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Design of dual band pattern diversity antenna with RFSR.


An antenna is a device that is used to transfer guided electromagnetic waves to radiating waves in an unbounded medium, usually free space, and vice versa (i.e., in either the transmitting or receiving mode of operation). Antennas are frequency-dependent devices. Each antenna is designed for a certain frequency band. Beyond the operating band, the antenna rejects the signal. Therefore, we might look at the antenna as a band pass filter and a transducer. Antennas are essential parts in communication systems. Therefore, understanding their principles is important. In this chapter, we introduce the reader to antenna fundamentals. There are many different antenna types. The isotropic point source radiator, one of the basic theoretical radiators, is useful because it can be considered a reference to other antennas. The isotropic point source radiator radiates equally in all directions in free space. Physically, such an isotropic point source cannot exist. Most antennas' gains are measured with reference to an isotropic radiator and are rated in decibels with respect to an isotropic radiator (dBi).A Dual-band RFSR is created to develop a dual-band pattern reconfigurable corner reflector antenna. The dimensions of the proposed antenna are very small. The size in each dimension is less than of the lower frequency. The transmission and reflection characteristics of the RFSR at 2.45 GHz and 5.25 GHz are designed to be controlled by only one switch. That is, four switches are enough to configure the reflection states of the side walls of the antenna, in order to adaptively form the radiation patterns. The switching circuits and the impedance-matching networks can be hidden beneath the ground plane to prevent the unwanted influences on electromagnetic waves.

Litrature Survey:

The operation frequencies for the IEEE 802.11 a/b/g/n are one of the most crowded bands in wireless communications since they are unlicensed by any international agreement or government authority. Therefore, efficiently utilizing the limited spectrum in such bands is very crucial and indispensable. Many solutions in relative fields have been proposed or under development. The pattern diversity antenna is a good candidate to solve the problem and mitigate the multipath effects. Its radiation pattern can be shaped to concentrate the energy to the directions of targets and minimize the gain in unwanted directions. Generally, an Omni directional pattern is also provided to communicate in all directions. The most suitable pattern can be configured on demand with the pattern reconfigurable antenna. Numerous pattern-reconfigurable antennas stemmed from the variations of the Yagi-Uda antenna.

When the length of the parasitic element is shorter than that of the active element, a pulling pattern is obtained. On the other hand, if the length of the parasitic one is longer than that of the active element, a pushing pattern is formed. Therefore, different arrangements of parasitic elements with different lengths around the active element yield different radiation patterns. This offers a simple and flexible method for beam forming. However, in order to have pattern reconfiguration, their designs need to place switches on the reflectors or directors, and they may severely affect the radiation patterns when real switches are implemented.

Software Description:

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Dual Band Pattern Diversity Antenna:

The proposed dual-band pattern- reconfigurable antenna by the RFSRs. It consists of a dual-band feeding antenna in the center, four dual-band RFSRs on the side walls, and a finite-square ground plate on which the feeding antenna and RFSRs are perpendicularly mounted. Each dual-band RFSR has two groups of rectangular loops. The transmission and reflection properties of the RFSRs are controlled by four switches. In one switch state, both groups of rectangular loops are at resonance when excited by vertically polarized incident waves at the two resonant frequencies and, thus, the waves will be reflected. In the other switch state, those rectangular loops are out of resonance, so they are transparent to waves. Only one switch is needed for each dual-band reflector.

Multiple radiation patterns can be achieved according to the combinations of the switch states. The ground plane is on the top surface of an FR4 laminate. The dual-band Feeding antenna is located at the center of the ground plate and designed for operating at 2.45 and 5.25 GHz. The matching circuit for the feeding antenna can be printed on the bottom side of the ground substrate if necessary. In our work, a feeding antenna, Which has relatively broad bandwidths around both frequencies, was used. Hence, no additional impedance - matching network is required, which greatly simplifies the antenna design. Moreover, the associate circuits for the switches can also be fabricated underneath the ground plane. This advantage makes the design much easier since it can avoid the undesired electro-magnetic interactions between the antenna and the circuits.


