1. MICROSTRIP ANTENNA TECHNOLOGY

2. MICROSTRIP ANTENNA TECHNOLOGY
simple structure
low profile
light weight
low cost
Adjustable beam shape like antennas
It is a high performance, multifunction, low cost antenna and is used for various communication purposes.
The new Class of Antenna to form the feed networks and a radiators is present in this communication these antennas have four different advantages:
1) Low cost
2) High performance
3) ease of installation and
4) Low profile conformal design the applications of these antennas is limited to some bandwidths.

3. Microstrip arrays can be designed from several fundamentally different kinds of elements.
The key features of microstrip antennas are:
1. relative ease of construction
2.light weight
3. low cost
4. conformability to the mounting surface and
5.extremely thin protraction from the surface.

4. FIRST GENERATION MICROSTRIP ARRAYS
The antenna arrays used before the present microstrip antenna came into being included:
1 classic monolithic microstrip array proposed by Munson
2.The etched broadside and endfire arrays of Fubini
3.The narrow line radiators of James and Wilson 4.Arrays of the multilayer radiators proposed by Collings.
The above said antennas are termed as" first generation” because they represent four basically independent solutions to the problem of providing very light weight and inexpensive arrays.

5. Fixed Beam Arrays
Microstrips are widely used from a few hundreds of MHz to 10 GHz, because of its simplicity and its low fabrication cost.
Microstrips consist of a metal strips and a ground metallic sheet separated by a layer of dielectric.

6. PRESENT MICROSTRIP ANTENNA ARRAY TECHNOLOGY
Arrays for the Wide angle Coverage
Array geometry is a key design feature in the electro magnetic switched special array for satellite use.
The 38 cm radius dome array weighs 3 kg creates in the 2.0 – 2.3 GHz consumes 1W dc, and produces 1024 beams to cover the hemisphere.

7. This technique of using a shorted quarter wave rectangular patch elements reduces the element size, and by eliminating one of the two radiating slots, provides a broader radiation pattern in one plane Combining four such elements, as shown in Figure.
Wide angle scanning in phased arrays requires closely spaced elements to avoid grating lobes.
Finding space on the array board for the elements in complicated by the fact that in microstrip arrays, elements, phase shifters, and feed network can all be placed in proximity on the same side of one dielectric board, greatly aggravating the mutual coupling between the elements and also between the elements and feed lines.

8. Multiple Layer Arrays
The development of special compact elements, such as the shorted quarter-wave patch, reduced element size to the point where it was possible to keep elements, phase shifter, and feed lines all on one side of the board.
The figure beside shows such an array with 21 elements producing a measured 15.7-dBi gain (compared to the maximum area gain of 17.2 dBi) at 4.6 GHz. The beam was scanned to 550 in both E-and H-planes, VSWR was less than two to one at all beam positions, and gain fell off about 1.6 dB at MHz around the design center frequency.
It soon became apparent, however, that the one sided board, although a direct out growth of early microstrip antenna technology which promised simple microstrip fabrication, introduced problems.

9. MICROSTRIP ANTENNA DEVELOPMENTS FOR FUTURE SYSTEM REQUIREMENTS
There are still a vast number of military and civilian requirements that demand low cost, lightweight arrays, and yet place far greater burdens on antennas than can be met by present microstrip techniques that include:
the need for microstrip array developments at millimeter wavelengths.
Applications requiring greater conrol of antenna pattern characteristics than compared to monolithic counterparts.
wider bandwidth applications.
wide angle scanning requirements.

10. Competing Array Technology
The Microstrip array has multilayer configurations combining microstrip, waveguide, and stripline for higher power transmission.
Furthermore, they are substantially more complex and costly than monolithic microstrip arrays and so have compromised some of the advantages that originally brought microstrip its popularity.
Microstrip array bandwidth restrictions can be alleviated by the use of thicker substrates, but there are no data on array behavior for such designs and hence no indications as to whether internal mutual coupling will become a factor in large arrays with thick substrates.

11. Stripline flat plate slot arrays can be designed for wide angle scan using conventional methods.
Air stripline corporate feed networks have been designed to have near-in sidelobe level below – 35 dB, far sidelobes of less than -50 dB, and bandwidth in excess of 15 percent.
A cavity backed circularly polarized turnstile antenna, designed by Gregorwich to operate over a 40-percent bandwidth, has been incorporated into a flush mounted array for a cylindrical spacecraft.
The array does protrude to the spacecraft and so is hardly comparable with monolithic microstrip in its conformality, but is does represent a technology in competition with future high power multilayer microstrip designs.

12. The coplanar stripline element, promising reduced mutual coupling, cross polarizations 20 dB below the principle polarization, and bandwidths of 5-7 percent, has found, as yet, little application in arrays.
Wire grid microtrip antenna configurations are a new development with 6-12 percent bandwidth capability which can be configured both as resonant fixed beam arrays and also as traveling wave frequency scanned antennas.
Techniques for implementing amplitude control by varying the wire line widths have been developed and demonstrated.

13. Directions For Microstrip Array Development
Microstrip arrays are ideally suited to many applications requiring:
narrow bandwidth (a few pecent)
low power
extreme lightweight or conformality.
For these applications, little fundamental change is required of the technology.
A number of application areas require substantial evolution in microstrip technology in order that it play an increasing role in answering future system requirements.
Monolithic arrays have been limited to fixed beam or scanning in a single plane due to the following reasons:
not enough room for phase shifters
power dividing network and
Since all the elements should be placed on one surface.

14. For the microstrip technology to have a larger share of future radar and communications requirements, the trend toward multilayer boards must continue. This will provide independent ports for precise pattern control functions such as null steering and varying the aperture illumination between transmissions and reception.
Extension of multilayer techniques will also facilitate the synthesis of very low sidelobe aperture illuminations, the required development of sub array networks for wide-band and high power operation, and integration with solid-state transmit-receive modules for increased efficiency.
As regards bandwidth and multifrequency applications, it seems clear that there are a number of applications that do not require microstrip arrays as thin as are currently made but would benefit from the low production costs associated with this technology.
There have been significant advances using thick microstrip radiators of the Callings type.
These developments have potential bandwidths over 10 percent and so are suitable for a number of very advanced communication and radar functions.

15. DIADVANTAGES OF MICROSTRIPS:
Can be operated only in a short range of frequency.
Cannot operate at high power levels

16. CONCLUSION:
If microstrip technology is to evolve to fill yet a large share of future radar and communications requirement s, the trend towards multilayer boards must continue .
As regards band width and multifrequency applications, it seems clear that there are no.of applications that do not require microstrip arrays as thin as currently made but would benefit from the low production costs associated with this technology. The Low weight and Low Cost Antennas will continue to stimulate evolutionary Development in Microstrip Arrays throughout the foreseeable Future.

17. REFERENCES:
P.S.Hall and J.R. James, “A survey of flat profile microwave antennas”, Royal Military college of science, Tech.
A. Water man and D.Henrey, “Stripline strap on antennas”, presented at the 21st USAF antenna Symp.
H.P.Johnson, “An extremely thin Flush mounted slotted line array”, presented at the 16th USAF antenna Symp.
R.E. Munson, “microstrip phased array antennas”, presented at the 16th USAF antenna Symp.