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Performance enhancement of dielectric resonator antenna by using cross-resonator based filtering feed-network
Journal Pre-proofs Regular paper Performance Enhancement of Dielectric Resonator Antenna by Using Crossresonator Based Filtering Feed-Network Suparna Ballav, Susanta Kumar Parui PII: DOI: Reference:
S1434-8411(19)31046-5 https://doi.org/10.1016/j.aeue.2019.152989 AEUE 152989
To appear in:
International Journal of Electronics and Communications
Received Date: Revised Date: Accepted Date:
19 April 2019 3 September 2019 2 November 2019
Please cite this article as: S. Ballav, S. Kumar Parui, Performance Enhancement of Dielectric Resonator Antenna by Using Cross-resonator Based Filtering Feed-Network, International Journal of Electronics and Communications (2019), doi: https://doi.org/10.1016/j.aeue.2019.152989
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Suparna Ballav received the B.Sc. (Physics Hons) degree in 2011 and the B.Tech. and M.Tech in Radio Physics and Electronics from University of Calcutta, India in the year 2014 and 2016 respectively. She is pursuing Ph.D. degree in microwave engineering at Department Electronics and Tele-communication Engineering, Indian Institute of Engineering Science and Technology (IIEST), Shibpur, West Bengal, India since august 2016. Her research interests include dielectric resonators for microwave circuits and antenna application, printed antenna.
Susanta Kumar Parui received the B.Sc. degree in physics and B.Tech. degree in radio physics and electronics from University of Calcutta, India in the year 1987 and 1990 respectively and the Ph. D. degree in microwave engineering from Bengal Engineering and Science University (presently known as Indian Institute of Engineering Science and Technology), Shibpur, India.From 1993 to 2000, he was an Instrument Engineer in Process control Industries. Since 2000, he has been associated with the Department of Electronics and Tele-Communication Engineering, Indian Institute of Engineering Science & Technology, Shibpur and presently holds the post of Associate Professor. He is the author of more than 60 papers in referred journals and conference proceedings. His research interests include planar circuits, antennas, SIW, DGS, EBG, FSS and Metamaterials, DRA. Dr. Parui was awarded post doctoral fellowship from Royal Academy of Engineering, U.K in the year 2009. Author’s Name Suparna Ballav
Susanta Kumar Parui
Affiliation Department of Electronics and Telecommunication Engineering Indian Institute of Engineering Science and Technology, Shibpur, Howrah, India Department of Electronics and Telecommunication Engineering Indian Institute of Engineering Science and Technology, Shibpur, Howrah, India
E-mail ID [email protected]
[email protected]
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Performance Enhancement of Dielectric Resonator Antenna by Using Cross-resonator Based Filtering Feed-Network Suparna Ballav and Susanta Kumar Parui Abstract— A wideband filtering dielectric resonator antenna (DRA) is demonstrated in this paper. The filtering characteristics is obtained by integrating a triple pole cross-resonator filter in the feed line of the slot coupled rectangular DRA. The transmission poles of the resonator are adjusted in order to get the wideband filtering response. The proposed filtering DRA offers an impedance bandwidth of 15% from 3.06 GHz to 3.56 GHz. Electric field distribution of DRA within the passband confirmed that the rectangular DRA drives in TE111 mode which ensured the broadside radiation. A satisfactory stable gain pattern of 5.9±0.3 dBi within the pass-band has been achieved. The gain response falls sharply with two radiation-nulls beyond the passband at 3.9 GHz and 4.4 GHz and that increases the selectivity of the antenna. In conclusion, proposed design offers a robust technique to convert a conventional slot coupled rectangular DRA into a wideband antenna along with frequency selective gain response. Proposed configuration manifests as an ideal contender for some specific uses in S-band such as Wi-Max, TD-LTE (Time-Division Long Term Evaluation) application as it avoids the interference adjacent bands. Index Terms— Cross resonator, DRA, filtering, radiation null, transmission pole, wide band, broadside radiation.
1. INTRODUCTION With the enormous growth of wireless communication in recent years, integrating multiple components with antennas become a significant challenge to the researchers. In most of the RF front-end systems, the antenna always coexists with a bandpass filter to minimize the problem of overloading by out of band signals [1-2]. In recent times, a co-design procedure has been followed to implement the bandpass filter and the antenna into a single module, formally called as filtering antenna or filtenna, with both the filtering and radiation ability [3-4]. The filtering antenna not only improves the return loss characteristics but also produces filtering gain response. Several studies have been performed on printed antenna, horn antenna, substrate integrated waveguide-based antenna to achieve filtering performance [5-8]. Very few studies have been performed so far to achieve filtering performance of dielectric resonator antenna (DRA). Studies on DRAs are growing up day by day for its various appealing properties. Absence of metallic losses, high radiation efficiency, small footprint compared to traditional antennas, make it suitable contender for high frequency applications [9-11]. Research on various resonating modes of DRA with different geometrical structure such as rectangular, triangular, cylindrical, hemispherical [12-16] are found in literature. DRAs can be energized through variety of feeding techniques like coaxial probe [17], microstrip lines [18], coplanar waveguides (CPWs) [19], coupling slots [20], substrate integrated waveguide (SIW) [21] and conformal strip [22]. The most familiar method of feeding is slot-coupling. Desired polarization can be easily realized by selecting suitable slot shapes and adjusting its positions [21]. Since DRA supports a lot of modes, sometimes spurious modes are also excited with the desired radiating modes which cause unnecessary interference [23-24]. The problem of spurious modes can be resolved by using DRA with filtering characteristics. Pan et al recently reported some works on filtering DRA. They introduced a high gain filtering DRA in [25] using parasitic strips. They proposed a broadband filtering DRA based on cylindrical stacked DRA in [26]. In both cases, they used higher order mode of DRA to achieve wideband response. A filtering DRA is also designed in [27] by using hybrid microstrip feeding technique and an omnidirectional filtering DRA is modeled by hybrid coaxial feeding technique in [28]. A circular polarized filtering DRA is also reported recently with two transmissions zero [29] by Sahoo et al. A quasi-isotropic filtering DRA has been proposed lately [30] with 7% impedance bandwidth and 3.05 dBi average gain with radiation null in the gain response. An extremely narrow band filtering DRA is obtained by means of silver coated slots in [31].
