Diversity Antenna based on LTCC

2017 International Conference on Electrical and Computing Technologies and Applications (ICECTA)

Dual Polarized Semi-Circular MIMO/Diversity Antenna based on LTCC Technology Waleed Tariq Sethi1, Mohammed R. AlShareef2, Hatim M. Behairy2, M.Ashraf1 and S. Alshebeili1 1

2

Electrical Engg Dept., RFTONICS, King Saud University, Riyadh, Saudi Arabia National Center for Electronics and Photonics Technology, KACST, Riyadh, Saudi Arabia Email: [email protected]

Abstract—In this paper, we present simulated design of two antennas intended for Ultra-wideband Radio Frequency Identification (UWB-RFID) applications. Both antennas present multiple-input-multiple-output (MIMO) capabilities with dual polarization. The antennas have planar structure with semicircular radiating patches within a circular slot. To achieve dual polarization, both antenna designs with semi-circular patches are fed orthogonally via Co-Planar Waveguide (CPW) transmission lines. Numerical optimization, detailed design and analysis are presented and discussed which are carried out via electromagnetic simulation tools. The results obtained reveal that the antennas are matched over a wideband covering the band of interest i.e. UWBRFID band (6-8 GHz). Exciting the first antenna with two semicircular patches achieves an impedance bandwidth of 58% (6.05 – 10.1 GHz) and maximum gain of 9.26 dBi. Similarly, excitation of the second antenna with four elements achieve an impedance bandwidth of 114 % (5-13 GHz) with maximum gain of 6.8 dBi. Diversity performance in terms of envelope correlation coefficient (ECC) for both antenna designs are also studied. Keywords—LTCC Ferro A6M, Dual Polarized, UWB-RFID applications, semi-circular patches, circular slot antenna.

I. INTRODUCTION Ultra-wideband (UWB) technology is used in various modern radio and wireless communication systems for transmitting and receiving signals. After the allocation of an unlicensed wideband (3.1-11 GHz) by the Federal Communication Commission (FCC), UWB technology gained more importance. Antenna design in this wideband is a challenging task as signals of other narrow band systems such as WLAN and HIPER LAN/2 exist in this band [1]. But this challenge is taken as an opportunity by the researchers to design various kinds of antennas especially for the untouched realm of UWB-RFID technology [2-3]. UWB-RFID technologies offer numerous advantages such as target localization, increased security, time-of-arrival resolution, minimum interference probability, and low power consumption. Another important advantage of the wideband frequency spectrum is that it contains both the high and low frequencies. The high microwave frequencies can be used to localize microwave energy at specific target and low frequencies can be used to penetrate deeply through some obstacles [4-5]. Various antenna designs for UWB-RFID applications have been presented in literature. [6]. Since UWB comprises multiple bands of interest, shielding it from noise and other bands is an important task. One important technique that has gained immense credibility and appreciation is the Multiple-Input-Multiple-Output (MIMO) or diversity technique [7]. This technique has been implemented in mostly

