A thin and low-cost scalable waveguide load absorber

In this paper, a set of simple S-band waveguide absorbers are designed and implemented on a low-cost FR4 substrate. This is to provide an alternative for conventional waveguide absorbers, which are generally bulky and costly. The proposed structure is composed of only two open-ended resonator strips on a low-cost, 3.2-mm thick FR4 board. These absorbers operate with the same fundamentals as absorbers based on the frequency selective surfaces. The proposed innovative waveguide absorber load is mode-independent and designed without any connection between the strips and the waveguide. Simulations and measurements indicated an approximately 2.2% of bandwidth, with a 99% absorption rate at the center frequency. A complete parameter study is also performed to show the robustness of the design, besides enabling tuning for use in other microwave waveguides. A good agreement between simulated and measured results confirms the functionality of the absorber.