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In the present study, a broadside filtering DRA has been designed by modifying the feed line of conventional slot coupled rectangular DRA. The feed line is modified by integration of triple pole cross resonator based bandpass filter (BPF) [32] which offers wider impedance bandwidth and also provides filtering gain response with high selectivity. The filtering DRA, operates in TE111 mode, offers a 10dB impedance bandwidth of 15%. The DRA provides a stable broadside gain of 5.9±0.3 dBi throughout the operating band with two radiation nulls at 3.9 GHz and 4.4 GHz. A relative performance comparison is also shown between the conventional rectangular slot-coupled DRA and the proposed filtering DRA. All the simulation has been performed using finite element based high frequency structural simulator (HFSS). As the demand of high performance antenna array is increasing day by day [33-36], the proposed designed could be utilized as an elementary radiating element in future. With high demand of sub-6 GHz band [37-39], proposed configuration with capability of avoiding interference with adjacent bands could be an ideal contender for Wi-Max, TD-LTE (Time-Division Long Term Evaluation) application. Detailed discussion on design methodology of triple pole cross-resonator filtering feed network and design formulation of rectangular DRA is provided throughout this paper. The most noteworthy features of the proposed filtering DRA are outlined as follows: 1. A conventional slot coupled DRA is modified into a filtering DRA with wide impedance bandwidth. 2. Frequency selective gain pattern is achieved by inclusion of a cross resonator based triple pole bandpass filter in feedline of a conventional slot coupled DRA keeping intact the conventional antenna footprint. 3.Offers a very simple and standard size filtering DRA with stable broadside gain response. 2. DESCRIPTION OF THE WIDEBAND FILTERING DRA Design topology of the wideband filtering DRA is described in this section. 2.1 Filtering DRA Configuration The schematic of the proposed wideband filtering DRA is shown in Fig.1. It consists of a rectangular DRA of length = width (𝑙𝑑𝑟) = 18.5 mm, height (ℎ𝑑𝑟) = 15.3 mm, dielectric constant (εr) = 10 and loss tangent = 0.002. The filtering feed network is designed on a substrate of dielectric constant 2.7, thickness (ℎ𝑠𝑢𝑏) = 0.79 mm, length (𝑙𝑠𝑢𝑏) = 40 mm and width (𝑤𝑠𝑢𝑏) = 42.3 mm. Size of the slot on the ground plane is 𝑙𝑎 × 𝑤𝑏=18 × 1.5 mm2 to guide the signal from the feed line to the dielectric resonator. A filtering network is introduced in the conventional 50 ohm microstrip feed line in the bottom side of the substrate.
(a)
(b)
Fig. 1. Schematic view of the proposed DRA including filtering feed network.𝑤𝑓 = 2.2, 𝑤𝑟 = 1, 𝑙1 = 10.6, 𝑙𝑜 = 14.3, 𝐷v = 0.8, 𝑙2 = 3.9, g = 0.2 , 𝑙𝑚 = 16.2.(Unit: mm) (a)Side View (b) Bottom View
All the dimension of the filtering feed (FF) network is mentioned in Fig.1. As energy is coupled to DRA from feed network via a slot, degradation in antenna performance is negligible due to modification in feed
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network. In terms of design flexibility rectangular DRA with dimension of (𝑙𝑑𝑟 × 𝑙𝑑𝑟 × ℎ𝑑𝑟) is more advantageous compared to cylindrical and spherical DRA as resonance frequencies of rectangular DRA can be controlled by the length-width ratio and width-height ratio. The resonance frequency of rectangular DRA excited in TE111 mode can be calculated using (1) based on dielectric waveguide model [13]: 𝑐
𝑓𝑜 = 2𝜋 𝜋
𝜋
𝜀𝑟
𝑘𝑥2 + 𝑘𝑦2 + 𝑘𝑧2
𝑙𝑑𝑟𝑘𝑦 = 𝜋 ― 2tan ―1
,where 𝑘𝑥 = 𝑙𝑑𝑟 ; 𝑘𝑧 = 2ℎ𝑑𝑟 ;
{
(1) 𝑘𝑦
}
(2)
(𝜀𝑟 ― 1)𝑘02 ― 𝑘𝑦2
By solving these equations numerically, the theoretical resonance frequency can be estimated for a fixed DRA dimension. The initial dimensions of rectangular DRA are chosen in such a way that it operates in fundamental mode at the center frequency of the triple pole FF network. From the electric field configuration as mentioned in next section, it is verified that the DRA is exited in TE111 mode. Impedance matching is achieved by choosing the relevant length of microstrip feed line (𝑙𝑚) which acts as a matching stub. 2.2 Analysis of Filtering Feed (FF) Network The FF network for the proposed DRA consists of a half-wavelength resonator, an open stub, and a short stub. Since the stubs are intersected at the centre point of the half-wavelength resonator, it is named as crossresonator as shown in Fig.2 (a). As the cross resonator is symmetrical along the MM’ plane, even-odd mode approach [32,40-41] is applied to find the three independently controllable resonant modes. The odd mode transmission line model is shown in Fig.2(b). The odd mode resonance condition is given in (2) and the corresponding resonance frequency is given in (3) 𝑌
𝑌𝑖𝑛𝑜𝑑𝑑 = 𝑗tan (𝜃ℎ) = 0
(2)
𝑓𝑜𝑑𝑑 = 4𝑙
ℎ
𝑐 𝜀𝑒𝑓𝑓
, where 𝜃ℎ = 𝛽𝑙ℎ , 𝛽 = propagation constant and 𝜀𝑒𝑓𝑓 = effective dielectric constant.
(a)
(b)
(3)
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(c) Fig. 2. Topology of the Cross-resonator band-pass Filter.
