Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band

Transcription

1 ISS: Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band Asia Pacific University, Technology Park Malaysia, Bukit Jalil 5700, Kuala Lumpur, Malaysia Abstract: LMDS wireless technology is capable of handling high data rate and data volumes required for the recent mobile standards especially 5G. This paper presents the design and simulation based analysis of a Chebyshev band pass filter for LMDS band at a center frequency of GHz and bandwidth of GHz. The designed filter is tested on 5 different substrate materials which shows a good agreement with the theoretical results. Keywords: Microwave Filters, Chebyshev Filters, Bilinear Transformation, LMDS. 1. Introduction Local Multipoint Point Distribution Service (LMDS) can be defined as a broadband wireless service that primarily centered within the 28 GHz and operates on microwave frequencies range of 26 GHz to 30 GHz bands [1]. Also, it can be considered as point-to-multipoint communication system which provides two-way voice, data and Internet services by utilizing microwave communications. Unlike LTE, LMDS uses a 1.3 GHz wideband spectrum around frequency of 28 GHz, where it can provide a 1Gpbs data rate for each LMDS channel [2]. Band Pass Filters (BPF) are mostly used in wireless applications in the transmitter and receiver. In the transmitter side, the filter can be used to limit the bandwidth of the output signal in order to transmit the required data at the desired speed. In the receiver side, the band pass filter allows signals at a specified range of frequency to pass through, while eliminating or preventing the unwanted signals at different frequencies to pass through. Where Band pass Filter (BPF) has a good optimization for Signal-to-oise Ratio (SR) for a receiver. Chebyshev is a type of filter that can be used in many applications, but mostly is used in RF application where its ripple is not an issue. Chebyshev filter has shown a better performance in term of frequency response [3], but it has a smaller transition region at the expense of ripples in its pass band [4]. Microstrip coupled line has been chosen as it fulfills the requirements of the band pass filter design because it is well confined for large line width over the substrate height ratios, and it is suitable for elements with low characteristic impedance and radiation loss. Microstrip coupled lines is the most suitable and widely used technology in microwave applications due to its lower cost comparing with other transmission line and it is easy to implement and fabricate on PCB substrate materials, and it has a light weight. 2. Design Methodology Table 1 shows the filter specifications, where some of the specifications have been taken from the filter proposed for FM wireless applications [5], while the filter order has been calculated by using Bilinear transformation method [6] as showing below: 1

2 Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band Pass band frequency = 27.5 GHz Stop band frequency = GHZ Pass band attenuation = 0.5 db Stop band attenuation = 25 db Lower cutoff frequency = 27.5 GHZ Upper cutoff frequency = GHZ Bandwidth BW = = = GHz Center frequency = GHz = = K = = 27.5 / = A = = / = = = After rounding to the next higher level, 9 Therefore, the obtained filter order is 9 Table 1 Specifications of the desired filter Filter Specifications Target Value Center frequency ( ) GHz Bandwidth (BW) GHz Insertion loss ( ) > -2 db Return loss ( ) < -10 db Stop band attenuation 25 db Ripple 0.5 Characteristic Impedance 50 Ω Filter order 9 th Order After the filter order has been obtained, the relevant element values that are shown in Table 2 have to be used to calculate the even and odd impedances where the obtained values will be used during the simulation design. The equation of calculating the impedances and the element values table have been taken from Microwave Engineering book [7]. Table 2 Element values of 9 th order Chebyshev band pass filter with 0.5 ripple Fractional bandwidth = Hz Where n = 2,3,4,5, For even impedance: For odd impedance:

3 ISS: Table 3 shows the complete calculations for the characteristic, even and odd impedance values. Table 3 Even and odd impedance for the designed filter (Ω) (Ω) By using the even and odd characteristic impedance values that are shown in Table 3, the physical parameters of the coupled line filter can be obtained be using LinCalc tool in ADS. Figure 1 shows the schematic diagram of the designed Chebyshev filter, where it is coupled line band pass filter, therefore each output of one coupled line has been connected to the input of the next pair and so on, and microwave ports have been connected at the input and output side of the circuit. Figure 1: Microstrip schematic diagram of Chebyshev filter Figure 2: Equivalent circuit diagram of the designed BPF Figure 2 shows the equivalent circuit diagram of the obtained 9 th order band pass filter by using lumped element. However, the circuit diagram is not important in this design because micro strip parallel coupled line technology is used over lumped components. 3

4 Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band 3. Simulation Results Figure 3 shows the initial simulation result, where as it can be seen the frequency response of the insertion and return losses is not acceptable. Therefore, the optimization tool that has been provided by ADS can be used to achieve the target values. Figure 3: Insertion and return losses before optimization The insertion loss S (2,1) and return loss S (1,1) that have been obtained for the Chebyshev filter are illustrated in Fig. 4. Where the filter has been designed by using FR4 specifications that are shown in Table 4. Table 4: FR4 substrate specifications Conductor thickness (T) 0.15 mm Permittivity ( ) 4.8 Tangent loss (TanD) Material thickness (H) 1 mm Figure 4: The bandwidth of FR4 at 3dB