(i) Antenna Size:

To design the proposed antenna, the spacing between the feeding antenna and he reflecting wall of a corner reflector antenna should be first determined. Then, the widths of the reflectors and the dimensions of the ground can be determined accordingly. shows the structure model used to determine the spacing. Two metal plates with a height of 40 mm are vertically mounted on the ground. The distance between the wall and the feeding antenna is denoted as . The width of these the metal walls is equal to twice the amount of spacing dimensions of the ground plate are fixed to be (140 mm, 140 mm) in this phase. The simulated radiation patterns for different spacing are shown in Figure It is found that the maximum gain and the shapes of the patterns at 5.25 GHz vary much with, whereas the patterns at 2.45 GHz are almost independent of . It is better to make the antenna as small as possible. In addition, the side lobe and back lobe levels are an important issue in a directional antenna. The patterns for 40 mm and 60 mm have inferior performances in terms of the front-to-back ratio, and the case with 20 mm has slightly lower directivity. Hence,by considering the aforemtioned factors, the spacing of 28 mm is chosen

(ii) Dual Band Feeding Antenna:

A dual-band feeding antenna that is less sensitive to the environment is required to maintain good impedance matching in different surrounding conditions caused by the combinations of the reflection states of the sidewalls. It is hard to use an impedance-matching network to satisfy the various radiating conditions at two frequencies. In this paper, the lower resonant frequency of the dual-band Feeding antenna is designed to be excited by couplings, which have relatively broad bandwidths at dual bands than by the conventional direct feeding method. Thus, acceptable return losses at the desired frequencies can be achieved for various switch states. The proposed dual-band feeding antenna is shown in Fig. 1 .It has two parts printed on both sides of a 0.8mm-thick, 30-mm wide and 40-mm-long FR4 substrate. The front part directly ex-cites the higher frequency radiation while the back part combined with the former by coupling effects resonates at the lower frequency. The suitable amount of coupling can be obtained by adjusting wt, h and g2. The optimized geometry parameters are shown in Table. I.




(iii)Dual-Band Rfsr:

The geometry of the dual-band RFSR is shown in Fig 4, which contains a center large rectangular loop for 2.45 GHz and two side small loops for 5.25GHz. The two small loops are connected by two side short vertical lines and a horizontal line of length 2L1. Notice that the horizontal line is close to the ground plane, with a spacing of only 0.5mm. Therefore, together with the ground plane, it forms a transmission line. For the central large loop, there is one central short line connected to the lower midpoint of the large loop.

A double-pole-double-throw switch (DPDT) is mounted on the backside of the RFSR to connect the center point a of the horizontal line, the end point b of the short vertical line, and the ground, where the point a and the point b are connected to the upper and lower input of the DPDT.

When the control signal is "on" both point a and b are switched to the right, which is short-circuited to the ground. On the other hand, when the control; signal is "off," both points are switched to the left, which are open-circuited. Through different states at the two points, the transmissive and reflective states can be controlled. According to the design in the previous subsection, the width W and the height H of the RFSR are set as 56 and 40 mm, respectively. In principle, the perimeter of a loop-type resonator should be about Hof the operating frequency.



The current distributions on these loops change significantly with the witch states, so their frequency responses are quite different in different switch states. Initially, consider only the center large loop and the side loop, but without the short vertical lines and the horizontal transmission line, Because of the symmetry in geometry and the perimeter, when vertically polarized plane waves at resonant frequencies impinge on the loops, current nulls appear at the midpoints of the top and bottom horizontal segments of the loops, and strong in phase currents occur at the midpoints of the vertical segments. Then, the reradiated fields excited from the induced currents would cancel the incoming waves at the backside of the reflector while generating a wave propagating toward the opposite direction. Hence, the RFSR structures reflect the incident waves back. Next, consider the existence of the transmission line and the vertical short lines. The end point b of the central short line connecting the bottom middle point of the center large loop is open-circuited if the switch is off. When a vertically polarized plane wave at 2.45GHz is incident on the center large loop, the open-circuit condition extends to the bottom middle point of the center loop because the length of the vertical line is relatively short compared with the wavelength of 2.45 GHz. As a result, the resonant current distribution excited by the incident wave remains as the one without the transmission line, and the incident waves will be reflected. In order to minimize the number of switches, we built a mechanism to configure the two groups of rectangular loops in the same state with one switch.


