An overview of Broadband and Miniaturization Techniques of Microstrip Patch Antenna Tej Raj Assistant Professor DBIT Dehradun, Himanshu Saini Assistant Professor DBIT Dehradun, Arjun Singh Assistant Professor DBIT Dehradun Abstract In present wireless communication devices are getting smaller in size but the operation is held by such devices are needed much greater bandwidth. Microstrip antennas are smaller in size but having drawback of low bandwidth and low efficiency. Literature shows that the leading work on MSA is focused on designing compact sized broadband MSA. Last few years many miniaturization and bandwidth enhancement techniques have been developed. In this paper broad banding and miniaturization techniques of MSA have been studied and comparative analysis is done. Index Terms MSA Microstrip Patch Antenna I. INTRODUCTION Microstrip patch antenna becomes most attractive antenna design today because of many commercial applications such as cellular mobile communication and satellite communication etc. But MSA suffers from many of drawback like low impedance bandwidth, low gain low efficiency. The numerous advantages of MSA, such as its low weight, small volume, and ease of fabrication using printed-circuit technology, led to the design of several configurations for various applications [1 5]. With increasing requirements for personal and mobile communications, the demand for smaller and low-profile antennas has brought the MSA to the forefront. An MSA in its simplest form consists of a radiating patch on one side of a dielectric substrate and a ground plane on the other side. Other shapes, such as the square, circular, triangular, semicircular, sectoral, and annular ring shapes are also used. Radiation from the MSA can occur from the fringing fields between the periphery of the patch and the ground plane. The length L of the rectangular patch for the fundamental TM10 mode excitation is slightly smaller than λ/2. 2. BROADBAND TECHNIQUES OF MSA 2.1 Multilayer or Stacked Patch Broadband MSA Multilayer structure MSA more than one patch is stacked on substrate of different layer. The overall height of the antenna is increased but size in planner direction is remaining constant. Two coupling techniques are commonly used in layered structure 1. Electromagnetic coupled MSA 2. Aperture coupled MSA [6]. Using multilayer structure yield impedance bandwidth of 114% [7] has been achieved. In [7] MSA has implemented using patch and parasitic radiating element on a stacked FR4 substrate. Parasitic patches are optimized to produce two resonances within central location of frequency band 3-11 GHz. Figure 1 shows the geometry of antenna. In this structure the additional c- 73
slot is introduced in ground plane and then optimized with E-slot on the parasitic patch which enhances the bandwidth more. Antenna gain is about 12dB is obtained at center frequency 7 GHZ. There are two types of electromagnetically coupled MSA shown in fig. 2(a) and 2(b) bottom patch is fed with coaxial cable and upper patch is excited due to coupling. Patches can be fabricated on a different substrate and air gap is also introduced between the layers. FIGURE 1: PROPOSED GEOMETRY OF STACKED PATCH ANTENNA [7] With the use of layered structure the parasitic patches are optimized to obtain the broad bandwidth [7-14]. The effect of the length of upper patch and lower patch in the stacked configuration is very important to remain the VSWR=2 circle. For wide bandwidth and gain requirement the value of air gap is chosen accordingly. For different value of Δ (air gap) bandwidth is increase and decrease given in [15]. Another techniques to enhance the Microstrip antenna is aperture coupled MSA which yield a bandwidth of 70 %given in [16]. ACMSA consist of two substrate separated by a ground plane and an aperture is cut in the ground plane that Electromagnetically coupled the upper patch with the Microstrip line feed on the lower substrate. Aperture is cut in the ground plane at the centre location of the patch to provide the maximum coupling and symmetrical radiation pattern. Advantages of such configuration are that patch is fabricated on the top patch that enhances the BW and feed line is at the lower substrate that reduces the radiation losses. Figure 2(a) electromagnetically coupled MSA normal geometry 2(b) Inverted geometry Another techniques to enhance the Microstrip antenna is aperture coupled MSA which yield a bandwidth of 70 %given in [17]. ACMSA consist of two substrate separated by a ground plane and an aperture is cut in the ground plane that Electromagnetically coupled the upper patch with the Microstrip line feed on the lower substrate. Aperture is cut in the ground plane at the centre location 74
