|
1.INTRODUCTIONNowadays, one antenna should work in GSM, UMTS and LTE technologies. That is why it is required from telecommunication service providers to develop multi-range antennas. The antenna, which is an inseparable part of portable telecommunications devices, should be characterized by low weight, small size and wide bandwidth. In the practical design of mobile devices, antennas had limited space, especially a small thickness device like laptops, tablets, mobile phones and USB modems. Usually thickness is a range from 5 to 12 millimeters. Antennas, which are characterized by small size, low profile and the ability to work in many frequency bands are the planar antennas. The article presents the model of a dual-band LTE antenna operating on the 1800 MHz and 2600 MHz band and results of the impact of antenna dielectric thickness on selected parameters. LTE technology is revolutionizing the world by providing the fastest data transmission. It is a radical step forward for the wireless industry. The main goal of LTE is to provide a highly efficient, low latency and a safer service. This new system include OFDM (Orthogonal Frequency Division Multiplexing) to avoid interfering signals between symbols that typically limit the performance of high speed systems and MIMO (Multiple-Input Multiple-Output) techniques to increase speed data transmission. The designed and constructed antenna cover the 1.71-1.93 GHz frequency band for GSM 1800, GSM 1900 and 2.42 - 2.85 GHz for technology LTE 2500, LTE 2600. Using transmission line model, the initial antenna dimensions have been calculated. Flowingly by using optimization in CST Studio Suite environment, the presented parameters were obtained. Article presents parameters before and after changes of dielectric thickness and their comparison. The physical antenna was tested in the Electromagnetic Compatibility Laboratory of the Military University of Technology. The designed antenna model is a microstrip antenna operating in two bands used in Europe in the LTE standard, i.e. 1800 MHz and 2600 MHz1,4,5. The basic dimensions of the radiator of the microstrip antenna were calculated from the dependence (1) - width and (2) – length2,7. Where: The dimensions of the designed antenna were optimized by using the CST Studio Suite environment. Additionally, the main parameters for the selected dielectric thickness were calculated numbers. It should be in a one-column format. References are often noted in the text1 and cited at the end of the paper. 2.ANTENNAS CONSTRUCTIONIf the paper does not have the margins shown in Table 1, it will not upload properly. Fig. 1 shown construction of the dual-band antenna LTE. It is a microstrip antenna, powered by a microstrip line with a SMA female connector with 50 Ohm impedance. It was made on a FR-4 substrate from ROGERS CORPORATION with a size of 192 x 129 mm, dielectric thickness of t=1.5 mm and a relative permittivity єr = 4.6. The designed antenna was made practically and tested in the Electromagnetic Compatibility Laboratory of the Military University of Technology. Realized the antenna design presented in Figure 1, the assumptions presented in Table 1 were adopted. Table 1.Design assumptions.
3.SIMULATION RESULTSDuring change the thickness of the dielectric in CST Studio Suite environment the following parameters of designed antenna has been analyzed: S11 reflection coefficient, VSWR, input impedance and gain. 3.1S11 reflection coefficientFigure 2 presents the results obtained during computer simulation in the CST Studio Suite environment. As you can see, when the thickness of the dielectric increases, the width of the operating band decreases and the center frequencies shift towards the lower frequencies. In the case of reducing the dielectric thickness the situation is reversed – with the decreasing of the dielectric thickness, the operating band becomes wider, and the center frequencies shift towards higher frequencies. For the smallest thickness of the dielectric, i.e. t = 1 mm bandwidth f0 = 1.8 GHz increased from 196 MHz to 530 MHz, and for f0 = 2.6 GHz increased from 433 MHz to 800 MHz. Which means that the bands have almost doubled. While the center frequency shifted to the right sequentially from f0 = 1.8 GHz to f0≈1,9 GHz and from f0 = 2.6 GHz to f0≈2,9 GHz. For the largest thickness of the dielectric, i.e. t = 2 mm band was reduced from 223 MHz to 202 MHz, and for f0 = 2.6 GHz decreased from 433 MHz to 330 MHz. By contrast, the center frequencies shifted sequentially left from f0 = 1.8 GHz to f0≈1,7 GHz and from f0 = 2.6 GHz to f0≈2,5 GHz. Of course, the best results remain at the initial thickness of the dielectric, t = 1.5 mm. 3.2Input impedanceFigure 4 presents the results how the dielectric thickness influence on the input impedance obtained during computer simulation in the CST Studio Suite environment. When the thickness of the substrate decreases, the real part of the input impedance decreases. The best result for both