When a vertically polarized wave at 5.25 GHz is incident, due to the geometrical symmetry of the horizontal transmission line, an open circuit appears at the midpoint of this line when the switch is off. On the purpose of generating open circuits at both ends of the horizontal line, a -long transmission line at 5.25 GHz is required. According to the transmission-line theory, the open-circuit condition will show at the two ends of the line through the half-wavelength transformation at each side. As a result, the resonant current distribution excited by 5.25-GHz vertically polarized incident waves remains the same as the one without the transmission line, and incident waves will be reflected. The induced currents on the side small loops remain resonant.


Consequently, the RFSR is reflective at 2.45 GHz and 5.25 GHz when the switch is OFF. On the other hand, when the switch is on, the end of the central short line and the midpoint of the horizontal transmission line is short-circuited to ground. Nearly short-circuit conditions show at the bottom middle point of the center loop and at both ends of the horizontal line, which thus destroy the resonance requirement for both two types of loops. The induced currents will become weak and out of resonance, so that the re-radiated fields can be ignored. Consequently, the incoming waves will pass through the R.

Simulation Results (i)Return Loss:

The simulated return losses are shown in Fig.7. In the lower frequency band, the simulated -28dB bandwidth is from 2.31 to 2.76 GHz, and the best return loss occurs at 2.55 GHz. In the higher band, the simulated bandwidth is between 4.92 and 5.22 GHz and the best return loss occurs at 5.25 GHz. A slight frequency shift occurs in the higher frequency region and also occur one more bandwidth at 3.55, which might be caused by feeding method.


(ii)Radiation Pattern:

The measured radiation patterns of Cases 1 2.55 GHz shown in Fig 8. In Case, the maximum gain at 2.55 GHz of 50 dBi Therefore, good directivity can be achieved in Case 1, good Omni directional patterns are observed within 0 <0< 60o The shape of the Omni directional pattern is conical above the ground plane in 3-D space.





To prevent the unwanted influences on electromagnetic waves interaction between the antennas, Its compact size, Dual band operation and simple control scheme, The Frequencies are unlicensed by an international agreement or government authority. It makes the design much easier. No additional Impedance matching network is required.


In this paper compact dual-band pattern diversity antenna has been presented. This antenna combines the corner reflector antenna and dual-band RFSR. Each dual-band RFSR can be controlled to be transmissive or reflective to waves at a designated frequency with only one switch. Dual frequency bands around 2.45 GHz and 5.25 GHz by configuring the combination of the switch states. In the directional case (i.e., Case 1), the main lobes pointed toward the direction where the switch states are OFF at both frequencies. They are good enough to enhance the desired signals and minimize the unwanted ones. In the omnidirectional (ie, case 2) the proposed antenna has small pattern variations which are good for broad-casting communication. It is easy to integrate into many wireless communications systems.


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(1) S. Sankaranarayan, (2) Dr.M. Anto Bennet, (3) G. Vishaka, (4) R. Vimala, (5) S. Ashwini

(1) Assistant Professor, (2) Professor (3, 4, 5) UG Student, Department of Electronics and Communication Engineering, , VELTECH, Chennai-600062

Received 25 January 2016; Accepted 28 April 2016; Available 5 May 2016 Address For Correspondence:

Table I: Design parameters of dual band feeding antenna


h           2mm
ht1         1.5mm
ht2         3.75mm
lf1         10.5mm
lf2         11.25mm
g           4.25mm
Wf          10mm
[g.sub.1]   0.5mm
[g.sub.2]   0mm

Table II: Result of Design parameters of Proposed dual band RFSR

PARAMETERS             RFSR At 2.45GHz   RFSR At 5.25GHz

Max U (W/sr)           3.29637           3.29637
Peak Directivity       2.4708            57.9358
Peak Gain              2.4584            60.7728
Peak Realized Gain     2.2887            41.423
Radiated Power (W)     0.92631           0.715004
Accepted Power(W)      0.9309            0.6816
Incident Power(W)      1                 1.00003
Radiation Efficiency   0.9949            1.0489
Front to Back Ratio    1.0701            547.846
Delay Factor           0                 0
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Author:Sankaranarayan, S.; Bennet, Dr.M. Anto; Vishaka, G.; Vimala, R.; Ashwini, S.
Publication:Advances in Natural and Applied Sciences
Date:May 15, 2016
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