Akyildiz

Bancroft

Bianchi

Huang

James

Rabbani

Singh

Younssi

English

In this paper, a technique has been proposed to design microstrip antenna arrays at terahertz (THz) frequencies with improved gain and fabrication tolerance. The antenna is designed at 100GHz frequency and fabricated with simple laboratory based PCB etching process. The gain is improved to 13.4dBi with the help of only three patch elements. The measured -10dB return loss bandwidth (BW) is 5.55% of the central frequency. The measured and the simulation results are all in good agreement

Rabbani, Muhammad

Ghafouri-Shiraz, Hooshang

University of Birmingham Research Portal

  University of BirminghamFabrication tolerance and gain improvements ofmicrostrip patch antenna at terahertz frequenciesRabbani, Muhammad; Ghafouri-Shiraz, HooshangDOI:10.1002/mop.29920License:Creative Commons: Attribution-NonCommercial-NoDerivs (CC BY-NC-ND)Document VersionPeer reviewed versionCitation for published version (Harvard):Rabbani, M & Ghafouri-Shiraz, H 2016, 'Fabrication tolerance and gain improvements of microstrip patchantenna at terahertz frequencies', Microwave and Optical Technology Letters, vol. 58, no. 8, pp. 1819-1824.https://doi.org/10.1002/mop.29920Link to publication on Research at Birmingham portalPublisher Rights Statement:This is the peer reviewed version of the following article: Fabrication tolerance and gain improvements of microstrip patch antenna atterahertz frequencies, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/mop.29920/full. This article may beused for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.General rightsUnless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or thecopyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposespermitted by law.•	Users may freely distribute the URL that is used to identify this publication.•	Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of privatestudy or non-commercial research.•	User may use extracts from the document in line with the concept of ‘fair dealing’ under the Copyright, Designs and Patents Act 1988 (?)•	Users may not further distribute the material nor use it for the purposes of commercial gain.Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document.When citing, please reference the published version.Take down policyWhile the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has beenuploaded in error or has been deemed to be commercially or otherwise sensitive.If you believe that this is the case for this document, please contact UBIRA@lists.bham.ac.uk providing details and we will remove access tothe work immediately and investigate.Download date: 01. Mar. 20201   Fabrication Tolerance and Gain Improvements of Microstrip Patch Antenna at Terahertz Frequencies M. S. Rabbani* and H. Ghafouri-Shiraz† School of Electronic Electrical and System Engineering University of Birmingham, 52 Pritchatts Road Edgbaston, B15 2TT, UK *saqibrabbani05@hotmail.com and †ghafourh@bham.ac.uk ABSRACT: In this paper, a technique has been proposed to design microstrip antenna arrays at terahertz (THz) frequencies with improved gain and fabrication tolerance. The antenna is designed at 100GHz frequency and fabricated with simple laboratory based PCB etching process. The gain is improved to 13.4dBi with the help of only three patch elements. The measured -10dB return loss bandwidth (BW) is 5.55% of the central frequency.  The measured and the simulation results are all in good agreement.  Key words: THz microstrip antenna, 100GHz antenna, terahertz antenna, THz array, THz antenna fabrication  1. INTRODUCTION Terahertz frequency spectrum (100GHz-10THz) is envisioned to be the essential host for future wireless services offering wide spectral bandwidth and fine resolution [1]. However, in order to attain an effective link budget for a THz wireless radio link, high gain antennas are vital to compensate the enormously high free space path loss [2]. Moreover, since the wavelength is very small (0.03mm-3mm) at THz frequencies hence, enlargement of the antenna’s size, which is a fraction of the operating wavelength, is crucial to reimburse the fabrication cost and tolerance [3]. Also, integrability of the antenna with the other THz components is another obligation to acquire the overall device compactness [4]. Amongst the 2   other contender, microstrip antenna is one of the attractive candidates for THz wireless systems because of its potential robustness to encounter the aforementioned constraints [5].  