Interdigital Bandpass Filter for MetSat Dian Widi Astuti1, Widie Sella Fahmi2, and Mudrik Alaydrus3 1, 2,3
Departement of Electrical Engineering, Universitas Mercu Buana
[email protected],
[email protected],
[email protected]
Abstract — One kinds of waveguide filter is interdigital filter, which uses a cylindrical rod shaped resonators alternately. In this research resulted in an interdigital waveguide filter by using 6 pieces resonator cylinders for satellite meteorology applications at frequencies 1.675 to 1.710 GHz. The simulation with HFSS shows an insertion loss value of 0 dB and return loss of 5.48 dB while the measurement result has an insertion loss value of 2 dB and return loss of 7 dB. Keyword — Interdigital filters, satellite meteorology, waveguide filter. ABSTRAK — Salah satu bentuk waveguide filter adalah interdigital filter, yang mempergunakan resonator berbentuk batang silinder berselang-seling. Pada penelitian ini menghasilkan suatu interdigital waveguide filter dengan mempergunakan 6 buah resonator silinder untuk aplikasi meteorology satelit di frekuensi 1,675 – 1,710 GHz. Pada simulasi dengan HFSS memperlihatkan nilai insertion loss sebesar 0 dB dan return loss sebesar 5,48 dB sedangkan pada hasil pengukuran memiliki nilai insertion loss sebesar 2 dB dan return loss sebesar 7 dB. Kata kunci — Interdigital filters, meteorology satellite, waveguide filter.
I. INTRODUCTION There are any kinds of waveguide filters such as metal insert filters, iris coupled filters, post filter, combline filters, interdigital filters, corrugated waveguide filters, waveguide stub filters, waffle-iron and ridge waveguide filters. In interdigital filters which uses a cylindrical rod shaped resonators alternately likes combline filters. Research of interdigital waveguide filters has begins from 1960’s which is has references in [1] and [2]. In the reference [1] is explained how to make an interdigital filter from lowpass filter which is consist of resonators formed by coupled-line elements that are λ/4 long midband, with alternate ends of coupled-line elements grounded, and the opposite end opencircuited. While in the reference [2] shown that the coupledline elements can make shorted than λ/4 midband provided that loading capacitance are added at the open-circuited element ends. Combining of two interdigital waveguide filters can be result a cavity diplexer as shown in [3]. Interdigital shape can also be implemented to microstrip substrate as bandpass filter as shown in [4], [5] and [6]. In the reference [4] is modifying interdigital coupling structure by using quarter and half-wave resonators alternately, and a narrowband bandpass filter operating at X-band has been designed proving the feasibility of the proposed structure. While in the reference [5] proposed a simple procedure for the designing wide-band interdigital bandpass filter and in the reference [6] presented a novel compact interdigital
bandpass filters which used multilayer stepped impedance resonators (SIRs)/folded quarter-wavelength resonators. But, there is quite a limited publication research from interdigital waveguide. Making a passive filter from microstip technology often has a value of insertion loss and return loss which is greater when it compared with waveguide technology. It happens because the wave propagation through the waveguide is more directional while it propagates through the microstip. In addition, the waveguide filter allows for setting the depth of the resonator so that the value of insertion loss, return loss and frequency shift work simulation results to the results of measurements can be arranged. II. BANDPASS FILTER SPECIFICATION The specification of bandpass filter is shown in Table 1. It was applied to the meteorological satellite (MetSat) services.
No. 1 2 3 4 5 6 7
Table 1. Bandpass filter design specification. Parameter Specification Center Frequency 1692.41 MHz Lower frequency 1675 MHz Upper frequency 1710 MHz Bandwidth 35 MHz Insertion loss 0.25 dB nominal Return loss ≥ 15 dB Impedance 50 ohm
III. PARAMETER STUDY OF INTERDIGITAL FILTERS STRUCTURE Interdigital filters structure is made from a cylindrical rod shaped resonators alternately. As shown in the Table 1 that the application of filter work on narrow-band. According to norrow-band interdigital struture from the reference [7], we use ANSYS HFSS to simulate parameter of: A. The number of Interdigital Waveguide Resonators We configure the number resonator of interdigital waveguide filters as shown in Figure 1.
We simulate with different box size of interdigital waveguide filter, while the distance between the resonator and the number of resonator is fixed. The x-axis value is fixed 50 mm, while the y-axis and the z-axis are different. The y-axis and z-axis is made to increase. The simulation result can be seen at Fig. 4. 10
Fig. 1: Sum resonators of interdigital filter (a) two resonators, (b) four resonators, (c) six resonators.
Computer simulation with ANSYS HFSS, gives the result as shown in Fig. 2. 10
Transmission and Reflection Factor in dB
0
-20 -30 -40 -50 S11 Y70 Z10 S21 Y70 Z10 S11 Y76 Z12 S21 Y76 Z12 S11 Y80 Z15 S21 Y80 Z15
-60 -70 -80
0
Transmission and Reflection Factor in dB
-10
-90
-10
2.5
2
1.5
1
Frequency in GHz -20
Fig. 4: The simulation result of differences in the box size of interdigital waveguide filters.
-30 -40 -50
S11 2 Resonators S21 2 Resonators S11 4 Resonators S21 4 Resonators S11 6 Resonators S21 6 Resonators
-60 -70 -80
1
1.5
2
2.5
Frequency in GHz
Fig. 2: The simulation result of differences in the number of resonator interdigital waveguide filters.
