Fig. 10. Block diagram of the antenna array with the 4 × 4 BW.
The microstrip patch antenna design was widely used due the small size,
simple structure, and easy fabrication. A microstrip patche antenna
operating at 3.5 GHz. After applying the zig-zag structure at resonating
frequency to 3.5GHz with simulated a return loss (S11) of -20dB and a
bandwidth of 410MHz (3.36GHz- 3.77). The zig-zag structure of the
antenna have measured return loss -31dB and bandwidth of 460MHz
(3.33GHz-3.79GHz) as show in Fig.11 obtained good return loss for the
simulated and measured of the single element patch antenna. The back
side ground plane was reduced due to the back lobe level. Hence, the BM
signal feeding structure to the patch should be carefully designed.
Taking this into consideration. We designed and implemented the block
level for the 4 × 4 Butler matrix and 1 × 4 patch antenna array, then
optimised their performance independently.
In this work, we carefully implemented the Butler matrix overall, the
antenna elements, and the interface structures between our extensive
co-optimization. Fig. 12 exhibits the proposed design of the beamforming
antenna array. The 4 × 4 Butler matrix and 1 × 4 antenna array under
tested, in anechoic chamber were printed on the single layer, as
illustrated in Fig. 13. The single element of the rectangular patch
antenna had the overall size of 16.4 × 16.4 mm2 and the feed line of
1.50 mm was placed with a distance of
λ0/2
(λ0) as the wavelength. Due to this, the overall performance of the
Butler matrix and the antenna elements’ interfacing and interconnecting
were likely to be affected. The block diagram of the proposed Butler
matrix with antenna array was designed for the 5G application. The
substrate chosen was a
Rogers
RT5880LZ with the thickness of 0.25 mm, dielectric permittivity of 2,
and loss tangent of 0.0021, respectively. The inconsistencies may be due
to extra losses and phase shifts prompted by the SAM and coaxial cable.
From now onwards, discussions relating to the results will be based on
the compact structure of the SAA shown in Fig. 14. The radiation pattern
measurements of the fabricated SAA are then performed in the anechoic
chamber using Rohde & Schwarz ZVL-vector network analyzer (VNA) and
horn antenna. The BFN and distance between the antenna elements selected
the direction of the main beam radiation, as shown in Fig.14