(b)
Fig. 5. (a) 0dB crossover fabricated by compact two 3-dB BLC with dimension using RT5880LZ substrate (b) The proposed design 0dB crossover under test.
Design configuration butler matrix
The proposed design of the 4 × 4 BM was conducted using a computer simulation technology (CST) microwave studio. The BM implementation was created using combined 3dB BLC of Triangular slot and T-shape, two crossover structures, and 45o phase shifter at the operate frequency of 3.5 GHz. The proposed design BM fabricated on a single layer of RT588LZ substrate. The final fabrication of the proposed BM design, which had the overall area of 87.5mm × 75mm, is as shown in Fig. 6.
The BM provided four outputs with equal amplitude and phase difference of -45o, 135o, 45o, and -135o, respectively. As a result, each input port, specifically as port 1, port 2, port 3, and port 4 were designated as port 5, port 6, port 7, and port 8, was able to produce four beams in various directions, as illustrated in Fig. 6. This configuration was of a 4 × 4 BM. Table 3 shows the phase shift that would be generated on each output based on the excited of the input ports, and all other ports were terminated at 50Ω loads. There were four cases. When input port 1 is excited the phase difference between the output ports -45o. The output 135° phase difference when input port 2 is excited. The phase difference between the output ports in the third case will be -135o when input port 3 is excited. The last port phase difference of the output port is 45° when input port 4 is excited. The proposed BM was validated in accordance with design criteria provided in Table 1.
Table 3. The phase difference between the outputs ports of the Butler matrix feed.