Microstrip Antenna Pattern Reconfiguration Using On-Chip Parasitic Elements

In this paper, a design of pattern reconfigurable microstrip patch antenna and its simulation using CSTMW simulator is presented. The designed antenna is also fabricated and tested. The design consists of microstrip patch printed on FR-4 substrate with a coaxial line feeding on the back of the antenna which is the active element. Two on-chip parasitic elements (OCPE) also are printed on FR-4 substrate, each of which connected through a via hole to the ground. The proposed design has the advantage of movable parasitic chip elements with the same motherboard to control the reconfigurable pattern direction as well as operating frequency. It is also have the advantages of parasitic elements rotation to fit reception/transmission required steering angle. The results obtained show that the steering angle of the main beam in the H-plane depends upon the dimension of the parasitic element substrate as well as the type of the patch antenna. The presented antenna is suitable for different application, including Wifi and WiMax systems. <br>


Introduction
Over the past ten years, many antennas have been proven to be a very effective and sensitive part a communication system. Interference, energy waste, noisy environment and shadowing are the most serious problems that result in performance degradation of wireless communication systems. The solution to these problems is to direct the pattern to a desired user. This can be carried out using pattern reconfiguration (steering pattern) antenna techniques. This can effectively save energy and also overcome reception of unwanted signals. Antenna reconfiguration is classified into three categories, namely frequency, pattern and polarization reconfiguration. The first type is based upon controlling the frequency of radiating element within a specific margin without changing other radiating characteristics. One method or realizing frequency reconfiguration is by using Micro Electro Mechanical System Switch MEMS switches to switch between three types of antennas combined in one body to select different frequency bands (0.824-0.894 GHz, 1.75-2.48 GHz, 3.3-3.6 GHz) [1].Another approach is based upon using planar inverted F-antenna and a monopole antenna embedded in the same type of radiating element without changing switch between two slots in the ground plane designed in the patch to select either circular or the antenna radiation pattern between end fire and broad side reconfigurable antenna. One of these techniques is based with an active element and switch between one of them using technique relies upon using the same RF switches to switch between two types of antenna steer the main beam to certain approach by varying the permittivity of the substrate reconfigurable antennas can be implemented to control the antenna characteristics including frequency/pattern and/or polarization to short annular slot antenna in a preselected position to reconfigure its pattern [ in different application in wireless systems such as WiMax application as d paper, a modified version of the microstrip patch antenna is carried out by replacing the parasitic elements hole). This provides a switchable pattern toward certain direction package. It has also physically implemented and tested. both cases. The paper is arranged as section 2. Results discussions conclusion is in section 4.

Antenna Design and
The microstrip patch antenna that chip parasitic elements on the sides of an active patch instead of putting them on the same substrate with the active element. The design consists of the "subminiature version A" ( two parasitic elements located longitudinally proposed design allows the removal, rotation conditions. The proposed antenna figure1. The central element is the active patch which has and it is fed through an SMA probe from the back of the substrate of dimensions 30.0x60 optimized desired input impedance.
International Journal of Antennas (JANT) Vol. 1, No.1, October 2015 monopole antenna embedded in the same space [2]. The second type is to control the polarization without changing its orientation. This is done by using pin diodes to the ground plane [3], or using them to switch between either circular or linear polarization [4]. The last type either by changing the steering angle or by changing between end fire and broad side types. Other techniques have been devised to . One of these techniques is based upon using two parasitic elements active element and switch between one of them using pin/varactor diodes using the same RF switches to switch between two types of antenna steer the main beam to certain angles [8]. The main beam can also be steered using the permittivity of the substrate using applied DC volt [9].Other types of can be implemented to control the antenna characteristics including nd/or polarization by reconfiguring slot depth in each part of the to short annular slot antenna in a preselected position to reconfigure its pattern [11] in different application in wireless systems such as WiMax application as done by [12]. modified version of the microstrip patch antenna given [5] is presented. The modification is carried out by replacing the parasitic elements by parasitic chips with a short circuit switch (via switchable and movable parasitic chip that result in steering toward certain direction. The proposed antenna has been simulated using t has also physically implemented and tested. Satisfactory results have been obtained paper is arranged as follows the proposed design is described and presented s and experiment verification are given in section 3

