диафрагмированные волноводные фильтры / 201eab41-7127-4480-b776-d7a9624de251

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Waveguide Bandpass Filter with Easily Adjustable Transmission

Zeros and 3–dB Bandwidth

1Amit Bage, 2Sushrut Das, 3Lakhindar Murmu, 4Udayabhaskar Pattapu and 5Sonika Biswal

1,2,4,5 Department of Electronics Engineering, Indian Institute of Technology (Indian School of Mines) Dhanbad, 826004, Jharkhand, India

3Department of Electronic and Communication Engineering, VNR Vignana Jyothi Institute of Engineering and Technology, Hyderabad, Telangana, 500090, India

Amit Bage: - bageism@gmail.com, Sushrut Das:- sushrut das@yahoo.com, Lakhindar Murmu:- lakhindar.kgec25@gmail.com, Udayabhaskar Pattapu: uday.pattapu@gmail.comand Sonika Biswal:- sonika.priyadarsini8@gmail.com

Corresponding Author: Amit Bage

Email ID: bageism@gmail.com

Technical University Jalandhar, India, in 2012. He is currently pursuing his Ph.D. in the Department of Electronics Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, India. In his area of specialization, he is interested in

Electromagnetics and his recent research activities have focused on waveguide filters. He is a member of IEEE and Associate Member of IETE.

Sushrut Das received B.Sc. degree in 1999 from the department of Physics, Ramakrishna Mission Vidyamandira, West Bengal, India. He received M.Sc. degree in Physics with specialization in Electronics from the Department of Physics, Banaras Hindu University in 2001. After completion of Master of Science degree he joined Burdwan University and completed M.Tech in

microwave in 2003 from the Department of Physics. He worked towards his doctoral degree till January, 2007 in the department of Electronics and Electrical

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Communication Engineering, Indian Institute of Technology, Kharagpur, India. He joined Indian School of Mines, Dhanbad, Jharkhand, India in 2007 where he is currently an Assistant Professor in the Department of Electronics Engineering. He has authored one book, Microwave Engineering (Oxford University press, 2014) and published several research papers in referred International Journals. He has received URSI (International Union of Radio Science) Young Scientist Award in Istanbul, Turkey. He is carrying out two sponsored research project as Principal Investigator. His research interest includes Microwave Antennas, Microwave passive structures, Wireless energy

Lakhindar Murmu received his B.Tech degree in electronics and communication engineering from West Bengal University of Technology, India in 2009, master of engineering degree in electronics and telecommunication engineering from Bengal Engineering and Science Engineering, Shibpur, India in 2011, and PhD degree from IIT (ISM), Dhanbad, Indian in 2017. Presently, he is Assistant Professor in the Department of Electronics and Communication Engineering, VNR Vignana Jyothi Institute of

Engineering and Technology, Hyderabad, India. In his area of specialization, he is interested in electromagnetics and his recent research interest has focused on the novel microstrip circuits design for RF and microwave communication.

AcceptedUdayabhaskar Pattapu

born in Kothapatnam (Andhrapradesh),

India. He received his M.Tech in Electronics and Communication

Engineering from Acharya Nagarjuna University Andhra pradesh,

India, in 2009. He is currently pursuing his Ph.D. as Senior

Research Fellow in Department of Electronics Engineering from

IIT (Indian School of Mines) Dhanbad, India. He served as Junior

Research Fellow in the Department of Electronics Engineering, IIT

(Indian School of Mines) Dhanbad, India, during 2014 to 2016. His research interests include Rectenna Design System for Wireless Energy Transfer/ Harvesting.

Mrs. Sonika Priyadarsini Biswal received her M.Tech in Electronics and Communication Engineering from Institute of Technical Education and Research, Bhubaneswar, India, in 2014 and B. Tech in Electronics and Telecommunication from College Of engineering Bhubaneswar, India, in 2012. She is currently pursuing his Ph.D. in the Department of Electronics Engineering, Indian Institute of Technology (ISM), Dhanbad, India. In her area of specialization, she is interested in Microwave Antennas and her recent research activities have

focused on MIMO antenna design. She is a student member of IEEE.