In the recent years, some work has been reported on THz microstrip antenna designs [3]-[9]. However, in the reported THz microstrip antennas, the patch and the associated dimensions are calculated based on the conventional design equations and the overall antenna structure remained far below than the ordinary PCB etching limit of µm 152  line width/gap [10]. Moreover, only the simulation based results have been presented and there is a lack of experimental measurements to support the design concepts. To the best of the authors’ knowledge, no particular work has been reported to improve the microstrip antenna size for THz frequencies in combination with the improved performance and ordinary fabrication and practical measurements.   In the present paper, we have demonstrated a procedure to design microstrip patch array at THz frequencies. The proposed method is verified by designing and testing a prototype at 100GHz frequency. The tested antennas’ attributes are compared with a microstrip patch antenna designed at 100GHz with the traditional method. The proposed antenna gain has enhanced to a few folds while the antenna size has considerably improved to satisfy the conventional PCB etching restrictions as mentioned earlier. The return loss (S11) is measured with the help of Anritsu’s 145GHz VNA Apparatus ‘ME7838D’ incorporated with MA25300A module. The far-field pattern was measured with Agilent Technologies’ 110GHz PNA Network Analyzer “E8361C” in combined with the extension module “N5260-60003”.  2. MICROSTRIP ANTENNA DESIGN PROCEDURE Conventional rectangular microstrip patch antenna is half-wavelength resonator in which the patch length and width determine the operating frequency and the antenna’s input impedance, respectively [10]. Traditionally, for the low microwave frequency designs, the width of the 3   patch is set to be comparatively equal to the patch length to keep the antenna size small and to avoid the excitation of unwanted resonance modes [10]. In this way, an ordinary patch antenna gives a high input impedance of above 200Ω which is matched with the standard 50Ω impedance, in one way, by employing an impedance transformer (IT) of over 100Ω microstrip transmission line (MTL). Such a high impedance MTL is usually wide enough to be etched on a dielectric material of above 0.5mm substrate thickness which is commonly used for low microwave frequencies. However, for THz microstrip antennas, a very thin dielectric material is required to satisfy the limit: )4(0 rh ελ< [11] where h  is substrate thickness, 0λ  is the wavelength in free space and rε  is relative dielectric constant of the substrate material. Etching of the aforementioned high impedance microstrip line on such a thin material is challenging because the line width falls far below the PCB etching limit of µm 152 [10]. In order to overcome this problem, we have reduced the overall antenna’s input impedance )( inZ  much lower than 50Ω (i) by extending the patch width beyond the ordinary size, and (ii) by making an array of multiple patches fed in series. The total input impedance of an array of ‘n’ identical patch elements appropriately fed in series is expressed as [10]:  nZZ pin =                       (1) where pZ  is the input impedance of the individual patch element. Subsequently, such a low antenna input impedance is matched with the standard 50Ω impedance through the corresponding microstrip line IT of low impedance which is wide enough to convince the conventional fabrication limits. The geometry of the proposed microstrip array is illustrated in Fig. 1. The array consists of three wide patches of the same size which are fed in series.  