RF Design for Inkjet Technology: Antenna Geometries and Layer Thickness Optimization

The suitability of local conductive print-layer thickness variation for RF applications is demonstrated on flexible substrates. First, the concept is subjected to printed transmission lines as attenuation of one- and two-layer lines is compared to lines having additional layers only on critical high-current areas. Then, two antenna types are studied by applying local additions to the feed line and radiator with optimized print parameters for each layer utilizing low-temperature ink enabling a variety of substrate materials. For a narrow wire-type antenna, efficiency improvement with local thickness increase is observed both at 868 MHz and 2.4 GHz, reaching the efficiency level of a full two-layer antenna. For a wide monopole-type antenna at 2.4 GHz, the similar efficiency improvement up to the full two-layer level is seen already by increasing the edge thickness on the feed line. Accordingly, the antenna type is promising for printing with satisfactory efficiency only with one-layer print on the antenna element. The printed antennas also show good electrical performance, with only approximately 5%-10% decrease in efficiency compared to thick 18-μm copper reference antennas.