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Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology
G Model
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Int. J. Electron. Commun. (AEÜ) xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology
1
2
3
Q1
4
Bahram Khalichi ∗ , Saeid Nikmehr, Ali Pourziad Department of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran
5
6 16
a r t i c l e
i n f o
a b s t r a c t
7 8 9 10
Article history: Received 16 February 2015 Accepted 8 June 2015
11
15
Keywords: Substrate integrated waveguide (SIW) Horn antennas Wideband antennas
17
1. Introduction
12 13 14
18Q2 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
In this article, a novel wideband horn antenna based on substrate integrated waveguide (SIW) technology is proposed. Design procedure is explained in details. The designed antenna consists of asymmetric radiating slots. Microstrip line is used as a transition between the 50 standard source and the proposed antenna. The proposed antenna is designed to operate from 25 to over 55 GHz which exhibits 75% fractional bandwidth. Peak gain of the proposed antenna varies between 1 and 4 dB in its operating band. In addition, simulated radiation performances show approximately fixed and omnidirectional radiation patterns at the range of the operating frequencies. Furthermore, whole of the proposed antenna is implemented only on a single layer substrate with dimensions of 10.4 mm × 23.65 mm × 1.6 mm. Performances of the proposed antenna have been simulated with two different commercial software. In order to verify the design procedure and simulation results, the redesigned antenna for operation around 14 GHz has been simulated, fabricated, and tested. © 2015 Published by Elsevier GmbH.
Substrate integrated waveguide (SIW) technology is the most promising candidate for the implementation of millimeter-wave integrated circuits and high speed communication systems for the next decade. SIW structures offer a compact, flexible, and cost effective solution for integrating active circuits, passive components, and radiating elements on the same substrate. In recent years, there is growing interest for SIW-based antennas due to overcoming the problems of microstrip technology at millimeter-wave bands. Low antenna efficiency prevents the usage of microstrip due to severe power loss at millimeter-wave bands. Therefore, one of the promising candidates for solving such problem and developing microwave components in these bands is SIW technology. SIW structures have been widely employed in microwave components, antennas, and circuit designs [1–7]. Besides, SIW structures can be integrated with feeding network. They are also good candidate to feed the surfacewave or leaky-wave antennas [4]. Various planar antennas based on SIW technology have been investigated by numerous researchers since now [3–8]. However, design of wideband antennas is the most upcoming challenge at millimeter-wave bands (30–300 GHz). Different kinds of SIW H-plane horn antennas have been presented
∗ Corresponding author. E-mail address: b [email protected] (B. Khalichi).
in [3–7]; although some of the mentioned antennas have good radiation characteristics, they have limited bandwidth. A wideband H-plane horn antenna based on ridge substrate integrated waveguide (RSIW) has been developed in [8]. VSWR of this antenna is lower than 2.5 around 18–40 GHz. However, using RSIW to match the impedance between the port and antenna is not economical and the whole dimensions of aforementioned antenna are not suitable for compact requirements. In this paper, in order to overcome the challenges of impedance matching in wide frequency range at millimeter-wave bands, combination of linear slots and SIW technology is implemented. Various feeding networks can be used to excite SIW structures [9–13]. But, microstrip line transition is a good candidate due to its simplicity in designing, assembling, and compatibility with printed circuit board technology. Undesirable radiation effects of higher order modes are the most well-known problem in microstrip line. In this paper, a modified microstrip transition based on characteristics of SIW structure is proposed which can reduce radiation effects of higher order modes.
2. Excitation of SIW structure For better transition from standard source to SIW structure, the input impedance of SIW structure should be investigated. In previous works, it has been demonstrated that if the leakage loss of SIW structure be negligible, SIW structure can be considered as a
http://dx.doi.org/10.1016/j.aeue.2015.06.004 1434-8411/© 2015 Published by Elsevier GmbH.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 1. (a) Geometry of the SIW structure with relative permittivity of 4.4, S = 1.2 mm, d = 0.8 mm, h = 1.6 mm, WSIW = 3.563 mm, and LSIW = 14.2 mm. (b) Input impedance of the fundamental mode of SIW and corresponding RW.
Fig. 2. (a) The configuration of microstrip transition to SIW structure which is proposed in [10]. (b) Modified configuration of microstrip transition to SIW structure which is proposed in this paper.
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conventional dielectric-filled rectangular waveguide (RW) with an effective width [14,15]. A simple geometry of SIW structure with cutoff frequency of 23.83 GHz is considered in Fig. 1(a). Simulated input impedance of the fundamental mode of this SIW structure and corresponding RW is presented in Fig. 1(b). According to this figure, real and imaginary parts of the input impedance of the SIW structure swing around 150 and zero ohms, respectively. The diagram variation for SIW is slower than RW. Therefore, SIW structure can be matched easier than corresponding RW. However, matching SIW structure at all frequency ranges may not be practical because of the ripples of input impedance diagram. Therefore, designing a transition from 50 standard source to high input impedance of SIW structure is one of the main challenges in designing components based on SIW technology. In previously published papers, tapered profile microstrip line for excitation of SIW structures has been designed based on the formulas of [10]. Here, these formulas are repeated for the sake of comparison with our results.
