How a Folded Loop Antenna can Reduce Radiation Emission for Mobile Devices

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Abstract

This research paper sample provided by a professional academic writer from SmartWritingService.com essay writing company proposes an antenna made by combining elements of a planar inverted-F antenna with an added branch line for wide bandwidth and a folded-loop antenna. The loop antenna serves to reduce radiation and increase the working capability of the larger antenna.

Introduction

A loop antenna is an antenna made up of small multiple turns that are either circular or rectangular. Their dimensions are less than a wavelength and kept to the minimum which in turn ensures that current in the loop are always in phase. Due to this small size, current is constant at the circumference which in turn ensures that voltage induced along the plane of the loop cancel each other any time a perpendicular signal arrives at the axis making it null. Since the radiation pattern peaks in directions lying in the plane of the loop, signals received along that plane do not cancel each other due to the phase difference between the waves at the near side and far side of the loop. An effective way of tackling this and increasing its radiation resistance is by increasing the size of the loops which will further improve the efficiency of the loop. This goes a long way in reducing radiation leaks in antennas.

Full wave loop antennas are quieter than dipoles and have more gain broadside to the plane of the loop. It doesn’t have a particular shape that is effective as both circular and rectangular loops work alike. 

In this research paper, we used an antenna operating at a frequency of 2400 MHz.

Antenna Design

The antenna is designed on an FR-4 substrate of dimension 55mm x 110mm x 1mm with the dimensions of the antenna being 55mm x 12 mm x 4mm. The figure shows the radiating component of the design. The left-side structure is designed as a folded loop to make it a high-frequency band with a wide-bandwidth as a result of its 4mm thickness.PIFA on normal occasions have an insufficient frequency bandwidth for wireless communication,  so the antenna is designed with an PIFA with an added line that helps increase its bandwidth generating higher resonance as a result of the diverted capacitance between the line and the ground.

.Antenna under modification.

Design Procedure

Divide the antenna into two; a folded-loop and an MPIFA structure. The figure below (figure 2) shows the simulated characteristic of the two antennas.

The folded-loop antenna (Ref. 1), which has a high-frequency band, has a wide return loss bandwidth which is expected for its frequency, while the element of the MPIFA (Ref. 2) has narrow bandwidths at both the low and high bands.

 

When parametric studies and optimization are executed for impedance matching and determining each resonance frequency, the results are as below; (Figure 3)

 A decrease in W1 shifts the second resonant frequency to the flower frequency side and its matching impedance improved. The high-frequency band however remains unaffected.

We next try and test the effect a change in height has for the high-frequency band. When h, is increased, the return loss characteristic of the high-frequency band seems to increase and improve.  The same is not seen for the low-bend frequency band. Its resonance is largely maintained at between 800-980 mhz. this new bandwidth at the high-frequency band satisfies the GSM, UMTS, and LTE bands.

When the width is changed, the second resonance in the high-frequency band shifts on the increasing side-widener the overall bandwidth of the high-frequency band. This is observed in the figure below.

When the gap distance is shifted, the following can be observed as the distance is increased, the branch line becomes larger and the second resonance in the low-frequency band shifts toward the low-frequency side. When the distance G=0.5mm, the antenna has a dual resonance characteristic in the low-frequency band and the antenna satisfies 6 dB return loss bandwidth over the GSM 850 and GSM 900 bands. This results in a return loss bandwidth of 166 MHz (809–975 MHz) at the low-frequency band and at the high-frequency band it is 1028 MHz (1675–2703 MHz)  and can be observed in the figure below:

Results and Discussion

When we simulate the surface current distribution of the MPIFA, there’s a branch line at each low-band frequency resonance. One path flows through the MPIFA, while the other is formed due to the coupling between the branch line and the ground. This strong coupling of the two reduces the radiation of the antenna but there is a solution to this. We add a parasitic stub at the end of the branch line that was added and it stabilizes and becomes more efficient. These observations are illustrated below

This shows the first resonance at low band (850 MHz)

This image is the second resonance at low band (930 MHz)

 

First resonance at high band (1810 MHz)

Second resonance at high band (2640 MHz).

When the radiation patterns are measured, the results are as below:

At low frequencies of 828 and 902 MHz, the antenna shows omnidirectional patterns. At high frequencies of 1850 and 2680 MHz, the antenna shows directional patterns. These radiation patterns are suitable for practical mobile communication systems and show the effectiveness of this newly combined and made antenna in reducing the radiation problem in mobile communication devices.

We also evaluated the specific absorption rate (SAR) of the antenna, using SAR mockup model that includes head and hand phantoms supported by SEMCAD. The relative permittivity and conductivity of the phantom used in the simulation are listed in Table below:

We also measured the SAR distribution for the antenna on the head phantom. We used the SPEAG dissymmetric assessment system (DASY-4) to perform SAR measurements [15]. The 1 g and 10 g SAR values when the input power is 0.1 W and input powers that should not exceed the SAR limit [14] are listed in Table attached below. The antenna is attached to the phantom without a case resulting in higher measured SAR values than the simulated ones.

 

Distributions for the head phantom for different weight units are as below

Conclusion

This research paper proposes a new type of antenna that combines elements of two different types of antennas to build and enhance the mobile phone antenna. The new antenna is seen to have better working as well as has reduced the radiation released by mobile phones.


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