# Quasi-Isotropic Hybrid Dielectric Resonator Antenna--Bow-Tie Patch with Harmonic Suppression
## 1 Introduction  
Because the isotropic pattern can be transmitted to and received from all directions, it can be applied to various communication fields, such as radio frequency identification, wireless access points, and the internet of things, thereby increasing interest in isotropic antennas. However, realistically, it is impossible to realize an ideal isotropic radiation pattern that covers all directions; therefore, various studies have been conducted to implement a quasi-isotropic pattern [1; 2; 3; 4; 5; 6; 7]. Two omnidirectional patterns that have an orthogonal relationship are required to implement a quasi-isotropic pattern. A method of implementing a quasi-isotropic pattern by placing two electric field dipole antennas in a mechanically orthogonal state exists [2; 3; 4]. Furthermore, a method of implementing a quasi-isotropic pattern using an electric field dipole and a magnetic field dipole having a complementary relationship exists [5; 6; 7]. In previous studies [2; 3; 4], a quasi-isotropic pattern was realized by physically crossing two electric field dipoles. In another study [5], a quasi-isotropic pattern was implemented by making orthogonal electric and magnetic field dipoles using loops formed on the folded dipole and ground. An electric field dipole was implemented in the feeding structure of the loop antenna, and a quasi-isotropic pattern is implemented using a magnetic field dipole in the loop antenna in a previous study [6]. In the literature [7], a quasi-isotropic pattern was implemented using a dielectric resonator antenna (DRA) and a small ground. Here, DRA is equivalent to a magnetic field dipole. The small ground is equivalent to an electric field dipole, and the quasi-isotropic pattern is realized by synthesizing these two radiation patterns. However, since the study mentioned above has notconsidered radiation by harmonics other than the operating band, interference with other communication equipment may occur. In general, a filter structure is also used outside the antenna to suppress interference with communication equipment at other frequencies. However, this additional structure increases the system size, fabrication cost, and insertion loss [8]. Various research projects focusing on antennas with a harmonic suppression function are being conducted to solve this problem. For example, studies on integrating harmonic filters into antennas [9; 10; 11; 12; 13], using impedance transformers [14; 15], using harmonic canceling techniques [16], and using defected ground structures (DGS) [17; 18; 19] have been conducted. The authors of [9] used a coaxial line-type sixth-order Chebyshev low-pass filter as the feed structure for the cavity-back patch antenna to eliminate the generated harmonics. In [10], harmonics generated in a section other than the operating band were eliminated by implementing a coupled line-type bandpass filter in the ground region of the DRA. The authors of the paper [11] designed a multilayer consisting of a radiator, filtering, and slot stage and integrated a filter and antenna to suppress harmonics. In studies [12; 13], suppressing harmonics by implementing a notch filter in a T-shaped feeding structure and suppressing harmonics using a low-pass filter with ferrite are presented. The study [14] suppressed the harmonics of the patch antenna using a \(\lambda/4\) transformer and a shorting pin. The author of the thesis [15] removed the harmonics by integrating an impedance transformer that matches the impedance in the operating band and mismatches the impedance in the harmonic band into the antenna. In the study [16], harmonics were canceled by adding a \(\lambda/4\) stub of harmonic frequency to generate a field with an inverse phase of harmonics. In References [17; 18; 19], harmonics are suppressed by adding a slit or stub to the ground and feed line of the antenna.