This document describes a novel broadband cylindrical corner reflector antenna for 2.4GHz WiFi base station applications. The antenna uses a printed strip dipole fed cylindrical corner reflector to provide high directivity of 12dBi and impedance bandwidth of 310MHz. Two parasitic elements were added to broaden the bandwidth to cover 1.25GHz, maintaining consistent radiation patterns across frequency bands. Simulation and experimental results showed good agreement, validating the antenna's ability to support various wireless communication standards with a simple design.

1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 72-79© IAEME
72
BROADBAND CYLINDRICAL CORNER REFLECTOR
FOR 2.4GHZ WIFI BASE STATION APPLICATION
Eqab Khleif1
, Hassan Ragheb2
, Sharif Iqbal3
1,2,3
Department of Electrical Engineering,
King Fahad University for Petroleum and Minerals,
Dhahran, Kingdom of Saudi Arabia
ABSTRACT
Directional antenna for WiFi base station is an emerging field of research. In this work a
novel directional antenna based on Cylindrical Corner Reflector (CCR) fed by printed strip dipole is
presented. The antenna demonstrates a linearly polarized high gain 12dBi with impedance BW of
310Mhz, and HPBWH
of 57o
. Two parasitic elements were added along the main dipole strips to
broaden the bandwidth and to cover other 3GPP frequency bands for 3G/4G wireless
communications. 1.25GHz bandwidth was obtained with a consistent radiation patterns for E and H
planes. The proposed antennas is simulated and optimized using the FEM based EM solver, the
return loss, radiation patterns and input impedance were investigated. Fabrication of the prototype
and experimental results were also presented. The Experimental and simulations results were found
of a good agreement.
Keywords: Broadband Antenna, Cylindrical Corner Reflectors, Printed Strip Dipole, WiFi
Directional Antenna.
I. INTRODUCTION
WIRELESS system requires high directive antenna in order to extend the coverage range of
the base station, and provide noise rejection and interference mitigation. Recently the WiFi is gaining
huge focus from network operators and service providers to be used as a secondary layer of radio
system to offload the data traffic from the conventional-more expensive 3G/4G networks. The current
WiFi access points uses an omni directional 2x2 Multiple Input Multiple Output(MIMO) antenna, this
is going to be a problem when WiFi is extensively used for outdoor coverage purposes, due to limited
range, and low power. The proposed solution in this work mitigates this problem by providing a new
simple directional antenna with high directivity, that can be used in sector based applications.
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2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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Directional antenna for WiFi will enable new services over WiFi network like IPTV, due to better
coverage, and enhanced (Signal To Noise Ratio) SNR. The data throughput of the wireless channel
will increase and hence the user downloading experience.
Rectangular batch array, horn antenna, and corner reflectors (CR) are very popular techniques
for achieving high gain antennas. The corner reflector was found to be the simplest among all that
achieves this target. The first CR was introduced by Karus in 1940[1]. The CR was built based on
two super conductive reflecting plates joint at the corner with corner angle (α), the feed element is a
wire λ/2 half-wave dipole placed at a vertex distance (S) from the corner. Kraus has laid down the
foundation of Corner Reflector (CR) theory using the theoryof images to compute the fields resulted
due to presenceof reflecting plates. He also has experimented the CR andprovided recommendations
for the design. The CR was laterrevisited by Niff and Tillaman [2], in an attempt to simplifythe
formulation suggested by Kraus. The CR was investigatedby many others [3][4][5], addressing the
effect of finiteplates size, the feed orientation, and using of array as feedsystem on the radiation
patterns and input impedance. Al Kamchochi[7] has done a modification on the CR by addinga third
reflecting surface, which provided additional 2dB gainto the work done by Kraus. Later on, Abdulaziz
[6] has usedan array of dipole axially mounted parallel to the cornerwhich resulted in higher gain and
more directivity for theelevation plane.
In this paper, the proposed antenna is based on the CylindricalCR (CCR) suggested by Al
Kamchouchi[7] which uses thewire dipole as a feed element. However the feed system isreplaced by a
printed strip dipole on a cylindrical substrateto overcome the mechanical stability and provide
widerbandwidth, by exploiting the benefits of printed antennafound in literature.
Fig. 1. Proposed schematic diagram
The printed dipoles are very popular due to their simplicity of design, low profile, low cost,
conformable to non-planar surfaces, and possibility to integrate with MIC [8][9]. More importantly,
using the printed strip dipoles for the suggested antenna exploits a wide range of printed antenna
geometries found in literature optimized for 2.4GHz band [10][11], that can be used as a feed for the
conventional CCR. The broadband characteristics of an antenna is very important merit. For a base
station application and due to different radio access technologies co-existence, antenna must support
different frequency bands so as to save space and reduce system complexity. For our proposed WiFi
BS antenna we have added two parasitic elements beside the main dipole. The passive elements and
due to coupling have introduced anew resonance which broaden the bandwidth. The length and
width of the passive strips were optimized to bring a new resonance frequency and broaden the
bandwidth (BW).