of the patch to provide the maximum coupling and symmetrical radiation pattern. Advantages of such configuration are that patch is fabricated on the top patch that enhances the BW and feed line is at the lower substrate that reduces the radiation losses. The performance of ACMSA depends on the various parameters like aperture dimensions patch dimensions and feed network and thickness of the substrate. Geometry of ACMSA is shown in figure 3. In [18] a ACMSA is analyzed for various parameter. Aperture dimensions are plays an important role. If the slot is large then the more coupling that leads to increase the input impedance but slot length is small then the coupling is less that leads to less input impedance. Therefore to get resistive impedance, slot dimensions are optimized to get desired results. Except the aperture dimensions, location of aperture length and width of patch are discussed and analyzed in the [18-20]. 2.2 Slot Loaded Techniques : Figure 3: ACMSA: (a) exploded and (b) top views. U slot: U slot retains the size of an antenna and no parasitic elements are involved. U slot enhances the bandwidth since it compensates for the capacitive effect introduced by the use of coaxial probe feed. Due to merging of resonant frequencies, impedance bandwidth is increased [21]. Slots are embedded in the printed patch. Their dimensions and positions are properly selected in order to the first two broadside-radiation modes of the patch be perturbed such that their resonance frequencies get close to each other to form a wide impedance bandwidth.slots cut into the patch are of different types e.g. commonly used slot are u-slot, E-slot H-Slot etc. shown in figure 4. Figure 4: U shaped Microstrip Patch Antenna [21] 75
2.3 L probe feed: L probe feeding technique is used to increase impedance bandwidth. Any inductive effect introduced by probe itself is compensated by the bend, which adds capacitance to antenna design. The feed is simple L shaped bend probe. The L probe is excellent when applied with patch height of 0.01 λo. Figure 5: (a) Top view: Single probe fed square patch antenna with L probe (b) Side view: Patch with substrate thickness H and L probe feeding [22]. 3. Miniaturizations Techniques: 3.1 Shorting Pin A metallic shorting pin or via could be created to achieve minimization [22]. The radius of shorting pin and its location greatly influences the antenna output. Feed and shorting point location is optimized for better results. In this antenna design, shorting pin is used to minimize the area of square patch. The antenna design is presented in Figure 6. The square patch is fed with single coaxial probe of diameter 1 mm. Shorting pin is applied along the line of symmetry. Along this line, electric field is zero. The shorting pin is placed so as to short the metallic patch and ground plane and is positioned opposite to feeding point. If placed along the same side, the antenna does not perform well. The shorting pin position, feed position and patch dimensions are optimized. Figure 6: Top view of single probe fed square patch antenna with shorting pin [22]. 76
