A novel compact balun (balanced-to-unbalanced) that consists of a low-pass network served by a microstrip electromagnetic bandgap (EBG) cell and a high-pass π-network formed with an interdigital capacitor is presented. This proposed approach can effectively operate the compact balun without the use of λ/4 microstrip lines to reduce the circuit area over 50% compared to the conventional Marchand balun. The core dimension of the compact balun is 0.74 cm x 0.7 cm. The planar structure enables an efficient circuit design in printed circuit boards (PCB) without using any bonding wires, defected ground structures (DGS), or surface mounted devices (SMD). A compact balun operating in the 3 GHz band has been implemented in a FR-4 PCB. From the measured results, the return loss of the input port is better than 15 dB over the band from 2.6 to 4 GHz. The amplitude and phase imbalances are less than 1.4 dB and 3° with the 20% operational bandwidth ranging from 2.7 to 3.3 GHz, respectively.
2. Chiu, J. C., C. P. Chang, M. P. Houng, and Y. H. Wang, "A 12-36 GHz PHEMT MMIC balanced frequency tripler," IEEE Microw. Wireless Compon. Lett., Vol. 16, 19-21, June 2006.
doi:10.1109/LMWC.2005.861356
3. Marchand, N., "Transmission line conversion transformers," Electronics, Vol. 17, 142-145, December 1942.
4. Sun, J. S. and G. Y. Chen, "A novel design of the planar coupled line balun," IEEE Microwave and Millimeter Wave Technology Proceedings, 1117-1120, August 2002.
5. Lin, Y. S. and C. H. Chen, "Novel lumped-element uniplanar transitions," IEEE Trans. Microw. Theory Tech., Vol. 49, 2322-2330, December 2001.
doi:10.1109/22.971616
6. Kim, K. S., C. S. Kim, I. S. Song, and D. Ahn, "A novel balun with vertically periodic defected ground structure," IEEE Region 10 Conf., 1-4, November 2006.
7. Alley, G. D., "Interdigital capacitors and their application to lumped-element microwave integrated circuits," IEEE Trans. Microw. Theory Tech., Vol. 18, 1028-1033, 1970.
doi:10.1109/TMTT.1970.1127407
8. Bahl, I. and P. Bhartia, Microwave Solid State Circuit Design, 2nd Ed., Wiley, New York, 2003.
9. Xue, Q., K. M. Shum, and C. H. Chan, "Novel 1-D microstrip PBG cell," IEEE Microw. Guided Wave Lett., Vol. 10, 403-405, October 2000.
10. Ooi, B.-L., "Compact EBG in-phase hybrid-ring equal power divider," IEEE Trans. Microw. Theory Tech., Vol. 53, 2329-2334, July 2005.
doi:10.1109/LMWC.2005.850486
11. Zhang, Z. Y., Y. X. Guo, L. C. Ong, and M. Y. W. Chia, "A new wide-band planar balun on a single-layer PCB," IEEE Microw. Wireless Compon. Lett., Vol. 15, 416-418, June 2005.
Submit
