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Development a new wideband substrate integrated waveguide H-plane horn antenna loaded with periodically diamond patches
Int. J. Electron. Commun. (AEÜ) 105 (2019) 9–14
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
Development a new wideband substrate integrated waveguide H-plane horn antenna loaded with periodically diamond patches Hojjat Jamshidi-Zarmehri, Mohammad H. Neshati ⇑ Ferdowsi University of Mashhad, Mashhad, Iran
a r t i c l e
i n f o
Article history: Received 7 October 2018 Accepted 23 March 2019
Keywords: Horn antenna Substrate integrated waveguide (SIW) Side lobe level (SLL)
a b s t r a c t This paper presents a new wideband Substrate Integrated Waveguide (SIW) H-plane horn antenna. A few rows of diamond patches are printed on the top and bottom side of the dielectric slab at front of the radiating aperture of a conventional horn to improve impedance matching. The proposed antenna is numerically investigated using a software package and a prototype of the antenna is made to validate the obtained simulated results. The measured results show that the introduced antenna provides 22.7% impedance bandwidth, which covers from 20.8 GHz to 26.15 GHz with stable end-fire radiation patterns, while Side Lobe Level (SLL) is lower than 10 dB over the operating bandwidth. Ó 2019 Published by Elsevier GmbH.
1. Introduction Conventional metallic horn antennas provide a few advantages including high gain, high radiation efficiency and suitable radiation patterns. In spite of the benefits of these type of antennas, they are bulky and suffer from their 3-dimensional structure [1,2]. Recently, by introducing SIW technology, it is possible to implement microwave circuits and antennas in planar form [3]. However, the conventional SIW H-plane horn provides narrow impedance bandwidth due to poor impedance matching between the radiation aperture and free space [4]. To improve impedance bandwidth of these antennas, variety of methods has been introduced in literature. In case of thick substrate, h > k o/6, dielectric loaded SIW Hplane horn antenna with a narrow impedance bandwidth of 5% is introduced in [5]. Wideband SIW H-plane horn antenna using air-vias is presented in [6] with a reported impedance bandwidth of 40.5%. Another SIW H-plane horn antenna using two and three layers of substrates are introduced in [7] and [8], which provide impedance bandwidth of 12% and 44% respectively. Ridge substrate integrated waveguide (RSIW) H-plane horn antennas with ultra-wideband impedance bandwidth have been investigated in [9] and [10], which provide over 75% impedance bandwidth using a multi-layered structure, which involve lots of complexity in design and fabrication process. In case of thin substrate, h < k o/6, a novel and compact H-plane and a low-profile metamaterials-loaded SIW horn antenna provid⇑ Corresponding author. E-mail address: [email protected] (M.H. Neshati). https://doi.org/10.1016/j.aeue.2019.03.011 1434-8411/Ó 2019 Published by Elsevier GmbH.
ing over 10% impedance bandwidth are investigated in [11] and [12], whereas the antenna gain is low. In [13] and [14] two new structures using printed transitions are introduced with 10% and 20% impedance bandwidth respectively, but the number of designed parameters of these antennas are many. In this paper, a new wideband SIW H-plane horn antenna using a thin substrate is proposed. An external dielectric slab and a few rows of printed diamond patches are loaded at front of the radiating aperture of a conventional SIW horn, which act as an impedance transformer to improve impedance bandwidth. The proposed antenna is numerically investigated using High Frequency Structure Simulator (HFSS) software. Also, a prototype of the antenna is made and the measured radiation characteristics are reported. 2. Antenna structure Fig. 1 shows the structure of the proposed antenna including conventional one. It is designed using TLY062 substrate with dielectric constant of 2.2, thickness of 1.576 mm and loss tangent of 0.001. For H-plane horn antennas, to achieve maximum directivity, Eq. (1) has to be satisfied [15].
A
qffiffiffiffiffiffiffiffiffiffiffiffi 3kg Lh
ð1Þ
In which kg is guided wavelength, Lh is antenna length and A is the width of the radiating aperture. The distance between adjacent vias is selected in such a way that power leakage can be neglected [16]. The structure is fed by 50 O coaxial line made by a probe with
10
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Fig. 2. The magnitude of the simulated S11 of the conventional and dielectric loaded SIW H-plane horn antennas versus frequency.
which confirms the effect of dielectric slab for thin substrate is negligible [4]. 3.2. The proposed SIW horn antenna
Fig. 1. The geometry of (a) conventional SIW horn antenna, (b) proposed SIW horn antenna (L1 = 8.4 mm, L2 = 19.6 mm, Lh = 28 mm, Lp = 2.8 mm, a = 8.7 mm, A = 25 mm, R1 = 0.35 mm, R2 = 1.15 mm, p = 1.4 mm, d = 0.8 mm, L3 = 10.4 mm, L4 = 4 mm, Lg = 0.2 mm, h = 23°).
inner radius of R1 and outer radius of R2, which is placed at the distance of Lp kg/4 from the vertical wall of the waveguide to obtain the best impedance matching condition [17]. An external dielectric slab with length of L3 is placed in front of the radiating aperture. In addition, a few rows of diamond patches with diameter of L4 are printed on the top and bottom side of the dielectric slab. The distance between patches is designated by Lg. The detail parameters of the both horns are summarized at the bottom of Fig. 1. The number of patches along antenna width and length are designated by n and m respectively. These are the design parameters of the antenna and are equivalent to the diameter of patches L4 and the distance between adjacent patches gap Lg. The relation between n, Lg and L4 is given by Eq. (2).
