Broadband antennas have gained popularity for applications in numerous wireless communications systems. During the past decade, we have used 4G technology instead of 3G while looking forward to 5G. The improvement of wireless communications technologies not only increases the peak capacity but also the operating frequency and bandwidth; for example, the 5G standard opened up a new spectrum which doubles the bandwidth of the unlicensed frequency band from 7 GHz to 14 GHz. A novel broadband unidirectional antenna, namely the magneto-electric (ME) dipole antenna, was proposed in 2006. The antenna has virtues of wide bandwidth and good performance in gain and front-to-back ratio. Thus, following the concept of ME dipole antennas, three designs of ME dipole antennas are proposed in this thesis.

The first design is an ME dipole antenna with a defected ground structure (DGS). This design contains a conventional half-wave planar dipole and a vertical-oriented quarter-wave-shorted patch using the DGS. Applying the DGS on the shorted patch antenna is an innovative and effective method to solve the impedance matching problem. This design also adopts a Γ-shaped stripe line as the feed network. For attesting to the high performance of the design, an archetype is fabricated and tested. The presentation validates that a broad operating bandwidth of 86.9%, a gain of 7.2±1.2 dBi, and a low cross-polarization level and a high front-to-back ratio are achieved. This antenna element has only three components, thus providing simplicity in configuration and ease of implementation.

During the research period, the Federal Communications Commission (FCC) issued the 5G criterion, and subsequently other countries announced their own 5G standards. A new communications technological innovation trend has emerged. The design of antennas in the new communications frequency band is yet to be well explored. In this thesis, a new ME dipole antenna for wireless equipment is presented. Based on this antenna, we design the ME dipole antenna with end-fire radiation.

The second antenna proposed in this thesis is a wideband ME dipole antenna with end-fire radiation for millimeter-wave applications. The antenna element is composed of a planar dipole antenna and a single-loop antenna. A balun is designed on the basis of the horizontal slot. A 1×4 antenna array is designed and fabricated. The antenna array covers a bandwidth of 55.4% with a peak gain of 11.9 dBi. This design entirely covers the 28, 37, and 39 GHz band of the 5G standard. The proposed array has various merits, such as wide operating bandwidth, a small size, and a low back lobe level. The reported array is built by PCB technology, which is easy to be manufactured and cost-effective. We believe that this antenna is an attractive application for the 5G component.

Third, a wideband broadside ME dipole antenna is studied. In this design, the antenna comprises a planar dipole antenna and a vertical single-loop antenna. The antenna provides a wide bandwidth of 40.3% (27.9-42 GHz), with a peak gain of 8.1 dBi. A 1×16 antenna array is designed, which also entirely covers the 28, 37, and 39 GHz band of the 5G spectrum. The antenna array applies phase inverter for beam scanning. This design has the same advantages as that of the second design and can be combined with the second design to achieve larger signal coverage.