# Low-Profile Dual-Polarized Antenna Integrated with Horn and Vivaldi Antenna in Millimeter-Wave Band
## 1 Introduction
The dual-polarized antenna is realized by feeding two ports of the same antenna to excite two orthogonal polarization modes. At present, many dual-polarized antennas have been published, such as magnetoelectric dipole (ME-dipole) antennas [13; 14; 15], horn antennas [16; 17], substrate-integrated waveguide (SIW) antennas [18; 19], and patch antennas [20; 21]. In [13], a wideband dual-polarized antenna in a millimeter wave band is investigated. The ME-dipole is composed of four patches and fed by two pairs of orthogonal T-shaped probes. A port is connected with a pair of probes by a T-shaped power divider; thus, dual-polarized performance is realized when the different port is excited. The antenna achieves an overlapped impedance bandwidth of over 50% and isolation higher than 17.8 dB. An \(8\times 8\) dual-polarized ME-dipole antenna array is published in [14]. The antenna element employs the metallic pillars and cavity as ME-dipoles. A cross slots is used to excite two polarizations. Finally, the antenna array maintains an impedance bandwidth from 34.7 to 39.7 GHz (13.4%), as well as a mutual coupling of below 27 dB in the operating band. In [15], a dual-polarized ME-dipole antenna fed by a fork-shaped microstrip line is present. The antenna element is formed with four patches and two cross slots. Then, a \(1\times 4\) antenna array is designed, fabricated, and tested. The antenna array has an overlapped \(-10\) dB impedance bandwidth in 28-33.5 GHz. In [16], a L-shaped horn antenna is proposed. The antenna is filled with dielectric material and fed by two orthogonal waveguides. A wide impedance bandwidth is obtained within 34-40 GHz, and the mutual coupling of the two ports is below 15 dB. In [18], a dual-polarized SIW phased array is investigated. By curving slots on the SIW cavity surface, the antenna can radiate electromagnetic waves. Dual polarization is realized by a differentially fed SIW cavity and a microstrip line. A \(1\times 4\) antenna array is then constructed. The antenna array obtains an impedance bandwidth from 25.8 to 28.8 GHz (11.0%). The isolation is higher than 31.5 dB. A substrate-integrated mode-based end-fire antenna is presented in [19]. A sandwich structure, which is composed of two metal blocks with an open-ended slot, is designed to radiate electromagnetic waves. And the horizontal polarization (HP) is based on the transverse electromagnetic (TEM) mode; in addition, the vertical polarization (VP) is excited by TE\({}_{10}\) mode. The antenna achieves a wide impedance bandwidth of 24.8-32.5 GHz (26.9%). A high isolation between the two polarizations of over 36 dB is also realized. A dual-polarized Spoof-surface-plasmon-polaritons (SSPP) fed patch antenna array is proposed in [20]. Two orthogonal SSPPs are simply connected to a square patch. Therefore, the TM\({}_{01}\) mode and TM\({}_{10}\) mode can be excited simultaneously, and the dual polarization is obtained. Measurement results shows that the antenna has the \(-10\) dB impedance bandwidth of 13.7% and the isolation is more than 15 dB. In [21], a dual-band dual-polarized patch antenna is studied. The antenna uses two pairs of stacked ring patches to obtain dual-band performance. The feeding structure is formed by two striplines coupled with orthogonal H-slots, which makes the antenna gain the dual-polarization in two bands. There are still lots of way to promote the performance of dual-polarized antennas. However, in order to chase wide impedance matching, the configuration of antennas becomes more complex. It also led to an increase in antenna size and a decrease in radiation efficiency. To maintain wideband performance and simple structure, horn antennas can be seen as a potential candidate. However, horn antennas are always designed in microwave bands with an all-metal configuration. They are not suitable in millimeter wave bands because of their bulky size and difficulty to integrate. To solve this problem, horn antennas in the millimeter wave band can be designed using substrate-integrated waveguide technology.