Similarly, the even mode transmission line model is depicted in Fig.2(c) and the even mode resonance condition is given in (4). 2tan (𝜃ℎ) + tan( 𝜃𝑜) ― cot ( 𝜃𝑠)
𝑌𝑖𝑛𝑒𝑣𝑒𝑛 = 𝑗𝑌1 ― tan 𝜃ℎ(tan 𝜃ℎ + tan 𝜃𝑜 ― cot 𝜃𝑠) = 0
(4)
Further, even mode resonance is decomposed into two halves 𝑓𝑒𝑣𝑒𝑛1 and 𝑓𝑒𝑣𝑒𝑛2 as shown in Fig.2(c) and the resonance frequencies can be derived using equation (4). We can obtain the resonance frequencies 𝑓𝑒𝑣𝑒𝑛1 & 𝑓𝑒𝑣𝑒𝑛2 from the even mode transmission line model as follows: 𝑓𝑒𝑣𝑒𝑛1 = 4 ∗ (𝑙
𝑐
ℎ + 𝑙𝑠) 𝜀𝑒𝑓𝑓
and 𝑓𝑒𝑣𝑒𝑛2 = 2(𝑙
𝑐
ℎ + 𝑙𝑜) 𝜀𝑒𝑓𝑓
(5)
,where quarter wavelength transmission line is responsible for 𝑓𝑒𝑣𝑒𝑛1. 𝑓𝑒𝑣𝑒𝑛2 is obtained from halfwavelength transmission line as shown in Fig.2(c). Based on the observation given in [32], we can write 𝑓𝑒𝑣𝑒𝑛1 𝑓𝑜𝑑𝑑
= 𝑘1 and
𝑓𝑒𝑣𝑒𝑛2 𝑓𝑜𝑑𝑑
= 𝑘2
(6)
,where 𝑘1 and 𝑘2 can be tuned by varying 𝜃𝑠 = 𝛽𝑙𝑠 and 𝜃𝑜 = 𝛽𝑙𝑜 respectively. For 𝑘1 ≈ 1 and 𝑘2 ≈ 1 i.e for 𝜃𝑠 ≈ 0 and 𝜃0 ≈ 900 the triple-pole bandpass response has been achieved with a transmission zero (TZ) at the upper side of the passband. The schematic of FF is given in Fig.3(a) and the S-parameter responses are shown in Fig.3(b) for both weak and strong coupling. From Fig.3(b) it is found that passband response is 2.98 GHz to 3.46 GHz with three transmission poles (TP). Existence of three TPs is confirmed from the weak coupling response whereas a stable response with minimum insertion loss of 1.0 dB is achieved using strong coupling. These TPs (TPevn1, TPevn2, TPodd) can be tuned by varying the lengths of the resonators 𝑙𝑠 , 𝑙𝑜, 𝑙ℎ = 𝑙1+𝑙2 to achieve wider bandwidth which is confirmed from Fig.4(a-c).The resonance frequencies of TPevn1 and TPevn2 can be tuned by varying the length 𝑙𝑠 and 𝑙𝑜 respectively by keeping intact the length 𝑙ℎ as shown from Fig.4(a & b).Whereas the resonance frequency of TPodd is solely determined by the length 𝑙ℎ.So the design guidelines of the FF network is given as follows: First calculate the length 𝑙ℎ corresponding to the resonance frequency of TPodd from equation (3) and then by adjusting the length 𝑙𝑠 and 𝑙𝑜 as per equation (5-6) desired resonance frequencies of TPevn1 and TPevn2 is obtained.
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(a)
(b)
Fig. 3. (a)Schematic diagram and (b) frequency responses of the triple pole FF under the weak coupling (g=1 mm) and strong coupling (g=0.2 mm) condition .
(a)
(b)
.
(c) Fig. 4. Frequency responses of the FF under the weak coupling condition for varying length of (a) 𝑙𝑠 (b) 𝑙𝑜 (c) 𝑙ℎ = 𝑙1+𝑙2
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(a)
(b)
Fig. 5. (a) S11 response of the conventional slot fed DRA, the proposed filtering DRA and the triple-pole FF, (b) Simulated Gain and Radiation Efficiency Plot of the proposed filtering DRA
(a)
(b)
Fig. 6. Electric Fields distribution within the rectangular DRA:(a) Ideal electric fields distribution of TE111 mode (b) Simulated electric fields distribution in three different frequencies within the passband
3. RESULTS AND VERIFICATION A relative performance between conventional slot-fed rectangular DRA (Antenna Conv.) and proposed filtering DRA is discussed in this section. S11-plots of both antennas are shown in Fig.5(a) and there it is clear that Antenna-Conv. resonates at 3.27 GHz in the fundamental mode. On the other hand, response of the proposed filtering DRA is analogous with the triple-pole FF. The radiation efficiency and gain of the filtering DRA as a function of frequency are depicted in Fig.5(b). The radiation efficiency plot also confirms the filtering response. It can be observed that the efficiency remains stable approximately at 90% within passband. It drops sharply below 20% beyond passband. Ideal electric field distributions of TE111 mode of a rectangular DRA with ground plane and without ground plane [18,24] are schematically portrayed in Fig.6 (a) to compare it with the simulated one. From the simulated electric fields distribution within DRA as represented in Fig.6(b), excitation of TE111 mode of rectangular DRA is verified as the fields orientation
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closely resemble the ideal one for all three frequencies within the passband.
Fig. 7. Fabricated prototype of the proposed DRA
(a)
(b)
Fig. 8. Simulated and measured (a) S11 and (b) gain of the DRA
The FF network of the proposed wideband filtering DRA is fabricated on Arlon AD270 substrate and ECCOSTOCK Hik material is used as DRA as shown in Fig.7.The DRA is attached on the top of the ground plane using adhesive which has negligible effect on TE111 mode of the DRA. The S-parameter response of the DRA is measured using an Agilent’s N5230A vector network analyzer and reasonable agreement is obtained between simulation and measured results. The proposed filtering DRA offers a wide impedance bandwidth of 15 % over a frequency range of 3.06 GHz to 3.56 GHz as shown in Fig.8(a) whereas 10% impedance bandwidth is obtained for the Antenna Conv. as shown in Fig.5.The gain vs frequency plot for both the Antenna Conv. and the filtering DRA is demonstrated in Fig.8(b). Where gain response of the Antenna Conv. does not fall beyond the operational band, sharp transitions of gain response beyond the passband are clearly visible with two radiation nulls (RN1 & RN2) at 3.9 GHz and 4.4 GHz for the proposed DRA. The first null i.e RN1 is occurred due to the presence of transmission zero in the filtering feed network. The second nulls i.e RN2 is caused by the matching stub (𝑙𝑚) which is remained opened circuited at the end of the feed line. When 𝑙𝑚 is half of the guided wavelength (λg) long current at the coupling slot becomes minimum. Then no energy gets coupled to the DRA, and that generates the null in the gain response [25]. In the proposed design 𝑙𝑚=16.2 mm which is nearly equal with λg/2 at 4.4 GHz, is responsible for RN2. The DRA possess flat gain responses within the passband with a sharp roll off near the passband edge. The measured gain remains 5.9±0.3 dBi within passband and falls sharply below -14 dBi and -18.5 dBi at 3.9 GHz and 4.4 GHz respectively. The radiation pattern for both E-plane (φ = 00) and H-plane (φ = 900) in three different frequencies of 3.1 GHz, 3.2 GHz and 3.4 GHz in the passband region is shown in Fig.9(a-c).
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Both simulation and measurement verified that the main beam directed in broadside over the operating band with co-to-cross-pol isolation is greater than 20 dB.
