Design and fabrication of broadband planar

monopole antenna operating in 1.2-6 GHz band

Zill-e-Tooba1,Hasan Raza2, Hiba Hussain Mashhadi3, Asaf Khan4
CESAT
Islamabad Pakistan
zill_1988@yahoo.com1, shrzaidi@yahoo.com2,hibamashhadi@gmail.com3, engrasafkhan@yahoo.com4

Abstract—This paper presents the design of a broadband a relatively degraded pattern in comparison with rectangular
planar monopole antenna intended for airborne communication or square geometries [4].
applications. The proposed design is a low profile hexagonal planar The intended goal is to design an antenna capable of
blade antenna with slant tapered edges which covers a bandwidth covering frequency band from 1-6 GHZ with minimal
133% (1.2-6GHz) with VSWR less than 2. The antenna exhibits reflection coefficient and stable omni-directional radiation
radiation pattern providing full 3600 coverage in the intended field
pattern throughout the band with better efficiency. This paper
of view with a gain variation not greater than 3dBi over the band.
Prototype of the design is fabricated using metal sheets. The details focuses on design and analysis of planar plate monopole
of aforementioned specialized design along with its measured and antenna which is the preferable configuration to meet our
simulated results are reported in this paper. desired requirements Various bandwidth enhancement
Keywords—planar monopole antenna; low profile; airborne techniques including structural modifications are implemented
to achieve the desired goals. During the structural
modifications the perspective of attaining aerodynamic profile
I.INTRODUCTION and size constraints are also kept under consideration. The
A single wideband antenna capable of covering a wide techniques that are specifically executed are summarized in
range of frequencies finds its application in various section II. Afterwards the design, fabrication and analysis of
communication applications. Planar monopoles tend to be a the proposed antenna are detailed out in section III and IV,
suitable candidate for their appealing physical features as well respectively.
as interesting response and design versatility. Requirements
posed on an antenna to be considered suitable for a wideband II. DESIGN CONSIDERATIONS FOR PMA
application are not only the impedance bandwidth with low Various modifications of shapes and configuration of
VSWR and radiation pattern stability over the desired band planar plate monopole cause improvements in bandwidth
but also linear phase response and optimum radiation along with enhancement of the profile. This is because of the
efficiency. Since planar monopoles have a constant phase fact that the geometry affects the current flow path.
centre over a wide band of frequencies they offer a linear Perturbation in the geometry directly influences the
phase response (constant group delay) over a wide band [1]. distribution of current and hence excitation of higher order
Besides that they can be designed for coverage of modes and produces multiple resonances which causes
exceptionally wide impedance bandwidth with stable omni- improvement in bandwidth [1].
directional radiation pattern and optimum radiation efficiency. Profiling and meandering of edges, changing length-to-
Apart from their well suited frequency response characteristics width ratio, introducing slots and use of shorting post are some
this category of antennas offer attractive physical features of the popular techniques applied in planar monopoles to
being small in size, light weight, simple planar conformable improve the bandwidth. In this work main emphasis is on the
structure with an additional attribute of cost effective profiling of the lower edge of planar radiating plate. It has
fabrication. been reported that modification in the shape of the lower edge
A myriad of shapes and configurations of PMA are being of planar radiating plate results in improvement of the higher
investigated in various research works [1, 2]. They can be frequency side of the band [5, 6]. This is because of excitation
configured either in the form of metal plates of various of higher order modes of current [7]. Various ways to profile
geometrical shapes placed perpendicular to ground plane with the lower edge are investigated. Curving the lower edge at a
an air gap in between or printed on a dielectric substrates with radius, creating a staircase profile and tapering the lower
ground plane on the back of the substrate. Tradeoffs on the edges are the three methods which are specifically
basis of desirable applications are deciding factors for implemented. It is found that tapering the lower edge at an
selection of configuration type and geometric shape. Planar angle provided best results because it causes smooth transition
plate antennas offer less pattern degradation than the printed of impedance with frequency resulting in multiple resonances
circuit designs [1] and among the shapes circular or elliptical and hence a wide impedance bandwidth. Another interesting
designs offer exceptionally wide impedance bandwidth [3] but observation is the fact that among all the other techniques


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tapering method provides best results for the farfield pattern TABLE I ANTENNA PARAMETERS
along with the impedance bandwidth. Component Attributes
Antenna
Similarly, addition of shorting post results in increase in Component Parameter Name Symbol Size
the effective length of the radiating element and hence helps in
improvement of lower edge of the frequency band [7]. Length of radiating plate Lp 6.5 cm
Implementation of this technique revealed that the Width of radiating plate Wp 4.8 cm
improvement in the bandwidth by addition of shorting post is Width of lower edge of
not that significant. Additionally, it results in the degradation Blade
plate Wl 3 cm
of the radiation pattern because of the asymmetry introduced Tapering angle lower edge α 50.480
in the structure. Length and width of plate and feed gap are the
critical parameters in calculation of effective height which is thickness tp 0.5mm

