For wireless personal-area networks (WPANs), the 60-GHz unlicensed frequency band offers the hope of multi-gigabit-per-second wireless connectivity for short distances between devices. Impressively, the data rates that are being touted exceed the rates offered by current lower-frequency wireless-local-area-networking (WLAN) technologies by 40 to 100 times. As complementary-metal-oxide-semiconductor (CMOS) approaches are trialed for such applications, however, most on-chip antennas provide poor radiation efficiency. A solution has been presented in the form of a 60-GHz artificial-magnetic-conductor (AMC) -based circularly polarized (CP) antenna from Xiao-Yue Bao and Yong-Xin Guo from the National University of Singapore, along with Yong-Zhong Xiong from the Institute of Microelectronics.
The design comprises a wideband, circularly polarized loop antenna (top layer) and an AMC structure (bottom layer). With the circular open-loop structure, the gap within the loop can excite the traveling-wave current. It may then achieve circular polarized radiation. The researchers found that the circular-polarization bandwidth can be significantly increased by introducing an additional inner parasitic loop.
When the modified AMC structure is integrated into the bottom layer, antenna performance can be optimized. The AMC plane is designated as a high-impedance surface (HIS) or perfect magnetic conductor (PMC). As a result, an AMC plane can produce constructively in-phase reflections with the incident wave at a specified operating frequency band. The stronger radiation required for transmission can therefore be generated. Design flexibility also increases as a result of this approach.
The antenna and modified AMC structure measure 1.8 x 1.8 x 0.3 mm3. The proposed antenna provides simulated peak gain of -3.7 dBi and measured gain of -4.4 dBi. It offers a simulated and measured axial ratio (AR below 3) bandwidth covering 57 to 67 GHz. See “60-GHz AMC-Based Circularly Polarized On-Chip Antenna Using Standard 0.18-μm CMOS Technology,” IEEE Transactions On Antennas And Propagation, May 2012, p. 2234.