ranges is for the initial thickness, i.e. t = 1.5 mm. However, for the center frequency f0 = 2.6 GHz beginning from the ground thickness t = 1.33 mm, the value of Rwe oscillates around 50 Ω. For the center frequency f0 = 1.8 GHz the best level of Rwe is for the initial thickness. This means that the antenna could be used for the center frequency f0 = 2.6 GHz with a higher dielectric thickness while for f0 = 1.8 GHz antenna would not work properly because of some noise and interference. For the imaginary part Zwe the situation is reversed. When thickness of the substrate decreases, the imaginary part of the input impedance grows, whereas with the increase of the dielectric thickness the imaginary part of the input impedance decreases. The best result for both ranges is for the output thickness, i.e. t = 1.5 mm. In this case, better level of Zwe is for frequency f0 = 1.8 GHz. From the ground thickness t = 1.5 mm, the value jXwe oscillates within 0 Ω. The best result is for the dielectric thickness t = 1.77 mm where the - jXwe = 0.95 Ω. For the frequency f0 = 2.6 GHz, the best values of jXwe oscillates around initial substrate thickness. To improve the antenna work on both frequencies when the dielectric thickness is changed, we can place a tuner to the power line, which will get a better matching. 3.3GainFigure 5 presents the results how the dielectric thickness influence on gain obtained during computer simulation in the CST Studio Suite environment. With the reduction of the thickness of the substrate, the gain decreases and with the increase of the dielectric thickness the gain grows. The lower frequency f0 = 1.8 GHz let to more noticeable this increase. The value of gain changed from G = 3.65 dB to G = 3.83 dB. In the case of the higher frequency f0 = 2.6 GHz, this change is smaller, however, there is also an increase from G = 4.27 dB to G = 4.33 dB. Therefore, with the increase of the dielectric thickness, the efficiency of the antenna grows. It means that most of the power supplied at its input terminals is converted into energy which is radiated into space with including its directional properties. 4.ANALYSIS OF PRACTICALLY OBTAINED RESULTSThe antenna designed and described in this article was physically made and research at the Faculty of Electronics of the Military University of Technology in the Laboratory of Electromagnetic Compatibility. The band obtained during computer simulations for VSWR<2 marginally differ from the results obtained during laboratory tests. Respectively for the range:
5.SUMMARY RESULTSReceived results physical antenna model research in the Electromagnetic Compatibility Laboratory slightly differ from those obtained during computer simulation in the CST Studio Suite environment. The laminate that was used to create the antenna was a substrate of the low quality. Choose of the substrate is very important on the stage of antenna design. For example we can find at ROGERS catalog materials, that the dielectric thickness tolerance for the majority of produced laminates is up to ± 7%, and for the FR-4 laminate family up to ± 15%.4,8 The antenna was designed in the CST Studio environment on the substrate FR - 4 with a dielectric constant εr = 4.6. The dielectric constant εr of most FR-4 laminate family can vary ±10% or more.8 The research the impact of antenna dielectric thickness on selected parameters showed that a change in thickness even of 0.1 mm causes a change in bandwidth, gain or impedance. The change in dielectric constant εr has a similar effect. The bands obtained in the laboratory almost completely overlap with the bands supported by LTE and GSM technology. Moreover the dielectric thickness significantly influence on selected antenna parameters. REFERENCESBugaj, J., Bugaj., M.,
“Analyze the impact of discretization on the structure of the simulation result,”
in PIERS Proceedings,
287
–291
(2015). Google Scholar
Balanis C.,
“Antenna Theory,”
4Wiley,2016). Google Scholar
Kubacki, R., Czyzewski, M., Laskowski, D.,
“Microstrip antennas based on fractal geometries for UWB application,”
in MIKON 2018 - 22nd International Microwave and Radar Conference,
352
–356 Google Scholar
Łata, K.,
“Analiza numeryczna wpływu grubości dielektryka na wybrane parametry i charakterystyki zaprojektowanej anteny LTE,”
Elektronika: konstrukcje, technologie, zastosowania, 59
(8),
(2018). Google Scholar
Kubacki, R., Lamari, S., Rudyk, K.,
“The microstrip antenna with periodic planar pattern,”
in 2016 Progress In Electromagnetics Research Symposium, PIERS 2016 - Proceedings,
1050
–1054
(2016). Google Scholar
Kelner, J.M., Ziolkowski, C., Nowosielski, L,
“Angular Dispersion Modelling for 5G Wireless Link with Directional Antennas,”
in 22nd International Conference Electronics, ELECTRONICS,
(2018). https://doi.org/10.1109/ELECTRONICS.2018.8443626 Google Scholar
Wnuk, M., Nowosielski, L.,
“Car microstrip GPS antenna,”
Progress in Electromagnetics Research Symposium 2017-November, 444
–448 Google Scholar
|