## 1 Introduction  
The Internet of Things (IoT) has become a major trend across a wide range of industries, and many IoT-based applications are beginning to scale up from pilot projects. As more IoT use cases are adopted, it is anticipated that the digital transformation of enterprises will accelerate. It is essential to combine the efforts of IoT and 5G technology in order to fully realize the potential of IoT and move toward the goal of pervasive data connectivity [1, 2]. The circularly polarized (CP) antennas can suppress the multipath effects and have great flexibility in the orientation of the transmitting and receiving antennas [3]. Thus, CP antennas are widely used in many applications, such as satellite communication and navigation, wireless identification, radar detection, etc. As the requirement for high data throughput grows dramatically, CP antennas with high directivity and wide bandwidth are in great demand to overcome path loss and increase the data rate.  
Many types of CP antennas have been designed, such as printed antennas [4, 5, 6], slot antennas [7], magnetoelectric dipole antennas [8], cavity antennas [9], helix antennas [10], and dielectric rod antennas [11], while the gains of these CP antennas are limited. The gain of these antennas depends on length and diameter [10, 11, 12]. Typically, a dielectric rod antenna with 11 \(\lambda\)-15 \(\lambda\) length can obtain a gain of up to 18-20 dBi [11, 13].  
There are two examples of designing CP dielectric antennas. One is to use linear polarized primary feeding with a rotated tapered dielectric rod [11], and the other is to adopt CP primary feeding with a rotationally symmetric dielectric rod [14; 15]. The antenna developed in [9] has good circular polarization performance, but the gain is only 9 dBi within the 4.2 \(\lambda\)\(\times\) 0.5 \(\lambda\) aperture. In [16], a bifilar helix is employed as a feeding structure to obtain CP radiation within the reduced dimension, but it can only realize a 9 dBi gain at 8 GHz.  
To obtain higher gains, a dielectric rod antenna with a larger size is presented in [17], and a linearly and curvilinear tapered cylindrical dielectric rod fed by a conical waveguide is designed to achieve 22 dBi gain with a total length of 20 \(\lambda\). However, its radiation efficiency will decrease quickly when the length is larger than 7 \(\lambda\)[18]. Moreover, the larger length of a typical dielectric rod antenna also increases the side lobe levels.  
In the presented structure, a tapered helix is used as the primary feeding of the dielectric rod antenna for CP. Further, extra tapered printed loops are also embedded with the rod to obtain higher gain and lower side lobe levels. The novelty of the presented structure lies in that, in comparison with previous dielectric rod antennas, extra printed loops are embedded dielectric rods instead of periodic surfaces to increase the gain further. Along with high gain, high polarization purity is successfully achieved for CP radiations.  
Moreover, in the proposed embedded structure, double gain can be achieved for the same electrical length of conventional dielectric rod antennas, SLL (Side Lobe Levels) are also lower than in conventional rod antennas, and SLL decreases as antenna length increases, whereas in conventional same class antennas SLL increases with the length of antenna for higher gain. A prototype operating around 9.5 GHz has been designed and fabricated, as shown in Figure 1b. The measured results show that the prototype can provide more gain within the same length of 7.7 \(\lambda\). Additionally, the axial ratio is smaller than 1.14 dB for the entire band. The comparison of simulated and measured results gives a good agreement of theoretical and practical structure.  
Figure 1: (a) Application areas of proposed antenna (b) Fabricated prototype of Embedded Helix and dielectric rod antenna.