5 ISS: From Figure 4, it can be seen that the insertion loss has achieved its expected target with a value of 0.825dB at its maximum slope at a frequency of 30.1 GHz. Likewise, the return loss has also achieved its target value which is dB at its highest ripple at a frequency of 29.43GHz. On the other hand, the bandwidth that has been obtained at 3dB is 4.12 GHz which exceeded the target value by GHz as shown in Fig. 4, while the obtained center frequency is GHz which is almost close to the calculated value. While, Table 5 shows the obtained physical parameters after performing optimization to the design Table 5 Physical parameters of the designed filter on FR Figure 5 shows the frequency responses in term of insertion and return losses for the for the simulated Chebyshev filter on Duroid 6002, where in this substrate material, the dielectric constant has been set to be 2.94, with a thickness of mm. The obtained results showed that the insertion loss at its highest point is dB at a frequency of GHz where it is labelled as m1 in the figure. Additionally, the return loss has been found to be db at a frequency of GHz which is labelled as m4. The bandwidth has been calculated at 3 db which means that 3dB has been taken before m1 and after m1, where they are labelled as m2 and m3 respectively, and then m2 has been subtracted from m3, eventually the found value is 4.31 GHz, and the center frequency is GHz. Whereas, Table 6 shows the obtained physical parameters after performing optimization to the design. Fig. 5: Insertion and return losses for Duroid

6 Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band Table 6 Physical parameters of the designed filter on Duroid Figure 6: Insertion and return losses for Duroid 5870 Table 7 Physical parameters of the designed filter on Duroid

7 ISS: Figure 6 shows another test of the designed filter but this time by using a different substrate which is Duroid 5780, where the dielectric constant and the substrate thickness is 2.35 and 0.508mm respectively. The obtained insertion loss at maximum point is db at a frequency of GHz which is labelled as m1 in the graph, while the label m4 indicates to the highest value of return loss which is db at frequency of GHz. The bandwidth and center frequency found to be 4.43 GHz and GHz respectively. Whereas, Table 7 shows the obtained physical parameters after performing optimization to the design. Figure 7: Insertion and return losses for Duroid 5880 Figure 7 shows the results of testing the designed Chebyshev filter on Duroid 5880 substrate material. Label m1 indicates to the highest value of insertion loss which is db at a frequency of GHz. Whereas, m4 indicates to the maximum value of return loss which is db at a frequency of GHz. The obtained bandwidth is 4.21 GHz and the center frequency is GHz. Whereas, Table 8 shows the obtained physical parameters after performing optimization to the design. Table 8 Physical parameters of the designed filter on Duroid

8 Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band Fig. 8 Insertion and return losses for Duroid 6006 Figure 8 illustrates the obtained frequency response in terms of insertion and return losses from testing the Chebyshev filter in Duroid 6006 substrate material, where in this case, the dielectric constant that has been given is 6.15 and the substrate thickness is mm. The maximum value of the insertion loss has been labelled as m1 where the value is dB at a frequency of 28.8 GHz. Similarly, the obtained return loss has been labelled as m4 at its highest ripple at a value of db. The calculated bandwidth and center frequency at 3dB is 3.84 GHz and GHz respectively. Whereas, Table 9 shows the obtained physical parameters after performing optimization to the design. Table 9 Physical parameters of the designed filter on Duroid Figure 9 presents the frequency responses that have been obtained from using Duroid substrate material which has a dielectric constant of 10.2 and a thickness of mm. The obtained insertion loss at maxima point has been labelled by m1 which has a value of db at 29.85GHz frequency, and the return loss has been obtained to be db at its highest which is labelled by m4. The obtained bandwidth is 4.13 GHz and center frequency GHz. Whereas, Table 10 shows the obtained physical parameters after performing optimization to the design.

9 ISS: Figure 9 Insertion and return losses for Duroid Table 10 Physical parameters of the designed filter on Duroid Fig. 10 Insertion and return losses for Duroid

10 Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band The last test has been done by using Duroid 6202 PCB material that has a thickness of mm and a dielectric constant of 2.9. Therefore, the simulation results have given an insertion loss of db, and return loss of db and their highest points which have been labelled as m1 and m4 respectively as showing in Fig. 10. On the other hand, the bandwidth that has been obtained by the simulation is 4.15 GHz and the center frequency is GHz. Whereas, Table 11 shows the obtained physical parameters after performing optimization to the design. Table 11 Physical parameters of the designed filter on Duroid Comparative Analysis Figure 11 shows the combined obtained testing results for insertion loss. Where the filter has been testted on different substrate materials, such as Duroid 6002, Duroid 5870, Duroid 6006 and more. It can be seen that all the results are higher than -2dB, where the highest value has been obtained from Duroid 6002 which has been labeled by m1 at a value of db. While the lowest insertion loss has been obtained from Duroid 6006 at a value of db which has been labeled by m2. Moreover the other values are in between -1 db and -2 db. Additionally, from Fig. 6, it be realized that all the insertion loss frequemcy reponses are having the same shape with a little difference in the values. Figure 11: Frequency responses for insertion loss results

