A Fullwave Loop and a Quarter Wave Monopole Antenna: a Comparative Study and Performance Analysis

A Fullwave Loop and a Quarter Wave Monopole Antenna: a Comparative Study and Performance Analysis

1B O. Sadiq, 1Obi E., 2Ibrahim Y., 2Kabir M. T. and 3Umar G.

Department of Electrical and Computer Engineering, Ahmadu Bello University, Zaria.

Abstract – This paper presents the performance analysis of a Full-wave Loop Antenna and a Quarter Wave Monopole Antenna. The Radiation Patterns of the two antennas were generated using the Lab-Volt Antenna Measurement System with a view to evaluating the Half Power Beam width, Directivity and Directive Gains of the two antennas. The directivity of the quarter wave monopole antenna was found to be 4.6dB which is almost twice 2.43dB of the full- wave loop antenna. Also, the directive gain of the quarter wave monopole antenna was found to be 1.96 dB higher than that of the full-wave loop antenna which was found to be -0.22dBd.

Keywords: Directivity, Beam width, Directive gain and Radiation pattern.

General Terms: Full wave loop antenna and Quarter wave monopole antenna

1. INTRODUCTION

In wireless radio communication, the information is a low frequency signal (audio or video). It isdesired to convey these low frequency signals to any location without difficulty. This brings about the need for antennas to send and to receive the information [1]. Wireless communication includes the radiation of waves by the transmitting stations, the propagation of these waves and their reception by the receiver. This papercompares the performance of a full wave loop antenna and a quarter wave monopole antenna based on radiation pattern plot and parameters such as; half power beamwidth, directivity and gain.Antenna can be said to be a transducer that converts electromagnetic energy to electrical energy and vice versa [2]. Different types of antennas can be categorized according to different parameters which are Bandwidth, Polarization, Resonance, Physical Structures and Number of Elements [1]. The radiation pattern or antenna pattern is the graphical representation of the radiation properties of the antenna as a function of space [3]. The antenna's pattern describes how the antenna radiates energy out into space (or how it receives energy). An antenna's beam width is usually referred to as half-power beam width. Antennas do not radiate energy equally in all direction [4]. Directivity is a measure of the concentration of radiation in the direction of the maximum. Given the half-power beam widths of the principal plane patterns, the directivity is approximately the product of the beam widths. Gain is a measure of the ability of the antenna to

direct the input power into radiation in a particular direction and is measured at the peak radiation intensity. The gain of antenna can be either directive gain or a power gain [5]. Directive gain of an antenna is a relative measure of the directivity of an antenna with respect to an isotropic radiator. Because an isotropic radiator is purely theoretical, the directive gain is evaluated with a reference to an omnidirectional antenna typically a half wave dipole antenna.

Antenna is a vital component of the wireless radio communication system. Several works have been carried out with a view to analyzing the performance of different types of antenna, amongst which are [5, 7, 8, and 9]. The authors in [5] studied the characteristic behavior of the feed-point input impedance and radiation fields of two thin-wire loop antenna types (one a circular-loop and the other, a square-loop antenna) both one wavelength long. The result indicated that the antennas' directive gains and input impedance profiles may be suitable for practical applications over a wide range of frequencies. In [7], the impact of rectangular plane ground on the radiations pattern of the monopole antenna was analyzed. The result showed that the larger the ground plane, the lower the direction of maximum radiation and as the ground plane approaches infinite size, the radiation pattern approaches maximum in the x-y plane. The authors in [8] analyzed the Radiation Characteristics of a Quarter-Wave Monopole Antenna above Virtual Ground. Analysis of the result shows that, for the case of the quarter-wave monopole antenna, twice the gain of a dipole antenna of half-wave- length long was achieved and the value of radiation resistance of the monopole is half of that of a dipole. [9] Analyzed the radiation pattern of a delta loop antenna with center fed ant apex feed at 1000MHz. The antennas were constructed of solid aluminum conductor and aluminum tube with arm lengths of 30cm each. Radiation pattern measurements on delta loop were made at 1000MHz. the vertically oriented delta-loop antenna provided the highest gain of 24dB as compared to the lowest gain of 12dB provided by the horizontally oriented delta-loop antenna.

2 METHODOLOGY

The methodology adopted for this work is as follows:

1. Setting up the LAB-VOLT Antenna Measurement System with a view to evaluating the Half Power

   Beamwidth, Directivity and Directive Gains of the two antennas.

2. Obtaining the characteristics of a full-wave square loop antenna

3. Obtaining the characteristics of quarter wave monopole antenna

4. Analyzing the results obtained

5. Comparison of the antennas based on the results obtained

2.1 Initializing the setup

The main elements of the Antenna Training and Measurement System that is the Data Acquisition Interface/Power Supply, the RF Generator, the Antenna Positioner and Computer were properly set up before beginning this experiment. The antenna mast with a horizontal clip was placed on the transmission support. The Yagi antenna was placed onto the mast oriented for an acquisition in the E-plane, and it was connected to the 1 GHz oscillator output of the RF Generator using the long SMA Cable. A receiving antenna was set up, the antenna mast with horizontal support was placed on the sliding support of the antenna positioner and the receiving antenna was attached to the mast for acquisition in E-Plane for both the loop and monopole. The antenna was adjusted so that it is in line with the rotation center of the antenna positioner. The 10dB attenuator was screwed to the RF output on top of the antenna positioner. And the antenna was connected to the attenuator using the intermediate SMA Cable. The antennas were positioned at a distance of r = 1m apart, and they were adjusted so that they were at the same height and facing each other directly.

