A Wideband Stacked Microstrip Patch Antenna for Telemetry Applications

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1 A Wideband Stacked Microstrip Patch Antenna for Telemetry Applications Item Type text; Proceedings Authors Hategekimana, Bayezi Publisher International Foundation for Telemetering Journal International Telemetering Conference Proceedings Rights Copyright held by the author; distribution rights International Foundation for Telemetering Download date 18/05/ :47:22 Link to Item

2 A WIDEBAND STACKED MICROSTRIP PATCH ANTENNA FOR TELEMETRY APPLICATIONS Bazeyi Hategekimana, Graduate Student Jeyasingh Nithianandam PhD, Advisor Electrical and Computer Engineering Department Morgan State University 5200 Perring Parkway, Baltimore, MD ABSTRACT This research article reports a design of a wide band multilayer microstrip patch antenna (MSPA). Positions of a coaxial probe feed to main patch of the multilayer MSPA, widths and lengths of main and parasitic patches, and height of a Rohacell foam layer in the multilayer MSPA were optimized to achieve desired performance in L-band. The work also reports a design of a two-by-two array of multilayer MSPA. We present results on antenna radiation patterns and return loss obtained with full wave finite element simulations with Ansoft HFSS software and measurements with a vector network analyzer. Key Words: Bandwidth, patch, multilayer, foam, array INTRODUCTION Microstrip patch antennas (MSPA) are small in size and have low profile and these advantages allow them to easily integrate in the body of aircrafts, missiles or other communication systems. They can be fabricated easily at low cost. Conventional microstrip patch antennas have small bandwidth of 1 to 2% around its resonant frequency. Narrow band response of microstrip patch antennas make them unsuitable for applications involving high bit data rate transfer. Our aim is to design a wide bandwidth microstrip patch antenna in the L-band that would be useful for high speed data transfer needed for aeronautical telemetry applications. In this work we present a design of parasitically coupled wideband patch antenna operating at a resonant frequency of 1.8GHz by modeling and simulation with Ansoft HFSS software. We also present a design of a microstrip feed network for a 2 x 2 array of wideband patch antennas with Ansoft Designer software. We performed a full wave finite element simulation of the 2 x 2 wideband antenna array with the feed network. We 1

3 present return loss as a function of frequency and radiation patterns of these antennas in this work. WIDEBAND MSPA DESIGN A schematic diagram of a multilayer microstrip patch antenna is shown in Figure 1. It has a main driven microstrip patch radiating element, a parasitic patch radiating element and a foam layer sandwiched between the two radiating elements. The patches are square in shape. The length of a side of the driven patch is half wavelength at resonant frequency. The length is computed by using expression (1). f r = resonant frequency c = speed of light in free space L = length of the patch ε eff = effective dielectric constant The presence of additional dielectric substrates above the main patch shown in figure 1 causes a shift of the operating frequency. An equivalent effective dielectric constant of the entire multilayer structure is needed to design wideband stacked patch antenna. Bernard and Toussignant utilized conformal mapping technique to obtain expressions for the effective dielectric constant ε eff and filling fractions for a microstrip transmission line in a multilayer structure [1]. We used expressions in their work and computed the dimensions of driven patch and parasitic patch in the multilayer antenna structure shown in figure 1. The correction factor ΔL in formula (1) was calculated using expressions from the work of Kirschning and coworkers [2]. Figure 1. A schematic diagram of a multilayer patch antenna Microstrip Square Patch Antenna The primary patch element is a square patch with sides equal to L. We used a coaxial probe to feed RF signal to the primary patch as shown in figure 1. The position Xp of the probe on the X-axis is calculated by using expression from reference [3]. The calculations 2

4 for the lengths of the patches, the probe position and effective dielectric constant were done using Matlab code. Multilayer Microstrip Patch Antenna The multilayer microstrip patch antenna resonating at 1.80GHz was designed and fabricated using RT Duroid 5880 substrate with a dielectric constant ε r = 2.2, a loss tangent tanδ = and height h 1 = 1.575mm. We placed a Rohacell foam of 10.5 mm height between the main patch substrate and the parasitic patch substrate. Rohacell foam has a dielectric constant ε r 1.05 and a low loss tangent tanδ < We performed our design calculations for the sizes of main patch and parasitic patch at 1.8 GHz. The square shaped patches have a value of 54 mm for the length of a side of the patches. The coaxial probe position was found to be Xp = 26mm. We found an effective dielectric constant for the dielectric multilayer structure to be ɛ eff = 2.1. We implemented the geometry of the multilayer stacked patch antenna in Ansoft HFSS software platform and it is shown in figure 2. We set boundary conditions, excitation port and frequency sweep parameters in the software. We performed full wave finite element electromagnetic calculations for the antenna. We fabricated the multilayer microstip patch antenna shown in figure 3. Figure2 Figure 3 Figure 2. A multilayer microstrip patch antenna (MSPA) design inside an air box shown as a wireframe in Ansoft HFSS. Figure 3. Picture of fabricated multilayer microstip patch antenna operating at 1.8GHz using Rogers RT-5880 Duroid. 3

5 Results and Discussion for the Multilayer MSPA Return Loss and Bandwidth The return loss of our antenna as a function of frequency obtained from HFSS simulations is shown in figure 4 and it is -40 db at a resonant frequency of 1.80GHz. The bandwidth is 138 MHz or 7.5%. We made return loss measurements on our antenna with an Anritsu vector network analyzer and the measured return loss is around -30dB with a bandwidth of 200MHz or 10.1% and it is shown in figure 4. Figure 4. A plot of simulated and measured return loss of the stacked patch antenna Input Impedance of Multilayer MSPA The multilayer microstrip patch antenna is designed to have a resonant input impedance of 50 Ohms at 1.80 GHz. The parasitic patch resonate at a frequency that is closer to main patch's resonant frequency of 1.80 GHz. The real and imaginary parts of the input impedance of multilayer MSPA that results from coupling between main and parasitic patches are shown in figure 5. Figure 5. Plot of the real and imaginary part of the input impedance of the antenna 4

