20-09-2009, 04:03 PM
Design and development of X-band micro strip patch antenna
Introduction
In high-performance aircraft, spacecraft, satellite and missile applications, where size, weight, cost, performance, ease of installation, and aerodynamic profiles are constraints, low profile antennas may be required. These antennas should have low profile, conformable to planar and non-planar surfaces, simple and inexpensive to manufacture using modern printed-circuit technology, mechanically robust when mounted on rigid surfaces, compatible with 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. To meet these requirements, micro strip antennas can be used.
Microstrip line is one of the most popular types of planar transmission lines, primarily because it can be fabricated by photolithographic process and is easily integrated with other passive and active devices.
Microstrip patch antenna or 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 with a continuous metal layer bonded to the opposite side of the substrate which forms a groundplane. Common microstrip antenna radiator shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas eschew a dielectric substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the resulting structure is less robust but provides better bandwidth. Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices. Microstrip antennas are also 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 resonance 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.
In its most basic form, a Microstrip patch antenna consists of a radiating patch on one side of a dielectric substrate which has a ground plane on the other side as shown in Figure .The patch is generally made of conducting material such as copper or gold and can take any possible shape. The radiating patch and the feed lines are usually photo etched on the dielectric substrate.
Figure“ Structure of a Microstrip Patch Antenna
Fig 2.8: Probe fed Rectangular Microstrip Patch Antenna
Design
The procedure for designing a rectangular microstrip patch antenna is explained below. Few micoistrip antennas with different slots are designed . Finally, the results obtained from the simulations are demonstrated.
Design Specifications: -
The three essential parameters for the design of a rectangular Microstrip Patch Antenna are:
¢ Frequency of operation (): The resonant frequency of the antenna must be selected appropriately. The microstrip antenna is designed in X Band The X band is part of the microwave region of the electromagnetic spectrum. Its frequency range is from 7 to 12.5 GHz. Hence the antenna designed must be able to operate in this frequency range. The resonant frequency selected for my design is 9.4GHz.
¢ Dielectric constant of the substrate (‚¬r): The dielectric material selected for my design is RTDuroid which has a dielectric constant of 2.2.for designing of antennas dielectric constant should be in the range of A substrate in the lower range of dielectric constant has been selected since it provides better efficiency, larger bandwidth.
¢ Height of dielectric substrate ( h ): In many applications it is essential that the antenna is not bulky.The height of the substrate should lie in the range .Hence, the height of the dielectric substrate is selected as 1.58 mm.
Hence, the essential parameters for the design are:
¢ = 9.4 GHz
¢ ‚¬r= 2.2
¢ h = 1.58mm
Technical details
The design of the micro strip antenna is carried through a powerfull simulator usually like ADVANCED DESIGN SIMULATION(ADS).Later on if necessary we can use IE3D which is 2-dimensional structuring and easy to use or HFSS(High frequency structural simulator) is fastest and most efficient one which is 3-dimensional.
After this process it is implemented in chamber where it inlcudes implementation on PCB and testing of the board for perfect functioning with less loss.Later on it is subjected to field testing after rigourous tests invovled then it is deployed to practical use.
It is generally used in Military and civilian purposes specially for hand held wireless sets.
Innovativeness and uses
The telemetry and communication antennas on missiles need to be thin and conformal and are often Microstrip patch antennas. Another area where they have been used successfully is in Satellite communication. Some of their principal advantages are given below:
Ø Light weight and low volume.
Ø Low profile planar configuration which can be easily made conformal to host surface.
Ø Low fabrication cost, hence can be manufactured in large quantities.
Ø Supports both, linear as well as circular polarization.
Ø Can be easily integrated with microwave integrated circuits (MICs).
Ø Capable of dual and triple frequency operations.
Ø Mechanically robust when mounted on rigid surfaces.
Microstrip patch antennas suffer from a number of disadvantages as compared to conventional antennas.
Applications
Notable system applications for which microstrip antennas have been developed include:
q Satellite communications
q Doppler and other radar
q Radio altimeters
q Missile telemetry
q Weapon fusing
q Man pack equipment
q Feed elements in complex antennas
q Satellite navigation receiver
q Biomedical radiator
q Command and control
This list is by no means exhaustive. As awareness of the possibilities of microstrip antennas increases, the number of applications will continue to grow.