The following adjustments were made ON THE RF GENERATOR

1GHz oscillator mode1 kHz 1GHz oscillator RF powerOFF 10GHz oscillator RF power..OFF

The RF Generator was powered up and then the computer was turn on and the LDVAM-ANT software was started. The 1GHz oscillator RF Power switch on the RF Generator was set up to on position. The attenuation level was adjusted to 6dB and this level was maintained throughout this experiment. An acquisition was performed and stored as an E-plane of document1. The mast with vertical clips was removed and replaced with the mast with horizontal clips and the transmitting antenna was rotated so that it was vertically polarized. An acquisition was performed and saved as an H-plane of document 1. The half power beam width of the full-wave loop antenna and quarter wave monopole antenna E-plane and H-Plane was evaluated. The antenna mast of the receiving antenna, with horizontal clips, was removed from the sliding support and was

replaced with the one with vertical clips and then a

2

dipole was set up, the transmitting antenna was rotated so

this orientation was taken and saved as E-Plane of document 2.The E-plane of the dipole and that of the full wave loop antenna and the quarter wave monopole antenna were compared and the gain of both the full wave loop antenna and the quarter wave monopole antenna was evaluated.

1. RESULT AND DISCUSSIONS

   The analysis of the result are discussed as follows:

2. Analysis of Full-Wave Loop Antenna

Figure 1 shows the E-Plane and H-plane plots of the radiation pattern of the full-wave loop antenna in two dimensions.

Figure 1: The 2 dimensional radiation pattern of the loop antenna

The radiation pattern plot of the full-wave square loop antenna obtained in Cartesian form is as shown in Figure 2

Figure 2: The E-Plane and H-Plane Radiation Pattern of the Loop Antenna in Cartesian Form

There 3 Dimensional plot of the radiation pattern of the full-wave square loop antenna is shown inFigure 3

Figure3: The 3 Dimensional View of the Loop Antenna Radiation Pattern

From the radiation pattern diagrams of the full-wave square loop antenna (in Cartesian form) above, it can be seen that the main lobe occurs at about 150 and 1950. This means that the antenna has a maximum radiation at 150 and 1950 away from the transmission antenna.

3.1.1 Halfpower Beamwidth

Directivity = 1.75

In decibel,

Directivity = 10Log10 1.75 = 2.43dB

In order to evaluate the directive gain, the directivity of the dipole antenna must be evaluated so as to have a reference value to which the directivity of the loop will be compared. The E-Plane Half Power Beam width of the dipole has been evaluated by the software as 124.720 as shown in Figure 3.10. The H-Plane Half Power Beam width of the dipole is 1800. This due to the fact that the dipole is omnidirectional (having circular radiation pattern in the H- Plane)

Figure 5: E-Plane Half Power Beamwidth of the dipole antenna

The approximate directivity of the dipole is calculated as

This is the angular separation between which radiation pattern decreases by 50% or 3dB. For this square loop antenna, the E-Plane and H-Plane Half Power Beam widths

Directivity = 41252 HPBW E ×HPBW H

1.84

Directivity = 41252 =

124 .72×180

were found by the software as 86.570 and 271.470; that is, between -32.220 and 53.350 for the E-Plane and between –

135.70 and 135.770 for the H-Plane on the Cartesian Plot.

In decibel (dB),Directivity = 10log101.84

= 2.64 dB

The directive gain of the loop antenna is obtained from

These values of E-plane and H-plane half power beam width were found with the aid of the LDVAM-ANT

Directive Gain = 10log

D

10 [ ]

Dref

software as in Figure 4

Figure 4: The E-Plane and H-Plane Half Power Beamwidth

The approximate directivity of the full-wave square loop antenna can be calculated using the relation as shown below.

In this case, Dref is the reference directivity which is the

directivity of the dipole antenna. Hence, the Directive Gain is;

10

DirectiveGain = 10log [1.75] = 0.22 dBd

1.84

3.2 Analysis of Quarter Wave

There two dimensional plot of the radiation pattern of the quarter wave monopole antenna is shown inFigure 6.