L4 ¼
A ðn 1ÞLg n
The main idea in design of our proposed antenna is the loading a structure in front of the aperture of the horn to improve matching condition between the aperture and free space. In fact, the patches and the distance between them can be modeled as an equivalent LC parallel resonant and in turn, input impedance matching is achieved at different frequencies. The simulated real and imaginary part of the input impedance of the proposed SIW horn including that of the conventional one are shown in Fig. 3. It can be seen that for the proposed antenna along a wide range of frequency, from 21 GHz up to 27 GHz, the real part of the input impedance is close to the characteristic impedance of SIW, ZSIW [6], while
ð2Þ
Eq. (3) shows the relation between m, Lg and L3.
L3 ¼
m L4 þ Lg 2
ð3Þ
3. Simulation results 3.1. The conventional SIW horn antenna First of all, the conventional SIW horn is designed to operate around 25 GHz based on Eq. (1). The magnitude of the simulated S11 of this horn is plotted in Fig. 2 versus frequency. It can be seen that this antenna provides few separates resonate frequency, in which impedance bandwidth is narrow at these frequencies. Also, the simulated S11 of the dielectric loaded horn is shown in Fig. 2,
Fig. 3. The simulated imaginary and real part of the input impedance of the proposed and conventional SIW horn antenna versus frequency.
H. Jamshidi-Zarmehri, M.H. Neshati / Int. J. Electron. Commun. (AEÜ) 105 (2019) 9–14
the imaginary part of the input impedance is nearly zero, whereas, in case of the conventional horn, for a narrow bandwidth around 25 GHz, the imaginary part of the input impedance is close to zero and its real part is close to ZSIW. In fact, Fig. 3 confirms that external dielectric slab and diamond patches act as an impedance transformer that is caused the input impedance of antenna in a wide range of frequency becomes close to ZSIW and so impedance matching of antenna is enhanced.
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radiation performances of the antenna, a few parametric study is carried out and the antenna parameters are studied. 3.4. The effects of number of patches along width, n As it mentioned in Section 3.2, the patches and the distance between them can be modeled as an equivalent LC parallel
3.3. Parametric study To study the effects of different parameters of the structure including the number of patches along width and the length and distance between patches of the proposed SIW horn on the
Fig. 6. The simulated gain of the proposed SIW horn for different values of m versus frequency.
Fig. 4. The simulated S11 of the proposed antenna for different values of n versus frequency.
Fig. 7. The simulated radiation pattern of the proposed antenna for m = 11 at 25.4 GHz frequency.
Fig. 5. Simulated aperture field distribution along antenna aperture for different values of m, (a) phase distribution (b) amplitude distribution.
Fig. 8. The simulated FTBR of the proposed antenna for different values of Lg versus frequency.
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resonant circuit and therefore, by changing the dimension of the patches the corresponding value of C and L of the equivalent circuit is altered and so, the frequency response is changed. The simulated result of S11 versus frequency for different values of n for Lg = 0.2 mm and m = 5 is shown in Fig. 4. It can be seen that by increasing n, impedance bandwidth is highly improved and it reaches to its maximum value for n = 6. Further increasing n, the impedance bandwidth nearly remains constant, but the operating frequency is increased. One can uses this property to design the antenna for a desired operation frequency. Also with change the dimension of patches, the matching between aperture and free space improves and the flattering of the curves is due to the impedance matching.
for different values of m, while Lg = 0.2 mm and n = 6. It is observed that uniform field distribution and decreasing phase variation of the field is obtained by increasing m, leading to obtain higher aperture efficiency and so, the antenna gain is highly improved [18]. The variation of the antenna gain versus frequency for different values of m, in their impedance bandwidth is shown in Fig. 6. It can be seen that by increasing m, the antenna gain is improved,
3.5. The effects of number of patches along length, m Fig. 5 shows the simulated amplitude and phase distributions of electric field along the radiation aperture of the proposed antenna
Fig. 9. The photo of the fabricated proposed SIW horn antenna.
Fig. 10. The measured and simulated S11 of the proposed antenna versus frequency.
Fig. 11. The measured and simulated gain and simulated radaition efficiency of the proposed antenna.
Fig. 12. The measured and simulated radiation patterns of the proposed SIW horn antenna, (a) 21.5 GHz (b) 23.6 GHz (c) 25.5 GHz.
