An Approach to Design and Embed a Printed
Dipole Antenna inside UAV Empennage
Diptiman Biswas, Sagar Sen, Vamshidhar S, Ramachandra Vulapalli
Aeronautical Development Establishment
DRDO, Ministry of Defence, Govt. of India
New Thippasandra, Bengaluru - 560075
diptimanbiswas@yahoo.co.in
Abstract – This paper describes about the design and
development of a Printed Dipole Antenna in UHF band and a
procedure to embed the antenna inside the vertical fin of the
empennage of a UAV (unmanned aerial vehicle) system. The
effect on the impedance and radiation characteristics of the
antenna inside the FRP fin has been studied and optimised
through comprehensive analysis.
I.
INTRODUCTION
The system requirement necessitates an onboard antenna
featured with omni directional radiation pattern in the yaw
plane of the UAV for providing essential wireless datalink
communication with the GCS (ground control station).
However, the fuselage and wings of a complex shaped UAV
contributes to distort the omni pattern of the antenna when it is
mounted directly on the surface. This may restrict the
operation of continuous and uninterrupted data link when the
UAV is expected to fly and maneuver at various aspect angles
with respect to the GCS.
The first level of solution approach to this problem is to
elevate the onboard antenna appropriately from the surface of
the UAV fuselage for obtaining maximum radiation clearance
required for line-of-sight communication between the two.
Further, there is a possibility of unwanted spurious radiation
generated due to various other onboard subsystems which may
likely to interfere and degrade the performance of a sensitive
RF data link receiver. In the present case, we experienced
similar problem and elevating antenna alone could not ensure
effective communication for receiving command information.
This was a crucial issue and to overcome the limitation, we
considered to relocate the onboard receiving antenna such that
the influence of interference be minimum. A comprehensive
study suggested that the antenna near empennage could be a
prominent location to satisfy both radiation and interference
issues. Embedding an omni antenna inside the vertical fin
would provide additional advantage of not being projected
outside of the UAV airframe and accordingly no associated
aerodynamic drag to be accounted for.
We explored the feasibility of embedding a printed
antenna at the top location of the vertical fin of the UAV and
carried out required study and analysis for providing solution
to a practical system.
II. DESIGN OF PRINTED DIPOLE ANTENNA (PDA)
A Printed Dipole Antenna is a planar and compact
radiating device which is used for the wireless communication
of vertically polarised radio signal with omni directional
radiation pattern. For airborne platform such as a UAV system,
the PDA need to be appropriately oriented with necessary
encapsulation within aerodynamically shaped radome and with
proper reinforcement so as to it can withstand required level of
aerodynamic drag, vibration etc.
Fig.1. Schematic of multi-layer Printed Dipole Antenna
The dipole is printed on both sides of the substrate with two
radiating arms designed to be very compact so that it can be
embedded easily inside the vertical empennage. The schematic
of the optimised Printed Dipole is shown in Fig.1. The
radiating arms each of length, L are oriented in opposite
direction and are open ended. However, the folded and printed
‘balun’ at both sides are of identical geometry and are
overlapped. The other end is for feeding through 50  coaxial
connector.
Fig.2. Simulated azimuth plane pattern of the PDA
Fig.4. Simulated 3D pattern of the PDA
The length of the PDA has been reduced for making it compact
and optimised to be 20% smaller than its usual length of /2 at
the operational center frequency. The design has been
simulated using Feko 6.1. Simulated radiation patterns of the
antenna at its azimuth and elevation planes are given in the fig.
2 & 3 respectively. Fig.4 shows the volumetric radiation
pattern of the antenna along with the printed dipole antenna as
reference.
A. Bandwidth Enhancement
There is a need to increase the operational bandwidth of
the PDA for meeting the required specification. The width of
the radiating arms contributes significantly for the bandwidth
of the antenna. A study has been carried out by varying the
width, W of the radiating arms in sub-multiple fraction of its
length, L. VSWR plots with varying widths have been shown
in Fig.5. The dependance of bandwidth as a function of
antenna width is shown in Fig.6. Bandwidth increases with the
width, W of the dipole arm. The PDA with narrow radiating
arms produces a bandwidth of merely 10% of its center
frequency. The bandwidth can be increased more than 30% of
its center frequency when the width of the dipole arm becomes
25% of its length, L.
Fig.3. Simulated elevation plane pattern of the PDA
Fig.5. VSWR Plots of PDAs with varying arm width, W
Fig.6. Bandwidth of PDA Vs. width, W of radiator
III. ANTENNA DEVELOPMENT
operational bandwidth of the antenna is exactly same that of
simulated result i.e. 32% of the center frequency.
The design of printed dipole antenna has been optimised
and fabricated by photo etching of the art work on both sides
of copper cladded substrate with dk =2.5 and thickness =1.6mm
as shown in Fig.7.
Fig.10. Measured VSWR plot of the fabricated PDA
Fig.7. Fabricated PDA indicating printed art-work
at both sides of the substrate
Fig.8. Azimuth plane pattern of the fabricated PDA
IV.