The patch width (W) and length (L) are calculated from the following expressions [12]:  4   ( )( )12120++=rMλWε                  (2) ( ) L∆-εNλLeff22120 +=            (3) where M and N are non-negative integers (in our present design we chose 1=M and 0=N ), rε and effε  are the relative and the effective dielectric constants, respectively, and L∆ is patch length extension due to the fringing filed effect [10]. The input impedance of the individual patch is given as [12]:  WZ p 081.59 λ=                     (4) By substituting Eq .(4) into Eq.(1), we can obtain the total array’s input impedance as: nWZin 081.59 λ=                    (5) Ultimately, ‘Zin’ is matched with the standard 50Ω impedance through the MTL used as quarter-wavelength impedance transformer. The characteristic impedance ‘Z0’ and the width ‘WT’ of the microstrip TL are given as [13]: inZZ 500 =                      (6) rT ZhWε099.376=                    (7) Substituting Eq. (5) into Eq. (6) and Eq. (6) into Eq. (7) give the following final expression for the width of the MTL in terms of the ‘W’ and ‘n’: 089.6 λε rTnWhW =               (8) Equation (8) explains the motive of increasing ‘n’ and ‘W’ to widen the transmission line width ‘ TW ’. Since the transmission lengths ‘LT1’ and ‘LT2’ provide impedance transformation 5   and phase matching on the patches, respectively, they can be computed by the following expressions [12]:  ( ) 4121 /λPLT +=                  (9) ( ) L∆/λQLT 22122 ++=      (10) where P and Q are non-negative integers (in our design we used P=1 and Q=0) and λ is the operating wavelength. The array’s final dimensions are acquired through the simulation based optimization process by using CST microwave studio.  3. RESULTS AND DISCUSSIONS For the comparison purpose, initially, a conventional single patch microstrip antenna is designed at 100GHz frequency on a low loss dielectric material ‘RT/Duroid5880’ with 2.2=rε  and substrate thickness µm127=h  based on the traditional method as described in the literature [10]. Figure 2 shows the structure of the patch antenna and its dimensions are given in Table I. From Table 1, it can be seen that the overall antenna size is quite small and the transmission line width ‘WT’ is µm100 which is far below the fabrication limit µm)152(  of the conventional cost-effective etching process. Figure 3 depicts the simulated return loss (S11) and far-field radiation patterns (FRP) of the designed patch antenna. Figure 3(a) indicates that the -10dB return loss BW is 6% whereas the antenna gain and efficiency at 100GHz are 7.56dBi and 66.7%, respectively. Subsequently, by using the proposed method as described in section II, a microstrip array of 3 patches is designed at 100GHz frequency on the same Duroid substrate as that used for the conventional antenna shown in Fig. 2. Table 2 shows the optimized dimensions of the array structure (see Fig. 1) where it is clear that all PCB dimensions are fabricable with the ordinary etching process. The fabricated prototype and the experimental set up are demonstrated in Fig. 4. A W-band flange launcher (also called 1-mm connector) is employed 6   to connect the antenna with the VNA module. The far-field radiation pattern is measured in the lab room assuming free space conditions considering negligible reflections from the surroundings because of the high signal attenuation (72.44dB/m) at 100GHz frequency.  Figure 5 shows the simulated and measured return loss and FRP of the 100GHz microstrip array designed using the proposed method. From Fig. 5 (a), it is clear that the minimum measured return loss is 17.97dB− at 99.27GHz and the simulated and measured BWs are 8.87 % and 5.55%, respectively. Both the simulated and measured antenna gains at the resonant frequency of 99.5GHz are, respectively, 13.4dB and 12.2dBi where the former is obtained by applying the two –identical antenna method explained in [14]. The antenna simulated efficiency is about 94%.  