(a)
(b)
(c)
φ = 00
φ = 900
Fig. 9. Simulated and Measured radiation pattern of the filtering DRA at (a) 3.1 GHz (b) 3.2 GHz (c) 3.4 GHz
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TABLE I Performance Summary of the Filtering DRA (λ0=free space wavelength)
[Ref], Year
[25], 2016
[26],2017
[27],2018
[30],2019
[31],2019
This Work
Shape Of DRA and ɛr Filtering & feeding Scheme
Complex ɛr=10
Rectangular (Conv.) ɛr=10 Hybrid feed Using conformal strip & microstrip line 1.965 GHz
Rectangular with slots ɛr=90 Silver Coated Slots,metal strips
Cylindrical ɛr=20
Rectangular (Conv.) ɛr=10 Triple Pole Filtering Feed,Conv. slot 3.31 GHz
Centre frequency (f0)
4.92 GHz
Cylindrical Stacked DRA ɛr=2.2,15 Shorting Via,Transvers e Stubs,Seperated Slot 6.09 GHz
Volume (xλ0×yλ0×zλ0)
1.23×0.82×0. 128
0.82×0.82 ×0.11
0.44×0.44 ×0.11
0.65×0.61×0.02
Bandwidth
20.3 %
61.4 %
21.9 %
No. of RN
2
2
2
Extremly Narrow (<100 MHz) 2
Avg. Gain(dBi)
9.05
8.7
5.1
4.8
Parasitic Strip,Seperated Slot
4.17 GHz
Microstrip Stubs of different length, microstrip line 2.4 GHz Circular (dia=0.204 λ0, height=0.1 λ0) 7%
0.47×0.44 ×0.17
2
2
3.05
6.0
15 %
The operating mechanism and performance characteristic of the proposed design and previously reported filtering DRA available in literature are tabulated in Table I. In [25-27], no specific filtering circuit is included in the feed to obtain the filtering response of the DRA. In this work, a triple pole filtering feed is included below the ground plane to obtain the desired filtering response, without increasing the footprint of Antennaconv. as mentioned before. Although the DRAs in [25-26], featured wide bandwidth and high gain but occupy a large volume with complex DRA structure compared to our design. In [27], a vertical conformal strip is glued on the DRA wall to obtain radiation nulls which increases the deign complexity. Whereas, the proposed technique is much more robust for filtering DRA design as it is easy to introduce the selective gain performance in any conventional slot coupled DRA. As compared to the antennas in [30] & [31], the proposed DRA has wider bandwidth, higher gain along with completely different filtering mechanism. 5. CONCLUSION A triple-pole cross-resonator based filtering feeding network is used to develop a wideband filtering DRA. In comparison with the conventional slot coupled DRA, the proposed design achieves 5% more impedance bandwidth. The proposed DRA operates 3.06 GHz to 3.56 GHz with S11 almost 0 dB at either side of passband, ensures superior filtering performance. Filtering response of the DRA not only improves the impedance characteristics but also enhances the radiation performance. A fairly flat broadside gain of 6dBi over the operating band and sharp roll-off beyond passband with two radiation nulls ensure selective performance of the antenna. With the high demand for low interfering signal, the proposed design has a large potential for WiMAX router applications. ACKNOWLEDGMENT The authors thank senior colleagues for their valuable comments which have helped to improve the quality of paper.
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[10] Ohlsson, Lars, et al. “Slot-coupled millimeter-wave dielectric resonator antenna for high-efficiency monolithic integration.” IEEE Transactions on Antennas and Propagation ,vol.61,no.4,pp.1599-1607,2012. [11] Sallam, Mai O., et al. “Micromachined on-chip dielectric resonator antenna operating at 60 GHz.” IEEE Transactions on Antennas and Propagation,vol.63,no.8,pp.3410-3416,2015. [12] Maity, Sudipta, and Bhaskar Gupta. “Theory and experiments on horizontally inhomogeneous rectangular dielectric resonator antenna." AEU-International Journal of Electronics and Communications ,vol.76,pp.158-165,2017. [13] Maity, Sudipta, and Bhaskar Gupta. “Closed form expressions to find radiation patterns of rectangular dielectric resonator antennas for various modes. ” IEEE Transactions on Antennas and Propagation ,vol.62, no.12 ,pp. 6524-6527,2014. [14] Wysin, Gary M. “Electromagnetic modes in dielectric equilateral triangle resonators. ” Journal of the Optical Society of America B Optical Physics ,vol.23,pp.1586-1599,2006. [15] Kajfez, Darko, Allen W. Glisson, and Joseph James. “Computed modal field distributions for isolated dielectric resonators. ” IEEE transactions on Microwave Theory and Techniques ,vol.32,no.12 ,pp.1609-1616,1984. [16] Petosa, Aldo, and Apisak Ittipiboon. “Dielectric resonator antennas: A historical review and the current state of the art. ” IEEE antennas and Propagation Magazine ,vol.52,no.5, pp.91-116, 2010. [17] K. W. Leung, K. M. Luk, K. Y. A. Lai, and D. Lin, “Theory and experiment of a coaxial probe fed hemispherical dielectric resonator antenna,” IEEE Trans. Antennas Propag., vol. 41, no. 10, pp. 1390–1398, Oct.1993. [18] G. Bit-Babik, C. Di Nallo and A. Faraone, "Multimode dielectric resonator antenna of very high permittivity," IEEE Antennas and Propagation Society Symposium, Vol.2, pp. 1383-1386 ,2004. [19] S. Ballav and S. K. Parui, “A Wideband uni-planner Dielectric Resonator Antenna Array Using Air-bridgeless CPW Power Divider ” International Journal of RF and Microwave Computer‐Aided Engineering , June 2019, DOI: 10.1002/mmce.21858 [20] Buerkle, Amelia, Kamal Sarabandi, and Hossein Mosallaei. "Compact slot and dielectric resonator antenna with dual-resonance, broadband characteristics. ” IEEE Transactions on Antennas and Propagation ,vol.53,no.3,pp.1020-1027, 2005. [21] Lai, Qinghua, et al. “60 GHz aperture-coupled dielectric resonator antennas fed by a half-mode substrate integrated waveguide. ” IEEE Transactions on Antennas and Propagation ,vol.58,no.6, pp.1856-1864,2010. [22] Leung, Kwok Wa. “Conformal strip excitation of dielectric resonator antenna.” IEEE Transactions on Antennas and Propagation ,vol.48,no.6,pp. 961-967, 2000. [23] K. M. Luk and K. W. Leung, “Dielectric Resonator Antennas, ”U. K., Research Studies Press, 2003. [24] A. Petosa, “Dielectric Resonator Antenna Handbook,” Norwood, Artech House Inc., 2007. [25] Hu, P. F., Y. M. Pan, X. Y. Zhang, and S. Y. Zheng, “A compact filtering dielectric resonator antenna with wide bandwidth and high gain.” IEEE Trans. Antennas Propag , vol.64, no. 8 ,pp. 3645-3651,2016. [26] Hu, P. F., Y. M. Pan, X. Y. Zhang, and S. Y. Zheng, “Broadband filtering dielectric resonator antenna with wide stopband.” IEEE Transactions on Antennas and Propagation, vol.65, no. 4, pp. 2079-2084, 2017. [27] Pan, Yong Mei, et al., “Compact Single-/Dual-Polarized Filtering Dielectric Resonator Antennas.” IEEE Transactions on Antennas and Propagation, vol.66, no.9, pp.4474-4484, 2018. [28] Hu, Peng Fei, Yong Mei Pan, Kwok Wa Leung, and Xiu Yin Zhang, “ Wide-/Dual-Band Omnidirectional Filtering Dielectric Resonator Antennas. ” IEEE Transactions on Antennas and Propagation, vol.66, no. 5, pp.2622-2627, 2018. [29] Sahoo, Anuj Kumar, Ravi Dutt Gupta, and Manoj Singh Parihar. "Circularly polarised filtering dielectric resonator antenna for X-band applications." IET Microwaves, Antennas & Propagation ,vol.12,no.9,pp.1514-1518,2018. [30] Hu, Peng Fei, Yong Mei Pan, Xiu Yin Zhang, and Bin Jie Hu. “A Compact Quasi-Isotropic Dielectric Resonator Antenna With Filtering Response.” IEEE Transactions on Antennas and Propagation, vol. 67, no. 2, pp.1294-1299,2019.