3.2 Shorting Wall Shorting wall is used to reduce the size of patch antenna. The radiating edge of patch antenna is folded to short with ground plane. Since the electric field is zero along the symmetry line of patch antenna, the antenna can be folded along it, thus resulting in minimization. The antenna design in this section deals with reducing the area of square patch antenna. The antenna design is shown in Figure 7. The antenna is shorted to ground plane using metallic patch between ground and radiating edge. Figure 7: Side view of single probe fed square patch antenna with shorting wall [22]. 4. CONCLUSION Narrow bandwidth is always a constraint on MSA. So different broadband techniques are used to enhance it. In this paper some of these techniques are reviewed and discussed. Out of all techniques Multilayer structure yields a maximum bandwidth. But it also increases the size of antenna as well due to more than one patch. Also slot loaded techniques and L probe feed are provides the bandwidth enhancement up to 30% and 40% respectively which has an advantage of size of antenna is remain small. Using shorting pin and shorting wall reduces the size of antenna significantly at the expense of bandwidth REFERENCES [1] Bahl, I. J., and P. Bhartia, Microstrip Antennas, Dedham, MA: Artech House, 1980. [2] Carver, K. R., and J. W. Mink, Microstrip Patch Antenna Technology, IEEE Trans. Antennas Propagation, Vol. AP-29, January 1981, pp. 2 24. [3] Mailloux, R. J., et al., Microstrip Array Technology, IEEE Trans. Antennas Propagation, Vol. AP-29, January 1981, pp. 25 37. [4] James, J. R., et al., Some Recent Development in Microstrip Antenna Design, IEEE Trans. Antennas Propagation, Vol. AP-29, January 1981, pp. 124 128. [5] James, J. R., and P. S. Hall, Handbook of Microstrip Antennas, Vol. 1, London: Peter Peregrinus Ltd., 1989. [6] Girish Kumar and K.P. Ray, Broadband microstrip antennas, Artech House antennas and propagation library, page number: 14, 89-90, ISBN 1-58053-244-6, 2003. [7]Sharif I.Mitu Sheikh, W. Abu-Al-Saud, and A. B.Numan Directive Stacked Patch Antenna for UWB Applications Hindawi Publishing Corporation International Journal of Antennas and Propagation Volume 2013, Article ID 389571, 6 pages http://dx.doi.org/10.1155/2013/389571. [8] James, J. R., and P. S. Hall, Handbook of Microstrip Antennas, Vol. 1, London: Peter Peregrinus, Ltd., 1989. 77
[9] Gupta, K. C, and A. Bennella, Microstrip Antennas Theory and Design, Norwood, MA: Artech House, 1988. [10] Pozar, D. M., and D. H. Schaubert, Microstrip Antennas: The Analysis and Design of Microstrip Antennas and Arrays, New York: IEEE Press, 1995. [11] Sainati, R. A., CAD of Microstrip Antennas for Wireless Applications, Norwood, MA: Artech House, 1996. [12] Lee, H. F., and W. Chen, Advances in Microstrip and Printed Antennas, New York: John Wiley & Sons, Inc., 1997. [13] Damiano, J. P., J. Bennegueouche, and A. Papiernik, Study of Multilayer Antennas with Radiating Elements of Various Geometry, Proc. IEE, Microwaves, Antennas Propagation, Pt. H, Vol. 137, No. 3, 1990, pp. 163 170. [14] Sabban, A. A New Broadband Stacked Two Layer Microstrip Antenna, IEEE AP-S Int. Symp. Digest, June 1983, pp. 63 66. Lee, R. Q., and K. F. Lee, Experimental Study of the Two-Layer Electromagnetically. [15] Coupled Rectangular Patch Antenna," IEEE Trans. Antennas Propagation, Vol. AP-38, August 1990, pp. 1298 1302. [16] Pozar, D. M., Microstrip Antenna Aperture Coupled to a Microstrip Line, Electronics Letters, Vol. 21, No. 2, 1985, pp. 49 50. [17] Sullivan, P. L., and D. H. Schaubert, Analysis of an Aperture-Coupled Microstrip Antenna, IEEE Trans. Antennas Propagation, Vol. AP-34, No. 8, 1986, pp. 977 984. [18] El Yazidi, M., M. Himdi, and J. P. Daniel, Transmission Line Analysis of Nonlinear Slot- Coupled Microstrip Antennas,Electronics Letters, Vol. 28, 1992, pp. 1406 1408. [19] Pozar, D. M., and S. D. Targonski, Improved Coupling for Aperture Coupled Microstrip Antennas, Electronics Letters, Vol. 27, No. 13, June 1991, pp. 1129 1131. [20] Rathi, V., G. Kumar, and K. P. Ray, Improved Coupling for Aperture Coupled Microstrip Antennas, IEEE Trans. Antennas Propagation, Vol. AP-44, No. 8, 1996,pp. 1196 1198. [21 ]Brajlata Chauhan Assistant Professor DIT University and Tej Raj M. Tech Scholar DIT University, Dehradun Review and Survey of Broadband Techniques of Microstrip Patch Antenna [22]Sanjeev Kumar Sharma and Munish Rattan Analysis of Broad Banding and Minimization Techniques for Square Patch Antenna IETE journal of research vol 56 issue 2 mar-apr 2010. 78