Figure 5(c) indicates that the main radiation beam is focused at around 00 in both planes. The simulated and measured 3dB beam widths in H planes are 40.20 and 48.280, respectively, and that in E plane is 26.10. Figure 6 shows the gain frequency plot of the designed antenna. The result shows that the gain is maximum at the resonant frequency of 99.5GHz and it remains above 11.5dB in the whole operating band (98GHz-103GHz). Table-3 compares, BW, gain and efficiencies of the two designed antennas (i.e. the conventional single patch antenna and the proposed 3-patch array). From Table 3 we can conclude that the performance of the proposed 3-patch array antenna is considerably enhanced as compared with the conventional patch antenna.  4. CONCLUSION A method has been developed to design THz microstrip antenna arrays with improved gain and geometrical dimensions to ease the fabrication reluctance when conventional PCB etching method is used. The design concept was verified through both simulation and measurement on a proposed 100GHz 3-patch array which was exited through a series feeding 7   networks. The overall antenna performance is enhanced as compared with the microstrip patch antenna designed using the conventional etching method.  In order to design microstrip antenna arrays at further higher THz frequencies, higher values of integers ‘M’, ‘N’, ‘P’ and ‘Q’ should be chosen in Eqs. (2) to (6) and (9) to (10) so that the antenna dimensions remain conventionally fabricable. However, much higher values of these constants may cause some unwanted resonances at undesired frequencies which may limit the antenna size extension and hence, the design frequency to go far beyond 1THz as discussed in [12].                   8   References: [1] K. Huang, and Z. Wang, Terahertz terabit wireless communication, Microwave  Magazine, IEEE 12, no. 4 (2011): 108-116. [2] F. I. Akyildiz, J. M. Jornet, and C. Han, Terahertz band: Next frontier for wireless  communications, Physical Communication 12 (2014): 16- 32. [3] K.R. Jha, G. Singh, Improved Performance Analysis of Square Patch Microstrip  Antenna at Terahertz Frequency, Advances in Recent Technologies in  Communication and Computing, 2009. ARTCom '09. International Conference on,  vol., no., pp.676, 679, 27-28 Oct. 2009 [4] E. Seok, C. Cao, D. Shim, D. J. Arenas, D. B. Tanner, and C. Hung, A 410GHz  CMOS push-push oscillator with an on-chip patch antenna. In Solid-State Circuits  Conference, 2008. ISSCC 2008. Digest of  Technical Papers. IEEE International, pp.  472-629. IEEE, 2008. [5] K.R. Jha, G. Singh, Terahertz planar antennas for future wireless communication: A  technical review. Infrared Physics & Technology  60 (2013): 71-80. [6] K.R. Jha, G. Singh, Terahertz planar antennas for future wireless communication: A  technical review. Infrared Physics & Technology 60 (2013): 71-80. [7] K. R. Jha, and G. Singh, Dual-band rectangular microstrip patch antenna at terahertz  frequency for surveillance system.  Journal of computational electronics 9, no. 1  (2010): 31-41. [8] M. Younssi, J. Achraf, M. H. Yaccoub, E-M. Ahmed El, and A. Noura, Study of a  Microstrip Antenna with and Without Superstrate for Terahertz Frequency,  International Journal of Innovation and Applied  Studies 2, no. 4 (2013): 369-371. 9   [9] G. Singh, Design considerations for rectangular microstrip patch antenna on  electromagnetic crystal substrate at terahertz frequency, Infrared Physics &  Technology 53, no. 1 (2010): 17-22.  [10]  R. Bancroft, (2009). Microstrip and printed antenna design [electronic resource].  Raleigh, NC, SciTech Pub. [11] James, J. R., and A. Henderson. High-frequency behaviour of  microstrip open- circuit terminations, IEE Journal on Microwaves, Optics and Acoustics 3, no. 5  (1979): 205-218. [12] M. S. Rabbani, and H. Ghafouri‐Shiraz, Size improvement of  rectangular microstrip  patch antenna at MM‐wave and terahertz frequencies, Microwave and Optical  Technology Letters 57, no. 11 (2015): 2585-2589. [13] G. Bianchi, and R. Sorrentino, Electronic filter simulation & design, New York:  McGraw-Hill, 2007. [14] McMaster University, Basic methods in Antenna Measurements, Online: accessed  on Oct. 26th, 2015 at: http://www.ece.mcmaster.ca/faculty/nikolova/antenna_dload/current_lectures/L08_Measure.pdf  

