This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg)
Nanyang Technological University, Singapore.
3D absorptive frequency‑selective reflection and
transmission structures with dual absorption
bands
Yu, Yufeng; Luo, Guo Qing; Ahmed Abdelmottaleb Omar; Liu, Xuan; Yu, Weiliang; Hao,
Zhang Cheng; Shen, Zhongxiang
2018
Yu, Y., Luo, G. Q., Ahmed Abdelmottaleb Omar, Liu, X., Yu, W., Hao, Z. C., & Shen, Z. (2018).
3D absorptive frequency‑selective reflection and transmission structures with dual
absorption bands. IEEE Access, 6, 72880‑72888. doi:10.1109/ACCESS.2018.2881744
https://hdl.handle.net/10356/103394
https://doi.org/10.1109/ACCESS.2018.2881744
© 2018 IEEE. Translations and content mining are permitted for academic research only.
Personal use is also permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more
information.
Downloaded on 12 Jun 2021 20:07:46 SGT
3D Absorptive Frequency-Selective Reflection
and Transmission Structures With
Dual Absorption Bands
YUFENG YU 1,2, (Member, IEEE), GUO QING LUO 1, (Member, IEEE),
AHMED ABDELMOTTALEB OMAR 3, (Student Member, IEEE), XUAN LIU1, WEILIANG YU1, ZHANG CHENG HAO 2, (Senior Member, IEEE),
AND ZHONGXIANG SHEN 3, (Fellow, IEEE)
1Key Laboratory of RF Circuits and System of Ministry of Education, Institute of Antennas and Microwave Technology,
Hangzhou Dianzi University, Hangzhou 310018, China
2State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 211189, China
3School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798
Corresponding authors: Guo Qing Luo ([email protected]) and Zhang Cheng Hao ([email protected])
This work was supported in part by the National Natural Science Foundation of China under Grant 61701152 and Grant 61722107 and in part by the Open Fund of the State Key Lab of Millimeter Waves of China under Grant K201914.
ABSTRACT This paper presents a 3D absorptive frequency-selective reflection structure (AFSR) and absorptive frequency-selective transmission structure (AFST) with one reflection/transmission band and two absorption bands. The 3D AFSR utilizes the intrinsic reflection band and higher order absorption band of a wideband 3D absorber. By simply loading a printed gap capacitor in the structure, the reflection band can be easily tuned by varying the capacitance of the capacitor. A design example is presented, with a reflection band of 24.7% fractional bandwidth (FBW), a lower absorption band of 72.5% FBW, and a higher absorption band of 48.6% FBW. A 3D AFST composed of the 3D AFSR and a parallel-plate waveguide is then proposed. Its general operating principle is demonstrated, such that the 3D AFST can be seen as a combination of a 3D AFSR and a 3D band-pass FSS, which can independently contribute to the absorption and transmission, respectively. A set of guidelines is proposed to facilitate the design. A prototype of the proposed AFST is fabricated and measured. The measured results show that the transmission band is with a minimum insertion loss of 0.4 dB and an FBW of 30%. Moreover, the lower and higher absorption bands are with 63.9 % and 47.6 % FBW, respectively. The proposed AFST has a simpler structure, wider lower absorption bandwidth, and thinner thickness compared with previous structures.
INDEX TERMS Absorptive frequency-selective reflector (AFSR), absorptive frequency-selective transmission (AFST) structure, frequency-selective surface, rasorber.
I. INTRODUCTION
Low-observable platforms have played an important role in modern military systems. Generally, the shape of the platform should be carefully designed in order to reduce its radar cross section (RCS). Moreover, the scattering from the devices on the platform such as antennas must also be taken under control. Among a number of techniques that can reduce the RCS of antennas, frequency selective surfaces/structures (FSSs) [1]–[5] as stealthy radomes have been widely used and extensively studied. These radomes allow the in-band electromagnetic (EM) waves to pass through, while they reflect the out-of-band EM waves to other directions resorting
to their conformal shapes. Obviously, only mono-static RCS is reduced in this way.
In order to reduce both mono- and bi-static RCS, a new kind of FSSs, termed as absorptive frequency-selective trans-mission structures (AFSTs) [6]–[25], was developed in recent years. They were also termed as frequency selective rasor-bers (FSRs) or absorptive/ transmissive frequency selec-tive surface (ATFSSs) in different literatures. An AFST is almost transparent within its transmission-band (similar to a band-pass FSS), while it absorbs the out-of-band incident EM waves instead of reflecting them. Therefore, both mono-static and bimono-static out-of-band RCS can be reduced. Over the
72880
2169-3536 2018 IEEE. Translations and content mining are permitted for academic research only.
