STUDY AND CHARACTERIZATION OF MICRO STRIP ANTENNA FOR SINGLE FREQUENCY OPERATION

BY 

ABHIK CHAKRABORTYAVIK GHOSH AVISHEK ASH INDRANIL ROY SOURAV LAHIRI

TAPAS SAHA

An antenna (plural antennae or antennas), is an electrical device which converts electric power into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an electric current oscillating at radio frequency (i.e. a high frequency alternating current (ac)) to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified.

WHAT IS ANTENNA?

WHAT IS MICROSTRIP PATCH ANTENNA? A patch antenna is a narrowband, wide-beam antenna fabricated by etching the

antenna element pattern in metal trace bonded to an insulating dielectric substrate, such as a printed circuit board, with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane. Common microstrip antenna shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas do not use a dielectric substrate and instead are made of a metal patch mounted above a ground plane using dielectric spacers; the resulting structure is less rugged but has a wider bandwidth. The most commonly employed microstrip antenna is a rectangular patch which looks like a truncated microstrip transmission line. It is approximately of one-half wavelength long. When air is used as the dielectric substrate, the length of the rectangular microstrip antenna is approximately one-half of a free-space wavelength.

MICROSTRIP PATCH ANTENNA

ADVANTAGES OF MICROSTRIP ANTENNA Microstrip antennas are relatively inexpensive to manufacture and design because of the

simple 2-dimensional physical geometry. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonant frequency. A single patch antenna provides a maximum directive gain of around 6-9 dBi. It is relatively easy to print an array of patches on a single (large) substrate using lithographic techniques. Patch arrays can provide much higher gains than a single patch at little additional cost; matching and phase adjustment can be performed with printed microstrip feed structures, again in the same operations that form the radiating patches. The ability to create high gain arrays in a low-profile antenna is one reason that patch arrays are common on airplanes and in other military applications. Such an array of patch antennas is an easy way to make a phased array of antennas with dynamic beam-forming ability. An advantage inherent to patch antennas is the ability to have polarization diversity. Patch antennas can easily be designed to have vertical, horizontal, right hand circular (RHCP) or left hand circular (LHCP) polarizations, using multiple feed points, or a single feedpoint with asymmetric patch structures. This unique property allows patch antennas to be used in many types of communications links that may have varied requirements.

OVERVIEW OF THE PROJECT

The project conducted here has gone through various phases of comprehension, research and development. Our first goal was to design a microstrip patch antenna fit to operate on 2.4 GHz frequency. It was designed as an antenna with a rectangular patch with lumped ports on either sides. The patch extended from one end of the substrate to the other to come in contact with the ports on either sides. Our plan was to design an antenna, observe its plot and then compare that with the plot of the same antenna with defected ground structure. Later, however, to get the right plot fit for our will to get an antenna operable in the very useful L-band we changed the operating frequency to 1.6 GHz and later to 1.2 GHz and finally came upon an S-shaped patch with a transmission line feed fit for our project.

ADVANTAGES AND APPLICATIONS

The L band, as defined by the IEEE, is the 1 to 2 GHz range of the radio spectrum. This range is exceptionally useful for satellite navigation systems and military surveillance systems like those of Indian Regional Navigation Satellite Surveillance, Global Positioning System, Galileo Positioning System, Global Navigation Satellite Surveillance, etc. Other than that, the L band has huge applications in mobile service. Aircraft can use Automatic dependent surveillance-broadcast (ADS-B) equipment at 1090 MHz to communicate position information to the ground as well as between them for traffic information and avoidance. Also Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range 1,240 to 1,300 MHz, and amateur satellite up-links are allowed in the range 1,260 to 1,270 MHz.

ADVANTAGES AND APPLICATIONS

In the United States and overseas territories, the L band is held by the military for telemetry, thereby forcing digital radio to in-band on-channel (IBOC) solutions. Digital Audio Broadcasting (DAB) is typically done in the 1452–1492-MHz range in most of the world, but some countries also use VHF and UHF bands. WorldSpace satellite radio broadcasts in the 1467–1492 MHz L sub-band. The band also contains the hyperfine transition of neutral hydrogen (the hydrogen line, 1420 MHz), which is of great astronomical interest as a means of imaging the normally invisible neutral atomic hydrogen in interstellar space. Consequently, parts of the L-band are protected radio astronomy allocations worldwide.

HARDWARE AND SOFTWARE REQUIREMENTS

i. FR4 epoxy substrate of dielectric 4.4.ii. S-shaped patch fed with a transmission line connecting patch with port.iii. Ground plane.iv. Rectangular port.v. HFSS (High Frequency Structural Simulator).

FR4 EPOXY SUBSTRATE

The substrate in a microstrip antenna is a body of rectangular parallelepiped shape separating the ground plane and the patch. The ground plane is below the substrate while the patch is etched above the substrate. The material used in this project is FR-4 epoxy of dielectric 4.4. FR-4 (or FR4) is a grade designation assigned to glass-reinforced epoxy laminate sheets, tubes, rods and printed circuit boards (PCB). FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing). "FR" stands for flame retardant, and denotes that safety of flammability of FR-4 is in compliance with the standard UL94V-0.

GROUND PLANE

The ground plane is the horizontal flat surface above which the antenna substrate is mounted while the patch is etched above the substrate. The ground plane is designed with a ‘perfect E’ boundary condition whereas the patch is applied with a ‘finite conductivity’ boundary condition with material specified as copper.

A ground plane is an electrically conductive surface, usually connected to electrical ground. The term has two different meanings in separate areas of electrical engineering. In antenna theory specifically, a ground plane is a conducting surface large in comparison to the wavelength, such as the Earth, which is connected to the transmitter's ground wire and serves as a reflecting surface for radio waves. It is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements.