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wideband antennas where selection of specific band of interest (i.e. UWB-RFID) and noise shielding from other bands is required. The advantages of this technique include dual polarization, high mutual coupling, and increased channel capacity among various users occupying the same band and offering wideband data transfer without additional power consumption [8]. A lot of interest has been seen in materials that can assist in making miniature circuits and compact packaging technology for many wireless and standalone applications [9-10]. One such technology that has gained attention is the Low Temperature CoFired Ceramic (LTCC). Its popularity lies in the fact that it can be easily integrated into arbitrary number of layers with circuit components like thick-films, cavities, via holes, lumped components and chip devices [11-13]. However, it is a challenging task to achieve a wide impedance bandwidth and high gain for any kind of antenna design due to typically the high values of dielectric constant of LTCC material. Some solutions in the literature have been offered that makes use of multiple stacked layers and slots to cope with this problem [14-16]. In this paper, we present two dual polarized MIMO/Diversity antennas based on LTCC Ferro A6M substrate. The designs are inspired by the work of T. A. Denidni and M. A. Habib [17]. The band of interest for the designs lies in the frequency range of 6-8 GHz. Both antenna designs have a circular slot and semi-circular patches fed via orthogonal CPW lines. The first antenna design with two semi-circular patches achieves a wide impedance bandwidth of 58 % (6.05-10.1 GHz) with a high gain of 9.26 dBi. Similarly, the second antenna design with four elements semi-circular patches achieves an improved bandwidth of 114 % (5-13 GHz) with acceptable maximum gain of 6.8 dBi. The mutual coupling between ports and diversity performance in terms of envelope correlation coefficient for both antenna designs are within the required limits. The results achieved for the proposed antennas show improvement over some similar designs available in the literature at the UWB band [18-20]. II. TWO ELEMENT SEMI-CIRCULAR MIMO/DIVERSITY ANTENNA A. Antenna Design The geometry of the proposed dual polarized antenna is shown in Fig.1. The antenna has been divided into different layers as shown in Fig.1 (a). Starting from the top, Layer -1 is a superstrate dielectric with thickness hsup made from LTCC material Ferro A6M having permittivity ɸr = 5.9 and loss tangent tanɷ = 0.002 at 10 GHz [21]. Layer-2 is sandwiched between the two air gaps of thickness hgs and hgr. This layer contains the planar structure with a circular slot in the center having certain


radius Rc. The circular slot, which controls the lowest frequency resonance in the spectrum, is fed via two orthogonal CPW lines feeding two semi-circular patches. The CPW lines have width and lengths of Wf and Lf , respectively. The semi-circular patches have optimized diameter of D. To control impedance matching, an important parameter in the CPW lines, which is the gap between the lines, denoted by g1, is optimized, while the matching of -10 dB resonance is controlled via gap g2. Details of these optimization parameters and other important parameters have been discussed widely in the literature [22-24]. Fig.1 (b) shows the detail dimensions and placement of each port and patch element on the planar structure at Layer-2. The conducting elements and ground plane have thicknesses of hg and are made from silver with conductivity ʍg = 7.4 x 106 S/m, which includes the roughness correction. The ground and radiating elements are placed on 6-sub layers of LTCC Ferro A6M material. The thickness of each LTCC layer is 0.127 mm. The total height of LTCC layer is hLTCC. Layer-3, which represents the final layer of the proposed structure, is placed at a certain distance from the main radiating elements of Layer-2. The material used for Layer-3 is silver with a thickness of href. Table.I lists the optimized parameters of the proposed dual polarized antenna. Working with LTCC materials introduces a new set of challenges as the radiation losses associated with them are very high i.e. ɸr > 5. In order to have an antenna that resonates in the required band of interest i.e. UWB-RFID (6-8 GHz), the antenna design shown in Layer-2 was selected to be the optimal choice. This simple planar design with sub-layers of LTCC achieves a very wideband covering almost all the UWB spectrum. It also offers an easiness in terms of fabrication as no additional or complex punching holes or cavities are needed as compared to other available LTCC antenna designs [25-26]. Another advantage of this design is the addition of Layer-1 and Layer-3, which assist in achieving high gains for the proposed applications.

of 7 GHz has been achieved. Similarly, exciting port-2 achieves an impedance bandwidth of 58% (6.05-10.1 GHz) and a gain of 9.26 dBi. An important factor in the MIMO/Diversity based antenna is the requirement of minimum mutual coupling. From Fig.2, it can be seen that the mutual coupling remains below -14 dB overall the bandwidth except in our band of interest where it reaches below -12 dB. Both the antennas offer wide bandwidth, high gain and high mutual coupling, thus fulfilling our requirements for the UWB-RFID applications i.e. (6-8 GHz). Fig.3 shows the surface current distribution at Layer-2 where the semi-circular patches are deposited. It is obvious that the maximum current distribution is concentrated around the edges and gaps between the semi-circular patches and around its relevant feed lines. Fig.4 shows the 3D radiation pattern of the proposed two element design when both ports are excited individually at the center frequency of 7 GHz. TABLE.I OPTIMIZED DIMENSIONS OF TWO ELEMENT MIMO/DIVERSITY ANTENNA (UNITS: MM) Parameter

