## 1 Introduction  
A dielectric resonator antenna (DRA) uses a material with a high dielectric constant as a radiator and possesses high radiation efficiency due to low conduction loss and the absence of surface waves. In addition, it is easy to process, making it suitable for fabricating into various shapes, while antennas can be excited easily via coupling and direct feeding. Generally, DRA has directional beam pattern characteristics in the fundamental mode but wide HPBW characteristics in certain modes. An antenna with a wide HPBW can be used in various fields such as wireless access points, radar, and communication, but there is a problem that the pattern is not flat. Recently, research on wide-beam DRA for solving this problem has being conducted. Studies that have attempted to overcome this problem include [1; 2; 3; 4; 5; 6]. In [1], unilateral rectangular DRA was designed to simultaneously excite the adjacent TE\({}_{j11}^{y}\) and TE\({}_{j21}^{y}\) modes by feeding the probe to make a quasi-omnidirectional radiation pattern. In [2], the ground and DRA were configured in a conformal manner to implement a wide-beamwidth radiation pattern, while in [3], high dielectric constant slabs were attached to the side of the DR to improve the beamwidth at an appropriate location by identifying the field formation inside the DRA. However, the above-noted papers included a wide HPBW only within a single-cut plane (only in the E plane or H plane). In the case of [4], which included wide-beam characteristics in both the E and H planes, the size of the antenna ground was extremely large due to the presence of a sidewall structure for widening the beamwidth, which potentially restricted the application. In [5], a mode with a broad E-plane and a narrow H-plane and a mode with a narrow E-plane and a wide H-plane were analyzed to find frequencies where the two modes are strongly coupled, and designed antennas with wide HPBW on both sides. Although it has the disadvantage of having a very large ground size compared to the wavelength, it was useful to the point that wide HPBW can be achieved if an appropriate mode fusion is achieved. Similar to [5], [6] also combined three excitation modes through irregular geometry to achieve a wide HPBW. Due to the nature of DRAs, in existing studies, unwanted radiation occurred from the use of various high operational band modes; this happened because too many modes were active once the antenna was excited. In general, by designing a filter on the radio-frequency (RF) stage, unwanted radiation in a section other than the operating band can be suppressed. However, its integration with additional filters increases the overall size of the system, based on the size of the filter itself and the impedance-matching circuit. To overcome these drawbacks, studies have been conducted on filter-integrated antennas (filtennas) [7; 8; 9; 10; 11; 12; 13; 14; 15]. In [7], a coaxial filter type was designed on a metal feeding rod and integrated with a radiator to suppress harmonics. However, as the order of the filter increased, the height of the cavity also increased. In [8], ferrite was placed on a feeding line to implement filter characteristics, although the addition of ferrite increased the weight of the antenna; therefore, to utilize a large amount of ferrite, the length of the feeding line must be extended. In [9], a band-pass filter was integrated, resulting in a decrease in gain due to a significant transmission line loss. In [10; 11], the low pass filter and the band pass filter were integrated into the feeding lines, respectively. Both suppressed broadband harmonics by adding a filter to microstrip patches fed by the CPW method. In [12; 13], without adding a filter structure, slots are applied to the patch antenna to form radiation nulls at the bottom and top of the passband. In [14; 15], a frequency selective surface (FSS) was attached to the aperture of a typical via feeding microstrip patch antenna to suppress unwanted harmonic radiation.