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ABSTRACT
In modern antenna designs, microstrip patch antennas are widely used for their low size, light weight and easy to integrate. This project is focusing the various shapes of microstrip patch antennas like J and L shapes using FR4 as dielectric material and copper as a ground plane and patch conductor. These antennas are mainly operated at the frequency range 4-8GHz(C-band). So they are applied in long distance communications like satellite communication. The parameters of antenna such as return loss, voltage standing wave ratio, radiation pattern, gain, directivity and power were measured. This antenna simulation is done by Advanced Design System (ADS) software version 2013. And the prototype is fabricated and measured using Vector Network Analyzer for validation.
1 INTRODUCTION
In high-performance aircraft, spacecraft, satellite, and missile applications, where size, weight, cost, performance, ease of installation, and aerodynamic profile are constraints, low-profile antennas may be required. Presently there are many other government and commercial applications, such as mobile radio and wireless communications that have similar specifications. To meet these requirements, patch antennas (microstrip, copolar, etc.) can be used. These antennas are low profile, conformable to planar and nonplanar surfaces, simple and inexpensive to manufacture using modern printed-circuit technology, mechanically robust when mounted on rigid surfaces, compatible MMIC designs, and when the particular patch shape and mode are selected, they are very versatile in terms of resonant frequency, polarization, pattern, and impedance. In addition, by adding loads between the patch and the ground plane, such as pins and varactor diodes, adaptive elements with variable resonant frequency, impedance, polarization, and pattern can be designed, Major operational disadvantages of microstrip antennas are their low efficiency, low power, high Q (sometimes in excess of 100), poor polarization purity, poor scan performance, spurious feed radiation and very narrow frequency bandwidth, which is typically only a fraction of a percent or at most a few percent. In some applications, such as in government security systems, narrow bandwidths are desirable. However, there are methods, such as increasing the height of the substrate that can be used to extend the efficiency (to as large as 90 percent if surface waves are not included) and bandwidth (up to about 35 percent). However, as the height increases, surface waves are introduced which usually are not desirable because they extract power from the total available for direct radiation (space waves).
The surface waves travel within the substrate and they are scattered at bends and surface discontinuities, such as the truncation of the dielectric and ground plane, and degrade the antenna pattern and polarization characteristics. Surface waves can be eliminated, while maintaining large bandwidths, by using cavities. Stacking, as well as other methods, of microstrip elements can also be used to increase the bandwidth. In addition, microstrip antennas also exhibit large electromagnetic signatures at certain frequencies outside the operating band, are rather large physically at VHF and possibly UHF frequencies, and in large arrays there is a trade-off between bandwidth and scan volume.
SOFTWARE IMPLEMENTATION OF MICROSTRIP PATCH ANTENNA
We have used Advanced Design System (ADS) as a software in order to make a simulations of antennas. ADS is an electronic design automation software system produced by Agilent EEsof EDA, a unit of Agilent Technologies. It provides an integrated design environment to designers of RF electronic products such as mobile phones, pagers, wireless networks, satellite communications, radar systems, and high-speed data links.
Agilent ADS supports every step of the design process—schematic capture, layout, frequency-domain and time-domain circuit simulation, and electromagnetic field simulation—allowing the engineer to fully characterize and optimize an RF design without changing tools.
Agilent EEsof has donated copies of the ADS software to the electrical engineering departments at many universities, and a large percentage of new graduates are experienced in its use. As a result, the system has found wide acceptance in industry.
MEASUREMENT OF MICROSTRIP PATCH ANTENNA
Antennas are fabricated using double side copper coated PCB board and ferrous chloride for etching purpose. Feed is given to the antenna through microstrip feed line using SMA female connector.
In practice, the most commonly quoted parameter in regards to antennas is S11. S11 represents how much power is reflected from the antenna, and hence is known as the reflection coefficient (sometimes written as gamma: or return loss). If S11=0 dB, then all the power is reflected from the antenna and nothing is radiated. If S11 = -10 dB, this implies that if 3 dB of power is delivered to the antenna, -7 dB is the reflected power. The remainder of the power was "accepted by" or delivered to the antenna. This accepted power is either radiated or absorbed as losses within the antenna. Since antennas are typically designed to be low loss, ideally the majority of the power delivered to the antenna is radiated.
Next measurement technique is a radiation pattern. A radiation pattern defines the variation of the power radiated by an antenna as a function of the direction away from the antenna. This power variation as a function of the arrival angle is observed in the antenna's far field.
Antenna measurements were made by using Agilent FieldFox handheld microwave analyzer N9916A shown in Figure 17. Frequency range of this device is 30 kHz - 14 GHz, work temperature is from -10 to 55 C degree, input impedance is 50 Ω (nominal). FieldFox N9916A was using to make a realistic S11 parameter of produced antenna on Smith chart and magnitude plot.
IMPLEMENTATION OF MICROSTRIP PATCH ANTENNA OF J and L-SHAPE IN C-BAND
These microstrip patch antennas are implemented using FR4 as dielectric material and copper as conductor. Patch is J and L- shaped and has a finite ground and its dimensions are in mm. Input is given using microstrip feeding with a SMA female connector.
4.1 FABRICATION
Antennas are fabricated using double side copper coated PCB board and ferrous chloride for etching purpose. Feed is given to the antenna through microstrip feed line using SMA female connector.
CONCLUSION
In this proposed work, c-band J and L shape microstrip patch antenna simulated in Advanced Design System software (ADS) and practical verification of the same was done. Comparing both that,
• A higher bandwidth of operation is obtained with proposed system.
• Reflection loss in low, thereby increasing the efficiency of the antenna.
• Stability of radiation pattern is increased.
• Good multi-band property.
Good return loss, antenna gain and radiation pattern characteristics are obtained in the c- band.