12 [31] Wang, Xue-Ying, Shi-Chang Tang, Xian-Feng Shi, and Jian-Xin Chen. “A Low-Profile Filtering Antenna Using Slotted Dense Dielectric Patch.” IEEE Antennas and Wireless Propagation Letters, vol.18, no. 3, pp.502-506, 2019. [32] Chu, Qing-Xin, Fu-Chang Chen, Zhi-Hong Tu, and Huan Wang, “A novel crossed resonator and its applications to bandpass filters. ” IEEE Trans. Microw. Theory Tech, vol.57, no. 7, pp.1753-1759, 2009. [33] S. Ballav and S. K. Parui, “Aperture Coupled Dielectric Resonator Antenna Embedded in a Secondary Substrate for Mechanical Firmness”, Radioengineering ,vol.27, no. 3, pp: 679,sep 2018. [34] Isernia, T., and A. F. Morabito. “Mask-constrained power synthesis of linear arrays with even excitations.” IEEE Transactions on Antennas and Propagation ,vol.64,vol.7,pp.3212-3217,2016. [35] H. Xu et al., “Analysis and Design of Two-Dimensional Resonant-Type Composite Right/Left-Handed Transmission Lines With Compact Gain-Enhanced Resonant Antennas, ” IEEE Transactions on Antennas and Propagation, vol. 61, no. 2, pp. 735-747, Feb. 2013. [36] H. Xu, G. Wang, M. Q. Qi and T. Cai, “Compact Fractal Left-Handed Structures for Improved Cross-Polarization Radiation Pattern, ” IEEE Transactions on Antennas and Propagation, vol. 62, no. 2, pp. 546-554, Feb. 2014 [37] H. Xu, G. Wang, J. Liang, M. Q. Qi and X. Gao, “Compact Circularly Polarized Antennas Combining Meta-Surfaces and Strong Space-Filling MetaResonators, ” IEEE Transactions on Antennas and Propagation, vol. 61, no. 7, pp. 3442-3450, July 2013. [38] Alibakhshikenari, Mohammad, et al. “A new wideband planar antenna with band-notch functionality at GPS, Bluetooth and WiFi bands for integration in portable wireless systems.” AEU-International Journal of Electronics and Communications, vol.72, pp.79-85,2017. [39] Alibakhshi-Kenari, Mohammad, et al. “Bandwidth extension of planar antennas using embedded slits for reliable multiband RF communications.” AEUInternational Journal of Electronics and Communications, vol.70, no.7, pp.910-919, 2016. [40] Chen, F-C., Q-X. Chu, and Z-H. Tu, “ Tri-band bandpass filter using stub loaded resonators. ” Electronics Letters, vol.44, no. 12, pp.747-749, 2008. [41] Zhang, Xiu Yin, Jian-Xin Chen, Quan Xue, and Si-Min Li, “Dual-band bandpass filters using stub-loaded resonators.” IEEE Microwave and Wireless Components Letters, vol.17, no. 8 , pp.583-585,2007.
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Declaration of interests ☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Declaration of interests: None
S1434-8411(19)31046-5 https://doi.org/10.1016/j.aeue.2019.152989 AEUE 152989
To appear in:
International Journal of Electronics and Communications
Received Date: Revised Date: Accepted Date:
19 April 2019 3 September 2019 2 November 2019
Please cite this article as: S. Ballav, S. Kumar Parui, Performance Enhancement of Dielectric Resonator Antenna by Using Cross-resonator Based Filtering Feed-Network, International Journal of Electronics and Communications (2019), doi: https://doi.org/10.1016/j.aeue.2019.152989
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Suparna Ballav received the B.Sc. (Physics Hons) degree in 2011 and the B.Tech. and M.Tech in Radio Physics and Electronics from University of Calcutta, India in the year 2014 and 2016 respectively. She is pursuing Ph.D. degree in microwave engineering at Department Electronics and Tele-communication Engineering, Indian Institute of Engineering Science and Technology (IIEST), Shibpur, West Bengal, India since august 2016. Her research interests include dielectric resonators for microwave circuits and antenna application, printed antenna.
Susanta Kumar Parui received the B.Sc. degree in physics and B.Tech. degree in radio physics and electronics from University of Calcutta, India in the year 1987 and 1990 respectively and the Ph. D. degree in microwave engineering from Bengal Engineering and Science University (presently known as Indian Institute of Engineering Science and Technology), Shibpur, India.From 1993 to 2000, he was an Instrument Engineer in Process control Industries. Since 2000, he has been associated with the Department of Electronics and Tele-Communication Engineering, Indian Institute of Engineering Science & Technology, Shibpur and presently holds the post of Associate Professor. He is the author of more than 60 papers in referred journals and conference proceedings. His research interests include planar circuits, antennas, SIW, DGS, EBG, FSS and Metamaterials, DRA. Dr. Parui was awarded post doctoral fellowship from Royal Academy of Engineering, U.K in the year 2009. Author’s Name Suparna Ballav
Susanta Kumar Parui
Affiliation Department of Electronics and Telecommunication Engineering Indian Institute of Engineering Science and Technology, Shibpur, Howrah, India Department of Electronics and Telecommunication Engineering Indian Institute of Engineering Science and Technology, Shibpur, Howrah, India
E-mail ID [email protected]
[email protected]
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Performance Enhancement of Dielectric Resonator Antenna by Using Cross-resonator Based Filtering Feed-Network Suparna Ballav and Susanta Kumar Parui Abstract— A wideband filtering dielectric resonator antenna (DRA) is demonstrated in this paper. The filtering characteristics is obtained by integrating a triple pole cross-resonator filter in the feed line of the slot coupled rectangular DRA. The transmission poles of the resonator are adjusted in order to get the wideband filtering response. The proposed filtering DRA offers an impedance bandwidth of 15% from 3.06 GHz to 3.56 GHz. Electric field distribution of DRA within the passband confirmed that the rectangular DRA drives in TE111 mode which ensured the broadside radiation. A satisfactory stable gain pattern of 5.9±0.3 dBi within the pass-band has been achieved. The gain response falls sharply with two radiation-nulls beyond the passband at 3.9 GHz and 4.4 GHz and that increases the selectivity of the antenna. In conclusion, proposed design offers a robust technique to convert a conventional slot coupled rectangular DRA into a wideband antenna along with frequency selective gain response. Proposed configuration manifests as an ideal contender for some specific uses in S-band such as Wi-Max, TD-LTE (Time-Division Long Term Evaluation) application as it avoids the interference adjacent bands. Index Terms— Cross resonator, DRA, filtering, radiation null, transmission pole, wide band, broadside radiation.