. Antenna Design and Operation
The microstrip patch antenna that has been designed in [5] is modified by introducing chip parasitic elements on the sides of an active patch instead of putting them on the same substrate with the active element. The design consists of an active element which is (SMA) cable from the back of the antenna. In addition, there are located longitudinally on both sides of the active element design allows the removal, rotation or insertion of elements in order to fit operational antenna with the active patch and the two parasitic patches the active patch which has the dimensions W=16 mm, L= SMA probe from the back of the antenna, which is located 60.0 mm 2 with thickness 1.6 mm. Feeding location "a" optimized desired input impedance. 50 the polarization by using pin diodes to using them to switch between cross slots The last type is to change or by changing patterns realize pattern parasitic elements along [5][6][7]. Another using the same RF switches to switch between two types of antennas to . The main beam can also be steered using another Other types of can be implemented to control the antenna characteristics including of the ring [10] or ].This may use one by [12].In this . The modification with a short circuit switch (via in steering far field using CST-MW have been obtained in described and presented in , and finally a introducing two onchip parasitic elements on the sides of an active patch instead of putting them on the same is connected to addition, there are the active element. The new or insertion of elements in order to fit operational patches are shown in W=16 mm, L=11.3 mm located on a FR-4 location "a" is chosen to The two parasitic elements which have the dimensionW1= 0.9W mm, L1= 0.97 L mm are set on a substrate FR-4 substrate with a thickness of 1.6 mm and copper pins used as switches. The pins exist in the parasitic elements located on the lower left hand corner of the left element or on the lower right hand corner of the right element. These switches have three modes, namely directorreflector (DR) mode, reflector-director (RD) mode and reflector-reflector (RR) mode. The DR mode exists when pin in right element is shorted (the right element is reflector, left element is director). The RD mode exists when pin in left element is shorted (the right element is director, left element is reflector), The RR mode exists when pins in left, right element are shorted (the right, left elements are reflectors). Coupling between active and parasitic elements, controls the radiation pattern. The physical dimensions of the proposed antenna are given in Table 1. It is worth noting that the dimension selected are the same as those of the antenna given in [5] in order to make it easier to comparison.

Results Discussion and experimental verification
The proposed microstrip antenna has been simulated using CST software package when different types of substrate have been used. Table 2 gives a summary of the results if using different substrate with different values of relative permittivity (ε r ) at the same height as the motherboard which is 1.6mm. The optimum physical dimension of this antenna is shown in the first row, which gives the better efficiency and doesn't shift the resonance frequency because of using the same material substrate as the mother board. This results in reducing the losses that may occur when using different material substrates. Electronic copy available at: https://ssrn.com/abstract=3429013 As could be noticed from Table 2, the tilt angle of the far field pattern is highly affected by the material relative permittivity and it is little bit shifted when using material with small relative permittivity while it is largely changed when using high ones. Side lobe levels also increase as the material relative permittivity increases. This is because of high losses in case of high relative permittivity materials. The reflection coefficient curves for dielectric materials with different relative permittivity are shown in Figure 2, It is observed from Figure 2 and table 2 that increasing value of the parasitic relative permittivity, increases main lobe tilt angle and decreases bandwidth and gain. It is clear that as the dielectric permittivity increases the return loss increases hence very small amount of power is forward to radiating element and hence radiating characteristics can be degraded. The best result occurs when we choose parasitic elements substrate to be of the same material as that of mother board (Fr4=4.3). This reduces the dielectric losses that may occur when choosing different materials with different relative permittivity. It is also noticed from the curve that, as the value of parasitic element material relative permittivity exceeds that of the relative permittivity of mother board, the resonance frequency shifted by 100 MHz. Electronic copy available at: https://ssrn.com/abstract=3429013    . The optimum this antenna is shown in the first row which gives reasonable Figure 3 illustrates the relation between the return loss (s frequency for different values of the substrate heights (h 2 ).It is noticed that as the thickness of decreases, the losses due to surface waves decrease and decreasing side lobe level. On the other hand, increasing the thickness results in better notch Electronic copy available at: https://ssrn.com/abstract=3429013  It is clear that the main beam direction is the same for both simulated and measured results. shows the comparison between simulated and measured S 11 for active element only is noticed that the resonance frequency is little bit shifted but it still -5.8GHz), Figure 6(b) shows the simulated and measured S for the case of existing parasitic elements with different switching modes. It is noticed that there result; this is due to connector and soldering effect. Figure measured radiation patterns for the designed antenna at various switching It is clear that the main beam direction is the same for both simulated and measured results.
(a) (b) (a) simulated and measured |S 11 | for active element,(b)S11 measured results for various switching modes.

