Analysis and design of microstrip to balanced stripline transitions RUZHDI SEFA 1 , ARIANIT MARAJ 2 1 Faculty of Electrical and Computer Engineering, University of Prishtina - Prishtina 2 Faculty of Software Design, Public University of Prizren - Prizren 1&2 REPUBLIC OF KOSOVA [email protected], [email protected]Abstract - A design method for microstrip to balanced stripline transition is presented. The transition is suitable for application in feeding arrays of double-side printed antennas. The transition is a Chebyshev taper impedance transformer and the conversion from unbalanced to balanced line relied on a gradual change of the cross-section of the line. The transmission parameters of an asymmetric line are derived with a method based on the quasi-TEM wave approximation. Also, in this paper are presented calculated results for 50 microstrip to 100 balanced stripline and 100 microstrip to 50 balanced stripline transitions. Keywords- Microstrip, Balanced stripline, Transformer, TEM mode 1 Introduction Printed dipole radiators have been popular candidates for phased-array antennas that contain many elements because of their suitability for integration with microwave integrated circuit modules [1]–[3]. Arrays of double-sided printed strip dipoles fed with corporate networks of parallel striplines and backed by conductor planes were developed for radar and various military applications [4]. Various antenna structures of double-sided printed strip dipoles connected through balanced striplines having dual-band and broadband properties have been reported [5]. These structures are suitable for low-cost base station antennas, because they have simple configuration and can be easily manufactured. To feed a double-sided printed strip antenna from a conventional coaxial connector, however, a transition from unbalanced line to a balanced line must be used to keep the antenna in a balanced state. The transition performs conversion of electromagnetic fields and can be used as impedance transformer. Moreover, the transition must be capable of operating over a large frequency range to be compatible with the antenna performance. Impedance transformation and matching are required in general microwave networks and antenna arrays to obtain maximum power transfer between the source and load. In addition, power often has to be divided between different network elements. At high frequencies, these common functions are usually performed with distributed elements consisting of sections of transmission lines. The most commonly used quarter-wave impedance transformer is shown in Fig. 1. A resistive load of impedance L Z can to be matched to a network with input impedance in Z by using a quarter- wave section of transmission line with impedance L in c Z Z Z . The impedance is perfectly matched only at the frequency at which the electrical length of the matching section is . 4 / L Figure 1. Quarter wave transformer The bandwidth provided by a quarter-wave transformer may be adequate in many applications, but there are also situations in which a much greater bandwidth must be provided. The bandwidth can be increased by using cascaded quarter wave transformers [6] as shown in Fig. 2. Each quarter wave section has the same electrical length, and by a proper choice of their characteristic impedances a variety of pass-band characteristics can be obtained [7]. The most commonly used multi- Recent Researches in Telecommunications, Informatics, Electronics and Signal Processing ISBN: 978-1-61804-005-3 137
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Analysis and design of microstrip to balanced stripline transitions
RUZHDI SEFA1, ARIANIT MARAJ
2
1Faculty of Electrical and Computer Engineering, University of Prishtina - Prishtina
2 Faculty of Software Design, Public University of Prizren - Prizren
1&2REPUBLIC OF KOSOVA
[email protected], [email protected] Abstract - A design method for microstrip to balanced stripline transition is presented. The transition is
suitable for application in feeding arrays of double-side printed antennas. The transition is a Chebyshev
taper impedance transformer and the conversion from unbalanced to balanced line relied on a gradual
change of the cross-section of the line. The transmission parameters of an asymmetric line are derived
with a method based on the quasi-TEM wave approximation. Also, in this paper are presented calculated
results for 50 microstrip to 100 balanced stripline and 100 microstrip to 50 balanced stripline
transitions.
Keywords- Microstrip, Balanced stripline, Transformer, TEM mode
1 Introduction Printed dipole radiators have been popular
candidates for phased-array antennas that
contain many elements because of their
suitability for integration with microwave
integrated circuit modules [1]–[3]. Arrays of
double-sided printed strip dipoles fed with
corporate networks of parallel striplines and
backed by conductor planes were developed for
radar and various military applications [4].
Various antenna structures of double-sided
printed strip dipoles connected through balanced
striplines having dual-band and broadband
properties have been reported [5]. These
structures are suitable for low-cost base station
antennas, because they have simple
configuration and can be easily manufactured.
To feed a double-sided printed strip antenna
from a conventional coaxial connector, however,
a transition from unbalanced line to a balanced
line must be used to keep the antenna in a
balanced state. The transition performs
conversion of electromagnetic fields and can be
used as impedance transformer. Moreover, the
transition must be capable of operating over a
large frequency range to be compatible with the
antenna performance.
Impedance transformation and matching are
required in general microwave networks and
antenna arrays to obtain maximum power
transfer between the source and load. In
addition, power often has to be divided between
different network elements. At high
frequencies, these common functions are usually
performed with distributed elements consisting
of sections of transmission lines. The most
commonly used quarter-wave impedance
transformer is shown in Fig. 1. A resistive load
of impedance LZ can to be matched to a network
with input impedance inZ by using a quarter-
wave section of transmission line with
impedance Linc ZZZ . The impedance is
perfectly matched only at the frequency at which
the electrical length of the matching section is
.4/L
Figure 1. Quarter wave transformer
The bandwidth provided by a quarter-wave
transformer may be adequate in many
applications, but there are also situations in
which a much greater bandwidth must be
provided. The bandwidth can be increased by
using cascaded quarter wave transformers [6] as
shown in Fig. 2. Each quarter wave section has
the same electrical length, and by a proper
choice of their characteristic impedances a
variety of pass-band characteristics can be
obtained [7]. The most commonly used multi-
Recent Researches in Telecommunications, Informatics, Electronics and Signal Processing