1. INTRODUCTION With the enormous growth of wireless communication in recent years, integrating multiple components with antennas become a significant challenge to the researchers. In most of the RF front-end systems, the antenna always coexists with a bandpass filter to minimize the problem of overloading by out of band signals [1-2]. In recent times, a co-design procedure has been followed to implement the bandpass filter and the antenna into a single module, formally called as filtering antenna or filtenna, with both the filtering and radiation ability [3-4]. The filtering antenna not only improves the return loss characteristics but also produces filtering gain response. Several studies have been performed on printed antenna, horn antenna, substrate integrated waveguide-based antenna to achieve filtering performance [5-8]. Very few studies have been performed so far to achieve filtering performance of dielectric resonator antenna (DRA). Studies on DRAs are growing up day by day for its various appealing properties. Absence of metallic losses, high radiation efficiency, small footprint compared to traditional antennas, make it suitable contender for high frequency applications [9-11]. Research on various resonating modes of DRA with different geometrical structure such as rectangular, triangular, cylindrical, hemispherical [12-16] are found in literature. DRAs can be energized through variety of feeding techniques like coaxial probe [17], microstrip lines [18], coplanar waveguides (CPWs) [19], coupling slots [20], substrate integrated waveguide (SIW) [21] and conformal strip [22]. The most familiar method of feeding is slot-coupling. Desired polarization can be easily realized by selecting suitable slot shapes and adjusting its positions [21]. Since DRA supports a lot of modes, sometimes spurious modes are also excited with the desired radiating modes which cause unnecessary interference [23-24]. The problem of spurious modes can be resolved by using DRA with filtering characteristics. Pan et al recently reported some works on filtering DRA. They introduced a high gain filtering DRA in [25] using parasitic strips. They proposed a broadband filtering DRA based on cylindrical stacked DRA in [26]. In both cases, they used higher order mode of DRA to achieve wideband response. A filtering DRA is also designed in [27] by using hybrid microstrip feeding technique and an omnidirectional filtering DRA is modeled by hybrid coaxial feeding technique in [28]. A circular polarized filtering DRA is also reported recently with two transmissions zero [29] by Sahoo et al. A quasi-isotropic filtering DRA has been proposed lately [30] with 7% impedance bandwidth and 3.05 dBi average gain with radiation null in the gain response. An extremely narrow band filtering DRA is obtained by means of silver coated slots in [31].
3
In the present study, a broadside filtering DRA has been designed by modifying the feed line of conventional slot coupled rectangular DRA. The feed line is modified by integration of triple pole cross resonator based bandpass filter (BPF) [32] which offers wider impedance bandwidth and also provides filtering gain response with high selectivity. The filtering DRA, operates in TE111 mode, offers a 10dB impedance bandwidth of 15%. The DRA provides a stable broadside gain of 5.9±0.3 dBi throughout the operating band with two radiation nulls at 3.9 GHz and 4.4 GHz. A relative performance comparison is also shown between the conventional rectangular slot-coupled DRA and the proposed filtering DRA. All the simulation has been performed using finite element based high frequency structural simulator (HFSS). As the demand of high performance antenna array is increasing day by day [33-36], the proposed designed could be utilized as an elementary radiating element in future. With high demand of sub-6 GHz band [37-39], proposed configuration with capability of avoiding interference with adjacent bands could be an ideal contender for Wi-Max, TD-LTE (Time-Division Long Term Evaluation) application. Detailed discussion on design methodology of triple pole cross-resonator filtering feed network and design formulation of rectangular DRA is provided throughout this paper. The most noteworthy features of the proposed filtering DRA are outlined as follows: 1. A conventional slot coupled DRA is modified into a filtering DRA with wide impedance bandwidth. 2. Frequency selective gain pattern is achieved by inclusion of a cross resonator based triple pole bandpass filter in feedline of a conventional slot coupled DRA keeping intact the conventional antenna footprint. 3.Offers a very simple and standard size filtering DRA with stable broadside gain response. 2. DESCRIPTION OF THE WIDEBAND FILTERING DRA Design topology of the wideband filtering DRA is described in this section. 2.1 Filtering DRA Configuration The schematic of the proposed wideband filtering DRA is shown in Fig.1. It consists of a rectangular DRA of length = width (𝑙𝑑𝑟) = 18.5 mm, height (ℎ𝑑𝑟) = 15.3 mm, dielectric constant (εr) = 10 and loss tangent = 0.002. The filtering feed network is designed on a substrate of dielectric constant 2.7, thickness (ℎ𝑠𝑢𝑏) = 0.79 mm, length (𝑙𝑠𝑢𝑏) = 40 mm and width (𝑤𝑠𝑢𝑏) = 42.3 mm. Size of the slot on the ground plane is 𝑙𝑎 × 𝑤𝑏=18 × 1.5 mm2 to guide the signal from the feed line to the dielectric resonator. A filtering network is introduced in the conventional 50 ohm microstrip feed line in the bottom side of the substrate.