⎧ 60 h ⎪ ⎨ 0 h ln 8 W
1 = ae ⎪
⎩
+ 0.25
W h
120 0 h[W/h + 1.393 + 0.667 ln(W/h + 1.444)]
83
85 86 87 88 89 90 91 92 93 94 95 96
W <1 h
for
W >1 h (1)
82
84
for
Fig. 3. Comparison of the scattering parameters between the proposed and conventional microstrip transition to SIW structure.
1 4.38 = e ae Weff
−0.627 ε +1 r + 2
εr
2
√ εr −1
(2)
1+12h/W
For a given substrate (with definite h and εr ) and SIW effective width (Weff ), Eqs. (1) and (2) can be solved to find W, which is the optimum tapered width according to Fig. 2(a). For the displayed structure in Fig. 1(a), W is obtained 0.054 mm which means that the width of the microstrip line dwindles as approaching to the SIW structure. This fact relatively diminishes the radiation effects of microstrip line. The length of tapered microstrip line and constant width microstrip line in this configuration is equal to 3g /4 and g /4, respectively. In this paper, in order to improve the impedance bandwidth of this transition with respect to −10 dB criteria, a modified configuration of microstrip transition is proposed. Considering that real part
Fig. 4. 3-D view of the proposed antenna.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 5. Configuration of the proposed antenna with modified microstrip transition. (a) Top view and (b) bottom view.
Table 1 Dimensions of the proposed antenna excited by microstrip transition. Parameters
W1
W2
W3
W4
W5
L1
L2
L3
L4
Value (mm)
10.4
4.92
3.56
0.3
4.2
17.73
1.48
4.44
2.9
Fig. 6. Block diagram modelling of the proposed antenna.
97 98 99 100
101
102
of input impedance for this SIW structure swings around 150 . The requirement is a transmission line to provide a transition between this characteristic impedance and 50 standard source. The width of tapered microstrip line can be calculated by [16]:
⎧ 8eA ⎪ ⎪ ⎪ 2A ⎪ e −2 ⎨
for
W <2 h
W 2 εr − 1 = B − 1 − ln(2B − 1) + h ⎪ 2εr ⎪ ⎪ ⎪ 0.61 W ⎩ >2 . ln(B − 1) + 0.39 − for εr h where Z0 A= 60
103
B=
εr − 1 εr + 1 + 2 εr + 1
377 √ 2Z0 εr
0.11 0.23 + εr
(3)
(4)
Therefore, the width of tapered microstrip W is obtained 0.2 mm. High input impedance of SIW structures at millimeter bands causes the width of microstrip transition to decrease similar to previous approach. Due to the discontinuity between microstrip and SIW structure, constant width microstrip line is considered to improve impedance matching. Furthermore, applying the proposed method, radiation of higher order modes in microstrip line reduces more in comparison with previous method. The length of tapered microstrip line is integer multiple of a quarter wavelength in order to provide better impedance matching. The total lengths for microstrip transition in both structures are the same. In Fig. 3, comparison between reflection coefficients of the proposed excitation method and conventional one is depicted. The results indicate that the proposed method has wider impedance bandwidth with respect to −10 dB criteria. Hence, this excitation method is utilized to improve impedance bandwidth of the antenna structure in next section. 3. Configuration of the proposed antenna In this section, the purpose is to design a SIW-based wideband antenna to operate above 25 GHz (central frequency of 37 GHz). Three dimensional Configuration of the proposed horn antenna based on SIW technology is shown in Fig. 4. Top and bottom views and dimensions of the proposed antenna with microstrip excitation are presented in Fig. 5 and Table 1, respectively. The proposed antenna is designed on a substrate with relative permittivity of 4.4 and tan ı = 0.02. The reason of choosing this substrate is related to the availability of FR4 substrate for prototype fabrication and verification of the design principle. However, the design principle can be applied to other substrates with similar characteristics which are suitable for millimeter-wave bands. Proposed antenna is designed based on designing procedure of horn antennas. The
Fig. 7. (a) Input impedance and (b) reflection coefficient of the antenna seen from A − A section.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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121
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Fig. 8. Simulated reflection coefficient of the proposed antenna excited by modified microstrip transition.