3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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II. ANTENNA DESIGN
Theproposed antenna is primarily consists of a CCR [7], with aperture-angle of 90o
and
using a strip printed dipole on a quarter cylindrical substrate as a feed element. The half wave dipole
length is optimized to 0.47λ which is slightly less the half wavelength to offset the effect of the
reactive fields around the antenna. Antenna parameters can be found using the transmission line
model. We have chosen the dielectric printed circuit board (PCB) for the substrate as Duroid(tm)
with dielectric constant of 2.2, permeability of 1, and dielectric loss tangent of 0.0009. The thickness
is chosen to be 1.6mm. Dipole radials width approximated to 4mm [17], [19]. The effective dielectric
constant was found to be 1.827. Dipole radial length is found based on the effective wavelength of
the propagating wave (λeff = 92mm ) at 2.4GHz to be equal to λ/4 = 23mm.Cylindrical substrate
radius is R = 0:687λ , and the substrate is placed at a distance of 0.25λ from the reflecting cylindrical
surface.
Printed dipole on a substrate provides a more rigid structure that the wire dipole type feeding
system doesn’t offer. The printed strips are fed from the center between the two strips via a coaxial
feed using 50 SMA connector, the inner of the connector is connected to one side of the strip and the
outer is terminated to the second side of the strip. From CCR equations [7] it’s clear that the radiated
field depends on the radius of the newly added cylindrical surface (a), and the distance from the
corner to the radiating element (R). The radiation beam is shaped accordingly and the impedance is
controlled by varying both parameters. The structure is analyzed and tested, found to provide 2dB
enhancement over the ordinary CR as per [7]. Many optimization techniques were found in literature
that enhances the CR and CCR performance, mainly the level of side lobe. For example adding
scatters or by folding the reflectors in different shapes[13], [14], [15]. These techniques mainly
operate on the H plane radiation. Other techniqueslike [3] increases the directivity by using array
corner reflector.
III. SIMULATION AND FABRICATION RESULTS
The simulation of the antenna is done using Finite Element Method (FEM) based professional
software that is a powerful EM solver that helps analyzing such 3D structures. Using simulator we
have built three antenna models. The first is a plane substrate with printed strip dipole, then a
cylindrical substrate was tried, and keeping all parameters unchanged. And finally addition of the
corner reflector and the cylindrical reflecting surface to increase the antenna gain.
A. Strip Printed Dipole on a Planar/Cylindrical Substrate
Printed strip dipole geometry mentioned in the design section is constructed and simulated.
The EM solver was set to produce the corresponding return loss for the range of frequencies from
0.1GHz to 4GHz. using the planar substrate the resonance occur at 2.4GHz with a dip at -22dB and an
impedance bandwidth of 350MHz at VSWR less than 1.8. We tried the cylindrical substrate with
proper dimensions, Fig.2 shows the return loss for both cases. The frequency resonance for the
cylindrical substrate case is shifted to higher frequency range. That is due to curvature of the substrate
and the fact that the printed dipole is conformed on the outer surface of the substrate.
B. Antenna Structure with Reflectors added
The structure is simulated and results are analyzed. The Return Loss (RL) graph is showing an
impedance bandwidth 60 MHz at VSWR=2 around the resonance frequency of 2.3GHz with a dip of
-23dB.

