Printed antennas are inexpensive, low profile, light weight, mechanically robust and easy to mass manufacture. For these reasons, they can be found in everything from cellular phones to radars. However, new technologies are placing two conflicting demands on these antennas. On one hand, they are required to operate over a wider range (or band) of frequencies; on the other hand, their size needs to be reduced to fit into new generations of devices, such as wearable sensors.
Meeting these challenges simultaneously is difficult because an antenna’s frequency is set in part by its dimensions. Now, Kah-Wee Khoo and co-workers at the Institute for Infocomm Research and the Singapore Institute of Manufacturing Technology, both A*STAR institutes in Singapore, have addressed this challenge by folding a wideband antenna across multiple layers, thus reducing its size without affecting its performance.
The advance exploits a fabrication process that allows a printed circuit to be put together across multiple layers. The process, called low-temperature co-fired ceramic (LTCC), involves the fabrication of multiple layers of printed circuits in parallel. These are then aligned into a stack and heated (or ‘fired’) to form a single unit (Fig. 1). While this approach has been used for years, Khoo and his co-workers applied it in a novel fashion to a printed monopole ultra wide band (UWB) antenna operating between 3.1 and 5.0 GHz.
The printed monopole antenna consists of a radiating element, a transmission line, and a metallic patch called a ground plane that acts as a kind of mirror to the radiating element. Khoo and his team distributed these components across three layers of LTCC laminates. Metal connectors called ‘vias’ then connected the appropriate portions together, effectively reconstructing the original antenna. This process of ‘folding’ the antenna allowed a 25% reduction in width. However, experiments proved that this reduction had little effect on key parameters of the antenna’s behavior, including its radiation pattern and gain.
Because the researchers accomplished this miniaturization with standard multi-layer techniques, the resulting antenna is quite versatile. “It can be easily integrated with radio and intermediate frequency electronics that are themselves fabricated across multiple layers of LTCC laminates,” says Khoo. The technique may also be extended to millimeter-wave antennas, which operate at the highest portion of the radio frequency band and are necessary for an emerging class of sensors and imaging systems.