Fabrication tolerance and gain improvements of microstrip patch antenna at terahertz frequencies

  Fabrication tolerance and gain improvements ofmicrostrip patch antenna at terahertz frequenciesRabbani, Muhammad; Ghafouri-Shiraz, HooshangDOI:10.1002/mop.29920License:Creative Commons: Attribution-NonCommercial-NoDerivs (CC BY-NC-ND)Document VersionPeer reviewed versionCitation for published version (Harvard):Rabbani, M & Ghafouri-Shiraz, H 2016, 'Fabrication tolerance and gain improvements of microstrip patchantenna at terahertz frequencies', Microwave and Optical Technology Letters, vol. 58, no. 8, pp. 1819-1824.https://doi.org/10.1002/mop.29920Link to publication on Research at Birmingham portalPublisher Rights Statement:This is the peer reviewed version of the following article: Fabrication tolerance and gain improvements of microstrip patch antenna atterahertz frequencies, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/mop.29920/full. This article may beused for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.General rightsUnless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or thecopyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposespermitted by law.•	Users may freely distribute the URL that is used to identify this publication.•	Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of privatestudy or non-commercial research.•	User may use extracts from the document in line with the concept of ‘fair dealing’ under the Copyright, Designs and Patents Act 1988 (?)•	Users may not further distribute the material nor use it for the purposes of commercial gain.Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document.When citing, please reference the published version.Take down policyWhile the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has beenuploaded in error or has been deemed to be commercially or otherwise sensitive.If you believe that this is the case for this document, please contact UBIRA@lists.bham.ac.uk providing details and we will remove access tothe work immediately and investigate.Download date: 01. Feb. 20191   Fabrication Tolerance and Gain Improvements of Microstrip Patch Antenna at Terahertz Frequencies M. S. Rabbani* and H. Ghafouri-Shiraz† School of Electronic Electrical and System Engineering University of Birmingham, 52 Pritchatts Road Edgbaston, B15 2TT, UK *saqibrabbani05@hotmail.com and †ghafourh@bham.ac.uk ABSRACT: In this paper, a technique has been proposed to design microstrip antenna arrays at terahertz (THz) frequencies with improved gain and fabrication tolerance. The antenna is designed at 100GHz frequency and fabricated with simple laboratory based PCB etching process. The gain is improved to 13.4dBi with the help of only three patch elements. The measured -10dB return loss bandwidth (BW) is 5.55% of the central frequency.  The measured and the simulation results are all in good agreement.  Key words: THz microstrip antenna, 100GHz antenna, terahertz antenna, THz array, THz antenna fabrication  1. INTRODUCTION Terahertz frequency spectrum (100GHz-10THz) is envisioned to be the essential host for future wireless services offering wide spectral bandwidth and fine resolution [1]. However, in order to attain an effective link budget for a THz wireless radio link, high gain antennas are vital to compensate the enormously high free space path loss [2]. Moreover, since the wavelength is very small (0.03mm-3mm) at THz frequencies hence, enlargement of the antenna’s size, which is a fraction of the operating wavelength, is crucial to reimburse the fabrication cost and tolerance [3]. Also, integrability of the antenna with the other THz components is another obligation to acquire the overall device compactness [4]. Amongst the 2   other contender, microstrip antenna is one of the attractive candidates for THz wireless systems because of its potential robustness to encounter the aforementioned constraints [5].  In the recent years, some work has been reported on THz microstrip antenna designs [3]-[9]. However, in the reported THz microstrip antennas, the patch and the associated dimensions are calculated based on the conventional design equations and the overall antenna structure remained far below than the ordinary PCB etching limit of µm 152  line width/gap [10]. Moreover, only the simulation based results have been presented and there is a lack of experimental measurements to support the design concepts. To the best of the authors’ knowledge, no particular work has been reported to improve the microstrip antenna size for THz frequencies in combination with the improved performance and ordinary fabrication and practical measurements.   In the present paper, we have demonstrated a procedure to design microstrip patch array at THz frequencies. The proposed method is verified by designing and testing a prototype at 100GHz frequency. The tested antennas’ attributes are compared with a microstrip patch antenna designed at 100GHz with the traditional method. The proposed antenna gain has enhanced to a few folds while the antenna size has considerably improved to satisfy the conventional PCB etching restrictions as mentioned earlier. The return loss (S11) is measured with the help of Anritsu’s 145GHz VNA Apparatus ‘ME7838D’ incorporated with MA25300A module. The far-field pattern was measured with Agilent Technologies’ 110GHz PNA Network Analyzer “E8361C” in combined with the extension module “N5260-60003”.  