An orthogonal beam-forming network (BFN) is proposed for 4G pattern-diversity applications. Different from the traditional Butler beam-forming networks with 2N orthogonal beams, the orthogonal BFN, composed of three 180° hybrids and a 90° phase shifter, provides three orthogonal beams. Design procedure of the orthogonal BFN based on the factorization of its transmission matrix is derived. Moreover, in order to implement the proposed orthogonal BFN with low insertion loss, a rat-race has been used to realize unequal power distribution between its two output ports. The measured scattering parameters of the orthogonal BFN are compared with the analytical and the simulated scattering parameters, validating the expected behavior. In addition, by varying the output power ratio of the non-equi-amplitude 180° hybrid, the performance of the orthogonal BFN is improved when the proposed orthogonal BFN is used in an antenna array.
2. Xu, H.-X., G.-M. Wang, and M.-Q. Qi, "A miniaturized triple-band metamaterial antenna with radiation pattern selectivity and polarization diversity," Progress In Electromagnetics Research, Vol. 137, 275-292, 2013.
3. Blass, J., "Multi-directional antenna: New approach top stacked beams," IRE Int. Convention Record, 48-50, Pt 1, 1960.
4. Nolen, J., "Synthesis of multiple beam networks for arbitrary illuminations,", Ph.D. Dissertation, Bendix Corporation, Radio Division, Baltimore, MD, Apr. 1965.
5. Rotman, W. and R. Tuner, "Wide-angle microwave lens for line source applications," IEEE Trans. Antennas Propagat., Vol. 11, 623-632, 1963.
6. Butler, J. and R. Lowe, "Beam-forming matrix simplifies design of electrically scanned antennas," IEEE Trans. Electron. Devices, 170-173, 1961.
7. Xu, H.-X., G.-M. Wang, and X. Wang, "Compact Butler matrix using composite right/left handed transmission line," Electron. Lett., Vol. 47, No. 19, 1081-1082, Sep. 2011.
8. Vassilakis, B. and S. Foo, "Dual beam sector antenna array with low loss beam forming network,", U. S. Patent 8 237 619 B2, Aug. 7, 2012.
9. Sodin, L. G., "Method of synthesizing a beam-forming device for the N-beam and N-element array antenna, for any N," IEEE Trans. Antennas Propagat., Vol. 60, No. 4, 1771-1776, Apr. 2012.
10. Pozar, D. M., Microwave Engineering, 4th Ed., 362-367, Wiley, New York, 2012.
11. Bahl, I. and P. Bhartia, Microwave Solid State Circuit Design, 2nd Ed., 195196, Wiley, New Jersey, 2003.
12. Balanis, C. A., Antenna Theory Analysis and Design, 3rd Ed., 811-814, Wiley, New Jersey, 2005.
13. Xu, H.-X., G.-M. Wang, X.-K. Zhang, and X.-L. Yang, "Novel compact dual-band rat-race coupler combining fractal geometry and CRLH TLs," Wireless Personal Communications, Vol. 66, No. 4, 855-864, 2012.
14. Xu, H.-X., G.-M. Wang, X. Chen, and T.-P. Li, "Broadband balun using fully artificial fractal-shaped composite right/left handed transmission line," IEEE Microw. Wireless Compon. Lett., Vol. 22, No. 1, 16-18, 2012.