ABSTRACT:- Microstrip array antennas are the most popular solution for a variety of system applications, including air traffic control and collision avoidance radar for WLAN and cellular communication. A microstrip antenna array is used since it is simple to design and fabricate. It has light weight, small size, and high gain. Antenna array designed are the important area of research in active RADAR system that can meet the subject requirement. Now a days Microstrip antennas are used in variety of wireless applications including radars,Satellites, cellular phones & in medical applications. This paper gives the design of different microstrip array antennas for Weather radar system.
Corporate feeding technique is also been used for the design of an array. Proposed antennas resonates at 5.8GHz. KeywordsMicrostripArray, 1. IntroductionMicrostrip antenna array are nowadays one of the fastest growing segments in the telecommunication industry and become a promising medium in the field of telecommunication in the future. Recent growth in civilian radar-based sensors & communication systems has drawn increasing interest in utilizing antenna array technology for commercial applications 2. Improving antenna directivity in order to improve long-range communication has been subject of extensive research since the time of Marconi’s paper entitled “Directive Antenna 3. Microstrip antennas (also known as patch antenna) 5 are currently one of the large bandwidth antennas in telecommunication industry.
Research has been carried out in the recent past to improve the performance & efficiency of these patch antennas .Rapid development in patch antennas started in 1970s & by the end of 1980s, the idea of using microstrip array antenna in wireless communication was well established 1. The light weight, reduced size, phase steering ability, ease of installation, low cost, possibility of integration of patch antennas make this antennas to the best choice of researchers & manufacturers 6. In single element antenna, the radiation pattern is usually very broad and the directivity is relatively low. This problem can be overcomed by enlarging the size of the patch element thus increasing the directivity. Another way to enlarge the antenna without changing the size of the individual elements is to assemble the radiating elements in a geometrical configuration known as array. The individual elements forming the array are usually identical and they can be of any form 3.
Section 1 briefs about different types of Antenna arrays like linear array, Planar array and Scanned array. Section 2 highlights on Design Methodology of an antenna array , steps of designing Microstrip antenna array and different types feeding techniques. Section 3 elaborates on Active Phased Array. In section 4 , we talked about Array Design Procedure like Coaxial feedline, Series fed taper antenna array design and corporate feed antenna array. In section 5 we have designed and presented different array antennas with their results. There results are also compared and analysed. In many applications it is necessary to design antennas with very directive characteristics to meet the demands of long distance communication especially in Radar Systems. This is accomplished by increasing the electrical size of the antenna.
Another way to enlarge the dimensions of the antenna is to form an assembly of radiating elements in an electrical and geometrical configurations. This new antenna formed by multi elements is referred to as an array. The total field of the array is determined by the vector addition of the fields radiated by the individual elements3.To provide very directive patterns, it is necessary that the fields from the elements of the array interfere constructively (add) in the desired directions and interfere destructively (cancel each other) in the remaining space. In an array of identical elements, there are at least five controls that can be used to shape the overall pattern of the antenna.
1. The geometrical configuration of the overall array2. The relative displacement between the elements.3.
The excitation amplitude of the individual elements.4. The excitation phase of the individual elements. 5.
The relative pattern of the individual elements. 2.Array Antennas : Linear array Some antenna sources can be seen as isotropic elements, which mean that they radiate equally well in all directions 18. An array of identical elements all of identical magnitude and each with progressive phase is referred to as a uniform array3. Design Methodology Antenna is an interface between the signal source and the air for any wireless application. The efficiency of an antenna array is a prominent figure of merit of any radar system.
Antenna efficiency can be in the terms of gain, directivity and return loss 3. Port impedance is normally chosen as 50 ?. To design an antenna array at a desired frequency , the first step is to design single antenna. FR-4 material can be used which is cheap and readily available.Design of microstrip array is divided into four steps(i) Defining specifications(ii) Design of single patch(iii) Design of an array(iv) Simulation of the arrayFeeding technique is another important aspect in the design of patch antennas. Some feeding techniques are given below.(i) Microstrip Line Feed(ii) Co-axial Probe Feed(iii) Aperture Coupling(iv) Proximity Coupling Microstrip patch antennas can be fed by a variety of methods.Microstrip Line Feed In this type of feeding technique, a conducting strip is connected directly to the edge of the microstrip patch.
The conducting Microstrip line is smaller in width as compared to the patch and this kind of feed arrangement has the advantage that the feed can be etched on the same substrate to provide a planar or linear structure.Co-axial Probe FeedThe coaxial feed is one of the very popular technique used for feeding Microstrip patch antennas. The inner conductor of the coaxial connector extends through the dielectric and is soldered to the radiating patch, while the outer conductor is connected to the ground plane. Aperture Coupled FeedIn this technique, the radiating patch and the microstrip feed line are separated by the ground plane.
Coupling between the patch and the feed line is made through a slot in the ground plane and variations in the coupling depends upon the size. Aperture couple feed has advantage such as no physical contact between the feed and the radiator, wider bandwidths and better isolation between antenna and feed network.Proximity Coupled FeedThis type of feed technique is also called as the electromagnetic coupling. Two dielectric substrates are used such that the feed line is between the two substrate and the radiating patch is on top of the upper substrate. The main advantage of this feed techniques is that it eliminates spurious feed radiation and provides very high bandwidth.