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whereas antenna bandwidth is decreased. Our study shows that for m = 11 antenna gain is improved up to 14 dBi. Fig. 7 shows the radiation patterns of the proposed antenna in both E- and H-planes for m = 11 at 25.4 GHz. It can be seen that the Side Lobe Level (SLL) of the H-plane horn is low. Therefore, this structure can be used as an alternative of the dielectric loaded structures introduced in [5] and [19], while our SIW horn provides higher gain and lower SLL with at least 10% impedance bandwidth. Also, it should be mentioned that the dielectric loaded antennas are only appropriate for thick substrate, but the proposed structure in this paper can be used for thin substrate. 3.6. The effects of distance between adjacent patches The distances between patches act as a radiation aperture and a portion of power radiate from these gaps. Then, by properly choosing the distance between patches, the radiation pattern and consequently front to back ratio (FTBR) of the proposed antenna is improved. Fig. 8 shows the FTBR of the proposed antenna versus frequency for different values of Lg in their impedance bandwidth. It can be seen that by increasing Lg, the antenna FTBR is improved, but the antenna bandwidth is decreased. Moreover, it should be say that for values of Lg greater than 0.4 mm, undesirable radiation is high and so, antenna performance is low. 3.7. Design guidelines The design process of the proposed antenna is including the following steps. 1. At first, design a conventional SIW horn in desired frequency based on Eq. (1) and the content is said in Section 2. 2. Select an initial value for Lg, n and m based on the previous discussions. 3. Based on Eqs. (2) and (3), find the required values of L3 and L4. 4. Based on the simulated results, change the values of design parameters to achieve desired radiation performance. 5. To obtain a suitable radiation characteristic, a trade-off between antenna bandwidth, gain and FTBR should be considered. In our case, antenna parameters n = 6, m = 5 and Lg = 0.2 mm is selected. 4. Measurement results To verify the simulation results, a prototype of the proposed SIW horn is made using TLY062 substrate and its radiation characteristics are measured. The photo of the fabricated antenna is shown in Fig. 9. Fig. 10 shows the measured reflection coefficient of the proposed antenna including the simulated one versus frequency.
Apart from a shift in frequency response due to the fabrication imperfection, the measured results agree well with those obtained by simulation. It can be seen that 22.7% impedance bandwidth is obtained, which covers from 20.8 GHz to 26.15 GHz. The simulated radiation efficiency is demonstrated in Fig. 11. Also the variation of the measured antenna gain including the simulated one is depicted in Fig. 11. The measured gain along the operating bandwidth is varied from 5 dBi to 9 dBi. It is believed that the deviation between simulation and measured results at a few frequencies is due to the fabrication imperfection, loss of connector, measurement inaccuracies and the effects of experimental setup environment. The simulation radiation patterns for the two standard E- and H-planes at 21.5 GHz, 23.6 GHz and 25.5 GHz for co- and crosspolarization are presented in Fig. 12 including the measured copolar patterns. It can be seen that the results agree well with each other except for backward radiation, which is believed is due to the measurement error. Moreover, our proposed antenna provides stable end-fire radiation patterns along operating bandwidth. The measured SLL is lower than 10 dB and FTBR is varying between 8 dB and 15 dB. The comparisons of the radiation performances of the proposed antenna with recently published wideband SIW H-plane horn antenna are summarized in Table 1. The antenna with highest impedance bandwidth SIW H-plane horn antennas is RSIW structure introduced in [10], which is a multi-layers structure and its design and fabrication process involves lots of complexity. In case of single-layer antenna structures, the impedance bandwidth of antennas is usually lower than 20%. Although, the proposed antenna in [6] provides 40.5% impedance bandwidth, but its radiation efficiency is low. Although SIW H-plane horn antenna using printed transition has been introduced before but they aren’t periodically and the number of design parameters are many. In this paper for the first time, periodically patches have been introduced to improve impedance bandwidth of SIW H-plane horn antenna with just three design parameters. Also, in our design, one can change the operating frequency, impedance bandwidth, FTBR and gain of antenna by selecting the design parameters based on the desirable characteristics. 5. Conclusion A new substrate integrated waveguide H-plane horn antenna loaded with external dielectric slab and some row of printed diamond patches is introduced in this paper. The external dielectric slab and patches act as an impedance transformer which improves impedance matching between aperture of horn antenna and air. The proposed antenna provides impedance bandwidth of 22.7%, which covers from 20.8 GHz up to 26.15 GHz. The gain of antenna over the operating bandwidth is between 5 dBi to 9 dBi and FTBR is