PATCH

The patch is a sheet or "patch" of metal etched over the substrate which determines the feed of an antenna, its emission potential in relation to the ports. Here, an S-shaped patch is used although many other shapes of patches are possible. The EM waves fringe off the top patch into the substrate, reflecting off the ground plane and radiates out into the air. Radiation occurs mostly due to the fringing field between the patch and ground.

MICROSTRIP LINE FEED Microstrip patch antennas can be fed by a variety of methods. These methods

can be classified into two categories- contacting and non-contacting. In the contacting method, the RF power is fed directly to the radiating patch using a connecting element such as a microstrip line. In the non-contacting scheme, electromagnetic field coupling is done to transfer power between the microstrip line and the radiating patch. The four most popular feed techniques used are the microstrip line, coaxial probe (both contacting schemes), aperture coupling and proximity coupling (both non-contacting schemes). In this type of feed technique, a conducting strip is connected directly to the edge of the microstrip patch. The conducting strip 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 structure.

HIGH FREQUENCY STRUCTURAL SIMULATOR

The HFSS software is the industry standard for simulating 3-D, full-wave, electromagnetic fields. Its accuracy, advanced solvers and high-performance computing technologies make it an essential tool for engineers tasked with executing accurate and rapid design in high-frequency and high-speed electronic devices and platforms. HFSS offers state-of the-art solver technologies based on finite element, integral equation, asymptotic and advanced hybrid methods to solve a wide range of microwave, RF and high-speed digital applications. It is a commercial finite element method solver for electromagnetic structures from Ansys. The acronym originally stood for High Frequency Structural Simulator. It is one of several commercial tools used for antenna design, and the design of complex RF electronic circuit elements including filters, transmission lines, and packaging. It was originally developed by Professor Zoltan Cendes and his students at Carnegie Mellon University. Prof. Cendes and his brother Nicholas Csendes founded Ansoft and sold HFSS stand-alone under a 1989 marketing relationship with Hewlett-Packard, and bundled into Ansoft products. Ansoft was later acquired by Ansys.

PROCEDURE OF THE EXPERIMENT

i. First the substrate is designed as a 3-D box is designed at the co-ordinates (0, 0, 0) with its length 100 mm in Y-axis and breadth 75 mm in X-axis. Its height on Z-axis is 0.254 mm. The material is chosen as FR4 Epoxy (dielectric 4.4).

ii. The bottom face of the substrate is selected and used as ground by creating an object from that face specifically using modeler. It has been assigned a boundary condition of ‘Perfect E.’

iii. A patch is drawn by drawing and joining rectangular planes on the upper surface of the substrate to form an S-shape. It spans for a length of 41 mm in Y-axis and a breadth of 3.8 mm in X-axis. The patch is assigned a boundary condition of ‘Perfect E’ like the ground.

iv. A rectangular port is created along the Y-axis. Its length is 16mm on X-axis and a breadth of 5 mm on Z-axis. It is used as a driven terminal.

PROCEDURE OF THE EXPERIMENT

v. A transmission line is fed from the S-shaped patch thereby bringing it in the connection with the port.

vi. The design is assigned a sweeping frequency, then validated and finally the simulation is run.

vii. A rectangular plot is observed between the frequency (GHz) as X-axis and intensity (dB) in Y-axis. The centre frequency of usable bandwidth is observed along and the return loss is evaluated.

viii. Also a far-field circular radiation pattern is observed.

DESIGNED ANTENNA USING HFSS

RADIATION PLOT AND RETURN LOSS

While two usable transmit-receive bandwidths are observed only one among them is practically feasible, thereby, giving a single-frequency microstrip antenna plot. We can see the centre-frequency of the usable bandwidth is around the operating frequency 1.2 GHz (1.16 GHz).

Also, the return loss calculated here at 1.16 GHz is -25 dB.

CONCLUSION

By executing this experiment, we have learnt the working mechanism and the process to design a single-frequency microstrip patch antenna that will find efficient uses in communication purposes at an operating frequency of 1.2 GHz. We have observed the frequency-intensity plot and have evaluated the return loss from it. We also have observed the far-field radiation pattern of this antenna design. Due to the shortage of time, we couldn’t however realize this in practical hardware form but only remained confined to our experiment on HFSS.

  Finally, whatever we have achieved in this project couldn’t have come into

being without the undying guidance of our mentor Prof. Anupa Chatterjee.

REFERENCES i. Wikipedia ii. Various Google Scholar publications. iii. Ansys tutorials on YouTube. iv. Antenna Theory: Analysis and Design, by Constantine A. Balanis. v. Analysis of Dual Frequency Microstrip Antenna Using Shorting Wall (International

Journal of Emerging Technology and Advanced Engineering), by Apeksha S. Chavan, Prof. Pragnesh N. Shah, Seema Mishra.

vi. Concentric Ring-Shaped Defected Ground Structures for Microstrip Applications (IEEE Antennas and Wireless Propagation Letters, Vol. 5, 2006) by Debatosh Guha, Senior Member, IEEE, Sujoy Biswas, Manotosh Biswas, Jawad Y. Siddiqui, Member, IEEE, and Yahia M. M. Antar, Fellow, IEEE.

vii. 2.45 GHz Microstrip Patch Antenna with Defected Ground Structure for Bluetooth (International Journal of Soft Computing and Engineering (IJSCE) ISSN: 2231-2307, Volume-1, Issue-6, January 2012) by Rajeshwar Lal Dua, Himanshu Singh, Neha Gambhir.

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