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flaring part determines the impedance bandwidth and ripples of radiation pattern. It improves impedance bandwidth by changing the guiding mode to propagating mode. However, as the flaring part (also known as radial waveguide) increases, excitation of higher order modes is unavoidable [3]. Excitation of higher order modes increases the ripples in the radiation pattern which is undesirable case [3]. Therefore we need to choose the dimensions as small as possible. Geometry of the proposed antenna can be divided into three sections as follows: (I) feeding, (II) guiding, and (III) radiating sections. Block diagram which models aforementioned three sections of the proposed antenna is presented in Fig. 6. Section 1 consists of modified feeding transition which connects 50 standard source to the antenna. In Section 2, the lowest frequency of the operating band is determined by SIW structure. In Section 3, electromagnetic wave is guided out through the asymmetric slots printed on top and bottom of the substrate and the aperture in front of the antenna. Considering the roll of free space as a spherical waveguide, transition between each section can be presented by S matrix parameters. Impedance matching between sections III and free space can be obtained by means of slots integrated with SIW technology. By introducing asymmetrical slots on top and bottom of the structure, the EM-wave propagates to outside as it reaches to end of the structure. Determining the size of W2 has a relation with the reflection coefficient of the antenna. Considering asymmetrical slots, there is common area between top and bottom plates. In order to reduce reflection from end of the structure, this area should be decreased gradually to avoid another discontinuity in the structure. Therefore, optimal case for triangular shape slots is that the common area should have one vertex at middle of the structure. By implementing whole structure, the dimensions of the structure were optimized only by decreasing the length of the antenna until it does not affect the reflection coefficient by considering −10 dB criteria. Input impedance seen from A − A section of the proposed antenna is presented in Fig. 7(a). As frequency increases, the real and imaginary parts of the input impedance are going to swing
Fig. 10. Simulated normalized radiation patterns in both xz and yz planes at 25 GHz, 35 GHz, 45 GHz, and 55 GHz.
around 170 and zero ohms, respectively. Frequency response of the antenna without feeding network is presented in Fig. 7(b). The acceptable frequency range for this configuration is from 28.5 to 41 GHz and above 46 GHz with respect to −10 dB criteria. Therefore, the proposed antenna just requires feeding transition to connect a 50 standard source to the second section of the structure. In
Fig. 9. (a) Simulated peak gain and (b) group delay of the proposed antenna.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 11. Fabricated prototype of the proposed antenna: (a) top view and (b) bottom view.
Table 2 Dimensions of the fabricated antenna. Parameters
W1
W2
W3
W4
W5
L1
L2
L3
L4
Value (mm)
52
24.57
17.82
6.7
3.11
88.6
7.74
24.16
7.32
Fig. 12. Measured and simulated reflection coefficient of the proposed antenna which is presented for lower frequencies.
the next, designing of the feeding network based on Section 2 is explained. According to Section 2, the lengths of tapering and constant width microstrip line is equal to 3g /4 and g /4, respectively. According to Fig. 7(a), microstrip line tapering should be from 50 characteristic impedance to 170 one. Frequency response of the proposed antenna with modified microstrip transition is simulated by two different commercial software (HFSS and CST) and results are presented in Fig. 8. According to this figure, results are consistent with each other. The simulated reflection coefficient shows acceptable impedance matching in millimeter-wave band. The peak gain of the proposed antenna as a function of frequency is displayed in Fig. 9(a). Accordingly, the peak gain is varying between 1 and 4 dB. In addition, wideband frequency response does not necessarily assure that the antenna behaves well in time domain. Ideal wideband antennas should be distortion free. Therefore, in order to ensure the usefulness of the proposed antenna, simulated group delay is considered in Fig. 9(b). The variation of group delay is within 3 ns. This ensures that the proposed antenna is distortion free and exhibits satisfactory time domain characteristic throughout its operating band. In addition, for this kind of antennas, an important additional criterion has to be taken into account,
Fig. 13. Simulated and measured normalized radiation patterns in xz plane at (a) 11 GHz, (b) 14 GHz, and (c) 17 GHz.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 14. Simulated and measured normalized radiation patterns in yz plane at (a) 11 GHz, (b) 14 GHz, and (c) 17 GHz.
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which is the dependence of antenna patterns on frequency. This criterion is considered essential in designing suitable wideband antennas. The simulated 2-D normalized radiation patterns of the proposed antenna in xz and yz planes are plotted in Fig. 10 at different operating frequencies. The results affirm that radiation patterns are approximately fixed and omnidirectional at the operating band.
4. Experimental results It should be noted that the important purpose to provide design principle at 37 GHz is the advantages of SIW structure in comparison with microstrip at higher frequencies. Therefore, designing procedure has been presented for higher frequencies. But, due to availability of suitable equipment for measurement (Agilent 8720ES), the antenna and feeding network have been redesigned to operate at central frequency of 14 GHz in order to verify the design principle presented for the proposed antenna. A prototype of the proposed antenna for mentioned central frequency has been fabricated and tested. The measurements of the reflection coefficient and radiation patterns were done in tapered anechoic chamber. Network analyzer (Agilent 8720ES) with low loss cable was used to investigate the S-parameter performance of the fabricated antenna. Fig. 11 shows the top and bottom views of the fabricated antenna. Dimensions of fabricated antenna are presented in Table 2. Simulated and measured reflection coefficients of the proposed antenna are presented in Fig. 12 which indicates that the experimental results are in good agreement with the simulated ones. In Figs. 13 and 14, simulated and measured normalized radiation patterns in both xz and yz planes are presented at different operating frequencies for this antenna. The measured results prove the design accuracy and simulated results. As it is seen, radiation patterns are approximately omnidirectional and fixed at this frequency band as expected.