Value

The proposed antenna shown in Fig.1 has been simulated with Computer Simulation Tool Microwave studio (CST MWS) [27]. S-parameter results for both orthogonal ports along with their gains are shown in Fig.2. It can be seen that the -10 dB bandwidth for the antenna is about 42.8 % (6.1-9.1 GHz) when port -1 is excited. The gain of 9.04 dBi at the center frequency

Value

Ls

80

Ws

80

Wf

2.5

Lf

16.2

D

50

Rc

24

g1

0.35

g2

0.86

hsup

1.2

hgs

3.8

hgr

7

hLTCC

0.762

href

1.6

hg

0.035

(a) (b) Fig.1 (a) Side view of proposed antenna (b) Front view of layer-2 with dimensions

B. Results and Discussion

Parameter


III. FOUR ELEMENTS SEMI-CIRCULAR MIMO/DIVERSITY ANTENNA A. Antenna Design

Fig.2 S-parameters and gain of two element dual polarized antenna

A well-known method to increase the channel capacity, gain and diversity of the antenna is to introduce multiple antenna elements [28]. Fig. 5 shows the geometry of the proposed four elements MIMO/Diversity antenna. This design is compact due to the earlier proposed two-element MIMO/Diversity antenna. The optimized antenna dimensions are 50 x 50 x 12 mm3. We also list all the detailed dimensions in Table.II. The four elements are placed along ± x,y coordinate axes. The substrate used in this design is LTCC Ferro A6M material as well. The thickness of each LTCC layer is 0.254 mm. In order to minimize the mutual coupling among the elements, the distance between them is kept less than Ȝo/2 at center frequency of 7 GHz. The antenna element # 1 is approximately perpendicular to the antenna element # 2, while the antenna elements # 3 and # 4 are placed perpendicularly to the first two antenna elements. B. Results and Discussion

(a) (b) Fig.3 (a) Current distribution port-1 (b) Current distribution port-2

Fig.6 shows the s-parameters and gain of the four element MIMO antenna. Since port-1 = port-3 and port-2 = port-4 are identical in terms of design and position on the LTCC substrate, the return loss results are shown with only two reflections below -10 dB. These same ports will have reflections equally but with negative amplitudes. Similarly, mutual coupling among similar ports are shown in Fig.6. It can be seen from the figure that the excitation of port-1 and port-3 achieved a wide impedance bandwidth of 97 % (6.2-13 GHz). The maximum gain achieved at center frequency of 7 GHz is 6.8 dBi. Similarly, excitation of port-2 and port-4 achieved an impedance bandwidth of 114 % (5.1-13.1 GHz) with gain of 6.2 dBi. The reduction in gain and increase in bandwidth is due the mutual coupling [29] among the reduced antenna dimensions compared to two element design. The mutual coupling among the ports have also improved. The four element design achieved high mutual coupling of below 20 dB overall the spectrum. For our band of interest the mutual coupling is below -15 dB.