From Fig. 2, we can conclude that the greater number of interdigital resonator waveguide, the more wider bandwidth that is produced, and vice versa. Also visible is also the value of the insertion loss is less good for the amount of resonator is less than the sum resonator more.
From Fig. 4 we can conclude that the larger size of the interdigital waveguide box filter, it will be the more bandwidth is generated. It’s be proven from the results of the simulation the box size of interdigital waveguide filter with a long axis x = 50 mm, y = 70 mm and z = 10 mm has a norrow bandwidth, rather than the box size of interdigital waveguide filter have x = 50 mm, y = 80 mm and z = 15 mm. C. Depth Resonator At this stage we do simulations by changing the parameters of the depth of the resonator. While the number of interdigital resonator waveguide filters and the size of the box is fixed. The results of the simulation are shown in Fig. 5. 10
B. The Box Size
0
Transmission and Reflection Factor in dB
HFFS is a simulation tool based frequency electromagnetic waves in three dimensions. So the depiction design interdigital waveguide filter has an axis x, y and z. In this case x-axis is the depth, y-axis is the length while the zaxis is the height of the interdigital waveguide box filters. As more details are shown in Fig. 3.
-10 -20 -30 -40 S11 39mm S21 39mm S11 33mm S21 33mm S11 30mm S21 30mm
-50 -60 -70 -80
1
1.2
1.4
1.6
1.8 2 2.2 Frequency in GHz
2.4
2.6
2.8
3
Fig. 5: The simulation result of differences in the deep resonators of interdigital waveguide filters. Fig. 3: Three-dimensional design of interdigital waveguide filter.
IV. DESIGN AND MEASUREMENT OF INTERDIGITAL WAVEGUIDE BANDPASS FILTER Based on studies parameters of the number of resonators, the size and depth of the box, it is referred draft interdigital resonator waveguide filters by using 6 pieces resonator, ie box dimensions are x = 50 mm, y = 152.8 mm and z = 25 mm with a depth of resonators are 39 mm. The design is shown in Fig. 6.
(a)
0
Transmission and Reflection Factor in dB
Fig. 6 shows the resonator with a depth of 39 mm has a frequency range of 1.29 to 2.29 GHz so that its bandwidth is 1 GHz. While the resonator with a depth of 30 mm have a limit working frequency of 1.8 to 2.65 GHz, so it has a bandwidth of 850 MHz. Therefore it can be concluded that the deeper of the interdigital resonator waveguide filters, the more bandwidth is generated and limits the working frequency bandpass filter will decrease.
-10
-20
-30
-40
-50 S11 Simulation S21 Simulation S11 Measurement S21 Measurement
-60
-70
1
2
1.5 Frequency in Hz
2.5 9
x 10
Fig. 7: Simulation (dash line) and measurement (solid line) result.
VII. CONCLUSION In this research, we concluded in the form of a growing number of resonator will be the more bandwidth that is produced. The size of the waveguide box has an influence on the resulting bandwidth where if the size of the box is wider the greater than its will be the more bandwidth is produced. Depth resonator also has an influence on the working frequency shifting of the filter, where the shorter of depth resonators than the working frequency resonator will be shifted to the right or becomes greater frequency. But in general the filter of waveguide technology has better results when compared with microstrip technology because it has the insertion loss and return loss is small and can set the value. REFERENCES
(b) Fig. 6: (a) Schematic filter (all dimensions in mm) and (b) prototype of interdigital waveguide filter.
Fig. 7 shows the simulation (blue line) and measurements (red line) results from prototype interdigital waveguide filters. It can be seen that it has a shifting in the value of insertion loss from 0 dB to 2.88 dB as the same as for the return loss from 5.48 dB to 7 dB. The fabrication doesn’t show shifting frequency center, because the shifting is very small, at 5 MHz from 1.685 GHz to 1.68 GHz.
[1] George. L. Matthaei, “Interdigital Band-Pass Filters,” IRE Trans. PGMTT-10, pp 479-491, November 1962. [2] Lloyd A. Robinson, “Wideband Interdigital Filters With Capacitively Loaded Resonator,” G-MTT Symposium Digest, pp 33-337, May 1965. [3] D. Packiaraj, M Ramesh and A. T. Kalghatgi, “Cavity Diplexer Using Tapped Line Interdigital Filters,” Asian Pasific Microwave Conference Proceedings 2005, 4-7 December 2005. [4] J.-J. Ge & L.Jin, “A Modified Interdigital Coupling Structure for Narrow Bandpass Filters Design,” Electromagnetics Volume 35, pp 550-556, 2015. [5] Bratislav Milovanovic, Miodrag Gmitrovic, Vladan Stankovic and Sladjana Djordjevic, IEEE 6th Mediterranean Electrotecnical Conference, pp 138-141, 22-24 May 1991. [6] Jia-Min Wu, Tian Bai, Wen-Zhong Lu, Fei Liang and Bin Luo, “Novel Compac Interdigital Bandpass Filters with Multilayers Stepped Impedance Resonators/Folded QuarterWavelength Resonators” Key Engineering Material Vol. 547, pp 19-24, 2013. [7] B.F. Nicholson, “The Practical Design of Interdigital and Comb-Line Filters,” The Radio and Electronic Engineer Vol. 34, pp 39-52, July 1967.
