Design and High Performance of a Micromachined $K$-Band Rectangular Coaxial Cable

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents the design and performance of a low-loss rectangular air-filled coaxial cable. A high-precision micromachining technique is used to fabricate the cable. It is assembled by bonding together five layers of gold-coated SU-8 photoresist fabricated using the ultraviolet photolithographic technique. As the cable is air filled, both the dielectric and radiation losses are negligible. The cross coupling is also very weak between the cable and other parts of the circuit in a system. These advantages make the proposed cable a very good candidate for low-cost high-performance miniaturized transmission lines. The cable is designed to work in the frequency range of 14–36 GHz, which covers the whole <formula><tex>$K$</tex></formula>-band. The size of the cable is only <formula formulatype="inline"><tex>${\hbox {8.9}}\ {\hbox {mm}}\times {\hbox {8.6}}\ {\hbox {mm}}\times {\hbox {1.5}}\ {\hbox {mm}}$</tex> </formula> and the measured minimum insertion loss of the as-made cable is approximately 0.6 dB. The return loss is better than 15 dB in the passband. </para>