Y. Yu et al.: 3D Absorptive Frequency-Selective Reflection and Transmission Structures
years, a variety of AFSTs have been proposed. A conceptual design was given in an early patent, which was realized by cascading a lossy layer above a band-pass lossless layer [6]. A number of 2D designs were reported in the subsequent publications [7]–[19]. Some 3D designs were also presented in [20]–[25], whose absorption and transmission paths were separately constructed utilizing lossless and lossy resonators in the 3D unit cells. 3D AFSTs have the advantages of higher selectivity of the transmission band and more stable filtering response under oblique incidence compared to 2D AFSTs, though their implementations are more complicated. It is worth mentioning that a key performance of AFSTs, both 2D and 3D designs, is the low insertion loss within the transmission band. For 2D designs, one way is to bypass the lossy components (resistors) of the lossy layer within the transmission band using series L-C resonators [11]. Another way, which was more widely used, is to introduce parallel L-C resonators into the lossy layer, which realize infinite impedance within the transmission band [12]–[19]. Similarly, for 3D designs, one way is also to bypass the resistors of the 3D lossy resonators within the transmission band using series L-C resonators [25]. Another way is to utilize the intrinsic zero impedance of short-circuited half-wavelength lossy resonators [21], [22].
Recently, one special kind of FSS, named absorp-tive frequency-selecabsorp-tive reflection structures (AFSRs) or absorptive frequency-selective reflectors (AFSRs), was pro-posed [25], [26]. An AFSR exhibits a frequency response of absorption-reflection-absorption. Specifically, an AFSR has one reflection band with two absorption bands located at its two sides. It can be seen as a counterpart of an AFST, whose transmission band is replaced by a reflection band. As indicated in [26], it can be used as a ground plane or reflector for an antenna, resulting in out-of-band RCS reduc-tion. According to the main features of an AFSR (a reflection band between two absorption bands), a number of reported absorbers (2D circuit-analog absorbers or 3D absorbers based on lossy resonators [27]) have similar characteristics due to their harmonic resonances, although the reflection band and higher-order absorption band have not been paid much attention at that time. However, there are three problems of directly applying these absorbers to AFSRs: i) The relative location of the two absorption bands and the reflection band is fixed, which is not desirable in designing an AFSR; ii) The higher absorption band is much narrower than the lower absorption band; iii) The selectivity of the reflection band is poor.
In this paper, an AFSR originated from the 3D wideband absorber in [27] is proposed in Section II. Unlike the solution of shunting the absorber with a series L-C resonator to realize a reflection band in [25], in this paper the intrinsic reflection band and the higher-order absorption band of the absorber are utilized. By simply loading a capacitor in the center of the structure, the reflection band can be flexibly lowered by varying the capacitance of the loaded capacitor. In addition, the selectivity of reflection band is improved, and the higher
absorption band is also extended. It is also worth noting that since the capacitor is of very small capacitance, it can be realized by a simple strip gap printed on a thin substrate. Therefore, the proposed AFSR needs fewer lumped elements compared with the one in [25], which results in lower fabri-cation cost.
A 3D AFST is then proposed in Section III, which is composed of the 3D AFSR described in Section II and a parallel-plate waveguide (PPW) with a central metalized via hole. The operating principle of the 3D AFST is demonstrated and it is considered as a combination of a 3D AFSR and a 3D band-pass FSS, which contribute to the absorption and transmission, respectively. This operating principle greatly facilitates the design of the AFST because its two components can be separately designed with little mutual interference. It is also worth mentioning that the operating principle and the design methodology are quite general and effective for all the 3D AFSTs with a pass-band of low insertion loss. A prototype of the proposed 3D AFST is then fabricated and measured, which exhibits a transmission band of 30% frac-tional bandwidth (FBW) and 0.4 dB insertion loss, a lower absorption band of 63.9 % FBW, and a higher absorption band of 47.6 % FBW.
II. 3D ABSORPTIVE FREQUENCY-SELECTIVE REFLECTION STRUCTURE
A. GERMETERY
The geometry of each unit-cell of the proposed 3D AFSR is shown in Fig. 1. It is originated from the 3D wideband absorber proposed in [27], and the periods along the x- and y- directions are denoted by W and Ha, respectively. The
structure is basically a shielded microstrip line that sup-ports two quasi-TEM modes (air mode and substrate mode). Shorted by a metallic plate at the back end (z = −L) and loaded by two resistors (Rs and Ra) and one capacitor (Ca),
the incident EM waves (along the z direction) can be absorbed within a wide frequency range. It is noted that this struc-ture can only operate when the electric field of the incident plane wave is in the yz-plane. An important improvement on the construction of an AFSR from the original absorber is the loading of gap capacitors in the center of the structure (z = −L2). Because the loaded capacitors are of very small capacitance, gap capacitors (instead of lumped capacitors) are used, which are printed on substrate A2 with a relative
permittivity of 2.2 and a thickness of 0.508 mm. The gap width and length of the gap capacitor is denoted as gc and
lc, respectively. It is noted that to allow the connection from
the top plate to the bottom plate, a metalized via hole with a diameter of dv is fabricated in substrate B of a relative
permittivity of 3.0 and a thickness of 1.5 mm.
B. EQUIVELENT CIRCUIT MODEL
In order to better understand the operation of the proposed AFSR, an equivalent circuit model is established and shown in Fig. 2. The top (Za,θa) and bottom (Zs,θs) transmission
FIGURE 1. Geometry of the unit cell of the proposed 3D AFSR.
(a) perspective view, and (b) side view. (Physical dimensions: L = 30 mm, W = 15 mm, Ha=13.7 mm, hsb=1.5 mm, Wm=2 mm, Ws1=1 mm, Ws2=1 mm, dvb=1.0 mm, lc=1.5 mm, gc=0.5 mm.