(a)
(b)
Fig. 1. Schematic view of the proposed DRA including filtering feed network.𝑤𝑓 = 2.2, 𝑤𝑟 = 1, 𝑙1 = 10.6, 𝑙𝑜 = 14.3, 𝐷v = 0.8, 𝑙2 = 3.9, g = 0.2 , 𝑙𝑚 = 16.2.(Unit: mm) (a)Side View (b) Bottom View
All the dimension of the filtering feed (FF) network is mentioned in Fig.1. As energy is coupled to DRA from feed network via a slot, degradation in antenna performance is negligible due to modification in feed
4
network. In terms of design flexibility rectangular DRA with dimension of (𝑙𝑑𝑟 × 𝑙𝑑𝑟 × ℎ𝑑𝑟) is more advantageous compared to cylindrical and spherical DRA as resonance frequencies of rectangular DRA can be controlled by the length-width ratio and width-height ratio. The resonance frequency of rectangular DRA excited in TE111 mode can be calculated using (1) based on dielectric waveguide model [13]: 𝑐
𝑓𝑜 = 2𝜋 𝜋
𝜋
𝜀𝑟
𝑘𝑥2 + 𝑘𝑦2 + 𝑘𝑧2
𝑙𝑑𝑟𝑘𝑦 = 𝜋 ― 2tan ―1
,where 𝑘𝑥 = 𝑙𝑑𝑟 ; 𝑘𝑧 = 2ℎ𝑑𝑟 ;
{
(1) 𝑘𝑦
}
(2)
(𝜀𝑟 ― 1)𝑘02 ― 𝑘𝑦2
By solving these equations numerically, the theoretical resonance frequency can be estimated for a fixed DRA dimension. The initial dimensions of rectangular DRA are chosen in such a way that it operates in fundamental mode at the center frequency of the triple pole FF network. From the electric field configuration as mentioned in next section, it is verified that the DRA is exited in TE111 mode. Impedance matching is achieved by choosing the relevant length of microstrip feed line (𝑙𝑚) which acts as a matching stub. 2.2 Analysis of Filtering Feed (FF) Network The FF network for the proposed DRA consists of a half-wavelength resonator, an open stub, and a short stub. Since the stubs are intersected at the centre point of the half-wavelength resonator, it is named as crossresonator as shown in Fig.2 (a). As the cross resonator is symmetrical along the MM’ plane, even-odd mode approach [32,40-41] is applied to find the three independently controllable resonant modes. The odd mode transmission line model is shown in Fig.2(b). The odd mode resonance condition is given in (2) and the corresponding resonance frequency is given in (3) 𝑌
𝑌𝑖𝑛𝑜𝑑𝑑 = 𝑗tan (𝜃ℎ) = 0
(2)
𝑓𝑜𝑑𝑑 = 4𝑙
ℎ
𝑐 𝜀𝑒𝑓𝑓
, where 𝜃ℎ = 𝛽𝑙ℎ , 𝛽 = propagation constant and 𝜀𝑒𝑓𝑓 = effective dielectric constant.
(a)
(b)
(3)
5
(c) Fig. 2. Topology of the Cross-resonator band-pass Filter.
Similarly, the even mode transmission line model is depicted in Fig.2(c) and the even mode resonance condition is given in (4). 2tan (𝜃ℎ) + tan( 𝜃𝑜) ― cot ( 𝜃𝑠)
𝑌𝑖𝑛𝑒𝑣𝑒𝑛 = 𝑗𝑌1 ― tan 𝜃ℎ(tan 𝜃ℎ + tan 𝜃𝑜 ― cot 𝜃𝑠) = 0
(4)
Further, even mode resonance is decomposed into two halves 𝑓𝑒𝑣𝑒𝑛1 and 𝑓𝑒𝑣𝑒𝑛2 as shown in Fig.2(c) and the resonance frequencies can be derived using equation (4). We can obtain the resonance frequencies 𝑓𝑒𝑣𝑒𝑛1 & 𝑓𝑒𝑣𝑒𝑛2 from the even mode transmission line model as follows: 𝑓𝑒𝑣𝑒𝑛1 = 4 ∗ (𝑙
𝑐
ℎ + 𝑙𝑠) 𝜀𝑒𝑓𝑓
and 𝑓𝑒𝑣𝑒𝑛2 = 2(𝑙
𝑐
ℎ + 𝑙𝑜) 𝜀𝑒𝑓𝑓
(5)
,where quarter wavelength transmission line is responsible for 𝑓𝑒𝑣𝑒𝑛1. 𝑓𝑒𝑣𝑒𝑛2 is obtained from halfwavelength transmission line as shown in Fig.2(c). Based on the observation given in [32], we can write 𝑓𝑒𝑣𝑒𝑛1 𝑓𝑜𝑑𝑑
= 𝑘1 and
𝑓𝑒𝑣𝑒𝑛2 𝑓𝑜𝑑𝑑
= 𝑘2
(6)
,where 𝑘1 and 𝑘2 can be tuned by varying 𝜃𝑠 = 𝛽𝑙𝑠 and 𝜃𝑜 = 𝛽𝑙𝑜 respectively. For 𝑘1 ≈ 1 and 𝑘2 ≈ 1 i.e for 𝜃𝑠 ≈ 0 and 𝜃0 ≈ 900 the triple-pole bandpass response has been achieved with a transmission zero (TZ) at the upper side of the passband. The schematic of FF is given in Fig.3(a) and the S-parameter responses are shown in Fig.3(b) for both weak and strong coupling. From Fig.3(b) it is found that passband response is 2.98 GHz to 3.46 GHz with three transmission poles (TP). Existence of three TPs is confirmed from the weak coupling response whereas a stable response with minimum insertion loss of 1.0 dB is achieved using strong coupling. These TPs (TPevn1, TPevn2, TPodd) can be tuned by varying the lengths of the resonators 𝑙𝑠 , 𝑙𝑜, 𝑙ℎ = 𝑙1+𝑙2 to achieve wider bandwidth which is confirmed from Fig.4(a-c).The resonance frequencies of TPevn1 and TPevn2 can be tuned by varying the length 𝑙𝑠 and 𝑙𝑜 respectively by keeping intact the length 𝑙ℎ as shown from Fig.4(a & b).Whereas the resonance frequency of TPodd is solely determined by the length 𝑙ℎ.So the design guidelines of the FF network is given as follows: First calculate the length 𝑙ℎ corresponding to the resonance frequency of TPodd from equation (3) and then by adjusting the length 𝑙𝑠 and 𝑙𝑜 as per equation (5-6) desired resonance frequencies of TPevn1 and TPevn2 is obtained.
6
(a)
(b)
Fig. 3. (a)Schematic diagram and (b) frequency responses of the triple pole FF under the weak coupling (g=1 mm) and strong coupling (g=0.2 mm) condition .
(a)
(b)
.
