Implementation of Meander Line Structure for Size Miniaturization of 4×4 Butler Matrix

One method to overcome the problem of co-channel interference in wireless communication systems is by employing a switched-beam antenna system. A Butler matrix is commonly utilized as a beam-forming network for some reasonable factors, e.g. low complexity, low loss, and simply fabrication. However, the bulky size of Butler matrix affects an incompatibility in developing compact devices. In this paper, a meander line structure which is an approach to reduce the physical dimension of radio frequency components is implemented to miniaturize the size of conventional 4 × 4 Bulter matrix. Some key parameters of Butler matrix including the amplitude and phase responses are characterized and investigated through several simulations. The characterization results demonstrate that the proposed Butler matrix takes the size of 57.5 mm by 136.4 mm shows good amplitude and phase performances. A phase difference of -46.98° ± 6.72° with an imbalance amplitude less than 5.97 dB was achieved at the operating frequency of 2.4 G. Meanwhile, a 10 dB return loss fractional bandwidth of 18.75% could be attained at the frequency range of 2.29 GHz to 2.74 GHz. Here, the use of meander line structure could exhibit a size miniaturization of 34.29% to the footprint of conventional 4 × 4 Butler matrix.