Contents I. Introduction
Capsule endoscope is an alternative to a fiber-based endoscope used in diagnosing diseases related to the gastrointestinal tract. It removes the inconvenience and pain suffered by the patients when wired endoscopes are used. A capsule endoscope can also reach areas such as the small intestine and deliver real-time images wirelessly to an external console. In addition to image data, navigation and control of a sophisticated capsule endoscope should be delivered over a high-capacity wireless link. For high data rate and short-range applications of this kind, ultrawideband (UWB) communication is an ideal physical-layer solution. Moreover, impulse-based UWB transmitters are simple and can be built compactly even with off-the-shelf components, ideal for size-restricted biomedical applications. UWB standards leave almost 7 GHz of frequency bandwidth license-free for low-power operation. Recently, a working group for Body Area Networks (BAN) known as IEEE 802.15.6 has been formed to develop a communication standard optimized for low-power devices operating near, on, or inside the human body. IEEE 802.15.4a, a UWB-based standard approved in March 2007, is one of the potential candidates for BAN applications, such as the capsule endoscope [7]. The frequency band 3.5–4.5 GHz, selected for our UWB development, avoids narrowband systems operating in the industry, scientific, and medical (ISM) bands. Furthermore, beyond 5 GHz, the tissue imposes strong attenuation to electromagnetic waves [2]. The antennas and applications that have been previously reported for endoscope applications operate in lower frequency bands [3] for this reason. Therefore, to obtain the full use of high data rate capabilities of UWB while minimizing through-body losses, it is best to select the lower end of the UWB band. The printed antenna presented in this letter is shaped to be used in a capsule and demonstrates good matching in the frequency band of 3.5–4.5GHz. The radiation performance has been evaluated experimentally using an impulse-based UWB transmitter/receiver testbed to show that it is suitable for endoscope-type implanted applications.