Conventional mobile base station antennas are composed of equally spaced linear array antennas. In order to achieve low side lobe characteristics, excitation coefficients for array elements are determined by a feeding network. Because of complexity of the feeding network, applicable frequency range is limited. In 5G mobile system, multi frequency band operation is requested. For achieving low sidelobe and wide frequency characteristics, a density tapered array configuration is promising. Because of uniform excitation coefficients, feed network has no frequency dependence and wide frequency range application is expected. In this paper, abilities and design method of low sidelobe characteristics are investigated. By density tapering, sidelobe levels are reduced from -13dB to -16dB. As for wide band characteristics, low sidelobe characteristics are maintained during 28GHz to 56GHz operations. Usefulness of a density tapered array is numerically clarified.

This paper presents the investigation on rectangular dielectric resonator antenna (RDRA) using three different feeding techniques that are microstrip slot aperture (MSA), microstrip line (ML) and open-end coplanar waveguide (OECPW). In order to increase the RDRA size and gain for 5G applications, the higher-order mode was used to excite the RDRA at the frequency resonant 28 GHz. Duroid dielectric substrate was used with a thickness of 0.254 mm, a permittivity of 2.2 and a loss tangent of 0.0009. Verification of the comparison was done by simulation using Ansoft HFSS. The simulated result for reflection coefficients, bandwidth, gain, radiation pattern and E-field strength was analyzed and compared.

Abstract-Unequally spaced arrays technique offers an alternative for limited sidelobe level reduction compared to conventional array antennas with equally spaced elements. In this paper, the abilities and design of microstrip linear array antenna, fed by multiport feeding with uniform excitation coefficient in all array elements are presented for sidelobe level reduction at 28 GHz. By using the proximity coupled feed, simulation result gave -10 dB impedance bandwidth of 1.42 GHz and reflection coefficient of -35.5 dB has been achieved. The sidelobe level at broadside decreased from -11.77 dB to -14.76 dB (N = 4) and -12.77 dB to -15.98 dB (N = 8) with unequally spaced array. This feature is suitable for 5G applications.Index Terms-5G antenna mobile, millimeter wave, unequally spaced array.