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Waveguide Bandpass Filterwith Easily Adjustable Transmission

Zerosand 3–dB Bandwidth

This paper presents a compact waveguide bandpass filter with adjustable transmission zeros (TZs) and bandwidth. The design provides the flexibility to

additional asymmetrical slot structures have been used with each of the above

place the TZs at the desired locations for better interference rejection. To demonstrate, initially a three pole Manuscriptbandpass filter has been designed by placing three single slot resonator structures inside a WR–90 waveguide. Next, two

resonators to generate two TZs, one on each side of the passband. Since three resonators were used, this process results in six asymmetric slot structures those results in six TZs. The final filter operates at 9.98 GHz with a 3–dB bandwidth of 1.02 GHz and TZs at 8.23/ 8.70/ 9.16/ 10.9/ 11.6 and 13.115 GHz. Equivalent circuits and necessary design equations have been provided. To validate the simulation, the proposed filter has been fabricated and measured. The measured data show good agreement with simulated data.

Keywords: 3-dB Bandwidth; Bandpass Filter; Slots; Transmission Zeros (TZs);

Waveguide.

Accepted1. Introduction

Waveguide bandpass filters play an important role in modern communication, radar, radiolocation and radio navigation systems by virtue of their numerous advantages. Due to this several waveguide bandpass filters have been proposed using complementary split ring resonator [1–2] and fractal irises [3–4], in recent times. The slot based cavity structure are also be used to design a bandstop filter and bandpass filter [5–10]. However the stopband performances of these filters are poor and therefore these filters are easily affected by out of band interfering signals. To reduce out of band interference, these filters should have very sharp cutoff skirt frequency response, which can be achieved by introducing a number of TZs on both sides of the passband. As the frequency of the interfering signals may vary case to case, the placement of these TZs should also be flexible and should be independently controlled without affecting the centre frequency and bandwidth. However, the independent control of these TZs is a challenging task.

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In practice there are different techniques that have been developed to control the TZs, for example, use of cross coupled resonator network [11], inline TM110 mode filter with TE10 mode bypass coupling [12], source load coupling to introduce multiple coupling paths between the input output port [13], dual mode or multimode cavities [14], higher order modes excitation in inductive window [15], frequency dependent techniques [16], cascading a group of cavity or nodes [17] etc. In [18–20], miniaturizations as well as

TZs were achieved. Inline extracted pole with non resonating nodes (NRN) is also a

controlled whereas by varying the dimensionsManuscriptof the slot resonator, bandwidth and center frequency can be controlled. Both these controls are independent to each other.

solution for forming TZs with wide stop band [21]. Ohira et. al., proposed frequency

selective surfaces (FSS) based waveguide bandpass filter which shows full transmission

(passband) and full reflection (stopband) [22–24]. Although these types of waveguide

filters can provide improved selectivity and low insertion loss performance, they suffer from design complexity, and high fabrication cost.

This paper presents an approach to design a waveguide bandpass filter with easily

adjustable transmission zeros, centre frequency and bandwidth. A pair of asymmetric

slot structures has been used with a slot resonator to insert TZs at both sides of the pass

band. It has been shown that by varying the asymmetric slot lengths, the TZs can be

2.Slot Resonator Analysis and Introduction of Transmission Zeros

The schematic diagram of the slot resonator structure is shown in Figure 1. (a).The dimensions of the resonator have been optimized so that it resonates at 10.09 GHz. The resonator has been designed on ROGER RO 4350 substrate with relative permittivity 3.66, dielectric loss tangent ( δ ) 0.004, substrate thickness 0.762 mm, and copper thickness 0.035 mm. To study the resonance property the structure has been placed on the transverse plane of a WR-90 waveguide, as shown at Figure 1 (b), and simulated using high frequency structure simulator (HFSS Version 14). The equivalent circuit of

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(a) (b)

Figure 1.Schematic diagra m of the (a) slot reson ator struct re (L = 10.7 mm and W =

para meters can be obtained using the relations provided in [ 25]. The comparisons of the

freq ency and b andwidth, parametric analysis of the slot structure has been carried out

whe n the slot idth (W) aries, the bandwidth changes but centre fr equency re mains almo st constant whereas w hen the slo t length (L) varies, the centre frequency changes but b andwidth remains alm ost consta nt. Therefo e by adjusting the “L” and “W” target

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centre frequency with the desired bandwidth can be achieved. The unloaded quality factor of the slot resonator is 295.50.

