications, especially at mmWave frequencies.
An Overview of How Microstrip filter Technology Works
At a high level, microstrip refers to a type of planar transmission line technology that consists of a conducting strip separated from a ground plane by a dielectric substrate as shown in Figure 1.
More specifically, the design and construction of a microstrip filter is similar to the way circuits are configured on a printed circuit board (PCB).
However, a key distinction of a microstrip filter is that the metal conductor patterns printed on the solid dielectric substrate are there to create resonators rather than just interconnects. The metal circuit patterns of strip elements are placed on a solid dielectric insulating layer with a metal ground layer below the dielectric.
The fields surrounding the strip permeate two different media, with part of the field in the substrate and another in the air above the strip. The higher permittivity of the dielectric substrate causes the electric field to concentrate in the substrate, which means field losses due to material choice become a factor. Standard PCB materials like FR4 can be used below 1GHz for low Q filters. Lower loss and increased Q can be achieved using ceramic materials.
This type of printed transmission line is a popular filtering option since these filters can cover a broad frequency range, are economical to produce, and are often lighter and more compact than alternative transmission line technologies such as waveguide.
Overcoming Issues with Loss for Microstrip Filters
The biggest concern with microstrip filters is the loss experienced compared with other transmission-line and waveguide filtering approaches. However, the evolution of high-k materials, such as our Rogers RO3010 and others is making it possible for RF engineers to develop low-loss microstrip transmission-line filters.
RFOXIA: RFXOIA team managed to build AI based software -AFD- that can design filters using these RF materials which guarantees the minimum losses and most requirements satisfaction
