Half Wavelength Double-ridged Half Height Rectangular Waveguide Resonator

Transcription

1 IJCSI International Journal of Computer Science Issues, Special Issue, ICVCI11, Vol. 1, Issue 1, November 211 ISSN (Online): Half Wavelength Double-ridged Half Height Rectangular Waveguide Resonator Divya Unnikrishnan 1 and Girish Kumar 2 Junior Research Fellow, Department of Electrical Engineering Indian Institute of Technology Bombay, Powai, India Professor, Department of Electrical Engineering Indian Institute of Technology, Bombay, Powai, India Abstract This paper presents a novel concept of half wavelength doubleridged half height rectangular resonator. The basic design consists of a double-ridged rectangular placed between two rectangular WR23. The resonance frequency, bandwidth, Q factor etc. can be controlled by varying the ridge parameters such as ridge length, width, height, ridge gap width, ridge gap height etc. by keeping the other parameters constant. Modeling and analysis have been carried out using High Frequency Structure Simulator (HFSS). Simulation results are obtained which are useful for microwave components and systems. Keywords: Rectangular, WR23, half wavelength, double-ridge, resonator. bandwidth improvement over the conventional rectangular. Frequency can be controlled by varying the dimension of ridge. This approach is also found to be effective for varying the Q factor. The observed variations described in the next sections can be applied to microwave devices for obtaining desired frequency and bandwidth. WR23 Double ridge WR23 1. Introduction The rectangular ridge has one or more longitudinal ridges that increase the transmission bandwidth by reducing the cut off frequency. In ridge design, the dimensions of the ridges can be varied to minimize the dominant cut off frequency while increasing the bandwidth. Compared to conventional rectangular, ridge possess several unique characteristics such as wide bandwidth and controlled resonance frequency. Because of these characteristic, ridge s have many applications in microwave and antenna systems [1-3]. It is also useful as transmission, where a wide frequency range must be covered. This paper presents a half wavelength double-ridged half height rectangular resonator. A double-ridged rectangular is inserted between two equal sections of rectangular WR23. The discontinuity created by the two ridges is considered as a capacitance [4]. The double ridge resonator supports the fundamental TE1 mode. This design offers considerable Figure 1. Block Diagram of half wavelength double-ridged rectangular resonator 2. Design Methodology l~ λ g /2 As stated earlier, half wavelength double-ridged half height rectangular resonator consists of two half height rectangular WR23 and one capacitive double ridged rectangular. Air is used as dielectric in the resonator and copper is used as conductive material. The ridge has ridges at the centre position of the. The simulated structure of half wavelength double-ridged rectangular resonator is shown in Figure 2. The whole structure has a copper coating of 1mm. The half height rectangular WR23 has a dimension of a=23 =584.2mm and b=5.75 =146.5mm. The other dimensions are shown in Figure 2. The gap between the two ridges is the parameter that mostly affects

2 IJCSI International Journal of Computer Science Issues, Special Issue, ICVCI11, Vol. 1, Issue 1, November 211 ISSN (Online): the bandwidth of the resonator. As the double-ridge behaves as a capacitor, by decreasing the gap between the two ridges, the capacitance between the ridges increases. As a result, the resonance frequency of the resonator decreases. The distance between the two half height rectangular WR23 is at least λ g /2 in order to avoid higher order mode coupling. It is also found that the ridge length has considerable effect in the resonance frequency. (c) Figure2: Simulated structure of half wavelength double-ridged half height rectangular resonator Side view, front view and (c) 3-D view (W=584.2mm,w=345mm,H=146.5mm,h=64mm,L=5mm, l=68mm,g h =11.5mm,G w =69.4mm) 3. Results and Discussions The electromagnetic simulation of half wavelength double-ridged half height rectangular resonator has been carried out using HFSS [5]. Figure 3 shows its transmission and reflection characteristics in db over the frequency range of 3 to 4 MHz. A half height WR23 housing is used for the input and output. The bandwidth of S12 obtained at -3dB is of 23 MHz at 355MHz frequency. The bandwidth and the frequency can be controlled by varying the ridge dimensions. Figure 3 shows the transmission and reflection characteristics and the input impedance plot for variation of length (l) of double-ridge. From the figure we can see that when the length is changed from 55mm to 67mm, the bandwidth has decreased from 27MHz to 19MHz and the frequency has decreased from 371MHZ to 331MHz. Figure 4 shows the transmission and reflection characteristics and the input impedance plot for variation of width (w) of double-ridge. From the figure we can see that when the width is varied from 315mm to 375mm, the bandwidth has increased from 17MHz to 25MHz and the frequency has decreased to 384MHz to 331MHz.By varying the height of the ridge (h), the frequency and bandwidth variations are as follows: By increasing the ridge height from 59mm to 69mm, bandwidth has decreased from 23MHz to 22MHz and frequency has decreased from 368MHz to 344 MHz. The variations are shown in Figure 5. From Figure 6, we can see that when the ridge gap width (G w ) is increased from 64.4mm to 74.4mm, the frequency variation is decreased from361mhz to 349MHz and the bandwidth is decreased from of 22MHz to 19MHz. By increasing the ridge gap height (G h ) from 9mm to 14mm, bandwidth has decreased from 29.69MHz to 1.95MHz and frequency has decreased from 382 MHz to 316MHz. The variations are shown in Figure7. Thus required resonance frequency and bandwidth are obtained by varying the corresponding dimension of the ridge. If the design is concentrating more on frequency than in bandwidth, then ridge width (G h ) should be varied. Frequency variation is also depends on ridge gap height variation and ridge length variation. Because, for 12mm variation, 4 MHz frequency has varied. By increasing and decreasing the ridge gap height, we can also obtain wide bandwidth and narrow band width respectively. Variation on ridge height is done when there is less variation in bandwidth, frequency and return loss is required. The summarized result on the half