Figure 3. Variation of bandwidth and center frequency with variation of slot width (W) and slot length (L).

Based on the above properties of the resonating slot, a 3rd order Chebyshev bandpass filter has been designed with lower cut–off frequency (fL ) 9.50 GHz, higher cut-off frequency (fH ) 10.73 GHz, centre frequency (f0 ) 10.09 GHz and passband ripple 0.17 dB. The corresponding BPF lumped element values, after impedance and

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lumped element circuit model of the BPF consists of two series resonators (with inductances LS (Ls = L1' .L'3 )and capacitances CS (Cs = C1'.C3' )) at both end and a parallel resonator (of inductance LP (LP = L'2 ) and capacitance CP (CP = C2' )) at the center. The

presence of both series and parallel resonators makes the fabrication of the filter complicated. Therefore to simplify it, the series resonators have been converted into

parallel resonators, with the help of inverters [26]. To further simplify the fabrication, the inductance and capacitance values of the converted parallel resonators have been made equal to LP and CP, respectively. This requires the value of impedance inverter to be [26]:

The equivalent circuit of the filter is shown in Figure 4 (a), whereas the 3D model of the filter is shown in Figure 4 (b).

Figure 4. Schematic diagram of the filter (a) lumped element equivalent model, and (b) 3D model.

To validate the analysis the frequency responses of the circuits, shown in Figure 4 (a) and (b), are plotted and compared in Figure 5. The figure shows good agreement between them.

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Figure 5. Frequency responses of the circuitsManuscriptin Figure 4. (a) and 4 (b).

The frequency response of Figure 5 shows a poor passband to stopband transition

and poor stopband characteristics. To improve them two additional asymmetric slots

have been used with the resonator, as shown in Figure 6 (a). The proposed resonator

structure, as before, has been placed on the transverse plane of a WR-90 waveguide

(Figure 6 (b)) and has been simulated using Ansoft HFSS.The simulated frequency

response of the modified unit cell (Figure 6 (b)) are plotted and compared with

frequency response of the single slot unit cell (Figure 1 (b)) in Figure 7. The figure Acceptedreveals that the centre frequencies of both the structures are same, i.e., the additional

asymmetric slot structures have no effect on centre frequency. However they introduce two TZs, above and below the passband. The unloaded quality factor of the three slot resonator is 310.67.

(a) (b)

Figure 6. Schematic diagram of the (a) asymmetric slot loaded resonator structure with its dimensions: (Slot 1): LRS = 10.6 mm, WRS = 1 mm, (Slot 2): LAS1 = 7 mm, WAS1 = 1 mm, (Slot 3): LAS2 = 15.4 mm, WAS2 = 1 mm, and (b) placement of the modified resonator inside a WR-90 waveguide.

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Figure 7. Comparison of the frequency responses of the circuits in Figure 1 (b) and Figure 6 (b).

The equivalent circuit of the proposed resonator is shown in Figure 8. It is represented by the series connection of three parallel LC resonators (each representing a slot) in shunt of the transmission line. At 10 GHz, the resonator slot (represented by LP and CP) resonates and provides infinite shunt impedance. Therefore all the power is transferred to the load and a transmission pole is generated. At other frequencies it behaves either as inductor (below the resonance) or as capacitor (above the resonance).

Manuscript

If the dimensions of the asymmetrical slots are chosen such that their resonance Acceptedfrequencies are well above and below the transmission pole then they will also behave as inductor / capacitor within the band of interest and the circuit (Figure 8) behaves as a

series LC network, except at the resonance of the resonator slot. At the resonance frequency of this series LC network, the shunt path becomes short circuited and transfers all the power to the ground. This results in a TZ. It may be noted that since the resonator slot behaves as inductor below the resonance and capacitor above the resonance, the series LC network will resonate twice, once below the resonance and once above the resonance. Thus two TZs can be achieved from the series network.