Table 1 The radiation performance comparison of the proposed SIW horn antenna with the results of recently published ones. Reference
Number of Antenna layers size (k3o)
Dielectric loaded [5] 1 Compact Air-via [6] 1 Open parallel transitions [7] 2 Dipole array [8] 3 Ridge substrate integrated waveguide [10] 4 Compact horn antenna [11] 1 Metamaterials Loaded [12] 1 Phase corrected H-plane horn [14] 1 This work 1
2.86 1.26 0.22 2.94 2.72 0.32 2 2.9 0.4 2.6 3.8 0.5 2.9 2.27 0.13 1.56 1.26 0.094 6 2.75 0.05 4.4 2.3 0.172 3 1.8 0.123
Substrate Resonate thickness (k0) frequency
0.22 0.32 0.2 0.165 0.13 0.094 0.05 0.172 0.123
GHz
FBW (%)
26.5 22.2 26 32.5 12.3 15.3 15 34 23.5
5 40.5 12 44 92.7 16 10.6 20 22.7
Antenna FTBR (dB) SLL (dB) gain (dBi)
9.7 8–9 NA. 9–12 3–15 6–8 4–8 10–11 5–9
20 10–20 8–12 10–20 NA. 15 9 NA. 8–15
8.27 10 to 20 10 to 20 15 to 20 5 to 15 20 NA. 10 to 20 10 to 20
Parameters of loaded structure
1 5 2 4 – 5 3 8 3
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between 8 dB and 15 dB. Also, the proposed antenna provides stable end-fire radiation pattern over the operation frequency with SLL lower than 10 dB. Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.aeue.2019.03.011. References [1] Balanis CA. Antenna theory analysis and design. 4th ed. Hoboken, New Jersey: John Wiley & Sons; 2016. [2] Sun D, Xu J. Compact phase corrected H-plane horn antenna using slow wave structures. IEEE Anten Wirel Propag Lett 2017;16:1032–5. [3] Dashti H, Neshati Mohammad H. Input impedance modeling of patch and semi-rectangular substrate integrated waveguide cavity hybrid antenna. Int J Electron Commun (AEÜ) 2018;89:1–5. [4] Jamshidi-Zarmehri H, Neshati Mohammad H. Design and development of a high gain SIW H-Plane horn antenna loaded with waveguide, dipole array and reflector nails using thin substrate. IEEE Trans antennas propagation IEEE-AP [in press]. [5] Wang H, Fang D-G, Zhang B, Che W-Q. Dielectric loaded substrate integrated waveguide (SIW) H-plane horn antennas. IEEE Trans Anten Propag 2010;58 (3):640–7. [6] Cai Y, Zhang Y, Wang L. Design of compact air-vias perforated SIW horn antenna with partially detached broad walls. IEEE Trans Anten Propag 2016;64 (6):2100–7. [7] Bayat-Makou N, Sorkherizi MS, Kishk AA. Substrate integrated horn antenna loaded with open parallel transitions. IEEE Anten Wirel Propag Lett 2017;16:349–51.
[8] Wang J, Li Y, Luk K-M. Wideband dipole array loaded substrate integrated Hplane horn antenna for millimeter waves. IEEE Trans Anten Propag 2017;65 (10):5211–9. [9] Mallahzadeh AR, Esfandiarpour S. Wideband h-plane horn antenna based on ridge substrate integrated waveguide (RSIW). IEEE Anten Wirel Propag Lett 2012;11:85–8. [10] Zhao Y, Shen Z, Wu W. Wideband and low-profile H-plane ridged SIW horn antenna mounted on a large conducting plane. IEEE Trans Anten Propag 2014;62(11):5895–900. [11] Esquius-Morote M, Fuchs B, Zürcher J-F, Mosig JR. Novel thin and compact Hplane SIW horn antenna. IEEE Trans Anten Propag 2013;61(6):2911–20. [12] Cai Y, Zhang Y, Qian Z. Design of low-profile metamaterials-loaded substrate integrated waveguide horn antenna and its array applications. IEEE Trans Anten Propag 2017;65(7):3732–7. [13] Esquius-Morote M, Fuchs B, Mosig JR. A printed transition for matching improvement of SIW horn antennas. IEEE Trans Anten Propag 2013;61 (4):1923–30. [14] Wang L, Esquius-Morote M, Mosig JR. Phase corrected H-plane horn antenna in gap SIW technology. IEEE Trans Anten Propag 2017;65(1):347–53. [15] Stutzman WL, Thiele GA. Antenna theory and design. 3rd ed. John Wiley & Sons; 2012. [16] Jamshidi-Zarmehri H, Neshati Mohammad H. Modified SIW H-plane horn antenna with improved gain using thin substrate. 26th Iranian conference on electrical engineering, ICEE 2018, Mashhad; May 2018. p. 412–415. [17] Collin RE. Foundations for microwave engineering. 2nd ed. New York: John Wiley & Sons; 2000. [18] Bayat-Makou N, Kishk AA. Substrate integrated horn antenna with uniform aperture distribution. IEEE Trans Anten Propag 2017;65(2):514–20. [19] Gong L, Ramer R. Substrate integrated waveguide h-plane horn antenna with improved front-to-back ratio and reduced side lobe level. IEEE Anten Wirel Propag Lett 2016;15:1835–8.