3 IJCSI International Journal of Computer Science Issues, Special Issue, ICVCI11, Vol. 1, Issue 1, November 211 ISSN (Online): wavelength double-ridged half height rectangular resonator is shown in Table 1. S11 &S12(dB) Figure 3:Effect of varying ridge length (l) on reflection and transmission coefficient and input impedance Figure 5:Effect of varying ridge height (h) on reflection and transmission coefficient and input impedance S11 &S12(in db) Figure 4:Effect of varying ridge width (w) on reflection and transmission coefficient and input impedance Figure 6:Effect of varying ridge gap width (G w ) on reflection and transmission coefficient and input impedance

4 IJCSI International Journal of Computer Science Issues, Special Issue, ICVCI11, Vol. 1, Issue 1, November 211 ISSN (Online): Freqquency(MHz) w Figure 8: Simulated structure for high Q half wavelength double-ridged half height rectangular resonator 3-D view, and front view (W=584.2mm, w=245mm, H=146.5mm, h=68mm, G h =6.1mm, G w =69.4mm) S11&S12(MHz) Figure 7:Effect of varying ridge gap height (G h ) on reflection and transmission coefficient and input impedance By using the above observed results, we did a simulation for obtaining high quality factor (Q) with narrow bandwidth. The simulated structure is shown in Figure 8. From the simulated structure it is clear that improved Q factor is obtained by decreasing the ridge width and increasing the ridge gap height. By increasing the ridge width and by decreasing the ridge gap height, the bandwidth is decreased drastically to 8 MHz. At the same time the resonant frequency remained same nearly at 355MHz. Q factor of has obtained through the above simulation. The transmission and reflection characteristics and the input impedance plot for high Q half wavelength double-ridged half height rectangular resonator are shown in Figure 9. Thus, these recommended dimensions are used where high Q is the primary requirement. Figure 9: Simulated structure of half wavelength double-ridged half height rectangular resonator with high Q and its Transmission and reflection co-efficients. Table 1. Effect of variation in ridge dimensions on resonance frequency and bandwidth. Parameter Variation in ridge dimension (mm) Variation in frequency (MHz) Variation in bandwidth (MHz) l w h G w G h

5 IJCSI International Journal of Computer Science Issues, Special Issue, ICVCI11, Vol. 1, Issue 1, November 211 ISSN (Online): Conclusion In this paper, a half wavelength double-ridged half height rectangular resonator is presented. It is observed that by varying the ridge dimensions, the bandwidth, frequency, impedance matching and Q-factor can be controlled. Frequency has varied from 316MHz to 384 MHz, and bandwidth has varied from 11MHz to 32MHz. Also the return loss has varied from 28dB to 48 db. Thus, this proposed mechanism can be used for the design of various microwave devices depending upon the requirement. References [1] J. Helszain, Ridge s and passive components, The institution of engineering and technology, London, United Kingdom 2. [2] Seymour B Cohn, Properties of ridge. Proc. of IEEE, pp , Sep. 26. [3] S.Hopfer. Thc design of ridged, IRE Trans. microwave Theory Tech., vol. MTT-3, pp. 2-29, Oct [4] David M. Pozar, Microwave Engineering, John Wiley & sons, Inc.,1997. [5] HFSS by Ansys (formerly Ansoft).