An extremely compact branch-line coupler operating at 900 MHz is presented without the use of viaholes, multilayered technique, or air-bridged. The technique presented here uses the concept of fractals to load a coupled transmission-line in order to realize a compact quarter-wavelength transmission-line, which forms the couplers arms. It is shown that the proposed branch-line coupler's performance is analogous to a conventional branch-line coupler with the benefit of substantially reduced physical dimensions by a factor of 78%. The measured result of the fabricated microstrip branch-line coupler is compared with the simulation data. The agreement of the measurement and simulated confirms the theory and validates the proposed coupler design.
2. Liao, S.-S. and P.-T. Sun, "A novel compact-size branch line coupler," IEEE Trans. Microwave Theory & Tech., Vol. 15, 588-590, Sep. 2005.
3. Vogel, R. W., "Analysis and design of lumped and lumped-distributed element directional coupler for MIC and MMIC applications," IEEE Trans. Microwave Theory & Tech., Vol. 41, 2116-2125, 1993.
4. Hirota, T., A. Minakawa, and M. Murauchi, "Reduced-size branch-line and rate-race hybrids for uniplanar MMICs," IEEE Trans. Microwave Theory & Tech., 270-275, 2002.
5. Chan, Y.-H. and J.-S. Hong, "Compact wide-band branch-line hybrids," IEEE Trans. Microwave Theory & Tech., Vol. 54, 704-709, 2006.
6. Nosrati, M., "An extremely miniaturized microstrip branch-line coupler," Microwave and Opt. Tech. Lett., Vol. 51, 1403-1406, 2009.
7. Shamsinejad, S., M. Soleimani, and N. Komjani, "Novel enhanced and miniaturized 90o coupler for 3g eh mixers," Progress In Electromagnetics Research Letters, Vol. 3, 43-50, 2008.
8. Nosrati, M. and S. K. Valashani, "A novel compact branch-line coupler using four coupled transmission lines," Microwave and Opt. Tech. Lett., Vol. 50, 1712-1714, 2008.
9. Hayati, M. and M. Nosrati, "Loaded coupled transmission line approach of left-handed (LH) structures and realization of a highly compact dual-band branch-line coupler ," Progress In Electromagnetics Research C, Vol. 10, 75-86, 2009.
10. Nosrati, M. and A. Najafi, "Bandwidth enhancement and further size reduction of a class of elliptic-function low-pass filter using modified hairpin resonators," Progress In Electromagnetics Research C, Vol. 5, 187-194, 2008.
11. Nosrati, M., T. Faraji, and Z. Atlasbaf, "A compact composite broad stop-band elliptic-function low-pass filter for ultra wide-band applications using interdigital capacitors," Progress In Electromagnetics Research Letters, Vol. 7, 87-95, 2009.
12. Malherbe, J. A. G., Microwave Transmission Line Filters, 24-26 and 71-79, Artech House, 1979.