FIGURE 2. Equivalent circuit model of the proposed AFSR. (Circuit parameters: Z0=369, Za=344, Zs=66, Ra=270, Ca=1 pF, La=3.7 nH, Ci=0.1 pF, Li=3.0 nH, Rs=180, θa=90◦at 5.0 GHz, θs=90◦at 3.62 GHz).
lines (TLs) represent the air and substrate microstrip lines, respectively. Each TL supports one quasi-TEM mode. Their characteristic impedances and electric lengths are extracted from Eigen-mode Solver of CST [28]. The series RLC circuit (Ra, La and Ca) that connects the front end of the air TL
represents the resistor, capacitor, and the connecting strip on substrate A1. The series LC circuit (Liand Ci) that connects
the top line of the air TL and bottom line of the substrate TL represents the gap capacitor and the connecting strip on substrate A2. Another resistor (Rs) at the end of the TLs is
shared by both air and substrate TLs. Therefore, it contributes to both air- and substrate- mode absorptions.
The reflection coefficients of the proposed AFSR, calcu-lated from Advanced Design System (ADS) and simucalcu-lated
FIGURE 3. Comparison of the reflection coefficients of the proposed AFSR under the normal incidence obtained from full-wave simulation (HFSS) and the equivalent circuit model (ADS).
using High Frequency Structure Simulator (HFSS), are plot-ted in Fig. 3. A good agreement between them can be observed. The simulated |S11|indicates a lower absorption
band (|S11| ≤ −10 dB) from 1.16 GHz to 2.48 GHz and a
higher absorption band from 4.27 GHz to 7.01 GHz, corre-sponding to 72.5% and 48.6% fractional bandwidth (FBW), respectively. The reflection band (|S11| ≥ −3 dB) is from
3.01 GHz to 3.86 GHz, with a FBW of 24.7%. To evaluate the selectivity of the reflection band, we define SRB as the ratio of the bandwidth for |S11| ≥ −10 dB and |S11| ≥ −3 dB,
which is
SRB = BW−3dB/BW−10dB (1)
It is noted that the frequency band for |S11| ≥ −10 dB is the
band between the lower and higher absorption bands, while one for |S11| ≥ −3 dB is the reflection band. The closer the
SRBvalue is to 1, the higher is the selectivity of the reflection band. For the proposed AFSR, SRB equals to 0.47.
C. OPERATING PRINCIPLE OF THE REFLECTION BAND In order to demonstrate the operating principle of the reflec-tion band of the proposed AFSR, we plot the evolureflec-tion of the proposed AFSR from a simple short-ended PPW lossy res-onator, as seen in Fig. 4. The PPW lossy resonator in Fig. 4(a) (denoted as AFSR #1), which has been fully described in [21], is a simple transmission line loaded with a resistor in the front and short-circuited at the end. The second one (denoted as AFSR #2) is proposed as a wideband absorber in [27]. Compared to AFSR #1, a microstrip line is added inside the PPW, which forms a shielded micrstrip line structure, and thus two quasi-TEM modes (air mode and substrate mode) are established. In addition, a resistor (Rs) is also added
to terminate both air and substrate modes. The third one (denoted as AFSR #3) is the proposed AFSR in this paper, which is a variation of AFSR #2 with a capacitor (Ci) loaded
inside the structure.
The reflection coefficients of these three AFSRs are plotted in Fig. 5. It is seen that for AFSR #1, a perfect reflection is obtained at 5 GHz, at which the thickness (L) of the AFSR is
Y. Yu et al.: 3D Absorptive Frequency-Selective Reflection and Transmission Structures
FIGURE 4. Illustration of the evolution of the proposed AFSR: (a) 3D AFSR based on parallel plate waveguide transmission line (#1), (b) 3D AFSR based on shielded microstrip lines (#2), and (c) the proposed AFSR (#3).
FIGURE 5. Reflection coefficients of three AFSRs depicted in Fig. 4.
almost half a wavelength. This is easy to understand because the input impedance of a short-circuited half-wavelength TL is zero. Therefore, the resistor Rs is bypassed and the input
impedance of AFSR #1 is also zero (Zin1=0), which results
in a perfect reflection.
For AFSR #2, it is seen that its reflection band is slightly lower than that of AFSR #1, and the maximum reflection occurs at 4.9 GHz with |S11| = −0.43 dB. Moreover, both
higher and lower absorption bands are lowered and expanded compared to AFSR #1. It is interesting to see that although AFSR #2 is with a more complicated structure compared with AFSR #1, their reflection bands are quite similar, which indicates similar operating principles. To further demonstrate this, the electric field distributions of AFSR #1 at 5 GHz and AFSR #2 at 4.9 GHz are plotted in Fig. 6 (a) and (b), respectively. A typical half-wavelength electric field distri-bution of AFSR #2 can be readily observed, which is almost the same as that of AFSR #1. Therefore, we can conclude that AFSR #2 also operates as a short-circuited half-wavelength TL within the reflection band.
Once the operating principle of the reflection band is clear, a straightforward method to tune the reflection band is to load a capacitor in the center of the TL (the location of the maximum electric field). As seen in Fig. 5, with the loaded capacitor, the perfect reflection of the proposed AFSR drops
FIGURE 6. Electric field distributions of (a) AFSR #1 at 5 GHz and (b) AFSR #2 at 4.9 GHz.
to 3.45 GHz, which is 30% lower than that of AFSR #2. In addition, the higher absorption band also decreases with a wider fractional bandwidth.