5. Conclusion In this paper, a novel approach in designing of wideband antennas by using characteristics of linear slots, horn antennas and substrate integrated waveguide technology was proposed. Design of proposed antenna was discussed in details. Implementing linear slots at the top and bottom of the substrate causes wider impedance matching with respect to previous works. Moreover, a modified microstrip transition was explained and utilized in configuration of the proposed antenna. The simulated results have been carried out with different commercial software in order to verify the operation of the proposed antenna. The proposed antenna exhibits 75% fractional bandwidth from 25 to over 55 GHz. Peak gain of the proposed antenna varies between 1 and 4 dB in its operating band. Besides good fractional bandwidth, the proposed antenna is compact and has approximately stable and omnidirectional radiation patterns at its operating band. Furthermore, whole of the proposed antenna is implemented only on a single layer substrate with dimensions of 10.4 mm × 23.65 mm × 1.6 mm. A low cost prototype of the proposed antenna at the central frequency of 14 GHz has been redesigned and fabricated to verify the proposed designing concepts. The results acknowledge the accuracy of proposed method.
References [1] He FF, Wu K, Hong W, Han L, Chen X. A planar magic-T structure using substrate integrated circuits concept and its mixer applications. IEEE Trans Microw Theory Tech 2011;59:72–9. [2] Suntives A, Abhari R. Design and application of multimode substrate integrated waveguides in parallel multichannel signaling systems. IEEE Trans Microw Theory Tech 2009;57:1563–71. [3] Khalichi B, Nikmehr S, pourziad A. Reconfigurable SIW antenna based on RFMEMS switches. Prog Electromagn Res 2013;142:189–205. [4] Wang H, Fang DG, Zhang B, Che WQ. Dielectric loaded substrate integrated waveguide (SIW) H-plane horn antennas. IEEE Trans Antennas Propag 2010;58:640–7.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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[5] E-Morote M, Fuchs B, Zurcher JF, Mosig JR. A printed transition for matching improvement of SIW horn antennas. IEEE Trans Antennas Propag 2013;61:1923–30. [6] E-Morote M, Fuchs B, Zurcher JF, Mosig JR. Novel thin and compact H-plane SIW horn antenna. IEEE Trans Antennas Propag 2013;61:2911–20. [7] Taringou F, Dousset D, Bornemann J, Wu K. Broadband CPW feed for millimeterwave SIW-based antipodal linearly tapered slot antennas. IEEE Trans Antennas Propag 2013;61:1987–95. [8] Mallahzadeh AR, Esfandiarpour S. Wideband H-plane horn antenna based on ridge substrate integrated waveguide. IEEE Antennas Wirel Propag Lett 2012;11:85–8. [9] Deslandes D, Wu K. Analysis and design of current probe transition from grounded coplanar to substrate integrated rectangular waveguides. IEEE Trans Microw Theory Tech 2005;53:2487–94. [10] Deslandes D. Design equations for tapered microstrip-to-substrate integrated waveguide transitions. In: IEEE International Microwave Symposium. 2010. p. 704–7.