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
Development a new wideband substrate integrated waveguide H-plane horn antenna loaded with periodically diamond patches Hojjat Jamshidi-Zarmehri, Mohammad H. Neshati ⇑ Ferdowsi University of Mashhad, Mashhad, Iran
a r t i c l e
i n f o
Article history: Received 7 October 2018 Accepted 23 March 2019
Keywords: Horn antenna Substrate integrated waveguide (SIW) Side lobe level (SLL)
a b s t r a c t This paper presents a new wideband Substrate Integrated Waveguide (SIW) H-plane horn antenna. A few rows of diamond patches are printed on the top and bottom side of the dielectric slab at front of the radiating aperture of a conventional horn to improve impedance matching. The proposed antenna is numerically investigated using a software package and a prototype of the antenna is made to validate the obtained simulated results. The measured results show that the introduced antenna provides 22.7% impedance bandwidth, which covers from 20.8 GHz to 26.15 GHz with stable end-fire radiation patterns, while Side Lobe Level (SLL) is lower than 10 dB over the operating bandwidth. Ó 2019 Published by Elsevier GmbH.
1. Introduction Conventional metallic horn antennas provide a few advantages including high gain, high radiation efficiency and suitable radiation patterns. In spite of the benefits of these type of antennas, they are bulky and suffer from their 3-dimensional structure [1,2]. Recently, by introducing SIW technology, it is possible to implement microwave circuits and antennas in planar form [3]. However, the conventional SIW H-plane horn provides narrow impedance bandwidth due to poor impedance matching between the radiation aperture and free space [4]. To improve impedance bandwidth of these antennas, variety of methods has been introduced in literature. In case of thick substrate, h > k o/6, dielectric loaded SIW Hplane horn antenna with a narrow impedance bandwidth of 5% is introduced in [5]. Wideband SIW H-plane horn antenna using air-vias is presented in [6] with a reported impedance bandwidth of 40.5%. Another SIW H-plane horn antenna using two and three layers of substrates are introduced in [7] and [8], which provide impedance bandwidth of 12% and 44% respectively. Ridge substrate integrated waveguide (RSIW) H-plane horn antennas with ultra-wideband impedance bandwidth have been investigated in [9] and [10], which provide over 75% impedance bandwidth using a multi-layered structure, which involve lots of complexity in design and fabrication process. In case of thin substrate, h < k o/6, a novel and compact H-plane and a low-profile metamaterials-loaded SIW horn antenna provid⇑ Corresponding author. E-mail address: [email protected] (M.H. Neshati). https://doi.org/10.1016/j.aeue.2019.03.011 1434-8411/Ó 2019 Published by Elsevier GmbH.
ing over 10% impedance bandwidth are investigated in [11] and [12], whereas the antenna gain is low. In [13] and [14] two new structures using printed transitions are introduced with 10% and 20% impedance bandwidth respectively, but the number of designed parameters of these antennas are many. In this paper, a new wideband SIW H-plane horn antenna using a thin substrate is proposed. An external dielectric slab and a few rows of printed diamond patches are loaded at front of the radiating aperture of a conventional SIW horn, which act as an impedance transformer to improve impedance bandwidth. The proposed antenna is numerically investigated using High Frequency Structure Simulator (HFSS) software. Also, a prototype of the antenna is made and the measured radiation characteristics are reported. 2. Antenna structure Fig. 1 shows the structure of the proposed antenna including conventional one. It is designed using TLY062 substrate with dielectric constant of 2.2, thickness of 1.576 mm and loss tangent of 0.001. For H-plane horn antennas, to achieve maximum directivity, Eq. (1) has to be satisfied [15].
A
qffiffiffiffiffiffiffiffiffiffiffiffi 3kg Lh
ð1Þ
In which kg is guided wavelength, Lh is antenna length and A is the width of the radiating aperture. The distance between adjacent vias is selected in such a way that power leakage can be neglected [16]. The structure is fed by 50 O coaxial line made by a probe with
10
H. Jamshidi-Zarmehri, M.H. Neshati / Int. J. Electron. Commun. (AEÜ) 105 (2019) 9–14
Fig. 2. The magnitude of the simulated S11 of the conventional and dielectric loaded SIW H-plane horn antennas versus frequency.
which confirms the effect of dielectric slab for thin substrate is negligible [4]. 3.2. The proposed SIW horn antenna
Fig. 1. The geometry of (a) conventional SIW horn antenna, (b) proposed SIW horn antenna (L1 = 8.4 mm, L2 = 19.6 mm, Lh = 28 mm, Lp = 2.8 mm, a = 8.7 mm, A = 25 mm, R1 = 0.35 mm, R2 = 1.15 mm, p = 1.4 mm, d = 0.8 mm, L3 = 10.4 mm, L4 = 4 mm, Lg = 0.2 mm, h = 23°).
inner radius of R1 and outer radius of R2, which is placed at the distance of Lp kg/4 from the vertical wall of the waveguide to obtain the best impedance matching condition [17]. An external dielectric slab with length of L3 is placed in front of the radiating aperture. In addition, a few rows of diamond patches with diameter of L4 are printed on the top and bottom side of the dielectric slab. The distance between patches is designated by Lg. The detail parameters of the both horns are summarized at the bottom of Fig. 1. The number of patches along antenna width and length are designated by n and m respectively. These are the design parameters of the antenna and are equivalent to the diameter of patches L4 and the distance between adjacent patches gap Lg. The relation between n, Lg and L4 is given by Eq. (2).
