BROADBAND COMMUNICATION USING MICROSTRIP PATCH ANTENNA
Here I discuss on topic BROADBAND COMMUNICATION USING MICROSTRIP PATCH ANTENNA. The basic geometry of a micro strip patch antenna (MPA) consists of a metallic patch printed on a grounded substrate. Three commonly used feeding methods are coaxial feed, strip line feed, and aperture-coupled feed. The patch antenna idea was first proposed in the early 1950s, but it was not until the late 1970s that this type of antenna attracted serious attention of the antenna community. The micro strip patch antenna offers the advantages of low profile, conformability to a shaped surface, ease of fabrication, and compatibility with integrated circuit technology, but the basic geometry suffers from narrow bandwidth. In the last three decades, extensive studies have been devoted to improve the performance of this antenna and the MPA has found numerous applications in both the military and the commercial sectors.
The micro strip patch antenna offers the advantages of low profile, ease of fabrication, and compatibility with integrated circuit technology. Active and passive circuit elements can be etched on the same substrate. It can also be made conformal to a shaped surface. Its main drawback is narrow bandwidth, typically less than 5%. The low profile advantage was particularly attractive for fast moving vehiclessuch as rockets, airplanes, and spacecrafts. Thus, it was not surprising that the early applications of MPA were in the military sector. With the development of techniques such as broadband and size reduction, theMPA soon found extensive applications in the commercial sector as well, and it is probably not an exaggeration to say that this type ofantenna has become the favorite of antenna designers.
The microstrip patch antenna inthe basic form of a conducting patch in a grounded substrate is inherently narrowband and is not able to meet the requirements of wireless communication systems. Whereas bandwidth can be increased by using lossy substrates,this is usually not desirable as efficiency will be reduced. In the last two and a half decades, a number of techniques have been developed to broaden the bandwidths of microstrip patch antennas, without compromising efficiency.The various designs provide bandwidths in the range from 10% to 60%.
The methods developed for efficient wideband patch antenna design are based on one or more of the following principles:
a) by means of parasitic elements or slots, additional resonances are introduced so that, in conjunction with the main resonance, an overall broader band response is obtained;
b) thick substrates of low permittivity are used;
c) a scheme is devised to reduce the mismatch problem associated with thick substrates.
We can use a broadband circularly polarized patch antenna using an artificial ground (AG) structure with rectangular unit cells as a reflector. The AG structure changes the reflection phase in accordance with the polarization state of the incident wave. By properly combining the transmitted wave from the antenna and the reflected wave from the AG structure, broadband circular polarization can be obtained. The AG structure and the antenna are simulated using a full-wave solver and the results show a 10 dB return loss bandwidth of 48.6% and a 3 dB axial ratio bandwidth of 20.4%.
A broadband microstrip patch antenna with double-layer substrate structure can also be used in case of broadband communications. The antenna is excited by a novel L-shaped coplanar waveguide(CPW) and can achieve wide bandwidths for Wibro (2300-2390MHz), Bluetooth(2400-2484MHz) and S-DMB (2605-2690MHz) operation. The antenna with three resonant frequencies at 2.25, 2.53 and 2.93GHz, provides 32.6% impedance bandwidth (2.18GHz ~3.05GHz) with return loss less than -10dB. The size of the antenna is 70*70*8mm. The study shows maximum achievable gain of about 8.4dBi and gain variation of 1.4dBi between the frequency ranges of 2.18GHz to 3.05GHz.
Another novel method of designing broadband microstrip antenna can also be used. By embedding a pair of Cross-shaped slots placed close to the non-radiating edges of a microstrip patch and adding an air layer between the substrate and the ground, the broadband character can be achieved.
What’s more, the formulas for calculating the two resonant frequencies have been experimentally deduced. Employing the method and the formulas, a antenna with a pair of double cross-shaped is designed. The measured bandwidth of 15.2% is achieved with small sizes, and the good radiation characteristic for operating frequencies within the impedance bandwidth is also observed.
Recently, broadband CP antennas are being more and more interested for applying in different communication systems such as thuraya satellite communication. Microstrip antennas are interested with the advantages of low cost, small size, low profile, conformity to the supporting structure and easy fabrication, and so to the microstrip broad band CP antennas. CP characteristic of microstrip antenna may be derived by approaches of single fed and hybrid fed . A single-fed CP antenna provides simple structure, easy manufacture, and advantage in array with small size. However, it has the disadvantages of both narrow AR bandwidth and impedance bandwidth. Many measures are taken for bandwidth widen of microstrip antennas. Stacked structure is an effective approach for enhancing the bandwidth for single fed microstrip antenna . For using stacked truncated square patches, relative bandwidth of 8% for AR value less than 3 dB is obtained. For using stacked almost square patches, relative bandwidth of 14% for AR value less than 3 dB isobtained.
For wireless communication systems, the antenna is one of the most critical components. A good design of the antenna can relax system requirements and improve overall system performance. A typical example is TV for which the overall broadcast reception can be improved by utilizing a high-performance antenna. The antenna serves to a communication system the same purpose that eyes and eyeglasses serve to a human. New antenna technologies such as smart antenna technology can significantly improve the performance of the system especially it provides a more efficient use of power and spectrum by separating the users through space division multiple access (SDMA) technique. The basic principle behind this is that these smart antennas have more gain comparatively to the ordinary one, with the minimal radiation patterns improves the communication links significantly. For such applications microstrip antennas are more preferred over other antennas because of their ease of analysis and fabrication and their attractive radiation characteristics, especially low cross-polarization radiation. The microstrip antennas are low profile, conformable to planar and nonplanar surfaces, simple and inexpensive to fabricate using modern printed-circuit technology, mechanically robust when mounted on rigid surfaces, compatible with MMIC designs, and very versatile in terms of resonant frequency, polarization, pattern, and impedance.