Directivity = 41252 HPBWE × HPBWH

As measured by the software,

HPBWE = 86.570 and HPBWH = 271.470

Therefore the approximate directivity is

Directivity = 41252

86.57 × 271.47

Figure 6: Two Dimensional E-Plane and H-Plane Radiation Patterns of the Quarter Wave Monopole Antenna

Figure 7 showed the E-Plane and H-plane plots of the radiation pattern of the quarter wave monopole antenna in Cartesian form

Directivity of the quarter wave monopole antenna

Directivity = 41252 HPBWE × HPBWH

HPBWE = 76.510 and HPBWH = 186.790Hence,

Directivity = 41252

76.51 ×186 .79

= 2.89

In decibel,

Directivity = 10log10 2.89

= 4.6dB

Directive gain of the quarter wave monopole antenna

Directive Gain = 10log

D

10 [ ]

Dref

Figure 7: E-plane and h-plane radiation patterns of the quarter wave monopole antenna in Cartesian form

A 3 Dimensional plot of the quarter wave monopole

Directive Gain = 10log

= 1.96 dB

10

1.84

antenna radiation pattern was obtained with the LAB- VOLTS LDVAM-ANT Software as shown in figure 8

Figure 8: 3D View of the Quarter Wave Monopole Antenna Radiation Pattern

The radiation pattern plot of the quarter wave monopole antenna E-Plane is such that the radiation pattern has its main beam at about 200 from the transmitting antenna. Also, on the H-Plane, the main beam has its maximum at about 3000 away from the transmitting antenna on the H- Plane.

3.2.1 Half Power Beamwidth

Figure 9: The E-Plane and H-Plane Half Power Beam width of the Quarter Wave Monopole Antenna evaluated with LDVAM-ANT Software

For this square loop antenna, the E-Plane and H-Plane Half Power Beam widths were found as shown in Figure 3.14 as

76.510 and 186.790; that is, between -44.240 and 32.270 for the E-Plane and between -98.850 and 89.190 for the H-

Plane on the Cartesian Plot.

The main beam of the loop E-plane radiation pattern occurs at 150 from the transmitting antenna (yagi antenna), while the main beam of the monopole antenna E-plane occurs at about 200 from the transmitting antenna. This means that the loop antenna on the E-Plane has a maximum power reception at 150 while the monopole has maximum reception at 200. On the H-Plane, the maximum reception for the loop antenna 150, while for the monopole it was 3000.The half power beamwidth of the full-wave square loop antenna is larger than that of the quarter wave monopole antenna on both E-plane (86.570>76.510) and H- plane (271.470> 186.790). The implication of this large half power beamwidth for the full-wave loop antenna is that the full-wave loop antenna directs its power into a wider area, while the quarter wave monopole antennas narrow half power beamwidth indicated that the power radiated by the quarter wave loop antenna is directed through a narrow area. Antennas with wide beamwidths typically have low gain and antennas with narrow beamwidths tend to have higher gain. In this case, the quarter wave monopole antenna has a higher directive gain (1.96 dB) over the full wave square loop antenna (-0.22 dB) as compared to the reference, half wave dipole antenna. Antennas having higher directive gain have an advantage of longer range and better signal quality in a particular direction. Therefore, quarter wave monopole antenna has a better signal quality as compared to the full wave square loop antenna.

4.0 CONCLUSION

The comparative analysis of the full-wave square loop antenna and the quarter wave monopole antenna has successfully been carried out as described in chapter three. The main objective of this project is to analyze and compare the performance parameters of the antennas. This has been achieved as seen in the previous chapter. This project has gave an insight about which antenna should be selected to suit a particular application while setting up a communication system so as to meet up with the optimal requirements. As a future work, other types of antennas such as horn antennas, aperture antennas, and parabolic antennas should be compared. The experiments should be carried out outside the laboratory so as to find the effect of weather on the performance of antenna. Phenomenon such as wind may also affect antenna performance. The performance of the antennas against an interfering signal should be compared.

REFERENCE

1. Y. Huang and K. Boyle Antennas from Theory To Practice John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom, 2008

2. G. Kennedy and B. Davis Electronics Communications systems 4th. ed., Tata McGraw-Hill New Delhi, India. 2009.

3. T. A. Milligan Modern Antenna Design 2nd. ed., Wiley and Sons Ltd. The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom. 2005.

4. J. J. Carr Practical Antenna Handbook 4th ed., the McGraw-Hill Companies, Inc. 2001

5. A. Ayorinde, S. A. Adekola, and A. I. Mowete, Performance Characteristics of Loop Antennas above a Ground Plane of Finite Extent Progress In Electromagnetics Research Symposium Proceedings, Taipei, March 25-28, 2013.

6. http://digikey.com/selection of antenna for embedded design Accessed 6th August, 2014.

7. L. Kibona Analysis of the effect of rectangular ground plane on radiation pattern of monopole antenna International Journal of Scientific and Research Publications,Volume 3, Issue 11, November 2013 ISSN 2250-3153

8. N. I. Khan, A. Azim, and S. Islam Radiation Characteristics of a Quarter-Wave Monopole Antenna above Virtual Ground Journal of Clean Energy Technologies, Vol. 2, No. 4, October 2014.

9. J. N. Tripathi Radiation Pattern Measurement of Delta Loop Antenna at 1000MHz West Indian Journal of Engineering, volume 18, No. 2, January 1996.

10. D. M. Pozar, Microwave Engineering 4th. ed., John Wiley and Sons Inc.New York. 2012.