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[11] Sunho L, Sangwoon J, Lee H. Ultra-wideband CPW-to-substrate integrated waveguide transition using an elevated-CPW section. IEEE Microw Wirel Compon Lett 2008;18:746–8. [12] Ding Y, Wu K. Substrate integrated waveguide-to-microstrip transition in multilayer substrate. IEEE Trans Microw Theory Tech 2007;55: 2839–44. [13] Suntives A, Abhari R. Transition structures for 3-D integration of substrate integrated waveguide interconnects. IEEE Microw Wirel Compon Lett 2007;17:697–9. [14] Xu F, Wu K. Guided-wave and leakage characteristics of substrate integrated waveguide. IEEE Trans Microw Theory Tech 2005;53:66–72. [15] Salehi M, Mehrshahi E. A closed-form formula for dispersion characteristics of fundamental SIW mode. IEEE Microw Wirel Compon Lett 2011;21: 4–6. [16] Pozar DM. Microwave engineering. 4th ed. Wiley; 2012. p. 147–9.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
281 282 283 284 285 286 287 288 289 290 291 292 293 294 295
ARTICLE IN PRESS
AEUE 51429 1–7
Int. J. Electron. Commun. (AEÜ) xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology
1
2
3
Q1
4
Bahram Khalichi ∗ , Saeid Nikmehr, Ali Pourziad Department of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran
5
6 16
a r t i c l e
i n f o
a b s t r a c t
7 8 9 10
Article history: Received 16 February 2015 Accepted 8 June 2015
11
15
Keywords: Substrate integrated waveguide (SIW) Horn antennas Wideband antennas
17
1. Introduction
12 13 14
18Q2 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
In this article, a novel wideband horn antenna based on substrate integrated waveguide (SIW) technology is proposed. Design procedure is explained in details. The designed antenna consists of asymmetric radiating slots. Microstrip line is used as a transition between the 50 standard source and the proposed antenna. The proposed antenna is designed to operate from 25 to over 55 GHz which exhibits 75% fractional bandwidth. Peak gain of the proposed antenna varies between 1 and 4 dB in its operating band. In addition, simulated radiation performances show approximately fixed and omnidirectional radiation patterns at the range of the operating frequencies. Furthermore, whole of the proposed antenna is implemented only on a single layer substrate with dimensions of 10.4 mm × 23.65 mm × 1.6 mm. Performances of the proposed antenna have been simulated with two different commercial software. In order to verify the design procedure and simulation results, the redesigned antenna for operation around 14 GHz has been simulated, fabricated, and tested. © 2015 Published by Elsevier GmbH.
Substrate integrated waveguide (SIW) technology is the most promising candidate for the implementation of millimeter-wave integrated circuits and high speed communication systems for the next decade. SIW structures offer a compact, flexible, and cost effective solution for integrating active circuits, passive components, and radiating elements on the same substrate. In recent years, there is growing interest for SIW-based antennas due to overcoming the problems of microstrip technology at millimeter-wave bands. Low antenna efficiency prevents the usage of microstrip due to severe power loss at millimeter-wave bands. Therefore, one of the promising candidates for solving such problem and developing microwave components in these bands is SIW technology. SIW structures have been widely employed in microwave components, antennas, and circuit designs [1–7]. Besides, SIW structures can be integrated with feeding network. They are also good candidate to feed the surfacewave or leaky-wave antennas [4]. Various planar antennas based on SIW technology have been investigated by numerous researchers since now [3–8]. However, design of wideband antennas is the most upcoming challenge at millimeter-wave bands (30–300 GHz). Different kinds of SIW H-plane horn antennas have been presented
∗ Corresponding author. E-mail address: b [email protected] (B. Khalichi).
in [3–7]; although some of the mentioned antennas have good radiation characteristics, they have limited bandwidth. A wideband H-plane horn antenna based on ridge substrate integrated waveguide (RSIW) has been developed in [8]. VSWR of this antenna is lower than 2.5 around 18–40 GHz. However, using RSIW to match the impedance between the port and antenna is not economical and the whole dimensions of aforementioned antenna are not suitable for compact requirements. In this paper, in order to overcome the challenges of impedance matching in wide frequency range at millimeter-wave bands, combination of linear slots and SIW technology is implemented. Various feeding networks can be used to excite SIW structures [9–13]. But, microstrip line transition is a good candidate due to its simplicity in designing, assembling, and compatibility with printed circuit board technology. Undesirable radiation effects of higher order modes are the most well-known problem in microstrip line. In this paper, a modified microstrip transition based on characteristics of SIW structure is proposed which can reduce radiation effects of higher order modes.
2. Excitation of SIW structure For better transition from standard source to SIW structure, the input impedance of SIW structure should be investigated. In previous works, it has been demonstrated that if the leakage loss of SIW structure be negligible, SIW structure can be considered as a
http://dx.doi.org/10.1016/j.aeue.2015.06.004 1434-8411/© 2015 Published by Elsevier GmbH.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 1. (a) Geometry of the SIW structure with relative permittivity of 4.4, S = 1.2 mm, d = 0.8 mm, h = 1.6 mm, WSIW = 3.563 mm, and LSIW = 14.2 mm. (b) Input impedance of the fundamental mode of SIW and corresponding RW.
Fig. 2. (a) The configuration of microstrip transition to SIW structure which is proposed in [10]. (b) Modified configuration of microstrip transition to SIW structure which is proposed in this paper.
62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80
81
conventional dielectric-filled rectangular waveguide (RW) with an effective width [14,15]. A simple geometry of SIW structure with cutoff frequency of 23.83 GHz is considered in Fig. 1(a). Simulated input impedance of the fundamental mode of this SIW structure and corresponding RW is presented in Fig. 1(b). According to this figure, real and imaginary parts of the input impedance of the SIW structure swing around 150 and zero ohms, respectively. The diagram variation for SIW is slower than RW. Therefore, SIW structure can be matched easier than corresponding RW. However, matching SIW structure at all frequency ranges may not be practical because of the ripples of input impedance diagram. Therefore, designing a transition from 50 standard source to high input impedance of SIW structure is one of the main challenges in designing components based on SIW technology. In previously published papers, tapered profile microstrip line for excitation of SIW structures has been designed based on the formulas of [10]. Here, these formulas are repeated for the sake of comparison with our results.
