International Journal of Microwave and Wireless Technologies cambridge.org/mrf Research Paper Cite this article: Varshney G, Pandey VS, Yaduvanshi RS (2018). Axial ratio bandwidth enhancement of a circularly polarized rectangular dielectric resonator antenna. International Journal of Microwave and Wireless Technologies 10, 984–990. https://doi.org/ 10.1017/S1759078718000764 Received: 14 November 2017 Revised: 16 April 2018 Accepted: 17 April 2018 First published online: 5 July 2018 Key words: Axial ratio; circular polarization; dielectric resonator antenna Author for correspondence: Gaurav Varshney, E-mail: gauravnitd@outlook. com © Cambridge University Press and the European Microwave Association 2018 Axial ratio bandwidth enhancement of a circularly polarized rectangular dielectric resonator antenna Gaurav Varshney 1 , V. S. Pandey 2 and R. S. Yaduvanshi 3 1 Department of Electronics and Communication Engineering, NIT Delhi, Delhi 110040, India; 2 Department of Applied Sciences, NIT Delhi, Delhi 110040, India and 3 Department of Electronics and Communication Engineering, AIACTR, Delhi 110031, India Abstract This paper presents a new technique for the enhancement of axial ratio (AR) bandwidth of a circularly polarized dielectric resonator antenna with a single feeding. To enhance the AR bandwidth, adjacent 3-dB AR passbands are merged by inserting the notches and conductive coating in the dielectric resonator. The dimensions of the notches and conductive coating are selected in such manner that impedance bandwidth remains approximately unchanged. The antenna provides the measured AR and impedance bandwidths of 55.22% and 66.45%, respectively. Introduction Dielectric resonator (DR) antenna (DRA) offers wide bandwidth, high gain, high radiation efficiency with minimal surface wave and conductor losses [1]. These features of DRA made it popular among the researchers. Earlier, the study was carried out on the linearly polar- ized (LP) DRA (LPDRA). It was observed that the misalignment of LP antennas causes polar- ization mismatch losses. Also, the signal degradation occurs in the case of the multipath reception if LPDRA is being used in a communication system. Replacing the LP antenna with a circularly polarized (CP) antenna prevents these limitations, so the development of CPDRA was promoted [2]. To achieve the circular polarization in DRA, numerous techniques have been reported in the literature [3–14]. Some of these can be categorized as single feeding, dual feeding, modified shape of the DR, and modified shape of the slot. The limitation of sin- gle feeding technique is that it provides a narrow axial ratio (AR) bandwidth [3, 4]. To increase the AR bandwidth, dual feeding structure was reported [5]. However, dual feeding structure becomes complex due to the requirement of the external power dividers. Later on, the shape of the DR was modified to increase the CP bandwidth, e.g., trapezoidal [6], stair shape [7], rotating stair [8], DR with diagonally inclined slits [9], and DR with parasitic strips [10]. These antennas provide wide CP bandwidth but the complexity of DR shape leads to the manufacturing difficulty. To achieve wide AR bandwidth, different shapes of the slot have been proposed like cross slot [11], modified cross slot [12], Archimedean spiral slot [13], and stair- shaped slot [14]. The use of the specific shaped slot in the antenna structure with single feed- ing provides wide CP bandwidth. Recently, a CPDRA was reported with stair-shaped slot pro- viding wide AR and impedance bandwidths of 41.01 and 49.67%, respectively [14]. Despite significant progress, obtaining the wide CP bandwidth with simple DR structures and single feeding is still a challenging task. In this context, this paper presents a new technique for the enhancement of AR bandwidth of CPDRA. The proposed antenna structure provides the multiple 3-dB AR passbands. The neighboring 3-dB AR passbands of the antenna are merged to enhance the AR bandwidth by introducing the notches and conductive coating in the DR. Previously, the diagonal vertices of the DR were removed to achieve the dual-band circular polarization [15]. Also, a CP antenna array was proposed with the chamfered DR structure [16]. Achieving the circular polarization in chamfered DR with aperture feeding is easy when the length and width aspect ratio of the rectangular DR is unity. When this aspect ratio of the rectangular DR is non-unity, the size of the notches must be selected prudently. In this paper, a rectangular DR is used with non-unity length/width aspect ratio. The size of the notches is selected so that the impedance bandwidth of antenna remains unaffected. After that conductive coating is applied on the notched wall of the DR for merging of the adjacent AR passbands. Earlier, parasitic strips were used in a complex DR structure to achieve the AR and impedance bandwidths of 25% and 24.5%, respectively [10]. The stair-shaped slot is used for excitation in the proposed antenna structure [14]. The proposed antenna provides the measured 3-dB AR bandwidth of 55.22% and 10-dB impedance bandwidth of 66.45%. The 3-dB AR passband completely overlaps with the 10-dB impedance passband which makes the antenna useful for C-band https://doi.org/10.1017/S1759078718000764 Downloaded from https://www.cambridge.org/core. IP address: 3.236.6.168, on 03 Jan 2022 at 02:09:22, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.