This thesis presents a series of wideband antenna arrays with end-fire radiation for millimeter-wave (MMW) applications. All proposed antenna arrays are linear arrays and exhibit high-gain unidirectional radiation characteristics to overcome the high propagation loss at MMW frequencies. All these antenna arrays are based on substrate integrated techniques, including the substrate integrated waveguide (SIW) and the substrate integrated coaxial line (SICL). Therefore, all of the presented designs have the advantages of low feed-network losses, low cost, ease of integration, and being fabrication-friendly. For these antenna arrays, two aspects are focused on: the wideband dual-polarization property and the wideband phased beam-scanning property. The common end-fire radiation characteristic enables them to be attractive for different terminals in MMW wireless communications.

Firstly, a dual linearly polarized magneto-electric (ME) dipole antenna array is presented in the 60-GHz band. The antenna array consists of two types of SIW-fed ME dipoles that operate in the vertical polarization (V-pol) and the horizontal polarization (H-pol), respectively. A 1×8-element array is designed and fabricated from multi-layer printed circuit boards (PCB). The fabricated prototype demonstrates excellent characteristics. For V-pol operation, the impedance bandwidth is 21% for |S₁₁| < −10 dB and the peak gain is 16.1 dBi. For H-pol operation, the impedance bandwidth is 18% and the peak gain is 15.1 dBi. The radiation patterns of both polarization modes are stable with varying frequency and the cross polarizations are below −30 dB. The isolation between two input ports is larger than 45 dB. The average radiation efficiency is 80%.

Secondly, a single-layer solution for the end-fire dual-polarized antenna array is proposed. A SIW-based 1×4-element array prototype is demonstrated in the 28-GHz band. This array is fabricated from a single-layer PCB. Similar to the first array, two types of orthogonally polarized radiators are used and arranged alternately. The crossover structure and phase shifters are adopted to construct the feed network. A wide impedance bandwidth of 28.6% with |S₁₁| < −10 dB for both polarization modes is obtained by the fabricated prototype. Peak gains of 10.5 dBi and 11.6 dBi are achieved for the H-pol and V-pol radiations, respectively. The isolation between two input ports is larger than 18.8 dB.

Thirdly, a new SICL-fed ME dipole antenna is studied and two phased arrays employing it are examined in the 30-GHz band. The proposed ME dipole antenna features a wide impedance bandwidth of 60% with |S₁₁| < −10 dB and a small gain variation of 1.1 dB. A 1×8-element fixed-beam array and a 1×4-element multi-beam array are designed and fabricated from multi-layer PCBs. The fixed-beam array prototype achieves an impedance bandwidth of 62%, a peak gain of 15.9 dBi, and a radiation efficiency of 79%. The multi-beam array exhibits four scan beams with a 4×4 SICL Butler matrix feed network. The fabricated prototype demonstrates excellent beam-scanning performance across a wide frequency band from 24 to 36 GHz, with maximum scan angles of ±51° at 24 GHz.

Finally, an ultra-wideband phased array excited by a long slot array (LSA) is investigated. The proposed array consists of an SICL-based LSA source and a TEM horn radiator. The array is fabricated using the PCB and conventional metal machining technologies. By employing the SICL feed network, the fabricated array prototype achieves an ultra-wide bandwidth of 3:1 or 100% with SWR < 2.3 (from 15.4 to 46.4 GHz). Within this operating band, an average scan angle of 48° and an average scan loss of 2.4 dB are demonstrated in measurements. The average radiation efficiency is greater than 73%.