The results presented in this figure are obtained using the finite-width gap source model described in [ 12 ]. It is well known that the bowtie antenna has wider bandwidth than that of the conventional dipole antenna.
Using this balun, the dependence of the input impedance on the frequency becomes as shown in Figure 18 a. As shown in both figures, connecting the balun results in almost complete matching at 2. Figure 19 shows a comparison among the return losses obtained when feeding a strip dipole antenna with i a conventional split coaxial balun as designed in [ 11 ], ii a split balun with a step transition of the inner conductor as optimized in the present work, and iii a coaxial line no balun is used.
A clear disadvantage of the balun proposed in [ 11 ] is that it causes a return loss worse than that obtained even when no balun is used to feed the dipole antenna. The results of comparison can be summarized as shown in Tables 1 and 2. From the comparison, one can conclude that the split coaxial balun with a step transition of the inner conductor, when used to feed a balanced dipole from unbalanced coaxial line has the ability to be optimized so as to get the best achievable performance regarding impedance matching at the design frequency and over a good bandwidth around it.
The parts of the balun used to feed the strip dipole are shown in Figure The measurement results are compared with the results obtained using the MoM as described in the present work as shown in Figure The dipole antenna dimensions are cm, mm. The balun dimensions are: mm, mm, mm, cm, cm, cm, cm, mm, and.
As shown in Figure 20 , the experimental results agree with the simulation results obtained using the MoM. A split coaxial balun with a step transition of the inner conductor diameter is proposed in the present work. The balun can be seen as composed of three successive sections: coaxial section, transitional section, and split section. The length of the transitional section and the step change of the inner conductor diameter are two additional dimensional parameters considering the conventional split coaxial balun that provide more flexibility to design a wideband impedance matching balun.
The effects of these dimensional parameters as well as the effect of the slot angle of the split section on the input impedance seen at the unbalanced coaxial line side of the balun are investigated when it is terminated with specific lumped impedance at its balanced split side. The results show that balun bandwidth depends on the difference between the two impedances on the sides of the balun; the larger the differences between the impedances to match, the narrower the bandwidth of impedance matching.
The proposed split coaxial balun is designed to feed balanced two-arm antennas such as the strip dipole and the bowtie antenna from unbalanced coaxial line where it is shown that the balun results in antenna impedance matching over a wide frequency band. The simulation results obtained using the MoM is compared with experimental measurements showing good agreement. The author declares that there is no conflict of interests regarding the publication of this paper.
This 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. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors.
Read the winning articles. Journal overview. Special Issues. Academic Editor: Sembiam R. Received 03 May Revised 20 Aug Accepted 11 Sep Published 14 Oct Abstract A split coaxial balun with a step transition of the inner conductor diameter is introduced to satisfy impedance matching between unbalanced feeder and balanced antennas. Introduction A balun balanced-to-unbalanced is a type of electrical transformer that can convert electrical signals balanced about ground differential to signals that are unbalanced single-ended and the reverse.
Figure 1. Split coaxial balun with a step-transition of the inner conductor: a waveguide transition from coaxial line to double-slotted coaxial line and b the same transition terminated with a short circuit at the double-slotted line side.
Figure 2. Figure 3. Split coaxial balun feeding a bowtie antenna balanced load through a coaxial line unbalanced transmission line. Figure 4. Current paths for a dipole fed by a coaxial line without a balun: a dipole antenna excited directly by a coaxial line without using a balun and b equivalent circuit of the radiating antenna arms. Figure 5. Equivalent circuit to evaluate the balance ratio of a balun. Figure 6. Flow chart for the optimization procedure to arrive at the dimensional parameters , , and for impedance matching between a coaxial feeder of characteristic impedance and balanced load.
Figure 7. Figure 8. Figure 9. Figure Geometric model of a strip dipole antenna with the dimensional parameters and b strip dipole antenna fed through a split coaxial balun zoom-in view at the feeding location. The current distribution on the dipole arms fed through a split coaxial balun with a step transition in the inner diameter conductor on the surface model of the balun and dipole a showing the sides of the triangular patches and b hiding the sides of the triangular patches, and c zoom-in view at the antenna connection with the balun;.
Variation of the strip-dipole antenna impedance with the frequency; dipole dimensions: cm and mm. Dipole dimensions: cm and mm. Geometric model of a bowtie antenna with the dimensional parameters and b bowtie antenna fed through a split coaxial balun zoom-in view at the feeding location.
Variation of the bowtie antenna impedance with the frequency; cm, mm, and. Bowtie dimensions: cm, mm, and. The return losses against the frequency obtained when feeding a strip dipole antenna with i a conventional split coaxial balun as designed in [ 11 ], ii a split balun with a step transition of the inner conductor as optimized in the present work, and iii a coaxial line no balun is used.
Table 1. Performance measure Performance at the design center frequency No balun Conventional split coaxial balun [ 11 ] Balun proposed in the present work VSWR 1. Table 2. The manufactured balun: a the inner conductor with a step transition in its diameter, b the doubly-slotted outer conductor mounted on a metal disc, c the bottom side of the metal disc with N-type coaxial connector. The return losses against the frequency obtained when feeding a strip dipole antenna using a split balun with a step transition of the inner conductor as optimized in the present work compared with the experimental results using vector network analyzer.
References A. Hempy, M. Civerolo, and D. Hong and J. View at: Google Scholar Z. Publication Type. More Filters. Fractal Hilbert sensor to detect partial discharge on transformer. The design of fractal Hilbert sensor is presented in this paper. The sensor is intended to detect partial discharge PD in transformer insulation. The fractal Hilbert sensor designed using 4 order … Expand. Characterisation and optimisation of a coplanar waveguide fed logarithmic spiral antenna.
A cavity backed coplanar waveguide CPW to coplanar strip CPS -fed logarithmic uniplanar spiral antenna, which covers a 9 to 1 bandwidth with a return loss better than 10 dB from 0.
Coplanar waveguide-fed uniplanar bow-tie antenna. The design of coplanar waveguide CPW -fed bow-tie antenna for the 2. View 1 excerpt, references background. Dual-frequency operation of the CPS dipole antenna … Expand.
Broadband coplanar waveguide-coplanar strip-fed spiral antenna. A novel broadband coaxial-coplanar waveguide-coplanar strip-fed spiral antenna is presented. The antenna has good radiation patterns and a return loss of better than 10 dB over a wide bandwidth from … Expand.
View 2 excerpts, references background. Antenna engineering handbook. Introduction to Antennas. Fundamentals of Antennas. The balun is inserted between the feed line and the antenna to provide a transition between the coplanar waveguide CPW and the coplanar strip line CPS. The balun produces a symmetrical radiation pattern. However, this article does not deal with the radiation from a connected antenna. In some applications, it is necessary to connect the feed terminals on the balanced antennas to an unbalanced coaxial cable that requires not only a balanced-to-unbalanced transformation circuit, but also an impedance match due to the different characteristic impedances of the antenna and the cable.
In the literature, different types of baluns are described [1, 2].
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