(a) (b) Fig.4 (a) 3D radiation pattern port-1; (b) 3D radiation pattern port-2

(a) (b) Fig.5 (a) Side view of proposed antenna (b) Front view of layer-2 with dimensions


C. Diversity Gain and Envelope Correlation Coefficient A crucial parameter pertaining to the design of a MIMO/Diversity antenna system is the diversity gain. Diversity gain determines how much transmitted power can be reduced without compromising the desired performance. It depends on envelope correlation coefficient which is taken from the cumulative distribute function (CDF). For 1% of CDF level using selection combining, the theoretic diversity gain ‫ ݒ݅݀ܩ‬is 10 dB according to the following approximate formula: ‫ܩ‬ௗ௜௩ ൌ ͳͲǤ ඥͳ െ ȁ‫݌‬௘௡௩ ȁଶ

Fig.6 S-parameters and gain of four element dual polarized antenna

TABLE.II OPTIMIZED DIMENSIONS OF FOUR ELEMENT MIMO/DIVERSITY ANTENNA (UNITS: MM) Parameter

Value

Parameter

Value

Ls

50

Ws

50

Wf

1.8

Lf

10.8

D

10

Rc

15

g1

0.35

g2

0.54

hsup

1

hgs

4.9

hgr

4

hLTCC

1

href

1

hg

0.035

(1)

where penv is the envelope correlation coefficient. It is calculated from either the radiation electric fields or the s-parameters [30]. To analyze the MIMO antenna over a wideband with less computational expenses, we opted for the s-parameter method compared to radiated fields approach. However, this approach assumes that the antennas are lossless and that incoming waves are uniformly distributed. The envelope correlation can be expressed in terms of the s-parameters of antenna system as: ‫݌‬௘௡௩ ൌ

మ

‫כ‬ ‫כ‬ ቚ௦೔೔ ௦೔ೕ ା௦ೕ೔ ௦ೕೕ ቚ మ

మ మ

మ

ሺଵିሺห௦೔ೕ ห ାห௦ೕ೔ ห ሻሺଵିቀห௦ೕೕ ห ାห௦೔ೕ ห ቁሻ

ሺʹሻ

where the asterisk denotes the complex conjugate. Deep fading of the received signals are a result of high correlation values. Therefore, ߩ݁݊‫ < ݒ‬0.5 is required to realize a diversity system [30]. Table. III shows the performance characteristics of proposed MIMO antenna based on equations stated above. TABLE.III PERFORMANCE CHARACTERISITCS OF PROPOSED MIMO ANTENNA Parameter

Frequency

Element 1 &2

Element 1 &3

Element 2 &3

Envelope Correlation Coefficient

7 GHz

0.002

0.0003

0.002

Diversity Gain

7 GHz

9.98

9.98

9.98

IV. CONCLUSION

Fig.7 3D radiation pattern of four element antenna at 7 GHz (a) Port-1 excited (b) Port-2 excited (c) Port-3 excited (d) Port-4 excited

Fig.7 shows the 3D radiation pattern of the four element MIMO/Diversity antenna. At the center frequency of 7 GHz, all the ports are individually excited to see the diversity of the MIMO antenna. The antenna radiates in negative X-axis, negative Y-axis, X-axis and Y-axis, thus confirming pattern diversity performance of the four element design.

Two antenna designs having MIMO/Diversity capabilities and dual polarization for the band of interest (6-8 GHz) have been proposed. The first antenna with two orthogonal semicircular patches within a circular slot achieved an impedance bandwidth of 58% (6.1-10.1 GHz) and a maximum gain of 9.26 dBi. The mutual coupling between the two ports was below -14 dB over the whole bandwidth, except a degradation of only two dBs within the band of interest. Comparison with some other similar work in the literature is shown in Table.IV. The second design having four element semi-circular radiating patches in a circular slot offered a further bandwidth improvement (114 %) and a limited gain of 6.8 dBi. The port mutual coupling remained below -20 dB over the whole bandwidth while it increased to 15 dB in the band of interest. Diversity and envelope correlation coefficient for the proposed MIMO design showed a high level of agreement with the acceptable values. With these merits, the proposed antenna designs are suitable candidates for UWBRFID applications. Finally, the proposed antenna structure based on LTCC technology has practical significance, since the


RF electronics required for diversity operation (switching) can be integrated by using multiple layers available beneath the antenna structure.

