Unequally spaced microstrip linear antenna arrays for fifth-generation base station

Abstract

Wireless technology communication has been continuously evolving towards future fifth generation (5G), whereby multi-beam, multi-frequency, and low sidelobe characteristics are required in the mobile base station. However, the low sidelobe level of conventional mobile base station antenna led to more complex of feeding network design in order to give an adequate excitation coefficients (amplitude and phase) to array elements. Thus, the current base station antennas are difficult for wide frequency use due to frequency range is limited. Subsequently in this research, an unequally spaced microstrip linear antenna arrays is proposed. The radiation pattern synthesis for low sidelobe and grating lobes suppression over wide frequency use are investigated. In the first stage, a single antenna is designed at frequency 28 GHz followed by 16 element linear arrays in order to achieve the gain requirement for mobile base station antenna. Next, the design of antenna arrays with sidelobe reduction is proposed. Three configurations of linear antenna arrays are designed, which are equally spaced array (ESA), unequally spaced array 1 (USA 1) and unequally spaced array 2 (USA 2) at frequency f! = 28 GHz, f1 = 42 GHz and f2 = 56 GHz with a similar array aperture, in order to investigate the antenna performance in wide frequency use characteristics. USA 1 and USA 2 are having different center spacing of array (dc), which are dc(USA1) = 0.6 mm and dc(USA2) = 0.5 mm, respectively. The simulation results are obtained by using High Frequency Structure Simulator (HFSS). The good results were observed, where the performance of sidelobe reduction are constant even though the frequency changes. Due to the lack of measurement facilities at higher frequency than 18 GHz, the antenna arrays are redesigned at lower frequency, which are 12 and 18 GHz. In order to achieve a wide frequency operation, a wide frequency use of ESA?, USA 1? and USA 2? feeding network (which notation ? indicates that the frequency of 12 GHz is chosen as reference) are designed by using Advanced Design System (ADS). An equal line lengths (ln) with equal power ratio dividers were constructed. The sidelobe reduced from -13 dB for ESA? to -19 dB for USA 2?. The measurement of S-parameter and radiation pattern are performed using a vector network analyzer (VNA) and anechoic chamber, respectively. The measured results were presented and a good correlation with simulations was observed. From the observation, the sidelobe level and grating lobe suppression of USA 2? is reduced rather well and recommended for wide frequency band for 5G mobile base station antenna.