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REVIEW ON DESIGNING APPROACH OF MICRO STRIP FILTERS Jitendra Kumar Ahirwar
Asst. Professor, (IMEC Sagar)
Abstract - Filters play a significant role in Communication System by attenuating the unwanted signal frequencies and permitting the desired frequencies. With the requirement of greater fractional bandwidth, it became imperative to design Cost effective filters without degrading the performance of filters. Use of new/different materials, improved fabrication techniques, availability and further development of Software played a significant role in the quest of researchers to design efficient Filters. The various important parameters considered in designing of filters include Pass Bandwidth, Stop Band Attenuation, Input and Output impedances, Return Loss, Insertion Loss and Group Delay. The practical filters have a small non zero attenuation and a small signal output in the attenuation band due to the presence of resistive losses in reactive elements and propagating medium Traditionally, designers used coaxial lines or waveguides as transmission lines, however now new types of filters are designed using microstrip lines. Thus, the area of study/research in today’s era encases the design of Microstrip Filters meeting the required bandwidth. An ideal filter would have perfect impedance matching, zero loss of insertion in the pass band, and infinite attenuation (rejection or insertion loss) everywhere else. In reality, there is loss of insertion in the pass band, and finite rejection elsewhere. The loss components of a single micro strip line include conductor loss, dielectric loss and radiation loss. The researchers have over a period of time, developed new technologies and materials for designing of Micro strip filters to meet the ever increasing severe requirement of the present era communication systems
Keyword: low pass filter (LPF) Industrial, Scientific and Medical (ISM), High-pass (HP), 1. INTRODUCTION
Filters play an important role in microwave communications and are used to pass or eliminate specific frequency bands.
Filters are classified as low-pass (LP), high-pass (HP), band-pass (BP), and band-stop (BS). LPF is used at the output of a power amplifier to eliminate the harmonics generated by the nonlinearity of the power amplifier, at the output of a mixer to pass only the intermediate frequency, at the input of a receiver to reject the unwanted higher frequencies and in conjunction with a HPF to realize a wideband band-pass filter.
Microwave filters can be divided into two main different types, lumped or distributed. Lumped elements consist of discrete elements, such as inductors and capacitors, while distributed elements use the lengths and widths of transmission lines to create their inductive or capacitive values.
Micro strip line is a good candidate for filter design due to its advantages of low cost, compact size, light weight, planar structure and easy integration with other components on
a single board. To achieve better performance for the microwave filters, such as increasing steepness of the cut- off slop, and to increase the stop band range of the microwave filters, defected ground structures (DGS) are used. This technique is realized by etching slots in the ground plane of the microwave circuit.
2. MICROSTRIP
A micro strip line filter type includes stub impedance, step impedance and coupled line filter. Parallel coupled
2.1 Design and Optimization of Low Pass Filter Using Micro Strip Lines Filter designs beyond 500MHz are difficult to realize with discrete components because the wavelength becomes comparable with the physical filter element dimensions, resulting in various losses severely degrading the circuit performance. Thus to arrive at practical filters, the lumped component filters must be converted into distribution element realizations. Richards Transformation. To accomplish the conversion from
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lumped and distributed circuit designs, Richards proposed a special transformation that allows open and short circuit transmission line segments to emulate the inductive and the design of micro strip low pass filters involves two main steps. The first one is to select an appropriate low pass prototype, The choice of the type of response, including pass band ripple and the number of reactive elements, will depend on the required specifications. The element values of the low pass prototype filter, which are usually normalized to make a source impedance g0=1 and a cutoff frequency Ωc=1.0, are then transformed to the L-C elements for the desired cutoff frequency and the desired source impedance, which is normally 50 ohms for micro strip filters.
Most communication system contains an RF front end which performs signal processing with RF filters. Micro strip filters are a low cost means of doing this. This paper describes the design of low cost and low insertion loss microstrip stepped impedance fractal low pass filter (LPF) by using microstrip layout which works at 0.4GHz for permittivity 4.7 value with a substrate thickness 1.6mm with pass band ripple 0.1dB. Microstrip technology is used for simplicity and ease of fabrication. The filter is required in all RF-communication techniques. Low pass filters play an important role in power transmission systems. Transmitted and received signals have to be filtered at a certain frequency with a specific bandwidth. The design of filter is done in the ISM (Industrial, Scientific and Medical) band whose frequency lies between 1.55GHz-3.99GHz. After getting the specifications required, The practical filters have a small non zero attenuation and a small signal output in the attenuation band due to the presence of resistive losses in reactive elements and propagating medium Traditionally, designers used coaxial lines or waveguides as transmission lines, however now new types of filters are designed using micro strip lines.