6 Radiation Patterns of Multilayer MSPA The far field radiation patterns are simulated using Ansoft HFSS software. The electric field results are shown in figure 6 with E-plane (E θ ) for φ = 90 0 and φ = 0 0. The electric field component E φ results are displayed in figure 7 for φ = 90 0 and φ = phi = phi = Figure 6. Simulated electric filed component E θ pattern of MSPA phi = phi = Figure 7. Simulated electric field component E φ pattern of MSPA 5

7 P=toport P=toport W = mm P=toport W = mm W 1= mm W 2= mm W 3=4.8008mm W = mm P=toport W 1= mm W 2= mm W 3=4.8008mm W = mm P=toport A TWO-BY-TWO ARRAY OF MULTILAYER MSPA Design of a 2x2 Multilayer MSPA Array A 2x2 array is designed and the configuration of the array in Ansoft HFSS is shown in figure 8. The four radiating elements are made of multilayer stacked microstrip patch antennas operating at 1.8GHz. Each of the radiating element has a SMA coaxial connector feed at the bottom of main substrate. The main patches are square in shape with a side length of 55 mm. A parasitic patches are rectangular in shape of size 55 mm x 58mm. The spacing between the radiating elements is 111 mm or 0.667λo where λ O is free space wavelength of electromagnetic waves at 1.8 GHz. The elements of the array are excited by using an H-shaped microstrip feeding network that is designed with Ansoft Designer software. The microstrip feed network is in a separate RT Duroid 5880 substrate of thickness mm. In order to perform simulations of the two-by-two multilayer MSPA array with the H-shaped microstrip feed network, we established a dynamic link between the power divider in Ansoft Designer and the 2x2 Array in Ansoft HFSS and the co-simulation set up in Ansoft Designer is shown in figure 9. Figure 8. A 2x2 Array configuration in Ansoft HFSS. port1:1 port3:1 port2:1 port4:1 W1=1.3526mm W2=1.3526mm W3=4.8008mm 1 2 W=4.8008mm W= mm W=1.3526mm 3 W=1.3526mm W= mm W=4.8008mm P=sndbr P=midl P=midl P=sndbr PNUM=1 RZ=50ohm IZ=0ohm Figure 9. A co-simulation set up in Ansoft Designer for the 2 x 2 stacked patch array. 6

8 db(s(port1,port1)) Results and Discussion for a 2x2 Multilayer MSPA Array Return Loss The 2 x 2 array has a return loss of -35 db at 1.8GHz and it has 10.1% band width at a - 10 db return loss level. The bandwidth of the antenna array is 182 MHz. These results were obtained from figure F [GHz] Figure 10. A plot of return loss of a 2x2 array from co-simulation describe above. Radiation patterns Polar plots of electric field components of the 2 x 2 array of multilayer MSPA are shown in figure 11 and side lobes are visible in the E θ polar plots. E θ E φ phi= phi = phi=0 phi= Figure 11. Simulated E θ and E φ radiations pattern of a 2x2 array of multilayer MSPA. 7

9 CONCLUSION A multilayer microstrip patch antenna that has a wide band width in the L-band was designed by full wave finite element simulations with Ansoft HFSS. We used a low dielectric constant substrates for a main patch and a parasitic patch. We inserted a thick Rohacell foam between a parasitic patch and main patch and thus improved the bandwidth of microstrip patch antenna from 1.5% to 7.5%. We also designed a 2x2 array of multilayer MSPA with a microstrip feed network and the designs were completed by co-simulations with Ansoft Designer and Ansoft HFSS. The measured return loss for the a multilayer MSPA that we fabricated with our design is -30dB at 1.8 GHz. The simulated return loss for a multilayer 2x2 array is -35dB at 1.8 GHz. Future work involves a phased array where the H-shaped feed network will be replaced with an active phase shifter network to steer the beam. ACKNOWLEDGEMENT The authors would like to thank the Test Resource Management Center (TRMC) Test Capabilities Development (TCD) technical development of T & E Resource Contract number SR for support of this INET program research. The authors would like to thank COMSARE at Morgan state University for their assistance with measurements and Rogers Corporation for providing the dielectric substrates. REFERENCES [1] Jennifer, B.T and Carolyn, T.J, "Resonant Frequencies of Rectangular Microstrip Antennas with Flush and Spaced Dielectric Superstrates", IEEE Transactions on Antennas and Propagation, vol. 47, No. 2, 1999, pp [2] Manfred, K; Rolf, J.H; Koster, H.L, "Accurate model for open end effect of microstrip lines", Electronic Letters, vol.17, 1981, pp [3] Balanis, C.A, "Antenna Theory, Analysis and Design", 3 rd Ed. John Wiley & Sons, NY, 2005, pp [4] Ramesh, G; Prakash, B; Bahl, I.J; Ittipiboon, A, "Microstrip Antenna Design Handbook", Artech House Inc, Norwood MA, [5] Nasimuddin, K.P; Esselle,P; Verma, A.K, "Wideband Circularly Polarized Stacked Microstrip Antennas", IEEE Antennas and Wireless Propagation Letters, vol. 6,2007, pp [6] Wong, K.L, "Compact and Broadband Microstrip Antennas", John Wiley & Sons, NY,