## 1 Introduction  
The outstanding features of circular polarization have forced researchers to delve into designing circularly polarized antennas for many wireless applications. The two main features of CP are its ability to combat multipath fading and polarization mismatching [1, 2] and its contribution to minimizing the Faraday rotation effect [2]. The applications of CP have been extended to include 5G applications, WiMax, WLAN, RFID, satellite communications, and so on [2, 3].  
Antennas with circular polarization can be designed as wideband CP antennas [4, 5, 6, 7] to achieve a wide operating bandwidth, dual-band CP [8, 9], and a dual-band dual-sense CP patch antenna [10]. There are many antennas that use single feeding to generate CP for 5G mid-band applications. A CP wide-slot antenna with left-hand circular polarization (LHCP) has been designed for standards LTE 42 and LTE 43 [11]. For standard LTE 43, a slotted-patch microstrip antenna that is fed by a proximity-coupled line with negligible back radiation is presented in [12]. In [13], a filtenna element comprises a filter and an antenna to cover the same band of frequencies. All of these antennas provide single circular polarization radiation, so dual polarization can be generated by using a dual feeding technique to realize polarization diversity and frequency reuse [1]. In addition, the impedance and axial ratio bandwidths are wider in dual feeding than those of the single feed [2]. With the aid of even and odd mode analyses, the coplanar waveguide (CPW) transmission line was exploited as a form of feeding to verify a dual-CP antenna [14]. In [15], a microstrip patch antenna array that consists of metallic plates around the patch is excited by a branch line coupler as a feeding network to provide an antenna bandwidthof 16.5%. An X-band patch antenna is fed by a quadrature hybrid coupler to excite right-hand CP (RHCP) or LHCP in [16]. A two-port, dual circularly polarized patch antenna for MIMO WLAN applications is presented using square ring slot feeding to operate along the range (2.4-2.485 GHz) [17]. A narrowband impedance bandwidth equal to 2.4% along the range of (2.41 to 2.47 GHz) is proposed as a 2 \(\times\) 2 dual-CP series-fed square patch antenna array that is fed with two hybrid couplers to achieve a 45 MHz axial ratio bandwidth [18]. The proposed design in [19] obtains a dual-CP series-fed patch antenna array through coplanar proximity coupling with seven patches and two ports, whose 3 dB axial ratio bandwidth (ARBW) is 10% from 9.66 to 10.66 GHz. Wideband dual-CP antennas are designed in [20; 21; 22], while a metasurface layer is positioned above the two-truncated-corner patch antenna to achieve an antenna bandwidth of 14.5% [20]. Another work related to the field of metasurfaces is proposed in [23]. A stacked patch is fed by a single-section hybrid coupler through aperture coupling to generate wideband dual-CP radiation at 5.5 GHz with an impedance bandwidth of 30.0% [21]. Four coupling slots are incorporated into the patch with multiple matching segments to achieve a wide impedance bandwidth equal to 24% and a 3 dB ARBW of 16% in [22].  
In this work, a simple and compact dual-CP antenna is proposed with the help of a 90\({}^{\circ}\) hybrid coupler as a form of external feeding to generate simultaneous dual-CP radiation. Moreover, the proximity-coupling structure is used to excite a modified circular patch antenna in order to provide a larger impedance bandwidth. Four identical slits are etched on the circular patch to improve the coverage of the axial ratio bandwidth (ARBW) to cover LTE 43 mid-band 5G applications (3.6-3.8 GHz). This antenna is fully covered by the ground plane to suppress back radiation. The simulated and measured results of the reflection coefficient and the axial ratio show good coverage of this frequency band with satisfactory radiation characteristics. The antenna's realized gain is within an average of 1.3 dBi along the antenna impedance bandwidth.