EMBEDDING METHODOLOGY
The embedding of printed dipole antenna inside
empennage is similar to designing a radome for the antenna to
ensure minimum deviation in the original characteristics of the
antenna. The presence of dielectric material in the vicinity of
the PDA influences the behaviour of the antenna which may
degrade its over all performance. The material properties of
radome mainly its dielectric constant (dk) and its thickness are
of important concern and need to be optimised for minimizing
unwanted distortion in the radiation pattern and also a
noticeable shift in the operational frequency band of the
antenna. To predict performance of the radome i.e. empennage
material in the present case, we need to carry out
electromagnetic study of the effect of the embedding material
on antenna. A comprehensive simulation study has been
carried out using Feko considering realistic material properties
of the empennage of the UAV to quantify their effects and
arrive at an optimum configuration.
Fig.9. Elevation plane pattern of the fabricated PDA
A 50 TNC (F) type connector is used appropriately to energise
the antenna. The experimental radiation patterns in the azimuth
and elevation planes measured in anechoic chamber are given
in Fig. 8 & 9 respectively. The experimental VSWR plot of the
antenna is shown in Fig.10. When compared with the
simulated bandwidth of the PDA, it was found that the
Fig.11. VSWR plots of PDA with different embedding material
The study of materials with varying dielectric constants has
been compared in Fig.11. It is observed that embedding
material with higher dk, the VSWR response of the antenna
gets affected adversely. Even with low dk values, there is a
marginal amount of shift in the resonating frequency of
operation. Further, considering the structural need for
providing necessary strength, a fin with low dielectric foam of
one inch thick with the outer covering skin of 2 mm made of
FRP found to be appropriate for embedding the PDA. This
combiation of empennage material has been simulated along
with the PDA sandwiched in between and found to be suitable
electrically. As shown in Fig.11, a nominal shift in the
operational frequency band resulted due to embedding of the
antenna with the optimised configuration, however, within
acceptable operational limit as the overall operational
bandwidth of the antenna is sufficiently high. The radiation
pattern of the antenna as embedded inside the vertical
empennage of the UAV has been simulated and its sectional
view is shown in Fig.12.
REFERENCES
[1]
[2]
[3]
Diptiman Biswas, Sagar Sen, Nataraj B, Ramachandra V, “An Analytical
Approach for Designing Compact Printed Dipole Antenna in S Band”,
Proceedings of 4th IEEE-AEMC-13; Bhubaneshwar, Dec, 2013.
Diptiman Biswas, Krishna Prasad D.S, Sagar Sen, Ramachandra V,
“Design of a Novel Printed Dipole Antenna and its Placement Analysis
on Indigenous UAV Platform”, Proceedings of 6th Conf. ATMS-13;
Kolkata, Feb, 2012.
Mohammad S. Sharawi, Daniel N. Aloi, Osamah A. Rawashdeh,
“Design and Implementation of Embedded Printed Antenna Arrays in
Small UAV Wing Structures”, IEEE Transactions on Antenna and
Propagation, Vol. 58, No. 8, August 2010.
BIODATA OF AUTHORS
Diptiman Biswas: Graduate in Electronics Engg
from NIT, Jamshedpur in 1993. M. Tech in
Microwave Engg. from IIT, BHU, Varanasi in
1995. Joined ADE as Scientist in 1996. At
present as Head of Antenna Lab, his prime
domain of research work includes configuration
& design of antennas for various indigenous
UAV systems. Using innovative & conceptual
approach of design, he has produced a number of critical antennas. He
has authored a number of technical papers and presented at various
conferences.
Sagar Sen: B.E. in Electronics & Comn.
Engineering (2013) from C M R Institute of
Technology, Bangalore under Visvesvaraya
Technological University, Belgaum. Presently
working as Graduate Trainee in ADE, DRDO,
Bangalore in the area of design and simulation of
antennae for various airborne applications.
Fig.12. Sectional 3D view of the simulated pattern of the PDA as
embedded
V.
CONCLUSION
A compact Printed Dipole Antenna has been designed
developed and embedded inside the vertical empennage of a
indigenous UAV system. The configuration has improved
antenna performance as it is elevated from the fuselage and
also minimised the influence of interference as the antenna is
placed far from the onboard interfering system.
ACKNOWLEDGMENT
The authors express their sincere thanks to
Sri P. Srikumar, Outstanding Scientist and Director, ADE and
Sri S. Sampath Kumar, Sc ‘G’ and Group Director for their
encouragement and constant support to carry out the work and
also for permitting this paper for publication and presentation
at the conference.
Vamshidhar S: M.Sc(Physics) in 2006 from
University of Hyderabad and M.Tech (Solid State
Technology) in 2008 from IIT, Kharagpur. Joined
ADE as a Scientist in the year 2008. He is
working in the specialised areas of R F and Digital
Communications for various UAV systems.
Ramachandra Vulapalli: Post Graduate from
Kakatiya University (1980) and Ph.D. from
BHU, Varanasi (1988). Joined as a Scientist at
ADE in the year 1984. Presently Scientist ‘G’
and Head of Flight Test Telecommand &
Tracking Division. He has invented and
productionised a number critical products such
as Luneberg Lens, DMDI Scoring System for
various indigenous UAV systems. He has
designed and developed number of import substitutes at ADE. Most
of his designs / products have been productionized and the items are
being used by Indian Armed Forces. He has more than 150 technical
publications and internal reports to his credits. He is a member of
IEEE.