D. DISCUSSIONS
After understanding the operating principle of the proposed AFSR, it is necessary to distinguish its advantages over AFSR #1 and AFSR #2. The first advantage, of course, is the flexibly to tune the reflection band. The reflection band can be lowered with the increase of the loaded capacitance (increase Lcor decrease gc). The other advantages with respect to the
performances are listed in Table 1. It is seen that compared to AFSR #1 and AFSR #2, the proposed AFSR has much wider upper absorption bandwidth, larger SRB value (higher selectivity of the reflection band), and thinner thickness with respect to the wavelength at both the lowest frequency of the absorption band and the center frequency of the reflection band.
TABLE 1.Performance comparison of AFSR #1, #2 and #3.
Finally, it is also necessary to compare the proposed AFSR with the one presented in [25], which correspond to two different techniques in achieving the reflection band. For our proposed one, as discussed in Section II.C, the reflection band is due to the zero impedance of the short-circuited half-wavelength TL. With a loaded capacitor, the reflection band can be lowered. However, for the AFSR in [25], an ultra-wide absorption band is realized at first by employing an additional resonator. Then a series L-C resonator is located in front of the absorber (in shunt with the absorber), which short-circuits the absorber at its resonate frequency (fs). Therefore, zero
impedance of the AFSR can be obtained at fs, which results
in a reflection band.
Although the upper absorption bandwidth of the AFSR in [25] is wider than our proposed one and its technique in designing 3D AFSRs is more general, it consumes eight lumped elements (four resistors, three capacitors and one inductor), while our proposed AFSR only needs three elements (two resistors and one capacitor). Moreover, the structure in [25] is more complicated due to the additional resonator. One may choose a suitable 3D AFSR considering both the performance requirements and fabrication cost.
FIGURE 7. Geometry of the unit cell of the proposed 3D AFST. (a) perspective view, and (b) top view of substrate C. (Physical dimensions: L = 30 mm, W = 15 mm, H = 16.7 mm, hsc=3.0 mm, dvc=1.75 mm, dhc=3.6 mm.
III. 3D ABSORPTIVE FREQUENCY-SELECTIVE TRANSMISSION STRUCTURE
A. GEOMETERY
Fig. 7 depicts the geometry of the unit cell of the proposed AFST. It is composed of an AFSR presented in Section II and a PPW with a central metalized via hole, which produce the absorption and transmission, respectively. The AFSR is the same as the one presented in Section II, thus its parameters are not repeated in Fig. 7. The PPW is filled with substrate C of a relative permittivity of 2.2 and a thickness of 3.0 mm. Air holes with diameters of dhcare drilled in substrate C, which
results in a lower effective relative permittivity. The PPW is equivalent to a simple TL, which produces a transmission pole at its resonance (half-wavelength). A metalized via hole with a diameter of dvcis fabricated at the center of substrate C,
which is equivalent to an inductor. It introduces an additional resonance below the original one, resulting in an extended transmission band and a sharp roll-off performance as well.
FIGURE 8. Illustration of the operating principle of the proposed AFST.
FIGURE 9. Comparison of the S-parameters of the 3D AFST, AFSR and band-pass FSS.
B. OPERATING PRINCIPLE
An AFST can be seen as a combination of a 3D AFSR and a 3D band-pass FSS, as illustrated in Fig. 8. The critical issue of designing an AFST is that the reflection band of the AFSR and the pass-band of the band-pass FSS must overlap. The reflection band of the AFSR can be easily tuned by varying the gap width and length of the printed capacitor, as mentioned in Section II. The pass-band of the band-pass FSS can also be tuned by changing the effective relative permittivity of substrate C. Therefore, tuning the transmission band of the AFST is quite straightforward.
As seen in Fig. 8, the AFST is almost similar to a band-pass FSS within the transmission band because the AFSR acts like a PEC block (zero input impedance, c.f. Section II.C). Therefore, the incident EM waves within the transmission band can only go through the PPW with very little absorption by the AFSR. However, the AFST is similar to the AFSR within the absorption bands, because the PPW almost acts as a PEC ground out of its pass-band. Therefore, the incident EM waves within the absorption bands are absorbed by the AFSR. To further validate the operating principle, the reflection and transmission coefficients of the proposed 3D AFST
Y. Yu et al.: 3D Absorptive Frequency-Selective Reflection and Transmission Structures
and its two components (the AFSR and band-pass FSS) in Fig. 8 are plotted in Fig. 9. It is clear to see that within the transmission band, both |S11|and |S21|of the AFST (blue
curves) are almost the same as that of a band-pass FSS (black curves). The transmission bands (|S21| ≥ −3 dB) range from
2.82 GHz to 3.94 and 2.84 GHz to 3.91 GHz for band-pass FSS and the AFST, respectively. Moreover, within the lower and higher absorption bands, |S11|of the AFST (blue solid
curve) is also very similar to that of the AFSR (orange solid curve).
It is worth mentioning that our approach of regarding an AFST as a combination of a 3D AFSR and 3D band-pass FSS is effective for all the 3D AFSTs with a pass-band of low insertion loss.