L4 ¼
A ðn 1ÞLg n
The main idea in design of our proposed antenna is the loading a structure in front of the aperture of the horn to improve matching condition between the aperture and free space. In fact, the patches and the distance between them can be modeled as an equivalent LC parallel resonant and in turn, input impedance matching is achieved at different frequencies. The simulated real and imaginary part of the input impedance of the proposed SIW horn including that of the conventional one are shown in Fig. 3. It can be seen that for the proposed antenna along a wide range of frequency, from 21 GHz up to 27 GHz, the real part of the input impedance is close to the characteristic impedance of SIW, ZSIW [6], while
ð2Þ
Eq. (3) shows the relation between m, Lg and L3.
L3 ¼
m L4 þ Lg 2
ð3Þ
3. Simulation results 3.1. The conventional SIW horn antenna First of all, the conventional SIW horn is designed to operate around 25 GHz based on Eq. (1). The magnitude of the simulated S11 of this horn is plotted in Fig. 2 versus frequency. It can be seen that this antenna provides few separates resonate frequency, in which impedance bandwidth is narrow at these frequencies. Also, the simulated S11 of the dielectric loaded horn is shown in Fig. 2,
Fig. 3. The simulated imaginary and real part of the input impedance of the proposed and conventional SIW horn antenna versus frequency.
H. Jamshidi-Zarmehri, M.H. Neshati / Int. J. Electron. Commun. (AEÜ) 105 (2019) 9–14
the imaginary part of the input impedance is nearly zero, whereas, in case of the conventional horn, for a narrow bandwidth around 25 GHz, the imaginary part of the input impedance is close to zero and its real part is close to ZSIW. In fact, Fig. 3 confirms that external dielectric slab and diamond patches act as an impedance transformer that is caused the input impedance of antenna in a wide range of frequency becomes close to ZSIW and so impedance matching of antenna is enhanced.
11
radiation performances of the antenna, a few parametric study is carried out and the antenna parameters are studied. 3.4. The effects of number of patches along width, n As it mentioned in Section 3.2, the patches and the distance between them can be modeled as an equivalent LC parallel
3.3. Parametric study To study the effects of different parameters of the structure including the number of patches along width and the length and distance between patches of the proposed SIW horn on the
Fig. 6. The simulated gain of the proposed SIW horn for different values of m versus frequency.
Fig. 4. The simulated S11 of the proposed antenna for different values of n versus frequency.
Fig. 7. The simulated radiation pattern of the proposed antenna for m = 11 at 25.4 GHz frequency.
Fig. 5. Simulated aperture field distribution along antenna aperture for different values of m, (a) phase distribution (b) amplitude distribution.
Fig. 8. The simulated FTBR of the proposed antenna for different values of Lg versus frequency.
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resonant circuit and therefore, by changing the dimension of the patches the corresponding value of C and L of the equivalent circuit is altered and so, the frequency response is changed. The simulated result of S11 versus frequency for different values of n for Lg = 0.2 mm and m = 5 is shown in Fig. 4. It can be seen that by increasing n, impedance bandwidth is highly improved and it reaches to its maximum value for n = 6. Further increasing n, the impedance bandwidth nearly remains constant, but the operating frequency is increased. One can uses this property to design the antenna for a desired operation frequency. Also with change the dimension of patches, the matching between aperture and free space improves and the flattering of the curves is due to the impedance matching.
for different values of m, while Lg = 0.2 mm and n = 6. It is observed that uniform field distribution and decreasing phase variation of the field is obtained by increasing m, leading to obtain higher aperture efficiency and so, the antenna gain is highly improved [18]. The variation of the antenna gain versus frequency for different values of m, in their impedance bandwidth is shown in Fig. 6. It can be seen that by increasing m, the antenna gain is improved,
3.5. The effects of number of patches along length, m Fig. 5 shows the simulated amplitude and phase distributions of electric field along the radiation aperture of the proposed antenna
Fig. 9. The photo of the fabricated proposed SIW horn antenna.
Fig. 10. The measured and simulated S11 of the proposed antenna versus frequency.
Fig. 11. The measured and simulated gain and simulated radaition efficiency of the proposed antenna.
Fig. 12. The measured and simulated radiation patterns of the proposed SIW horn antenna, (a) 21.5 GHz (b) 23.6 GHz (c) 25.5 GHz.
