Ka-Band Substrate Integrated Waveguide Equalizer With Larger Equalization Value Based on Capacitive Loading Technology and Tiny Gap Effect

In this article, an innovative design for the substrate integrated waveguide (SIW) equalizer operating in the Ka-band (millimeter waves) is proposed. This equalizer incorporates a capacitive loading technology and leverages the tiny gap effect to achieve a significantly enhanced equalization value. An equivalent capacitance can be created between the surface resistance layer of indium tin oxide (ITO) conductive film and the top metal layer of SIW body, due to tiny gap filled with a thin sheet of poly tetra fluoroethylene (PTFE). In this case, the area where surface current flows, characterized by surface resistance, has been enlarged. At lower operating frequencies, the expanded area is larger. Hence, the introductions of capacitive loading technology and tiny gap effect lead to a more prominent decrease in the attenuation constant $\vert \alpha \vert $ . This improvement is evident when compared to scenarios, where such technologies are not employed in previous studies. The measurement results show that the minimum/maximum equalization values are 3.95/14.77 dB ( $27\Omega $ /sq), 5.15/15.72 dB ( $37\Omega $ /sq), and 7.48/17.38 dB ( $50\Omega $ /sq), respectively. Significantly, the cost of SIW equalizer in this study is considerably lower than that of ceramic substrates. Moreover, the stability of the equalization value surpasses that of absorbing materials, which tend to exhibit slight variations under physical pressure.