C. DESIGN GUIDELINES
Based on the operating principle, we understand that the transmission and absorption performances of the AFST are almost independently determined by its two components: the band-pass FSS and AFSR, respectively. This feature is of great importance in designing an AFST because we can separately design these two components without mutual inter-ference.
The following design guidelines are suggested for a fast design.
1) Design of the 3D AFSR. As discussed in Section II. C, the reflection band of the AFSR without loading the capacitor is approximately around fr = c2L, where
c is the speed of light in free space. By tuning the gap (gc) and length (lc) of the loaded gap capacitor,
the reflection band of the AFSR can be lowered to overlap with the targeted transmission band of your AFST. A simulation is conducted initially to ensure the performance around the reflection band and the absorption bands.
2) Design of the 3D band-pass FSS. The higher transmis-sion pole of the transmistransmis-sion band is approximately around fhp = c 2L
√
εeff, whereεeff represents the
effective relative permittivity of the substrate filled in the PPW. It is obvious thatεeff is lower with more air
holes in substrate C. The lower transmission pole (flp) is
determined by the loaded inductor of the metalized via hole. Therefore, its diameter (dvc) can be tuned to make
sure flpis close to fhp. Generally, a larger Hsc(height of
the PPW) results in a wider bandwidth, a lower inser-tion loss and a worse selectivity of the transmission band. A simulation is conducted to initially verify the performance around the transmission band.
3) Combine the 3D AFSR and the band-pass FSS to form the AFST. All the parameters may be slightly tuned for its optimum performance.
It is seen that the design guidelines are quite straightfor-ward and easy to follow. It is also worth mentioning that if the transmission band is designed to lower frequencies, the air holes in substrate C are not needed. Moreover, the 3D AFSR
in the first step is not restricted to the design proposed in this paper (it can be of any type). For example, an AFSR proposed in [25] where the reflection band is realized by applying an L-C resonator in shunt with an ultra-wideband absorber is also suitable for designing an AFST following the above-mentioned design guideline.
D. EXPERIMENTAL VERIFICATION
In order to verify our design, a prototype of the proposed AFST is fabricated and measured. As seen in Fig. 10(a), the prototype consists of 11 × 1 unit-cells along the x- and y- directions, respectively, with a size of 154 mm × 16.7 mm × 30 mm. Taconic TLY is used for substrates A and C, while Taconic RF30 is used for substrate B.
FIGURE 10. (a) Fabricated prototype of the proposed AFST and (b) the prototype in a parallel plate waveguide measurement set-up.
The measurement is conducted using a parallel-plate waveguide setup, as seem in Fig. 10(b), which is similar to that described in [29]. It is noted that its upper plate is removed in the figure for a better view. The four edges of the PPW are covered with commercial polyurethane foam absorbers in order to avoid reflections from the edges. More-over, two cones are located at the ends of the PPW in order to achieve a good transition from the coaxial line to the PPW.
Fig. 11(a) shows the comparison of the simulated and measured transmission and reflection coefficients under the normal incidence, where a relatively good agreement can be observed. The measured transmission band (|S21| ≥ −3 dB)
ranges from 2.78 GHz to 3.75 GHz (corresponding to a 30% FBW), which is slightly lower and narrower than the simulated one. Moreover, the measured minimum insertion
FIGURE 11. Measured and simulated (a) S-parameters and (b) absorption rates under the normal incidence.
loss of the transmission band is 0.43 dB, which is slightly larger than the simulated one (0.19 dB). The difference between the measured and simulated results is possibly due to the assembly error of the prototype and the measurement error from the PPW setup (the foam absorbers are not perfect to prevent the reflected waves).
The simulated and measured absorption rates are corre-spondingly shown in Fig. 11(b). It is seen that two absorption bands are located at both sides of the transmission band. The lower absorption band for absorption rate higher than 90% ranges from 1.17 GHz to 2.27 GHz, while the higher absorption band ranges from 4.23 GHz to 6.87 GHz. The fractional bandwidth for the lower and higher absorption bands are 63.9 % and 47.6 %, respectively.
The simulated S-parameters under the oblique inci-dence scanned in the xz- and yz- planes are plotted in Figs. 12(a) and (b), respectively, which exhibit stable fre-quency responses. It is worth noting that under the oblique incidence scanned in the xz- and yz- planes, the E-field is along the y-direction and the H -field is along the x-direction, respectively. It is also seen that the stability under the oblique incidence in the yz- plane is better than that in the xz- plane, which is due to the fact that for each PPW section, the height (hsc, etc.) along the y-direction is much smaller than the
width in the x-direction (W ). We can also see an interesting performance from Fig. 12(b) that when the incident angle
FIGURE 12. Simulated S-parameters of the proposed AFST under the oblique incidence in (a) x-z (0◦, θ) and (b) y-z (90◦, θ) planes.
in the yz- plane increases to 45◦, |S11|is greatly improved
compared with that under the oblique incidence.
TABLE 2.Performance comparison of the state-of-the-art.
