Contents I. Introduction
Low-power wireless devices that operate on the basis of retransmitting a modified form of a received interrogation signal are desirable in certain sensing and tracking applications. There have been several published sensor designs that may be employed in such applications, including RFID transponders, surface acoustic wave sensors and a reflectenna design [1]–[3]. These configurations generally consist of a receiving antenna, a device such as a switch or an IC chip that modulates a received continuous wave tone and a transmit antenna. Most often the antennas occupy the majority of the overall device area. A reduction in the size of the antenna typically degrades its performance, which in turn impacts the overall efficiency of the system. Therefore, designs that reduce the footprint of the sensor device by incorporating efficient, compact antennas are desired.