[14]

TABLE.IV SPECIFICATIONS OF PROPOSED AND OTHER SIMILAR ANTENNAS REPORTED IN THE LITERATURE Ref This work [18] [19] [20]

B.W. (GHz) 6-10.1

Gain (dB) 9.26

Dimensions (LxWxH)mm3 30 x 30 x 6.9

Polarization

3-7 2-2.1

5 4.5

41 x 36 x 0.48 8.6 x 13 x1.1

Single Single

10.712.7

4.9

20 x 20 x 2.5

Dual

Dual

LTCC Tape Ferro A6M Ceramtec Zn2SiO4CaTiO3 Dupont 951

[15]

[16]

[17] [18]

ACKNOWLEDGMENT This research is supported by King Abdul Aziz City for Science and Technology (KACST) Innovation Center in RF and Photonics for the e- Society (RFTONICS) hosted at King Saud University (KSU).

[19]

[20]

REFERENCES [1]

[2] [3] [4]

[5]

[6]

[7]

[8]

[9] [10] [11]

[12]

[13]

Alarifi A.; Al-Salman A.; Alsaleh M.; Mihaylova L.; Kim B-G.; Dogra DP.:Ultra-Wideband Indoor Positioning Technologies: Analysis and Recent Advances. Sensors. Basel, Switzerland. (2016) A. Ramos.: RFID and wireless sensors using ultra-wideband technology. London: ISTE Press, Ltd.(2016) H. Schantz.:The art and science of ultrawideband antennas.Second Edition, Artech House.(2015) M. Khaliel.; A. Fawky.; M. EI-Hadidy.; T. Kaiser.: UWB Reflectarray Antenna for chipless RFID applications. Radio Science Conference (NRSC), 31st National Radar Symposium Conference. (2014) M. Pigeon.; R. D'Errico.; C. Delaveaud.:UHF-UWB tag antenna for passive RFID applications. Antennas and Propagation (EuCAP),7th European Conference.(2013) Peng Gao.; Shuang He.; Xubo Wei.; Ziqiang Xu.;Ning Wang.;Yi Zheng.:Compact Printed UWB Diversity Slot Antenna With 5. 5-GHz Band-Notched Characteristics. Antennas and Wireless Propagation Letters, IEEE.13, 376-379 (2014) B. P. Chacko.; G. Augustin.; T. A. Denidni.:Uniplanar polarisation diversity antenna for ultrawideband systems.Microwaves, Antennas & Propagation, IET. 7, 851-857 July (2013) Nguyen Khac Kiem.; Huynh Nguyen.; Bao Phuong.; Dao Ngoc Chien.: Design of Compact 4x4 UWB-MIMO Antenna with WLAN Band Rejection.International Journal of Antennas and Propagation. 1-11 (2014) K. Nair.; S. Priya.:Advances in electroceramic materials II. Hoboken, N.J. Wiley.(2010) K. Vinoy.:Micro and smart devices and systems. Springer (2014) Liang Chai.; A. Shaikh.;V. Stygar.:LTCC for wireless and photonic packaging applications. Proceedings of the 4th International Symposium on Electronic Materials and Packaging. (2002) P. C. Donahue et al.: A new low loss lead free LTCC system for wireless and RF applications.Multichip Modules and High Density Packaging, 1998. Proceedings. 1998 International Conference on. Denver, CO.(1998) Yu Wang.; Jianming Zhou.; Yinqiao Li.; Xiao Yang.:Design of a Ka band dual mode filter based on LTCC technology. 2015 IEEE 6th International

[21]

[22]

[23]

[24]

[25]

[26] [27]

[28]

[29]

[30]

