Tapered slot antennas (TSA) have been used for many decades. Possibly the most familiar form of a TSA is the Vivaldi antenna . This type of antenna has found extensive use in antenna array systems [2, 3]. Numerical methods have been used for their design such as the TLM method  and FDTD method . However, one limitation of Vivaldi type TSA antennas is they are electrically large, up to several wavelengths long  which can limit their application where size is a concern.
An alternative TSA is the dielectric notch radiator (DNR) antenna [7, 8] (the notch refers to the physical appearance of the antenna, and should be confused with a notch filter). It has the same positive benefits of the Vivaldi TSA, but it is much shorter. In fact, it can be fabricated with the taper section being less than a half wave length long. Prior work has been done on compact versions of Vivaldi antennas. In , for instance, a compact Vivaldi antenna was realized, but size compaction was achieved by embedding the antenna in a dielectric. The dielectric loading increases the size, weight, and cost of the antenna which limits the types of applications that can use it. Another example is similar to the DNR and is referred to here as the ZHG after the authors of the paper describing it . One drawback of the ZHG antenna is it uses slot line sections with abrupt bends. This can result in undesired parasitic radiation especially at higher frequencies. In contrast to this prior work, the DNR uses a smooth radius for the slot line section which minimizes the undesired radiation. Also, it avoids the need for dielectric loading for compaction.
My work in this area demonstrates the usefulness of the DNR antenna for radar, 5G, and IoT applications. It was presented at an IEEE conference and will be archived on the IEEE Xplore website. The paper describes the design procedure, test results for an antenna fabricated to cover X-band, and antenna designed nad fabricated to cover LTE band numbers 12 and 25, and 2.4GHz Wi-Fi band. These are popular bands for 5G and IoT applications. The antenna is integrated with diplexer filters which separate out the bands of interest.
Figure 1. Image of the measured radiation pattern of an X/Ku-Band dielectric notch radiator (a) single element, and (b) four element antenna.
Figure 2. Measured return loss showing the X/Ku-Band dielectric notch radiator has -10dB return loss from about 7.5 to 13GHz.
I designed antennas for operation at X-band and images of them and their measured radiation patterns are shown in Figure 1. Note in Figure 1(a) the radiation pattern of the single element antenna. As expected, it has a broad radiation pattern and about 3dB of peak gain. The radiation pattern of a four element array is shown in Figure 1(b) and it shows a maximum gain of about 6dB. This antenna was designed to support radar at X-Band and satellite communication at Ku-Band and the measured return loss in Figure 2 shows that it easily covers these bands.
Figure 3. Image of the measured return loss and test antenna for the Wi-Fi, LTE, and Zigbee bands.
Other antennas were fabricated and the version fabricated to cover Wi-Fi, LTE, and Zigbee is shown in Figure 3. The return loss is less than -10dB from about 900MHz to 2.6GHz which covers many useful communication bands.
The dielectric notch radiator antenna provides the advantage of having wide electrical bandwidth and small physical size.
 P. J. Gibson, “The Vivaldi Aerial,” 9th European Microwave Conference, Brighton, UK, 1979, pp. 101-105.
 M. Sims, D.E. Lawrence, R. Halladay, “A fully-integrated Vivaldi phased array for seeker applications,” IEEE International Symposium on Antennas and Prop., Washington, DC, July 3-8, 2005, pp. 445-448.
 N. Ardelina, E. Setijadi, P. Hari Mukti, B. Manhaval, “Comparison of array configuration for Antipodal Vivaldi antenna,” Intern. Conference on Radar, Antenna, Microwave, Electronics, and Telecom., Bandung, Indonesia, Oct 5-7, 2015, pp. 40-45.
 F. Ndagijimana, P. Saguet, and M. Bouthinon, “Application of the TLM method to slot antenna analysis. A new absorbing boundary for the TLM method,” Proc. 20th European Microwave Conference, vol. 2, 1990, pp. 1495–1500.
 E. Thiele and A. Taflove, “FD-TD analysis of Vivaldi flared horn antennas and arrays,” IEEE Trans. Antennas Propagation. , vol. 42, pp. 633–641, May 1994.
 K. Ebnabbasi, H.D. Foltz, “Vivaldi antenna taper design based on impedance matching,” IEEE Antennas and Propagation Society International Symposium, San Diego, CA, July 5-11, 2008, pp. 1-4.
 U.S. Patent Number 8063841.
 U.S. Patent Number 8730116.
 G. Adamiuk, T. Zwick, W. Wiesbeck, Compact, dual-polarization UWB-antenna, embedded in a dielectric, IEEE Trans. on Antennas and Propagation, vol. 58, no. 2, pp. 279-286, Feb. 2010.
 F. Zhu, S. Gao, A.T.S. Ho, T.W.C. Brown, J. Li, G. Wei, J. Xu, “Miniaturized Dual-Polarized Ultra-Wideband Tapered Slot Antenna,” International Symposium on Antennas and Propagation, Nanjing, China, Oct. 23-25, 2013, pp. 446-449.