13-11-2012, 01:28 PM
BROADBAND DESIGN OF MICROSTRIP ANTENNAS: RECENT TRENDS AND DEVELOPMENTS
[attachment=39226]
INTRODUCTION
With the development of MIC and high frequency semiconductor devices, microstrip
has drawn the maximum attention of the antenna community in recent years. In spite of
its various attractive features like, light weight, low cost, easy fabrication, conformability
on curved surface and so on, the microstrip element suffers from an inherent limitation of
narrow impedance bandwidth. So, along with other developments, widening the
bandwidth of microstrip elements, in general, has become a major branch of activities in
the field of printed antennas. Three books [1-3] and three book chapters [4-6] have
covered the developments occurred time to time during the last two decades. But the
advancement in this area is so fast and volumous that a review at every considerable
interval of time adds new techniques, structures and results.
In this paper, the author intends to present a comprehensive review of bandwidth
enhancement techniques in general with a major emphasis on the recent trends and
developments. The new investigations and their results show the maturity of this field of
research and also indicate the lacunae along with the scope of future works.
GUHA
Optimization of patch geometry is an ideal technique to have single or more
optimized figures of merit like, impedance bandwidth. The GA has been successfully
applied by a number of researchers to improve the impedance bandwidth . The optimized
shape, however is too much irregular and unconventional and as such this can only be
fabricated using the pattern produced in true scale by the GA code. One example of shape
optimization of a microstrip patch using the GA is shown in Fig. 3.
The principle of introducing low Q-factor of the cavity below the patch can be
achieved by lowering the dielectric constant of the substrate or by increasing the substrate
thickness. The latter one is more flexible for design purpose but restricted by the surface
wave generation leading to low gain and low efficiency of the antenna. Use of the PBG
structures as antenna substrates is one promising solution to this problem and thus it
attracts a large fraction of antenna people to work with PBG. [12-15]. The PBG structure
is basically a periodic metallic pattern printed on dielectric substrate for microwave and
millimeterwave applications and this provides a stop band of electromagnetic waves
propagating through it. The frequency range of the stop band depends on the pattern
geometry and its dimensions. If the antenna operating frequency falls within this stop
band, it is attenuated during propagating through the substrate. Thus the generation and
propagation of surface wave is stopped. Horii and Tsutsumi [15] used a two-dimensional
PBG pattern in the ground plane beneath the square patch. They used a 76×76 mm2
square patch on the glass-epoxy substrate with dimensions of 200×250×1.6 mm3 having
relative permittivity of εr = 4.8. 3×4 circles with diameter of 18mm were etched in the
ground plane at the period of 38mm as shown in Fig. 4. This arrangement produces the
required PBG structure having the stop band characteristic of the transmission parameter
at more than −20 dB form 1760 to 2720 MHz.
CONCLUSION
Enhancement of the impedance bandwidth of Microstrip elements is a challenge to
the researchers. Various techniques have been developed during last two decades. Still a
significant fraction of researchers is involved in this area resulting in new techniques
which are almost in their infancy. The techniques employing GA optimization of patch,
PBG structures as no-surface-wave-substrates, multiplayer FSS or FSS ground plane and
various new geometries with feed compensation are discussed. The first three techniques
are in their infancy and hence very few results are available in the literature. But the trend
reveals their highly promising scope in antenna applications.
[attachment=39226]
INTRODUCTION
With the development of MIC and high frequency semiconductor devices, microstrip
has drawn the maximum attention of the antenna community in recent years. In spite of
its various attractive features like, light weight, low cost, easy fabrication, conformability
on curved surface and so on, the microstrip element suffers from an inherent limitation of
narrow impedance bandwidth. So, along with other developments, widening the
bandwidth of microstrip elements, in general, has become a major branch of activities in
the field of printed antennas. Three books [1-3] and three book chapters [4-6] have
covered the developments occurred time to time during the last two decades. But the
advancement in this area is so fast and volumous that a review at every considerable
interval of time adds new techniques, structures and results.
In this paper, the author intends to present a comprehensive review of bandwidth
enhancement techniques in general with a major emphasis on the recent trends and
developments. The new investigations and their results show the maturity of this field of
research and also indicate the lacunae along with the scope of future works.
GUHA
Optimization of patch geometry is an ideal technique to have single or more
optimized figures of merit like, impedance bandwidth. The GA has been successfully
applied by a number of researchers to improve the impedance bandwidth . The optimized
shape, however is too much irregular and unconventional and as such this can only be
fabricated using the pattern produced in true scale by the GA code. One example of shape
optimization of a microstrip patch using the GA is shown in Fig. 3.
The principle of introducing low Q-factor of the cavity below the patch can be
achieved by lowering the dielectric constant of the substrate or by increasing the substrate
thickness. The latter one is more flexible for design purpose but restricted by the surface
wave generation leading to low gain and low efficiency of the antenna. Use of the PBG
structures as antenna substrates is one promising solution to this problem and thus it
attracts a large fraction of antenna people to work with PBG. [12-15]. The PBG structure
is basically a periodic metallic pattern printed on dielectric substrate for microwave and
millimeterwave applications and this provides a stop band of electromagnetic waves
propagating through it. The frequency range of the stop band depends on the pattern
geometry and its dimensions. If the antenna operating frequency falls within this stop
band, it is attenuated during propagating through the substrate. Thus the generation and
propagation of surface wave is stopped. Horii and Tsutsumi [15] used a two-dimensional
PBG pattern in the ground plane beneath the square patch. They used a 76×76 mm2
square patch on the glass-epoxy substrate with dimensions of 200×250×1.6 mm3 having
relative permittivity of εr = 4.8. 3×4 circles with diameter of 18mm were etched in the
ground plane at the period of 38mm as shown in Fig. 4. This arrangement produces the
required PBG structure having the stop band characteristic of the transmission parameter
at more than −20 dB form 1760 to 2720 MHz.
CONCLUSION
Enhancement of the impedance bandwidth of Microstrip elements is a challenge to
the researchers. Various techniques have been developed during last two decades. Still a
significant fraction of researchers is involved in this area resulting in new techniques
which are almost in their infancy. The techniques employing GA optimization of patch,
PBG structures as no-surface-wave-substrates, multiplayer FSS or FSS ground plane and
various new geometries with feed compensation are discussed. The first three techniques
are in their infancy and hence very few results are available in the literature. But the trend
reveals their highly promising scope in antenna applications.