Research Article
Compact Two-Section Half-Wave Balun Based on Planar
Artificial Transmission Lines
Changjun Liu,
1
Zhenyu Yin,
1
Yilan Yang,
1
and Wen Huang
2
1
School of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China
2
School of Optoelectronics Engineering, Chongqing University of Posts and Telecommunications, Chongqing 40065, China
Correspondence should be addressed to Changjun Liu; cjliu@ieee.org
Received September ; Accepted November
Academic Editor: Sanming Hu
Copyright © Changjun Liu et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Articial transmission lines are realized by a series of meandered-line inductors, parallel-plate capacitors, and interdigital
capacitors, which belong to metamaterial transmission lines. An ameliorated articial transmission line is proposed to realize a
low characteristic impedance transmission line. A two-section half-wave balun at MHz is designed, fabricated, and measured
in this paper. e compact balun is based on conventional and ameliorated planar articial transmission lines instead of microstrip
transmission lines. e main advantage of the proposed balun is its size reduction, which occupies only about % of a conventional
one. Measured results match well with theory and simulation. e balun features excellent amplitude and phase balance in
microwave power combining and a reasonable bandwidth of the return loss as well.
1. Introduction
Abalunisadevicetoactasatransformertomatchan
unbalanced circuit to a balanced one, or vice versa, which
was rst proposed by Marchand in . Owing to the output
balanced amplitude characteristic with its phase dierence of
degrees, it is a key component in balanced circuit topolo-
gies,suchasbalancedantennasandbalancedmixers.Various
balun congurations have been reported for applications in
microwave circuits, such as coupled-line baluns, composite
right/le-handed (CRLH) transmission line baluns, Wilkin-
son power divider baluns, three-line baluns, microstrip taper
baluns, and lumped baluns [–].
Recently, with the rapid development of modern commu-
nication systems, the increasing demands for miniaturized
components have been imposed on microwave circuits, as
the size reduction in radio frequency (RF) circuit is an
important part of the miniaturization and cost reduction of
wireless communication systems. e balun as an important
passive component was required to be designed to reach the
requirement.
In this paper, we proposed a compact two-section half-
wave balun at MHz, which was designed with articial
transmission lines. In recent years, articial transmission
lines []havebeenproposed,andsomemicrowavecompo-
nents with articial transmission lines have been realized,
such as branch-line couplers [], power dividers [], and
antennas [, ]. We proposed modied articial transmis-
sion lines to realize the transmission lines with low char-
acteristic impedance. e proposed design method adopts
seven transmission line sections composed of the articial
transmission lines to replace the conventional transmission
linessoastominiaturizethecircuitsizeofthebalunas
far as possible. e proposed balun demonstrates a very
compact dimension of . mm ×. mm, which is about
% of the area of a conventional balun of this same topology
without folded lines. e overall dimension of the proposed
realization is approximately 0.13
𝑔
×0.12
𝑔
.
2. Theoretical Analysis of -Section
Half-Wave Balun
e realization of a three-port balun is based on the forms of a
symmetricalfour-portnetworkasshowninFigure ,inwhich
one specied port is terminated with a short or open circuit,
Hindawi Publishing Corporation
International Journal of Antennas and Propagation
Volume 2015, Article ID 256536, 6 pages
http://dx.doi.org/10.1155/2015/256536