Growing requirements for short-range communications involving high data rates has sparked tremendous interest in the development of ultrawideband (UWB) technology. Since 2002, when the U.S. Federal Communications Commission (FCC) identified the frequency spectrum from 3.1 to 10.7 GHz as the place for UWB systems, work has continued in designing the various components needed for such systems, including antennas.
Basically, three types of antennas have been employed for UWB systems: microstrip, slot, and dielectric resonator antennas (DRAs). Microstrip and slot antennas provide the small sizes that are attractive for many UWB systems, but they exhibit extremely low gain. DRAs offer much higher gain, but they are also much larger than microstrip and slot antennas.
To overcome that limitation of DRAs, researchers from the Indian Institute of Technology (IIT) in Dhanbad, India, explored the miniaturization of a high-gain DRA capable of operating from 3.23 to 10.98 GHz. During their efforts, they used composite design techniques and adopted unique shapes for their antennas.
The researchers investigated the creation of antenna structures without unnecessary nonradiating field modes, planning to build their designs on low-cost circuit substrate materials, such as FR-4. They also relied on commercial electromagnetic (EM) simulation software, such as the high-frequency structure simulator (HFSS) from ANSYS to perform analysis of composite radiator structures.
For example, they performed studies of return loss for different annular-shaped transmission-line structures to better understand the surface current densities through various shapes of circuit structures at different frequencies within the UWB frequency range. By finding structures with multiple resonances that could be enhanced in terms of bandwidth via impedance transformers, they developed three-dimensional (3D) antenna structures that could cover the UWB frequency range by means of multiple resonances from a single structure.
One of the more effective printed-circuit antenna structures was a dumb-bell-shaped cylindrical DRA (CDRA). Using a novel feed structure, additional resonances in the DRA are excited, notably within the mid-UWB range at 5.2 GHz. The enhancement of these additional transverse-electromagnetic (TE) modes to higher frequencies enables this dumb-bell shaped DRA to provide relatively consistent return loss across the full UWB frequency range.
A prototype of the CDRA was fabricated and analyzed with the aid of ANSYS HFSS software as well as CST Microwave Studio simulation software. In addition, a commercial handheld vector network analyzer (VNA model N9916A) from Keysight Technologies was recruited for measurements from 30 kHz to 14 GHz.
The two software simulators agreed quite closely in their predictions, giving average values of gain and radiation efficiency of 3.1 dBi and 0.88, respectively, for the dumb-bell-shaped CDRA. Measurements with the VNA were made in the xz plane (the E plane) and the yz plane (the H plane) at various frequencies within the UWB range, including 3.3, 5.5, and 9.5 GHz; radiation patterns were measured in an anechoic chamber. Time-domain analysis with the CST Microwave Studio software was also performed to reinforce the discoveries made of the compact UWB antenna’s radiation patterns in the frequency domain.
See “Composite Antenna for Ultrawide Bandwidth Applications, IEEE Antennas & Propagation Magazine, Vol. 60, No. 3, June 2018, p. 57.