⎧ 60 h ⎪ ⎨ 0 h ln 8 W
1 = ae ⎪
⎩
+ 0.25
W h
120 0 h[W/h + 1.393 + 0.667 ln(W/h + 1.444)]
83
85 86 87 88 89 90 91 92 93 94 95 96
W <1 h
for
W >1 h (1)
82
84
for
Fig. 3. Comparison of the scattering parameters between the proposed and conventional microstrip transition to SIW structure.
1 4.38 = e ae Weff
−0.627 ε +1 r + 2
εr
2
√ εr −1
(2)
1+12h/W
For a given substrate (with definite h and εr ) and SIW effective width (Weff ), Eqs. (1) and (2) can be solved to find W, which is the optimum tapered width according to Fig. 2(a). For the displayed structure in Fig. 1(a), W is obtained 0.054 mm which means that the width of the microstrip line dwindles as approaching to the SIW structure. This fact relatively diminishes the radiation effects of microstrip line. The length of tapered microstrip line and constant width microstrip line in this configuration is equal to 3g /4 and g /4, respectively. In this paper, in order to improve the impedance bandwidth of this transition with respect to −10 dB criteria, a modified configuration of microstrip transition is proposed. Considering that real part
Fig. 4. 3-D view of the proposed antenna.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 5. Configuration of the proposed antenna with modified microstrip transition. (a) Top view and (b) bottom view.
Table 1 Dimensions of the proposed antenna excited by microstrip transition. Parameters
W1
W2
W3
W4
W5
L1
L2
L3
L4
Value (mm)
10.4
4.92
3.56
0.3
4.2
17.73
1.48
4.44
2.9
Fig. 6. Block diagram modelling of the proposed antenna.
97 98 99 100
101
102
of input impedance for this SIW structure swings around 150 . The requirement is a transmission line to provide a transition between this characteristic impedance and 50 standard source. The width of tapered microstrip line can be calculated by [16]:
⎧ 8eA ⎪ ⎪ ⎪ 2A ⎪ e −2 ⎨
for
W <2 h
W 2 εr − 1 = B − 1 − ln(2B − 1) + h ⎪ 2εr ⎪ ⎪ ⎪ 0.61 W ⎩ >2 . ln(B − 1) + 0.39 − for εr h where Z0 A= 60
103
B=
εr − 1 εr + 1 + 2 εr + 1
377 √ 2Z0 εr
0.11 0.23 + εr
(3)
(4)
Therefore, the width of tapered microstrip W is obtained 0.2 mm. High input impedance of SIW structures at millimeter bands causes the width of microstrip transition to decrease similar to previous approach. Due to the discontinuity between microstrip and SIW structure, constant width microstrip line is considered to improve impedance matching. Furthermore, applying the proposed method, radiation of higher order modes in microstrip line reduces more in comparison with previous method. The length of tapered microstrip line is integer multiple of a quarter wavelength in order to provide better impedance matching. The total lengths for microstrip transition in both structures are the same. In Fig. 3, comparison between reflection coefficients of the proposed excitation method and conventional one is depicted. The results indicate that the proposed method has wider impedance bandwidth with respect to −10 dB criteria. Hence, this excitation method is utilized to improve impedance bandwidth of the antenna structure in next section. 3. Configuration of the proposed antenna In this section, the purpose is to design a SIW-based wideband antenna to operate above 25 GHz (central frequency of 37 GHz). Three dimensional Configuration of the proposed horn antenna based on SIW technology is shown in Fig. 4. Top and bottom views and dimensions of the proposed antenna with microstrip excitation are presented in Fig. 5 and Table 1, respectively. The proposed antenna is designed on a substrate with relative permittivity of 4.4 and tan ı = 0.02. The reason of choosing this substrate is related to the availability of FR4 substrate for prototype fabrication and verification of the design principle. However, the design principle can be applied to other substrates with similar characteristics which are suitable for millimeter-wave bands. Proposed antenna is designed based on designing procedure of horn antennas. The
Fig. 7. (a) Input impedance and (b) reflection coefficient of the antenna seen from A − A section.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 8. Simulated reflection coefficient of the proposed antenna excited by modified microstrip transition.