Symposium on Microwave, Antenna, Propagation, and EMC Technologies (MAPE), Shanghai. (2015) L. Rong Lin.; G. Dejean.; M. Moonkyun.; L. Kyutae.; S. Pinel.; M. M. Tentzeris.; J. Laskar.:Design of compact stacked-patch antennas in LTCC multilayer packaging modules for wireless applications. IEEE Trans. on Advanced Packaging. 27, 581-589 (2004) A. Panther.; A. Petosa.; M.G. Stubbs.;K. Kautio.:A wideband array of stacked patch antennas using embedded air cavities in LTCC".IEEE Microw. Wireless Compon. Lett.15 916-918 (2005.) S. Du.; Q.-X. Chu.; W. Liao.:Dual-band circularly polarized stacked square microstrip antenna with small frequency ratio.Journal of Electromagnetic Waves and Applications. 24 (11-12) 1599-1608 (2010) T. A. Denidni.; M. A. Habib.:Broadband printed CPW-fed circular slot antenna.Electronics Letters. 42, no. 3, 135-136 2 Feb (2006) B. Hussain et al.:Design considerations for LTCC based UWB antennas for space applications.IEEE International Conference on Wireless for Space and Extreme Environments (WiSEE), Noordwijk.(2014) G. Dou.; Y. Li.; M. Guo.:Dual-band LTCC antenna based on 0.95Zn2SiO4-0.05CaTiO3ceramics for GPS/UMTS applications. Chinese Physics B. 24, no.10,108401 (2015) P. Moslemi,;A. Kouki.:A dual polarized, Ku-band patch antenna using hybrid LTCC-PCB technology.Microwave and Optical Technology Letters. 58, no. 1, 202-206 Jan (2016) Ferro,.:www.ferro.com. [Online]. Available: http://www.ferro.com/noncms/ems/EPM/content/docs/A6M%20LTCC%20System.pdf. Accessed: Aug. 16, (2016) Avez Syed.;Rabah W. Aldhaheri.:A Very Compact and Low Profile UWB Planar Antenna with WLAN Band Rejection. The Scientific World Journal. Article ID 3560938, 7 pages, (2016) Raj Kumar.; Gopal Surushe.:Design of microstrip-fed printed UWB diversity antenna with tee crossed shaped structure, Engineering Science and Technology, an International Journal. 19, Issue 2 946-955 June (2016) Ajay Yadav.; Dinesh Sethi.; R.K. Khanna.:Slot loaded UWB antenna: Dual band notched characteristics. AEU - International Journal of Electronics and Communications.70, Issue 3 March (2016) S. H. Wi.; Y. P. Zhang.; H. Kim.; I. Y. Oh.; J. G. Yook.:Integration of Antenna and Feeding Network for Compact UWB Transceiver Package. IEEE Transactions on Components, Packaging and Manufacturing Technology. 1, no. 1 111-118 Jan. (2011) Y. P. Zhang.; M. Sun.; W. Lin.:Novel Antenna-in-Package Design in LTCC for Single-Chip RF Transceivers. IEEE Transactions on Antennas and Propagation. 56, no. 7 2079-2088 July (2008) Computer Simulation Technology, Microwave Studio (2014) M. Koohestani.; A. Hussain.; A. A. Moreira.;A. K. Skrivervik.:Diversity Gain Influenced by Polarization and Spatial Diversity Techniques in Ultrawideband. IEEE Access. 3, 281-286 (2015) P. C. Donahue et al.:A new low loss lead free LTCC system for wireless and RF applications.Multichip Modules and High Density Packaging, Proceedings., Denver, CO, (1998) Min Wang, Wen Wu, and Zhongxiang Shen, “Bandwidth Enhancement of Antenna Arrays Utilizing Mutual Coupling between Antenna Elements,” International Journal of Antennas and Propagation, vol. 2010, Article ID 690713, 9 pages, 2010. Ming-Iu Lai; Tzung-Yu Wu; Jung-Chin Hsieh; Chun-Hsiung Wang; Shyh Kang Jeng.: Compact Switched-Beam Antenna Employing a FourElement Slot Antenna Array for Digital Home Applications. Antennas and Propagation, IEEE Transactions. 6, no.9, 2929,2936, Sept. (2008)