3. FABRICATION PROCESS IN MICROSTRIP
With the advent of technology, researchers and designers use various technologies aided software’s, machines and techniques for fabricating a micro strip effectively. The modern day technology helps in simulation and designing of a micro strip as per requirement. The fabrication process consists of the following steps:
1. A mask or transparency is prepared with the help of the available software.
2. The next step in the fabrication process consist of creating a photo resist pattern for which a photo resist material (consisting of photo resist solution and plastic tray) and photo resist equipment consisting of Ultra Violet light compartment and temperature controlled hot plate.
3. The next step involved in the process of fabrication consists of removing or etching the unwanted copper using some common solution so as to get the required copper as conductor pattern.
4. The next step associated with the fabrication process involves preparing a Micro strip housing i.e.
the micro strip base using good conductor materials like aluminum or copper.
5. The final step involves soldering the connectors into the circuit of micro strip after the same are properly screwed with the ground plane.
3.1 Fabrication Technologies:
The researchers and designers embarked on the development of printed circuits which were planar in nature and also the efficacy of lumped components in the domain of microwave frequencies subsequent to the development of transmission lines which were planar in nature like the micro strip lines and also the strip lines.
The microwave industry witnessed a sea change with the miniaturization as well as the batch fabrication of large number microwave functions in respect of bulk volume production. Preliminary research on printed circuits which were planar in nature
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Figure 1
Micro strip transmission lines consist of a conductive strip of width "W" and thickness "T" and a wider ground plane, separated by a dielectric layer (the
"substrate") of thickness "H" as shown in the figure 1. The micro strip has most of its field lines in the dielectric region, concentrated between the strip conductor and the ground plane, and some fraction in the air region above the substrate as shown in fig. Micro strip is by far the most popular microwave transmission line, especially for microwave integrated circuits and MMICs. The major advantage of micro strip is that all active components can be mounted on top of the board. Having a finite thickness of metal for the conductor strips tends to increase the capacitance of the lines, which affect the effective dielectric constant and the characteristic impendence.
4. CONCLUSION
Wireless and mobile communication systems have presented new challenges to the design of high quality miniature filters. The miniaturization of filters remains an active area of research due to the relatively large physical size of traditional resonators and the great demand from the wireless communication industry. One of the most popular structures for micro strip implementations is the folded hairpin square open loop resonator due to its compact size and versatility.
REFERENCES
1. Ker Cha Lee “Compact Microwave Microstrip Resonator Bandpass Filters”
Swirnbourne University of Technology, 2014.
2. R. J. Cameron, C. M. Kudsia, and R. R.
Mansour, Microwave Filters for Communication Systems: Fundamentals,
Design and Applications, John Wiley &
Sons, Hoboken, NJ, USA, 2007.
3. J.-S. Hong, Microstrip Filters for RF/Microwave Applications, John Wiley &
Sons, Hoboken,NJ, USA, 2nd edition, 2011.
4. Ralph Levy, Rechard V Snyder and George Matthaei “Design of Microwave filters” IEEE MTT Vol 50, No 3, March 2002, pp 783-793 5. Hunter, R. Ranson, A. Guyette, and A.
Abunjaileh, “Microwave filter design from a systems perspective,” IEEE Microwave Magazine, vol. 8, no. 5, p. 71, Oct. 2007.
6. R. V. Snyder, “Practical aspects of microwave filter development,” IEEE Microwave Magazine, vol. 8, no. 2, pp. 42- 54, Apr. 2007.
7. R. R. Mansour, “Filter technologies for wireless base stations,” IEEE Microwave Magazine, vol. 5, no. 1, pp. 68–74, Mar.
2004.
8. C. Wangand K. A. Zaki, “Dielectric resoantors and filters,” IEEE Microwave Magazine, vol. 8, no. 5, pp. 115–127, Oct.
2007.
9. M. Makimoto and S. Yamashita, Microwave Resonators and Filter for Wireless Communication, Theory, Design, and Application. Berlin, Germany: Springer, 2001.