4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 72-79© IAEME
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Fig. 2.RL of the Final CCR antenna, compared to the planarand cylindrical substrate models
The antenna directivity and gain have increased in the maxdirection of θ = π/2 as expected
with new bandwidth of 260MHz (13% of the operating frequency). The simulation for H and E planes
radiation patterns are shown in Fig.3.
Fig. 3. E And H Radiation Patterns of CCR
Fig. 4. RL of the broadband CCR

5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 72-79© IAEME
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Fig. 5. H-Plane Radiation at different 3GG frequencies
C. Broad Band Antenna
As discussed in the introduction section, broadband antenna characteristics can be achieved by
addition of two parasitic elements on the outer surface of the cylindrical substrate. The coupling
between the parasitic elements and the main strip dipole resulted in a new resonance that increased the
-10dB bandwidth to around 1.25Ghz. Fig.4 is showing the return loss diagram. Another figure of
merit for the broadband antenna is the radiation pattern, which should be kept unchanged for all
frequency range. The radiation pattern for H plane is plotted against different frequency bands defined
by 3GPP standard, 2.1G, 2.3G, and 2.6G radiation plots are shown in Fig.5.
IV. FABRICATION RESUILTS
After The proposed antenna is fabricated locally at the lab and tested using the Agilent vector
network analyzer E5071C (ENA series) to measure the return loss scattering parameter. The Printed
strip antenna was printed on a semi rigid Roger PCB Duroid TM, and using LPKF printing board
plotter machine(S63)for Milling and Drilling of the prototype, the drilling of the PCB is needed to be
able to solder the SMA 3.5mm co axial connector as center feed. The result PCB with printed dipole
antenna is treated with heat and pressure to allow a curvature of the quarter cylindrical shape with
designed radius. The obtained curved PCB is tested via the network analyzer and found to be having
antenna parametersunaffected. Further step is taken to prepare the CCR reflecting surfaces, cutting
and welding using designed dimensions. The final prototype is shown in the Fig.6.
Fig. 6. Fabricated model

6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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The measured return loss Fig.7 is showing a very good results with -10dB impedance
bandwidth of 310MHz, which is in match with the simulation results. The measurement is done for
two different values of CCR radius versus the vertex distance R, results are showing some
dependency of the resonance frequency on the location of the feed with respect to reflecting surfaces,
similar observation was mentioned by [5], which normally the case when antenna is placed close to
perfectly conductive reflecting surfaces.
Fig. 7. Measured RL for different values of (a)
To test the radiation characteristics of the proposed antenna, the fabricated prototype is placed
into the anechoic chamber for testing of the radiation pattern.
Fig. 8. E and H measured Radiation patterns
The radiation pattern test result is compared to simulation and found in agreement. The
obtained gain is 12dBi and the HPBWH
= 57o
while the HPBWE
= 48o
. Fig.8 shows both E and H
plane measured radiation patterns, and Fig.9 shows the simulated and measured E plane radiation
pattern.

7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 72-79© IAEME
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V. CONCLUSIONS
A low cost strip dipole antenna was used as a feed for theconventional cylindrical corner
reflector operating at 2.4GHzfor WiFi base station applications. The proposed antennashown a
performance improvement in gain and directivity by12dBi, with HPBWH = 57o
, this enables using it
for sectorzone base station applications. The simulation indicates animpedance bandwidth of 310
MHz at VSWR=2. A broad bandoperation was achieved by adding two passive elements
and1.25GHz was obtained, it covers the main 3GPP frequencybands for wireless communications. A
prototype was fabricatedand experimentally tested; the obtained results were inmatch with
simulation with regard to the return loss and the radiation characteristics
Fig. 9. Measured and simulated RL
AKNOWLEDMENST
Many thanks go to King Fahad University for Petroleum and Minerals for providing the
facility and resources for this research.
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