the deciding factor for the lower edge frequency of the band. It Feed Feed gap f_g 0.3 cm
is reported that reduction in the width [8,1] and increase in mechanism Feed probe diameter f_p 0.12 cm
feed gap results in improvement of bandwidth. Consequently,
keeping the length constant width of the radiating plate and Width of the ground plane Wg 2 cm
feed gap are optimized for the improvement of lower side of Ground
Length of ground plane Lg 5.8 cm
the bandwidth. plane
Modification of shape and size of ground plane is also thickness tg 0.5 mm
investigated and it was analyzed that this modification
significantly affects the radiation pattern and shifts the
bandwidth to some extent. Reducing the size of ground plane
is proved to adversely affect both the bandwidth and radiation
pattern. Since the reduced size is a major consideration for
airborne application. A tradeoff is made by optimizing the
design so that the size of the ground plane is relatively small
without affecting the desired frequency response.
Use of slots and shaping of the edges of the plate can be
helpful in improvement of aerodynamic profile by improving
the wind resistance of the structure. This aspect is addressed
by tapering the upper edge profile of the blade to make it more
wind resistant.

III. DESIGN AND FABRICATION

The specialized design comprises of a planar radiating
plate placed perpendicular to a rectangular ground plane. The
structural modifications of the initially implemented
rectangular plate resulted in a unique hexagonal structure with
slant tapered edges. Figure 1 shows the front view of the
designed antenna.
Length of the plate Lp, width of the plate Wp and feed gap
f_g are the deciding factors for lower frequency of the band.
Whereas, the lower edges of the radiating plate are tapered at
an angle α, to achieve an enhanced bandwidth on the higher Fig.1.Two dimensional view of design
frequency side of the band. This angle is optimized to achieve
best results. Moreover, optimization of width of lower edge Wl The simulation model of the antenna is excited with
results in great deal of improvement in bandwidth. Size of the split pin model of standard 50Ω SMA connector whose pin
ground plane is also optimized to achieve best results. The diameter and length satisfy our desired probe excitation
values of the optimized parameters are enlisted in Table I. requirement. Three dimensional view of simulation model is
shown in Figure 2.
The edge intended to face the air is tapered at an
angle β on the upper side of the radiating plate for attaining
more aerodynamic profile. Since negligible mode current
flows on the upper edges of the blade this design modification
does not affect the desired results however achieving a better
aerodynamic profile.

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 Simulated results of VSWR and reflection coefficient
are shown in Figures 4 and 5 respectively. The result shows
that VSWR is less than 2 in the entire band from 1.2-6GHz.

Fig.5.Reflection Coefficient simulated result

Fig.2. Three dimensional Simulation model

Measured results of reflection coefficient and VSWR are
The optimized antenna is fabricated with copper plates of shown in Figures 6 and 7 respectively. It can be seen that the
0.5mm thickness. SMA connector is used for excitation while results are in good agreement with simulated results.
maintaining the desired feed gap. The prototype is shown in
Figure 3.

Fig.3.Fabricated Prototype Fig.6. Frequency versus Reflection coefficient measured in dB

IV. SIMULATION AND MEASUREMENT RESULTS

The final blade antenna with SMA connector is simulated
using CST microwave studio. The prototype is tested using NI
PXIe 5632 Vector Network Analyzer.

Fig.7. Frequency versus VSWR measured value

Fig.4. VSWR simulated result

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 Simulation result of E-plane radiation pattern at Ф=900 is V. CONCLUSION
shown in Figure 8. Radiation pattern characteristics are
The aspect of wideband coverage of planar monopole
enlisted in Table II.
antenna has been investigated. A range of techniques for the
TABLE II RADIATION PATTERN CHARACTERISTICS FOR Ф=900
improvement of bandwidth of rectangular planar monopoles
have been analyzed. The analysis revealed that changing the
Frequency Main lobe Main lobe Angular width profile of the edges closer to the ground plane results in a
direction magnitude (3dB)
(GHz) (degree)
great deal of improvement on the higher side of the band.
(dBi) Variation in the feed gap, reduction in width and use of
1 88 1.9 86.2 shorting pins are the techniques for improvement of
bandwidth on the lower side of the band. Moreover, it is
2 72 3.5 70.2
proposed that among the various ways of modifying the lower
3 56 4.9 50.7 edge geometry, the angular tapering provides better
4 48 4.4 42
impedance bandwidth as well as radiation pattern.

5 40 4.2 36 All these techniques are implemented to improve the

6 37 4.6 33.2 bandwidth of a simple planar rectangular monopole. The final
structure after optimization is a hexagonal planar blade
The result shows a maximum gain of 4.6dBi at 6GHz and antenna with slant tapered edges. The designed antenna covers
1.9 dBi at 1 GHz which signifies that gain variation is less a bandwidth 1.2 to 6 GHz (133%) with VSWR less than 2
than 3dBi in the entire band. Minimum angular width is 33 over the entire band. The antenna exhibits radiation pattern
degree at 6GHz which meets the design requirement. providing full 3600 coverage in azimuth and at least 300 in the
intended field of view (i.e. in elevation) with a gain variation
not greater than 3dBi over the entire band.

References
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[7] E.Lee, P.S.Hall and P.Gardner, “Compact wideband planar monopole
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Fig.8. E-plane Radiation pattern (Ф=900) at 1GHz, 2GHz, 3GHz, 4GHz,

5GHz and 6GHz

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