In order to demonstrate the advantages of our proposed AFST, a comparison with the current state of the art designs is shown in Table 2. It is seen that our proposed design and that in [14] has the smallest thickness. However, the design in [14] has only one-sided absorption band. The design in [25], which constructs multiple resonances to obtain wide absorption bands, has 1.5 times higher absorption bandwidth compared with our proposed one. However, our proposed
Y. Yu et al.: 3D Absorptive Frequency-Selective Reflection and Transmission Structures
design has superior performance in terms of wider lower absorption bandwidth, lower insertion loss and thinner thick-ness. Moreover, only three lumped elements are needed in one unit-cell of the proposed design, which is one third of those used in [25].
IV. CONCLUSION
This paper has introduced a 3D AFSR that utilizes the intrin-sic reflection band and higher-order absorption band of a 3D absorber by simply loading a capacitor inside the structure. The 3D AFSR exhibits a reflection band and two absorption bands located at two sides of the reflection band, whose FBW are 24.7%, 72.5% and 48.6%, respectively. An advantage of this structure is that its reflection band can be easily tuned by varying the gap width and length of the printed gap capacitor. A 3D AFST is then presented, which consists of the 3D AFSR and a 3D band-pass FSS (a PPW in this design). The operating principle is demonstrated, revealing that the absorption and transmission performance are almost independently determined by the AFSR and the band-pass FSS. A prototype of the proposed 3D AFST is fabricated and measured, which exhibits a transmission band of 30% FBW and 0.4 dB insertion loss, a lower absorption band of 63.9 % FBW and a higher absorption band of 47.6 % FBW. Compared to previous structures, our proposed AFST has simpler structure, thinner thickness and wider lower absorp-tion bandwidth.
REFERENCES
[1] B. A. Munk, Frequency Selective Surfaces: Theory and Design. New York, NY, USA: Wiley, 2000.
[2] G. Q. Luo et al., ‘‘Theory and experiment of novel frequency selective surface based on substrate integrated waveguide technology,’’ IEEE Trans.
Antennas Propag., vol. 53, no. 12, pp. 4035–4043, Dec. 2005.
[3] G. Q. Luo et al., ‘‘Filtenna consisting of horn antenna and substrate integrated waveguide cavity FSS,’’ IEEE Trans. Antennas Propag., vol. 55, no. 1, pp. 92–98, Jan. 2007.
[4] G. Q. Luo, W. Hong, Q. H. Lai, K. Wu, and L. L. Sun, ‘‘Design and experimental verification of compact frequency-selective surface with quasi-elliptic bandpass response,’’ IEEE Trans. Microw. Theory Techn., vol. 55, no. 12, pp. 2481–2487, Dec. 2007.
[5] A. Qasim and Z. Shen, ‘‘Design of wideband bandstop frequency-selective structures using stacked parallel strip line arrays,’’ IEEE Trans. Antennas
Propag., vol. 64, no. 8, pp. 3401–3409, Aug. 2016.
[6] W. S. Arceneaux, R. D. Akins, and W. B. May, ‘‘Absorptive/transmissive radome,’’ U.S. Patent 5 400 043, Mar. 21, 1995.
[7] B. A. Munk, Metamaterials: Critique and Alternatives. Hoboken, NJ, USA: Wiley, 2009.
[8] F. Costa and A. Monorchio, ‘‘A frequency selective radome with wideband absorbing properties,’’ IEEE Trans. Antennas Propag., vol. 60, no. 6, pp. 2740–2747, Jun. 2012.
[9] A. Motevasselian and B. L. G. Jonsson, ‘‘Design of a wideband rasorber with a polarisationsensitive transparent window,’’ IET Microw. Antenna
Propag., vol. 6, no. 7, pp. 747–755, May 2012.
[10] H. Zhou et al., ‘‘Experimental demonstration of an absorptive/transmissive FSS with magnetic material,’’ IEEE Antennas Wireless Propag. Lett., vol. 13, pp. 114–117, 2014.
[11] Y. Shang, Z. Shen, and S. Xiao, ‘‘Frequency-selective rasorber based on square-loop and cross-dipole arrays,’’ IEEE Trans. Antennas Propag., vol. 62, no. 11, pp. 5581–5589, Nov. 2014.
[12] Q. Chen, J. Bai, L. Chen, and Y. Fu, ‘‘A miniaturized absorptive fre-quency selective surface,’’ IEEE Antennas Wireless Propag. Lett., vol. 15, pp. 80–83, Sep. 2015.
[13] Q. Chen, L. Liu, L. Chen, J. Bai, and Y. Fu, ‘‘Absorptive frequency selective surface using parallel LC resonance,’’ Electron. Lett., vol. 52, no. 6, pp. 418–419, Mar. 2016.
[14] Q. Chen, S. Yang, J. Bai, and Y. Fu, ‘‘Design of absorptive/transmissive frequency-selective surface based on parallel resonance,’’ IEEE Trans.
Antennas Propag., vol. 65, no. 9, pp. 4897–4902, Sep. 2017.
[15] H. Huang and Z. Shen, ‘‘Absorptive frequency-selective transmission structure with square-loop hybrid resonator,’’ IEEE Antennas Wireless
Propag. Lett., vol. 16, pp. 3212–3215, 2017.
[16] K. Zhang, W. Jiang, and S. Gong, ‘‘Design bandpass frequency selective surface absorber using LC resonators,’’ IEEE Antennas Wireless Propag.
Lett., vol. 16, pp. 2586–2589, 2017.