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whereas antenna bandwidth is decreased. Our study shows that for m = 11 antenna gain is improved up to 14 dBi. Fig. 7 shows the radiation patterns of the proposed antenna in both E- and H-planes for m = 11 at 25.4 GHz. It can be seen that the Side Lobe Level (SLL) of the H-plane horn is low. Therefore, this structure can be used as an alternative of the dielectric loaded structures introduced in [5] and [19], while our SIW horn provides higher gain and lower SLL with at least 10% impedance bandwidth. Also, it should be mentioned that the dielectric loaded antennas are only appropriate for thick substrate, but the proposed structure in this paper can be used for thin substrate. 3.6. The effects of distance between adjacent patches The distances between patches act as a radiation aperture and a portion of power radiate from these gaps. Then, by properly choosing the distance between patches, the radiation pattern and consequently front to back ratio (FTBR) of the proposed antenna is improved. Fig. 8 shows the FTBR of the proposed antenna versus frequency for different values of Lg in their impedance bandwidth. It can be seen that by increasing Lg, the antenna FTBR is improved, but the antenna bandwidth is decreased. Moreover, it should be say that for values of Lg greater than 0.4 mm, undesirable radiation is high and so, antenna performance is low. 3.7. Design guidelines The design process of the proposed antenna is including the following steps. 1. At first, design a conventional SIW horn in desired frequency based on Eq. (1) and the content is said in Section 2. 2. Select an initial value for Lg, n and m based on the previous discussions. 3. Based on Eqs. (2) and (3), find the required values of L3 and L4. 4. Based on the simulated results, change the values of design parameters to achieve desired radiation performance. 5. To obtain a suitable radiation characteristic, a trade-off between antenna bandwidth, gain and FTBR should be considered. In our case, antenna parameters n = 6, m = 5 and Lg = 0.2 mm is selected. 4. Measurement results To verify the simulation results, a prototype of the proposed SIW horn is made using TLY062 substrate and its radiation characteristics are measured. The photo of the fabricated antenna is shown in Fig. 9. Fig. 10 shows the measured reflection coefficient of the proposed antenna including the simulated one versus frequency.
Apart from a shift in frequency response due to the fabrication imperfection, the measured results agree well with those obtained by simulation. It can be seen that 22.7% impedance bandwidth is obtained, which covers from 20.8 GHz to 26.15 GHz. The simulated radiation efficiency is demonstrated in Fig. 11. Also the variation of the measured antenna gain including the simulated one is depicted in Fig. 11. The measured gain along the operating bandwidth is varied from 5 dBi to 9 dBi. It is believed that the deviation between simulation and measured results at a few frequencies is due to the fabrication imperfection, loss of connector, measurement inaccuracies and the effects of experimental setup environment. The simulation radiation patterns for the two standard E- and H-planes at 21.5 GHz, 23.6 GHz and 25.5 GHz for co- and crosspolarization are presented in Fig. 12 including the measured copolar patterns. It can be seen that the results agree well with each other except for backward radiation, which is believed is due to the measurement error. Moreover, our proposed antenna provides stable end-fire radiation patterns along operating bandwidth. The measured SLL is lower than 10 dB and FTBR is varying between 8 dB and 15 dB. The comparisons of the radiation performances of the proposed antenna with recently published wideband SIW H-plane horn antenna are summarized in Table 1. The antenna with highest impedance bandwidth SIW H-plane horn antennas is RSIW structure introduced in [10], which is a multi-layers structure and its design and fabrication process involves lots of complexity. In case of single-layer antenna structures, the impedance bandwidth of antennas is usually lower than 20%. Although, the proposed antenna in [6] provides 40.5% impedance bandwidth, but its radiation efficiency is low. Although SIW H-plane horn antenna using printed transition has been introduced before but they aren’t periodically and the number of design parameters are many. In this paper for the first time, periodically patches have been introduced to improve impedance bandwidth of SIW H-plane horn antenna with just three design parameters. Also, in our design, one can change the operating frequency, impedance bandwidth, FTBR and gain of antenna by selecting the design parameters based on the desirable characteristics. 5. Conclusion A new substrate integrated waveguide H-plane horn antenna loaded with external dielectric slab and some row of printed diamond patches is introduced in this paper. The external dielectric slab and patches act as an impedance transformer which improves impedance matching between aperture of horn antenna and air. The proposed antenna provides impedance bandwidth of 22.7%, which covers from 20.8 GHz up to 26.15 GHz. The gain of antenna over the operating bandwidth is between 5 dBi to 9 dBi and FTBR is