2. MICROSTRIP ANTENNA DESIGN PROCEDURE Conventional rectangular microstrip patch antenna is half-wavelength resonator in which the patch length and width determine the operating frequency and the antenna’s input impedance, respectively [10]. Traditionally, for the low microwave frequency designs, the width of the 3   patch is set to be comparatively equal to the patch length to keep the antenna size small and to avoid the excitation of unwanted resonance modes [10]. In this way, an ordinary patch antenna gives a high input impedance of above 200Ω which is matched with the standard 50Ω impedance, in one way, by employing an impedance transformer (IT) of over 100Ω microstrip transmission line (MTL). Such a high impedance MTL is usually wide enough to be etched on a dielectric material of above 0.5mm substrate thickness which is commonly used for low microwave frequencies. However, for THz microstrip antennas, a very thin dielectric material is required to satisfy the limit: )4(0 rh ελ< [11] where h  is substrate thickness, 0λ  is the wavelength in free space and rε  is relative dielectric constant of the substrate material. Etching of the aforementioned high impedance microstrip line on such a thin material is challenging because the line width falls far below the PCB etching limit of µm 152 [10]. In order to overcome this problem, we have reduced the overall antenna’s input impedance )( inZ  much lower than 50Ω (i) by extending the patch width beyond the ordinary size, and (ii) by making an array of multiple patches fed in series. The total input impedance of an array of ‘n’ identical patch elements appropriately fed in series is expressed as [10]:  nZZ pin =                       (1) where pZ  is the input impedance of the individual patch element. Subsequently, such a low antenna input impedance is matched with the standard 50Ω impedance through the corresponding microstrip line IT of low impedance which is wide enough to convince the conventional fabrication limits. The geometry of the proposed microstrip array is illustrated in Fig. 1. The array consists of three wide patches of the same size which are fed in series.  The patch width (W) and length (L) are calculated from the following expressions [12]:  4   ( )( )12120++=rMλWε                  (2) ( ) L∆-εNλLeff22120 +=            (3) where M and N are non-negative integers (in our present design we chose 1=M and 0=N ), rε and effε  are the relative and the effective dielectric constants, respectively, and L∆ is patch length extension due to the fringing filed effect [10]. The input impedance of the individual patch is given as [12]:  WZ p 081.59 λ=                     (4) By substituting Eq .(4) into Eq.(1), we can obtain the total array’s input impedance as: nWZin 081.59 λ=                    (5) Ultimately, ‘Zin’ is matched with the standard 50Ω impedance through the MTL used as quarter-wavelength impedance transformer. The characteristic impedance ‘Z0’ and the width ‘WT’ of the microstrip TL are given as [13]: inZZ 500 =                      (6) rT ZhWε099.376=                    (7) Substituting Eq. (5) into Eq. (6) and Eq. (6) into Eq. (7) give the following final expression for the width of the MTL in terms of the ‘W’ and ‘n’: 089.6 λε rTnWhW =               (8) Equation (8) explains the motive of increasing ‘n’ and ‘W’ to widen the transmission line width ‘ TW ’. Since the transmission lengths ‘LT1’ and ‘LT2’ provide impedance transformation 5   and phase matching on the patches, respectively, they can be computed by the following expressions [12]:  ( ) 4121 /λPLT +=                  (9) ( ) L∆/λQLT 22122 ++=      (10) where P and Q are non-negative integers (in our design we used P=1 and Q=0) and λ is the operating wavelength. The array’s final dimensions are acquired through the simulation based optimization process by using CST microwave studio.  3. RESULTS AND DISCUSSIONS For the comparison purpose, initially, a conventional single patch microstrip antenna is designed at 100GHz frequency on a low loss dielectric material ‘RT/Duroid5880’ with 2.2=rε  and substrate thickness µm127=h  based on the traditional method as described in the literature [10]. Figure 2 shows the structure of the patch antenna and its dimensions are given in Table I. From Table 1, it can be seen that the overall antenna size is quite small and the transmission line width ‘WT’ is µm100 which is far below the fabrication limit µm)152(  of the conventional cost-effective etching process. Figure 3 depicts the simulated return loss (S11) and far-field radiation patterns (FRP) of the designed patch antenna. Figure 3(a) indicates that the -10dB return loss BW is 6% whereas the antenna gain and efficiency at 100GHz are 7.56dBi and 66.7%, respectively. Subsequently, by using the proposed method as described in section II, a microstrip array of 3 patches is designed at 100GHz frequency on the same Duroid substrate as that used for the conventional antenna shown in Fig. 2. Table 2 shows the optimized dimensions of the array structure (see Fig. 1) where it is clear that all PCB dimensions are fabricable with the ordinary etching process. The fabricated prototype and the experimental set up are demonstrated in Fig. 4. A W-band flange launcher (also called 1-mm connector) is employed 6   to connect the antenna with the VNA module. The far-field radiation pattern is measured in the lab room assuming free space conditions considering negligible reflections from the surroundings because of the high signal attenuation (72.44dB/m) at 100GHz frequency.  