11 ISS: Figure 12 and Figure 13 show the combined test results for return losses. The results have been split into two graphs according to the similarity in the frequency response. Where in Fig. 12, the testing results of Duroid 5870, Duroid 6006, and Duroid almost have the same responses with around 2 ripples in the passband, and label m3 indicates the highest value which has been obtained from Duroid which is dB. Figure 12 Frequency responses for return loss results While in Figure 13, the frequency responses for Duroid 6202, FR4, Duroid 5880, and Duroid 6002 have been combined together where the highest point has been found at db for Duroid 6002 which has been labeled by m4. However, from Fig. 12 and Fig. 13 it can be agreed that the return loss test result for Duroid 5880 has the best frequency response. Figure 13: Frequency responses for return loss results Table 6 shows the discrepancies between the design specifications and the test results. From the table it can be seen that the bandwidth (BW) has exceeded the target value in all cases, where the closest value has been obtained from Duroid 6006 with a difference of 115 MHz compared with target value. Whereas, the 11

12 Design and Simulative Analysis of Chebyshev Band Pass Filter For LMDS Band center frequency has been achieved from testing the filter on Duroid 5870 substrate material which gives a value of GHz, moreover, FR4 and Duroid have almost achieved it with a difference between the simulated and target values of 28 MHz and 7 MHz respectively. While the other simulation test values are far from the target value, such as Duroid where it exceeds the target value by 243 MHz. On the other hand, the insertion loss has been achieved in all simulation tests where the maximum value has been obtained from Druoid 6002 which is db, and the lowest one is db from Duroid 6006 which is still higher than the specified value -2 db. Similarly, the return loss has been achieved in all cases, where the closest value to the design specification is db which has been obtained from Druoid 6006, and the minimum one has been obtained from testing the filter on Duroid 5880 which gives a value of db. Overall, Duroid 5870 has met all the design specifications, and it is the most suitable one to be used for fabrication. However, Duroid 5880 is also a suitable material to be used for fabrication if the design required low power loss, since it has given an insertion loss of db Table 12 Comparison between target and simulation results part Parameters Simulation Results Design Duroid Duroid Duroid Duroid Duroid Duroid specifications FR BW GHz GHz db > db < Fig. 14 Chebyshev bandpass filter layout Figure 14 shows the 3D layout of the designed filter on FR4 PCB material, which can be used as reference during the fabrication. 5. Conclusion It can be concluded that the proposed filter for LMDS band has been successfully designed, simulated, tested and analyzed on different material. Appropriate choice of the material can be done based on the application and cost. The simulation shows a good match with the desired design. However, further enhancement can be carried out for this project such as to increase the physical space between two

13 ISS: microwave pairs, and that can be done by doing tuning or additional optimization, because the physical space between two microwave pairs was one of the reasons for not fabricating the simulated filter, where the obtained physical parameters were too small, and the values were in term of micrometer, which makes the fabrication process too difficult at these aspects. Thus, by doing that enhancement, the simulated filter can be fabricated and hence, the fabrication and simulation performances can be compared, which leads to further analysis to enhance the designed filter. References [1] J. Kshirsagar and A. Kachole, Local Multipoint Distribution System (LMDS) Definition Int. J. Emerg. Technol. Adv. Eng., vol. 3, no. 4, pp. 1 28, [2] Z. Pi, J. Choi, and R. Heath, Millimeter-wave gigabit broadband evolution toward 5G: Fixed access and backhaul, IEEE Commun. Mag., vol. 54, no. 4, pp , [3] S. Duraikannan and M. A. Salum, Design Optimization for Diminution of GHZ Chebyshev Bandpass Filter, 2013 IEEE Int. Conf. Circuits Syst., pp , [4] M. A. Thilagavathi and A. Beno, Design of Butterworth Bandpass Filter for Broadband Wireless Onchip Receiver, J. Recent Res. Appl. Stud., vol. 2, no. 12, pp , [5] S. Seghier,. Benahmed, F. T. Bendimerad, and. Benabdallah, Design of parallel coupled microstrip bandpass filter for FM Wireless applications, in th International Conference on Sciences of Electronics, Technologies of Information and Telecommunications (SETIT), 2012, vol. 2, no. 1, pp [6] L. Tan and J. Jiang, Digital Signal Processing, 2nd ed. Oxford, USA: Academic Press, [7] D. M. Pozar, Microwave Engineering, 4th ed. Phoenix, AZ, USA: JohnWiley &Sons, Inc.,