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flaring part determines the impedance bandwidth and ripples of radiation pattern. It improves impedance bandwidth by changing the guiding mode to propagating mode. However, as the flaring part (also known as radial waveguide) increases, excitation of higher order modes is unavoidable [3]. Excitation of higher order modes increases the ripples in the radiation pattern which is undesirable case [3]. Therefore we need to choose the dimensions as small as possible. Geometry of the proposed antenna can be divided into three sections as follows: (I) feeding, (II) guiding, and (III) radiating sections. Block diagram which models aforementioned three sections of the proposed antenna is presented in Fig. 6. Section 1 consists of modified feeding transition which connects 50 standard source to the antenna. In Section 2, the lowest frequency of the operating band is determined by SIW structure. In Section 3, electromagnetic wave is guided out through the asymmetric slots printed on top and bottom of the substrate and the aperture in front of the antenna. Considering the roll of free space as a spherical waveguide, transition between each section can be presented by S matrix parameters. Impedance matching between sections III and free space can be obtained by means of slots integrated with SIW technology. By introducing asymmetrical slots on top and bottom of the structure, the EM-wave propagates to outside as it reaches to end of the structure. Determining the size of W2 has a relation with the reflection coefficient of the antenna. Considering asymmetrical slots, there is common area between top and bottom plates. In order to reduce reflection from end of the structure, this area should be decreased gradually to avoid another discontinuity in the structure. Therefore, optimal case for triangular shape slots is that the common area should have one vertex at middle of the structure. By implementing whole structure, the dimensions of the structure were optimized only by decreasing the length of the antenna until it does not affect the reflection coefficient by considering −10 dB criteria. Input impedance seen from A − A section of the proposed antenna is presented in Fig. 7(a). As frequency increases, the real and imaginary parts of the input impedance are going to swing
Fig. 10. Simulated normalized radiation patterns in both xz and yz planes at 25 GHz, 35 GHz, 45 GHz, and 55 GHz.
around 170 and zero ohms, respectively. Frequency response of the antenna without feeding network is presented in Fig. 7(b). The acceptable frequency range for this configuration is from 28.5 to 41 GHz and above 46 GHz with respect to −10 dB criteria. Therefore, the proposed antenna just requires feeding transition to connect a 50 standard source to the second section of the structure. In
Fig. 9. (a) Simulated peak gain and (b) group delay of the proposed antenna.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 11. Fabricated prototype of the proposed antenna: (a) top view and (b) bottom view.
Table 2 Dimensions of the fabricated antenna. Parameters
W1
W2
W3
W4
W5
L1
L2
L3
L4
Value (mm)
52
24.57
17.82
6.7
3.11
88.6
7.74
24.16
7.32
Fig. 12. Measured and simulated reflection coefficient of the proposed antenna which is presented for lower frequencies.
the next, designing of the feeding network based on Section 2 is explained. According to Section 2, the lengths of tapering and constant width microstrip line is equal to 3g /4 and g /4, respectively. According to Fig. 7(a), microstrip line tapering should be from 50 characteristic impedance to 170 one. Frequency response of the proposed antenna with modified microstrip transition is simulated by two different commercial software (HFSS and CST) and results are presented in Fig. 8. According to this figure, results are consistent with each other. The simulated reflection coefficient shows acceptable impedance matching in millimeter-wave band. The peak gain of the proposed antenna as a function of frequency is displayed in Fig. 9(a). Accordingly, the peak gain is varying between 1 and 4 dB. In addition, wideband frequency response does not necessarily assure that the antenna behaves well in time domain. Ideal wideband antennas should be distortion free. Therefore, in order to ensure the usefulness of the proposed antenna, simulated group delay is considered in Fig. 9(b). The variation of group delay is within 3 ns. This ensures that the proposed antenna is distortion free and exhibits satisfactory time domain characteristic throughout its operating band. In addition, for this kind of antennas, an important additional criterion has to be taken into account,
Fig. 13. Simulated and measured normalized radiation patterns in xz plane at (a) 11 GHz, (b) 14 GHz, and (c) 17 GHz.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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Fig. 14. Simulated and measured normalized radiation patterns in yz plane at (a) 11 GHz, (b) 14 GHz, and (c) 17 GHz.
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which is the dependence of antenna patterns on frequency. This criterion is considered essential in designing suitable wideband antennas. The simulated 2-D normalized radiation patterns of the proposed antenna in xz and yz planes are plotted in Fig. 10 at different operating frequencies. The results affirm that radiation patterns are approximately fixed and omnidirectional at the operating band.
4. Experimental results It should be noted that the important purpose to provide design principle at 37 GHz is the advantages of SIW structure in comparison with microstrip at higher frequencies. Therefore, designing procedure has been presented for higher frequencies. But, due to availability of suitable equipment for measurement (Agilent 8720ES), the antenna and feeding network have been redesigned to operate at central frequency of 14 GHz in order to verify the design principle presented for the proposed antenna. A prototype of the proposed antenna for mentioned central frequency has been fabricated and tested. The measurements of the reflection coefficient and radiation patterns were done in tapered anechoic chamber. Network analyzer (Agilent 8720ES) with low loss cable was used to investigate the S-parameter performance of the fabricated antenna. Fig. 11 shows the top and bottom views of the fabricated antenna. Dimensions of fabricated antenna are presented in Table 2. Simulated and measured reflection coefficients of the proposed antenna are presented in Fig. 12 which indicates that the experimental results are in good agreement with the simulated ones. In Figs. 13 and 14, simulated and measured normalized radiation patterns in both xz and yz planes are presented at different operating frequencies for this antenna. The measured results prove the design accuracy and simulated results. As it is seen, radiation patterns are approximately omnidirectional and fixed at this frequency band as expected.