Figure 5 shows the simulated and measured return loss and FRP of the 100GHz microstrip array designed using the proposed method. From Fig. 5 (a), it is clear that the minimum measured return loss is 17.97dB− at 99.27GHz and the simulated and measured BWs are 8.87 % and 5.55%, respectively. Both the simulated and measured antenna gains at the resonant frequency of 99.5GHz are, respectively, 13.4dB and 12.2dBi where the former is obtained by applying the two –identical antenna method explained in [14]. The antenna simulated efficiency is about 94%.  Figure 5(c) indicates that the main radiation beam is focused at around 00 in both planes. The simulated and measured 3dB beam widths in H planes are 40.20 and 48.280, respectively, and that in E plane is 26.10. Figure 6 shows the gain frequency plot of the designed antenna. The result shows that the gain is maximum at the resonant frequency of 99.5GHz and it remains above 11.5dB in the whole operating band (98GHz-103GHz). Table-3 compares, BW, gain and efficiencies of the two designed antennas (i.e. the conventional single patch antenna and the proposed 3-patch array). From Table 3 we can conclude that the performance of the proposed 3-patch array antenna is considerably enhanced as compared with the conventional patch antenna.  4. CONCLUSION A method has been developed to design THz microstrip antenna arrays with improved gain and geometrical dimensions to ease the fabrication reluctance when conventional PCB etching method is used. The design concept was verified through both simulation and measurement on a proposed 100GHz 3-patch array which was exited through a series feeding 7   networks. The overall antenna performance is enhanced as compared with the microstrip patch antenna designed using the conventional etching method.  In order to design microstrip antenna arrays at further higher THz frequencies, higher values of integers ‘M’, ‘N’, ‘P’ and ‘Q’ should be chosen in Eqs. (2) to (6) and (9) to (10) so that the antenna dimensions remain conventionally fabricable. However, much higher values of these constants may cause some unwanted resonances at undesired frequencies which may limit the antenna size extension and hence, the design frequency to go far beyond 1THz as discussed in [12].                   8   References: [1] K. Huang, and Z. Wang, Terahertz terabit wireless communication, Microwave  Magazine, IEEE 12, no. 4 (2011): 108-116. [2] F. I. Akyildiz, J. M. Jornet, and C. Han, Terahertz band: Next frontier for wireless  communications, Physical Communication 12 (2014): 16- 32. [3] K.R. Jha, G. Singh, Improved Performance Analysis of Square Patch Microstrip  Antenna at Terahertz Frequency, Advances in Recent Technologies in  Communication and Computing, 2009. ARTCom '09. International Conference on,  vol., no., pp.676, 679, 27-28 Oct. 2009 [4] E. Seok, C. Cao, D. Shim, D. J. Arenas, D. B. Tanner, and C. Hung, A 410GHz  CMOS push-push oscillator with an on-chip patch antenna. In Solid-State Circuits  Conference, 2008. ISSCC 2008. Digest of  Technical Papers. IEEE International, pp.  472-629. IEEE, 2008. [5] K.R. Jha, G. Singh, Terahertz planar antennas for future wireless communication: A  technical review. Infrared Physics & Technology  60 (2013): 71-80. [6] K.R. Jha, G. Singh, Terahertz planar antennas for future wireless communication: A  technical review. Infrared Physics & Technology 60 (2013): 71-80. [7] K. R. Jha, and G. Singh, Dual-band rectangular microstrip patch antenna at terahertz  frequency for surveillance system.  Journal of computational electronics 9, no. 1  (2010): 31-41. [8] M. Younssi, J. Achraf, M. H. Yaccoub, E-M. Ahmed El, and A. Noura, Study of a  Microstrip Antenna with and Without Superstrate for Terahertz Frequency,  International Journal of Innovation and Applied  Studies 2, no. 4 (2013): 369-371. 9   [9] G. Singh, Design considerations for rectangular microstrip patch antenna on  electromagnetic crystal substrate at terahertz frequency, Infrared Physics &  Technology 53, no. 1 (2010): 17-22.  [10]  R. Bancroft, (2009). Microstrip and printed antenna design [electronic resource].  Raleigh, NC, SciTech Pub. [11] James, J. R., and A. Henderson. High-frequency behaviour of  microstrip open- circuit terminations, IEE Journal on Microwaves, Optics and Acoustics 3, no. 5  (1979): 205-218. [12] M. S. Rabbani, and H. Ghafouri‐Shiraz, Size improvement of  rectangular microstrip  patch antenna at MM‐wave and terahertz frequencies, Microwave and Optical  Technology Letters 57, no. 11 (2015): 2585-2589. [13] G. Bianchi, and R. Sorrentino, Electronic filter simulation & design, New York:  McGraw-Hill, 2007. [14] McMaster University, Basic methods in Antenna Measurements, Online: accessed  on Oct. 26th, 2015 at: http://www.ece.mcmaster.ca/faculty/nikolova/antenna_dload/current_lectures/L08_Measure.pdf  

Fabrication tolerance and gain improvements of microstrip patch antenna at terahertz frequencies

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