(c) Fig. 4. Frequency responses of the FF under the weak coupling condition for varying length of (a) 𝑙𝑠 (b) 𝑙𝑜 (c) 𝑙ℎ = 𝑙1+𝑙2
7
(a)
(b)
Fig. 5. (a) S11 response of the conventional slot fed DRA, the proposed filtering DRA and the triple-pole FF, (b) Simulated Gain and Radiation Efficiency Plot of the proposed filtering DRA
(a)
(b)
Fig. 6. Electric Fields distribution within the rectangular DRA:(a) Ideal electric fields distribution of TE111 mode (b) Simulated electric fields distribution in three different frequencies within the passband
3. RESULTS AND VERIFICATION A relative performance between conventional slot-fed rectangular DRA (Antenna Conv.) and proposed filtering DRA is discussed in this section. S11-plots of both antennas are shown in Fig.5(a) and there it is clear that Antenna-Conv. resonates at 3.27 GHz in the fundamental mode. On the other hand, response of the proposed filtering DRA is analogous with the triple-pole FF. The radiation efficiency and gain of the filtering DRA as a function of frequency are depicted in Fig.5(b). The radiation efficiency plot also confirms the filtering response. It can be observed that the efficiency remains stable approximately at 90% within passband. It drops sharply below 20% beyond passband. Ideal electric field distributions of TE111 mode of a rectangular DRA with ground plane and without ground plane [18,24] are schematically portrayed in Fig.6 (a) to compare it with the simulated one. From the simulated electric fields distribution within DRA as represented in Fig.6(b), excitation of TE111 mode of rectangular DRA is verified as the fields orientation
8
closely resemble the ideal one for all three frequencies within the passband.
Fig. 7. Fabricated prototype of the proposed DRA
(a)
(b)
Fig. 8. Simulated and measured (a) S11 and (b) gain of the DRA
The FF network of the proposed wideband filtering DRA is fabricated on Arlon AD270 substrate and ECCOSTOCK Hik material is used as DRA as shown in Fig.7.The DRA is attached on the top of the ground plane using adhesive which has negligible effect on TE111 mode of the DRA. The S-parameter response of the DRA is measured using an Agilent’s N5230A vector network analyzer and reasonable agreement is obtained between simulation and measured results. The proposed filtering DRA offers a wide impedance bandwidth of 15 % over a frequency range of 3.06 GHz to 3.56 GHz as shown in Fig.8(a) whereas 10% impedance bandwidth is obtained for the Antenna Conv. as shown in Fig.5.The gain vs frequency plot for both the Antenna Conv. and the filtering DRA is demonstrated in Fig.8(b). Where gain response of the Antenna Conv. does not fall beyond the operational band, sharp transitions of gain response beyond the passband are clearly visible with two radiation nulls (RN1 & RN2) at 3.9 GHz and 4.4 GHz for the proposed DRA. The first null i.e RN1 is occurred due to the presence of transmission zero in the filtering feed network. The second nulls i.e RN2 is caused by the matching stub (𝑙𝑚) which is remained opened circuited at the end of the feed line. When 𝑙𝑚 is half of the guided wavelength (λg) long current at the coupling slot becomes minimum. Then no energy gets coupled to the DRA, and that generates the null in the gain response [25]. In the proposed design 𝑙𝑚=16.2 mm which is nearly equal with λg/2 at 4.4 GHz, is responsible for RN2. The DRA possess flat gain responses within the passband with a sharp roll off near the passband edge. The measured gain remains 5.9±0.3 dBi within passband and falls sharply below -14 dBi and -18.5 dBi at 3.9 GHz and 4.4 GHz respectively. The radiation pattern for both E-plane (φ = 00) and H-plane (φ = 900) in three different frequencies of 3.1 GHz, 3.2 GHz and 3.4 GHz in the passband region is shown in Fig.9(a-c).
9
Both simulation and measurement verified that the main beam directed in broadside over the operating band with co-to-cross-pol isolation is greater than 20 dB.
(a)
(b)
(c)
φ = 00
φ = 900
Fig. 9. Simulated and Measured radiation pattern of the filtering DRA at (a) 3.1 GHz (b) 3.2 GHz (c) 3.4 GHz
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TABLE I Performance Summary of the Filtering DRA (λ0=free space wavelength)
[Ref], Year
[25], 2016
[26],2017
[27],2018
[30],2019
[31],2019
This Work
Shape Of DRA and ɛr Filtering & feeding Scheme
Complex ɛr=10
Rectangular (Conv.) ɛr=10 Hybrid feed Using conformal strip & microstrip line 1.965 GHz
Rectangular with slots ɛr=90 Silver Coated Slots,metal strips
Cylindrical ɛr=20
Rectangular (Conv.) ɛr=10 Triple Pole Filtering Feed,Conv. slot 3.31 GHz
Centre frequency (f0)
4.92 GHz
Cylindrical Stacked DRA ɛr=2.2,15 Shorting Via,Transvers e Stubs,Seperated Slot 6.09 GHz
Volume (xλ0×yλ0×zλ0)
1.23×0.82×0. 128
0.82×0.82 ×0.11
0.44×0.44 ×0.11
0.65×0.61×0.02
Bandwidth
20.3 %
61.4 %
21.9 %
No. of RN
2
2
2
Extremly Narrow (<100 MHz) 2
Avg. Gain(dBi)
9.05
8.7
5.1
4.8
Parasitic Strip,Seperated Slot
4.17 GHz
Microstrip Stubs of different length, microstrip line 2.4 GHz Circular (dia=0.204 λ0, height=0.1 λ0) 7%
0.47×0.44 ×0.17
2
2
3.05
6.0
15 %
The operating mechanism and performance characteristic of the proposed design and previously reported filtering DRA available in literature are tabulated in Table I. In [25-27], no specific filtering circuit is included in the feed to obtain the filtering response of the DRA. In this work, a triple pole filtering feed is included below the ground plane to obtain the desired filtering response, without increasing the footprint of Antennaconv. as mentioned before. Although the DRAs in [25-26], featured wide bandwidth and high gain but occupy a large volume with complex DRA structure compared to our design. In [27], a vertical conformal strip is glued on the DRA wall to obtain radiation nulls which increases the deign complexity. Whereas, the proposed technique is much more robust for filtering DRA design as it is easy to introduce the selective gain performance in any conventional slot coupled DRA. As compared to the antennas in [30] & [31], the proposed DRA has wider bandwidth, higher gain along with completely different filtering mechanism. 5. CONCLUSION A triple-pole cross-resonator based filtering feeding network is used to develop a wideband filtering DRA. In comparison with the conventional slot coupled DRA, the proposed design achieves 5% more impedance bandwidth. The proposed DRA operates 3.06 GHz to 3.56 GHz with S11 almost 0 dB at either side of passband, ensures superior filtering performance. Filtering response of the DRA not only improves the impedance characteristics but also enhances the radiation performance. A fairly flat broadside gain of 6dBi over the operating band and sharp roll-off beyond passband with two radiation nulls ensure selective performance of the antenna. With the high demand for low interfering signal, the proposed design has a large potential for WiMAX router applications. ACKNOWLEDGMENT The authors thank senior colleagues for their valuable comments which have helped to improve the quality of paper.
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Declaration of interests ☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Declaration of interests: None