[17] Y. Han, W. Che, X. Xiu, W. Yang, and C. Christopoulos, ‘‘Switchable low-profile broadband frequency-selective rasorber/absorber based on slot arrays,’’ IEEE Trans. Antennas Propag., vol. 65, no. 12, pp. 6998–7008, Dec. 2017.
[18] Z. Wang et al., ‘‘A high-transmittance frequency-selective rasorber based on dipole arrays,’’ IEEE Access, vol. 6, pp. 31367–31374, 2018. [19] X. Xiu, W. Che, Y. Han, and W. Yang, ‘‘Low-profile dual-polarization
frequency-selective rasorbers based on simple-structure lossy cross-frame elements,’’ IEEE Antennas Wireless Propag. Lett., vol. 17, no. 6, pp. 1002–1005, Jun. 2018.
[20] B. Li and Z. Shen, ‘‘Wideband 3D frequency selective rasorber,’’ IEEE
Trans. Antennas Propag., vol. 62, no. 12, pp. 6536–6541, Dec. 2014. [21] Z. Shen, J. Wang, and B. Li, ‘‘3-D frequency selective rasorber: Concept,
analysis, and design,’’ IEEE Trans. Microw. Theory Techn., vol. 64, no. 10, pp. 3087–3096, Oct. 2016.
[22] Y. Yu, Z. Shen, T. Deng, and G. Luo, ‘‘3-D frequency-selective rasorber with wide upper absorption band,’’ IEEE Trans. Antennas Propag., vol. 65, no. 8, pp. 4363–4367, Aug. 2017.
[23] T. Deng, Y. Yu, and Z. N. Chen, ‘‘A Broadband 3D frequency selective rasorber by using magnetic materials,’’ in Proc. Int. Conf. Electromagn.
Adv. Appl. (ICEAA), Verona, Italy, Sep. 2017, pp. 1731–1734.
[24] Y. Zhang, B. Li, L. Zhu, Y. Tang, Y. Chang, and Y. Bo, ‘‘Frequency selective rasorber with low insertion loss and dual-band absorptions using planar slotline structures,’’ IEEE Antennas Wireless Propag. Lett., vol. 17, no. 4, pp. 633–636, Apr. 2018.
[25] A. A. Omar, Z. Shen, and H. Huang, ‘‘Absorptive frequency-selective reflection and transmission structures,’’ IEEE Trans. Antennas Propag., vol. 65, no. 11, pp. 6173–6178, Nov. 2017.
[26] H. Huang, Z. Shen, and A. A. Omar, ‘‘3-D absorptive frequency selective reflector for antenna radar cross section reduction,’’ IEEE Trans. Antennas
Propag., vol. 65, no. 11, pp. 5908–5917, Nov. 2017.
[27] A. K. Rashid, Z. Shen, and S. Aditya, ‘‘Wideband microwave absorber based on a two-dimensional periodic array of microstrip lines,’’ IEEE
Trans. Antennas Propag., vol. 58, no. 12, pp. 3913–3922, Dec. 2010. [28] A. A. Omar and Z. Shen, ‘‘Double-sided parallel-strip line resonator
for dual-polarized 3-D frequency-selective structure and absorber,’’ IEEE
Trans. Microw. Theory Techn., vol. 65, no. 10, pp. 3744–3752, Oct. 2017. [29] Y. Shang, Z. Shen, and S. Xiao, ‘‘On the design of single-layer circuit analog absorber using double-square-loop array,’’ IEEE Trans. Antenna
Propag., vol. 61, no. 12, pp. 6022–6029, Dec. 2013.
YUFENG YU received the B.S. degree from the University of Electronic Science and Technology of China, Chengdu, China, in 2008, and the Ph.D. degree from Zhejiang University, Hangzhou, China, in 2013.
From 2013 to 2017, he was with the No. 36 Research Institute, China Electronics Tech-nology Group Corporation, where he has been a Senior Engineer since 2015. In 2016, he was a Research Scientist with Temasek Laboratories, National University of Singapore. Since 2017, he has been with the School of Electronics and Information, Hangzhou Dianzi University, Hangzhou, China.
Dr. Yu has authored or co-authored over 30 technical papers in refereed journals and conferences and holds three patents. His current research interests include frequency-selective surfaces/structures and antennas.
GUO QING LUO (M’08) received the B.S. degree from the China University of Geosciences, Wuhan, China, in 2000, the M.S. degree from Northwest Polytechnical University, Xi’an, China, in 2003, and the Ph.D. degree from Southeast University, Nanjing, China, in 2007.
Since 2007, he has been a Lecturer with the School of Electronics and Information, Hangzhou Dianzi University, Hangzhou, China. He was pro-moted to Professor in 2011. From 2013 to 2014, he joined the Department of Electrical, Electronic and Computer Engi-neering, Heriot-Watt University, Edinburgh, U.K., as a Research Associate, where he was involved in developing low-profile antennas for UAV applica-tions. He has authored or co-authored over 80 technical papers in refereed journals and conferences and holds 16 patents. His current research interests include RF, microwave and millimeter-wave passive devices, antennas, and frequency-selective surfaces.