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for active element only shifted but it still (b) shows the simulated and measured S 11 that . It is noticed that there effect. Figure 7 shows ious switching It is clear that the main beam direction is the same for both simulated and measured results. The designed antenna has the ability to rotation could be either clockwise or counter clockwise as shown in Figure  flexibility in the design to meet different application needs. This is a major existing similar antennas. However limited to certain values. Table 4 gives the result of a simulated design in which the parasitic elements have been rotated counter clockwise with different restricted angles.  The designed antenna has the ability to rotate the parasitic elements around switches rotation could be either clockwise or counter clockwise as shown in Figure 8. This allows more flexibility in the design to meet different application needs. This is a major advantage over However, Due to geometry restrictions the rotation angle will be Table 4 gives the result of a simulated design in which the parasitic elements have been rotated counter clockwise with different restricted angles.
: rotated parasitic elements clockwise and counter clockwise direction parasitic elements around switches exist; the . This allows more advantage over ns the rotation angle will be Table 4 gives the result of a simulated design in which the parasitic elements have been rotated counter clockwise and counter clockwise direction It is clear from this table that the tilt angle is affected by the rotation of the parasitic elements. But the parameters are in general not much affected. Figure 9: rotation angle versus pattern tilt angle Figure 9 shows the relation between parasitic element orientation and the beam tilt angle. It is clear that the relation is non-continuous. This means that an optimization process should be adopted to select the suitable rotation angle to give the required beam tilt angle.  Table 5 gives a comparison between the simulated results of the patch with rotated parasitic elements (γ=10°), and the patch with non-rotated parasitic elements (γ=0°) and the patch in ref [5]. It is clear that the highest tilt angles are obtained with the rotated patches. The result is also illustrated in the simulated farfield patters of the three cases in figure 7. Electronic copy available at: https://ssrn.com/abstract=3429013  Figure 10 shows the reflection coefficient difference between previous and proposed design. It shows that proposed design has wider bandwidth at the same resonance frequency and the rotated parasitic elements give deeper notch ever. Figure 11.Simulated far field patterns for pervious and Figure11 (a) illustrate H-plane radiation pat and rotated parasitic elements by 10°.It is noticed that side lobe level is reduces in proposed work and the tilt angle deflects toward 28° instead of 34° as the parasitic elements rotated by 10° it will give better tilt angle to 43° which is 79% better th (θ=90°) in which the main beam tilt angle decreased and also beam width while side lobe level decreases. Figure11(c) illustrate E changes anymore and beam width become more directive.

Conclusion
International Journal of Antennas (JANT) Vol.1, No.1, October 2015 Reflection coefficient for pervious and proposed work shows the reflection coefficient difference between previous and proposed design. It shows that proposed design has wider bandwidth at the same resonance frequency and the rotated parasitic elements give deeper notch ever. ld patterns for pervious and proposed work: (a) H-plane (φ =0°), (θ=90°) and (c)E-plane(φ=90°) plane radiation pattern in the patch given in [5], and the purposed design and rotated parasitic elements by 10°.It is noticed that side lobe level is reduces in proposed work and the tilt angle deflects toward 28° instead of 34° as the parasitic elements rotated by 10° it will give better tilt angle to 43° which is 79% better than [5] . Figure11 (b) illustrate X =90°) in which the main beam tilt angle decreased and also beam width while side lobe level (c) illustrate E-plane (φ=90°) in which the main beam tilt angle doesn't idth become more directive. 60 shows the reflection coefficient difference between previous and proposed design. It shows that proposed design has wider bandwidth at the same resonance frequency and the rotated φ =0°),(b) X-Y plane purposed design and rotated parasitic elements by 10°.It is noticed that side lobe level is reduces in proposed work and the tilt angle deflects toward 28° instead of 34° as the parasitic elements rotated by 10° it will b) illustrate X-Y plane =90°) in which the main beam tilt angle decreased and also beam width while side lobe level =90°) in which the main beam tilt angle doesn't Pattern reconfigurable microstrip antenna with on chip parasitic elements has been proposed and designed. It has been demonstrated that flexible pattern reconfigurable antenna can be achieved with better gain of 5.6 dB and bandwidth of 309MHz. The proposed design is characterized by physical removal or placement of parasitic elements so as to fit system requirements or environmental changes. The compact size of the antenna and its characteristics makes it appropriate for WiMax and Wifi application.