Design of Compact Planar Filters Miniaturization Challenges

Introduction

In recent years, in the field of telecommunications, traffic, speeds and the demand for mobility, with the use of wireless communication systems have continued to grow. These various developments require a constant effort from manufacturers to improve the quality of services while minimizing production costs (Ahmed et al., 2018). A filter is an element or a function whose purpose is to select one or more frequency bands from the electromagnetic spectrum and eliminate others. The miniaturization of electronic devices is a major challenge in the context of microwave telecommunications. When compared to other filters, such as waveguide filters, Microstrip filters are already modest in size (Wahab et al., 2018). Smaller Microstrip filters are still preferred for some applications where size reduction is crucial, despite the fact that shrinking a filter size typically results in higher dissipation losses in a given material and lower performance (Kavitha & Jayakumar, 2018). By using lumped elements or substrates with a high dielectric constant, Microstrip filters can be made smaller. The number of new filter configurations increases. New ideas, approaches, and designs for compact filters and filter miniaturization are covered in this chapter (Dabhi & Dwivedi, 2016). Compact resonator filters, downsized dual-mode filters, and Quasilumped-element filters are a few of the novel filter types that are covered.

Planar technology is very widely used in the field of microwave filtering because it allows reduced size and great topological flexibility. Indeed, the manufacturing of the circuits is well controlled, reproducible and has a low manufacturing cost. This technology consists of a dielectric substrate plate metalized on one or two sides (Haddi et al., 2020) . For filters design, planar technology is widely used because of its small size, its good compatibility with other external circuits, its low manufacturing cost and its good reproducibility (Chhabra et al., 2016) . The fundamental mode of propagation of such a structure is a quasi-TEM mode. With this technology, we can design Band Pass, Band Stop, Low Pass and High Pass filters by using many techniques taking into account their performances, seize and integration (Pozar, 2011).

Planar technologies are complementary to solid technologies. Where the latter struggle because of their excessive size and weight, or because of their poor connectivity, planar technologies respond favorably to these criteria (Nasiri et al., 2020).

They are also suitable for mass production, and therefore for cost reduction. These qualities have a price that is paid for by much lower quality coefficients, and admissible powers limited to the Watt. The principle is on the use of a dielectric substrate in the form of a plate, metalized on one or both sides. The Microstrip, Coplanar, and Stripline technologies with suspended substrate are the most crucial ones employed in the implementation of filters. Resonators have been popular in the design of filters in recent years. Open loop, miniature hairpin, stepped-impedance, quarter-wave, and quasi-quarter-wave resonator-based filters have been proposed for either performance increase or size reduction (Makimoto, 2001). Due to their high performance and low loss features, dual-mode resonators have recently gained popularity in microwave and radio frequency (RF) wireless communication applications. Due to its doubly resonant nature, a dual-mode bandpass filter of a given order only needs half as many resonators as a normal setup (Wahab et al., 2020).