Dr. Luo is a member of the IEEE AP-Society and MTT-Society. He was a recipient of the CST University Publication Award in 2007, the National Excellent Doctoral Dissertation of China in 2009, and the National Natural Science Award (the Second Class) of China in 2016. He has served as the TPC Chair of the 2018 UK-Europe-China Workshop on Millimetre-Waves and Terahertz Technologies and the 2017 National Conference on Microwave and Millimeter Waves and the Organizing Committee Chair of the 2011 China-Japan Joint Microwave Conference. He also serves a Reviewer for many technical journals, including the IEEE TRANSACTIONS ON ANTENNAS ANDPROPAGATION, the IEEE TRANSACTIONS ONMICROWAVETHEORY ANDTECHNIQUES, the IEEE ANTENNAS ANDWIRELESSPROPAGATIONLETTERS, and the IEEE MICROWAVE ANDWIRELESSCOMPONENTSLETTERS.
AHMED ABDELMOTTALEB OMAR was born in Giza, Egypt, in 1982. He received the B.Eng. and M.Sc. degrees in electrical engi-neering from Benha University, Benha, Egypt, in 2005 and 2010, respectively. He is currently pursuing the Ph.D. degree with Nanyang Techno-logical University, Singapore.
Since 2007, he has been a Teaching and Research Assistant with the Faculty of Engineer-ing, Benha University. From 2012 to 2014, he was a Research Assistant with the Faculty of Engineering, Ain Shams University, Cairo, Egypt. His current research interests include the analysis and design of frequency-selective surfaces/structures, microwave absorbers, and antennas.
XUAN LIU received the B.S. degree in electronic information engineering from Hangzhou Dianzi University, Hangzhou, China, in 2017, where he is currently pursuing the M.S. degree in electromag-netic field and microwave technology. His current research interests involve frequency-selective sur-faces/structures and antennas.
WEILIANG YU received the B.S. degree in elec-tronic information engineering from Hangzhou Dianzi University, Hangzhou, China, in 2016, where he is currently pursuing the Ph.D. degree in electromagnetic field and microwave technol-ogy. His current research interest lies on the areas of frequency-selective structures and microwave absorbers.
ZHANG CHENG HAO (M’08–SM’15) received the B.S. degree in microwave engineering from Xidian University, Xi’an, China, in 1997, and the M.S. and Ph.D. degrees in radio engineer-ing from Southeast University, Nanjengineer-ing, China, in 2002 and 2006, respectively.
In 2006, he was a Post-Doctoral Researcher with the Laboratory of Electronics and Systems for Telecommunications, École Nationale Supérieure des Télécommunications de Bretagne, Bretagne, France, where he was involved in developing millimeter-wave antennas. In 2007, he joined the Department of Electrical, Electronic and Computer Engineering, Heriot-Watt University, Edinburgh, U.K., as a Research Asso-ciate, where he was involved in developing multilayer integrated circuits and ultra-wide-band components. In 2011, he joined the School of Information Science and Engineering, Southeast University, Nanjing, as a Professor. He has authored and co-authored over 150 referred journal and conference papers. He holds 20 granted patents. His current research interests involve microwave and millimeter-wave systems, submillimeter-wave and terahertz components, and passive circuits, including filters, antenna arrays, couplers, and multiplexers.
Dr. Hao was a recipient of the Thousands of Young Talents presented by the China Government in 2011 and the High Level Innovative and Entrepreneurial Talent presented by Jiangsu Province, China, in 2012. He has served as a Reviewer for many technical journals, including the IEEE TRANSACTIONS ONMICROWAVETHEORY ANDTECHNIQUES, the IEEE TRANSACTIONS ONANTENNAS ANDPROPAGATION, the IEEE ANTENNAS ANDWIRELESSPROPAGATION LETTERS, and the IEEE MICROWAVE ANDWIRELESSCOMPONENTSLETTERS.
ZHONGXIANG SHEN (M’98–SM’04–F’17) received the B.Eng. degree from the University of Electronic Science and Technology of China, Chengdu, China, in 1987, the M.S. degree from Southeast University, Nanjing, China, in 1990, and the Ph.D. degree from the University of Waterloo, Waterloo, ON, Canada, in 1997, all in electrical engineering.
From 1990 to 1994, he was with the Nan-jing University of Aeronautics and Astronautics, China. In 1997, he was an Advanced Member of Technical Staff with Com Dev Ltd., Cambridge, Canada. In 1998, he was a Post-Doctoral Fellow with the Gordon McKay Laboratory, Harvard University, Cambridge, MA, USA, and then with the Radiation Laboratory, University of Michigan, Ann Arbor, MI, USA, for six months. In 1999, he joined Nanyang Technological University, Singapore, as an Assistant Professor, where he is currently a Full Professor. He served as the Chair of the IEEE MTT/AP Singapore Chapter in 2009. He was the Chair of the IEEE AP-S Chapter Activities Committee from 2010 to 2014. He is currently the Secretary of the IEEE AP-S and an Associate Editor of the IEEE TRANSACTIONS ONANTENNAS AND PROPAGATION.
He has authored or co-authored more than 170 journal papers (among them, 100 were published in IEEE journals) and presented more than 160 conference papers. His research interests include the design of small and planar antennas for various wireless communication systems, analysis and design of frequency-selective structures, and hybrid numerical techniques for modeling RF/microwave components and antennas.