Table 1 The radiation performance comparison of the proposed SIW horn antenna with the results of recently published ones. Reference
Number of Antenna layers size (k3o)
Dielectric loaded [5] 1 Compact Air-via [6] 1 Open parallel transitions [7] 2 Dipole array [8] 3 Ridge substrate integrated waveguide [10] 4 Compact horn antenna [11] 1 Metamaterials Loaded [12] 1 Phase corrected H-plane horn [14] 1 This work 1
2.86 1.26 0.22 2.94 2.72 0.32 2 2.9 0.4 2.6 3.8 0.5 2.9 2.27 0.13 1.56 1.26 0.094 6 2.75 0.05 4.4 2.3 0.172 3 1.8 0.123
Substrate Resonate thickness (k0) frequency
0.22 0.32 0.2 0.165 0.13 0.094 0.05 0.172 0.123
GHz
FBW (%)
26.5 22.2 26 32.5 12.3 15.3 15 34 23.5
5 40.5 12 44 92.7 16 10.6 20 22.7
Antenna FTBR (dB) SLL (dB) gain (dBi)
9.7 8–9 NA. 9–12 3–15 6–8 4–8 10–11 5–9
20 10–20 8–12 10–20 NA. 15 9 NA. 8–15
8.27 10 to 20 10 to 20 15 to 20 5 to 15 20 NA. 10 to 20 10 to 20
Parameters of loaded structure
1 5 2 4 – 5 3 8 3
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between 8 dB and 15 dB. Also, the proposed antenna provides stable end-fire radiation pattern over the operation frequency with SLL lower than 10 dB. Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.aeue.2019.03.011. References [1] Balanis CA. Antenna theory analysis and design. 4th ed. Hoboken, New Jersey: John Wiley & Sons; 2016. [2] Sun D, Xu J. Compact phase corrected H-plane horn antenna using slow wave structures. IEEE Anten Wirel Propag Lett 2017;16:1032–5. [3] Dashti H, Neshati Mohammad H. Input impedance modeling of patch and semi-rectangular substrate integrated waveguide cavity hybrid antenna. Int J Electron Commun (AEÜ) 2018;89:1–5. [4] Jamshidi-Zarmehri H, Neshati Mohammad H. Design and development of a high gain SIW H-Plane horn antenna loaded with waveguide, dipole array and reflector nails using thin substrate. IEEE Trans antennas propagation IEEE-AP [in press]. [5] Wang H, Fang D-G, Zhang B, Che W-Q. Dielectric loaded substrate integrated waveguide (SIW) H-plane horn antennas. IEEE Trans Anten Propag 2010;58 (3):640–7. [6] Cai Y, Zhang Y, Wang L. Design of compact air-vias perforated SIW horn antenna with partially detached broad walls. IEEE Trans Anten Propag 2016;64 (6):2100–7. [7] Bayat-Makou N, Sorkherizi MS, Kishk AA. Substrate integrated horn antenna loaded with open parallel transitions. IEEE Anten Wirel Propag Lett 2017;16:349–51.
[8] Wang J, Li Y, Luk K-M. Wideband dipole array loaded substrate integrated Hplane horn antenna for millimeter waves. IEEE Trans Anten Propag 2017;65 (10):5211–9. [9] Mallahzadeh AR, Esfandiarpour S. Wideband h-plane horn antenna based on ridge substrate integrated waveguide (RSIW). IEEE Anten Wirel Propag Lett 2012;11:85–8. [10] Zhao Y, Shen Z, Wu W. Wideband and low-profile H-plane ridged SIW horn antenna mounted on a large conducting plane. IEEE Trans Anten Propag 2014;62(11):5895–900. [11] Esquius-Morote M, Fuchs B, Zürcher J-F, Mosig JR. Novel thin and compact Hplane SIW horn antenna. IEEE Trans Anten Propag 2013;61(6):2911–20. [12] Cai Y, Zhang Y, Qian Z. Design of low-profile metamaterials-loaded substrate integrated waveguide horn antenna and its array applications. IEEE Trans Anten Propag 2017;65(7):3732–7. [13] Esquius-Morote M, Fuchs B, Mosig JR. A printed transition for matching improvement of SIW horn antennas. IEEE Trans Anten Propag 2013;61 (4):1923–30. [14] Wang L, Esquius-Morote M, Mosig JR. Phase corrected H-plane horn antenna in gap SIW technology. IEEE Trans Anten Propag 2017;65(1):347–53. [15] Stutzman WL, Thiele GA. Antenna theory and design. 3rd ed. John Wiley & Sons; 2012. [16] Jamshidi-Zarmehri H, Neshati Mohammad H. Modified SIW H-plane horn antenna with improved gain using thin substrate. 26th Iranian conference on electrical engineering, ICEE 2018, Mashhad; May 2018. p. 412–415. [17] Collin RE. Foundations for microwave engineering. 2nd ed. New York: John Wiley & Sons; 2000. [18] Bayat-Makou N, Kishk AA. Substrate integrated horn antenna with uniform aperture distribution. IEEE Trans Anten Propag 2017;65(2):514–20. [19] Gong L, Ramer R. Substrate integrated waveguide h-plane horn antenna with improved front-to-back ratio and reduced side lobe level. IEEE Anten Wirel Propag Lett 2016;15:1835–8.