5. Conclusion In this paper, a novel approach in designing of wideband antennas by using characteristics of linear slots, horn antennas and substrate integrated waveguide technology was proposed. Design of proposed antenna was discussed in details. Implementing linear slots at the top and bottom of the substrate causes wider impedance matching with respect to previous works. Moreover, a modified microstrip transition was explained and utilized in configuration of the proposed antenna. The simulated results have been carried out with different commercial software in order to verify the operation of the proposed antenna. The proposed antenna exhibits 75% fractional bandwidth from 25 to over 55 GHz. Peak gain of the proposed antenna varies between 1 and 4 dB in its operating band. Besides good fractional bandwidth, the proposed antenna is compact and has approximately stable and omnidirectional radiation patterns at its operating band. Furthermore, whole of the proposed antenna is implemented only on a single layer substrate with dimensions of 10.4 mm × 23.65 mm × 1.6 mm. A low cost prototype of the proposed antenna at the central frequency of 14 GHz has been redesigned and fabricated to verify the proposed designing concepts. The results acknowledge the accuracy of proposed method.
References [1] He FF, Wu K, Hong W, Han L, Chen X. A planar magic-T structure using substrate integrated circuits concept and its mixer applications. IEEE Trans Microw Theory Tech 2011;59:72–9. [2] Suntives A, Abhari R. Design and application of multimode substrate integrated waveguides in parallel multichannel signaling systems. IEEE Trans Microw Theory Tech 2009;57:1563–71. [3] Khalichi B, Nikmehr S, pourziad A. Reconfigurable SIW antenna based on RFMEMS switches. Prog Electromagn Res 2013;142:189–205. [4] Wang H, Fang DG, Zhang B, Che WQ. Dielectric loaded substrate integrated waveguide (SIW) H-plane horn antennas. IEEE Trans Antennas Propag 2010;58:640–7.
Please cite this article in press as: Khalichi B, et al. Development of novel wideband H-plane horn antennas by employing asymmetrical slots based on SIW technology. Int J Electron Commun (AEÜ) (2015), http://dx.doi.org/10.1016/j.aeue.2015.06.004
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[5] E-Morote M, Fuchs B, Zurcher JF, Mosig JR. A printed transition for matching improvement of SIW horn antennas. IEEE Trans Antennas Propag 2013;61:1923–30. [6] E-Morote M, Fuchs B, Zurcher JF, Mosig JR. Novel thin and compact H-plane SIW horn antenna. IEEE Trans Antennas Propag 2013;61:2911–20. [7] Taringou F, Dousset D, Bornemann J, Wu K. Broadband CPW feed for millimeterwave SIW-based antipodal linearly tapered slot antennas. IEEE Trans Antennas Propag 2013;61:1987–95. [8] Mallahzadeh AR, Esfandiarpour S. Wideband H-plane horn antenna based on ridge substrate integrated waveguide. IEEE Antennas Wirel Propag Lett 2012;11:85–8. [9] Deslandes D, Wu K. Analysis and design of current probe transition from grounded coplanar to substrate integrated rectangular waveguides. IEEE Trans Microw Theory Tech 2005;53:2487–94. [10] Deslandes D. Design equations for tapered microstrip-to-substrate integrated waveguide transitions. In: IEEE International Microwave Symposium. 2010. p. 704–7.
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[11] Sunho L, Sangwoon J, Lee H. Ultra-wideband CPW-to-substrate integrated waveguide transition using an elevated-CPW section. IEEE Microw Wirel Compon Lett 2008;18:746–8. [12] Ding Y, Wu K. Substrate integrated waveguide-to-microstrip transition in multilayer substrate. IEEE Trans Microw Theory Tech 2007;55: 2839–44. [13] Suntives A, Abhari R. Transition structures for 3-D integration of substrate integrated waveguide interconnects. IEEE Microw Wirel Compon Lett 2007;17:697–9. [14] Xu F, Wu K. Guided-wave and leakage characteristics of substrate integrated waveguide. IEEE Trans Microw Theory Tech 2005;53:66–72. [15] Salehi M, Mehrshahi E. A closed-form formula for dispersion characteristics of fundamental SIW mode. IEEE Microw Wirel Compon Lett 2011;21: 4–6. [16] Pozar DM. Microwave engineering. 4th ed. Wiley; 2012. p. 147–9.
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