Design, Development and testing of Conical Horn Antenna at 6.93GHz for Ground based Microwave Radiometer

1. Design, Development and testing of Conical Horn Antenna at 6.93GHz for Ground based
Microwave Radiometer
OPN Calla’, Amit Kumar’, Shruti Singhal’, Nikhil Parihar#, Reshma Meena*, Ritu Nagar*
opnc06@gmail.com, amit.icrs@gmail.com, shrutisinghal21@gmail.com nikhilparihar1994@gmail.com,
reshmabyadwal94@gmail.com, ritunagar157@gmail.com,
‘International centre for Radio Science, Jodhpur
# Vyas Institute of Engineering and Technology, Jodhpur
* Government Women Engineering College, Ajmer
Abstract— Microwave Radiometer measures the
electromagnetic radiations emitted from the targets. The
principle of radiometer is that it selects a certain portion of the
available output power from the antenna. It is widely used for
sensing the properties of the earth and it measurements were
analysed to study the large area soil moisture variation of land
surfaces. For microwave radiometer a high gain with low side
lobes antenna is needed to detect weak radiation.
The main objective of this paper is to design a horn antenna
at 6.93GHz frequency for ground based Microwave Remote
Sensing applications using microwave radiometer. Two
different antennas, pyramidal and conical horn antennas were
designed. But conical horn antenna was chosen to get equal
and narrow beam-width in both E and H-plane and to obtain
an acceptable size for antenna fabrication. Conical horn
antenna designed could be fabricated at very low cost has light
weight and acceptable size. The antenna designed is fed using
a circular waveguide. Our goal was to design an antenna that
has narrow beam width and low side lobes to maximize the
power transfer from the source to the radiating system. In this
the length, flare angle, diameter of conical horn antenna is
varied to get a desired result
After fabrication, testing of this antenna is done and following
parameters like gain, beam-width, side lobes were measured
which indeed met the designed specifications required. It can
be used with ground based measurement using microwave
radiometer for Microwave Remote Sensing.
Keywords— microwave radiometer, horn antenna, conical
horn, microwave remote sensing
I. INTRODUCTION
The purpose of this paper is to provide researchers a
systematic survey of low cost conical horn antenna for
microwave radiometer. Radiometer is a passive sensor that
detects radiation emitted or reflected by an object in the
microwave range.
The microwave radiometer antenna receives the
electromagnetic energy radiated by the target. It is widely
used in sensing the properties of the earth and other
microwave remote sensing applications. The antennas are
constructed in wide variety of geometrical, theoretical and
practical configuration. The properties for which specific
antenna type is chosen are: antenna radiation pattern, beam-
width, suppressed side lobes, high gain and directivity.
Horn antennas have been widely used for microwave remote
sensing and space applications due to their capability of being
best operation from megahertz to gigahertz to terra hertz
range.
Advantages of horn antenna over other types of antennas are:
(a) high data rate systems needs to be operated at a
higher frequency range in order to achieve higher
bandwidth. this can be easily achieved using a horn
antenna.
(b) complexity involve in the design of horn antenna is
less as compared to phased array antennas.
(c) feeding a horn antenna is less complex as compared
to other antennas which require complex feeding
techniques.
(d) if horn antenna is properly designed & optimized
than side lobes can be suppressed to very low levels.
(e) power handling capability of horn antenna is superior
to other antennas as it is waveguide fed antenna.
Other application of Horn Antennas includes satellite
communication, geographic information & weather satellite,
and terrestrial microwave communications.
II. DESCRIPTION OF CONICAL HORN
ANTENNA
In the literature, various pyramidal and conical horn antennas
have been designed and demonstrated using different
techniques which have different applications. But Conical
Horn is one of the best horn antennas for sensing the
properties of the earth and Microwave Remote Sensing
applications. It has equal and narrow radiation patterns in both
E-plane and H-plane along with its high gain and directivity.
This designed antenna is very light in weight (made up of
aluminum). Conical horn antenna is being developed that
radiates high power microwaves at 6.93GHz frequency range
which provide high gain and highly directive radiation

2. patterns in the feeding circular waveguide. The behavior of
these high power electromagnetic waves can be accurately
measures inside the waveguide as well as in the near and far
field regions. The goal of conical horn antenna design is to
maximize the power transfer from the source to the radiating
system while keeping the antenna at acceptable size. For this
the length, flare angle, diameter of conical horn antenna is
varied to get a desired result.
III. EXPERIMENTAL: DESIGN, FABRICATION AND TESTING
Formula used for design:
This antenna is designed at 6.93 GHz frequency using
formula,
D= 58λ/θ
l= D²/3λ
L= √l²+ (D/2)²
Where, D is diameter of an antenna, L is axial length of cone,
l is slant height.
Values of designed antenna are:
Wavelength: 43.29mm
Beam-width: 100
Diameter, D: 250mm
Axial length, L: 300mm
Fig.1: Geometry of conical horn antenna Fabrication:
For fabrication antenna material should be of good corrosion
resistance and light weight. Lightweight construction is
needed to ease operation and to decrease robustness
requirements of the antenna. This antenna body is made of
aluminium and it could be re-used. The antenna is fabricated
using sheet metal process which contains three main stages:
cutting, bending and joining. Sheet metal parts are bent to
their geometry according to required angles and bending
radius bent sheet are joined together by gas welding. Because
of aluminium’s high reflectivity and high purity requirements,
extra attention has to be paid on acceptable welding process
arrangements.
Antenna after fabrication is shown in fig.2.
Fig.2.Conical horn antenna
Testing of this antenna is done by rotating receiving antenna
about the centre of its aperture, at different angles. The
received power readings in both directions that are clockwise
and anti-clockwise recorded in each case by using power
meter and they are plotted on a graph sheet. The measured
parameters like gain, beam-width, and side lobes met the
designed specifications. Our goal was to design an antenna
that has narrow beam width and low side lobes to maximize
the power transfer from the source to the radiating system. In
this the length, flare angle, diameter of conical horn antenna is
varied to get a desired result.
The testing of VSWR or Return Loss is done to determine the
matching properties of an antenna. It indicates that how much
efficiently antenna is transmitting/receiving electromagnetic
wave over particular band of frequency. Gain is also measured
which defined the increase in signal strength as the signal is
processed by the antenna for a given incident angle.
Measurement of the beam width of the antenna is used to
describe the resolution capabilities of the antenna to
distinguish between two adjacent radiating sources or radar
targets. Directivity of an antenna is determines the ratio of
maximum radiation intensity to its average radiation intensity.
To judge the quality of transmitting and receiving antennas
beam efficiency is measured.
Setup for measurement of VSWR and testing of conical horn
antenna is shown in fig.3 and fig.4.
Fig.3.Setup for measurement of VSWR of conical horn
antenna

3. Fig.4.Setup for testing of conical horn antenna
Radiation patterns: An antenna radiation pattern or antenna
pattern is defined as “a mathematical function or a graphical
representation of the radiation properties of the antenna as a
function of space coordinates. The radiation pattern is
determined in the far field region and is represented as a
function of the directional coordinates. Radiation properties
include power flux density, radiation intensity, field strength,
directivity, phase or polarization.” For a linearly polarized
antenna, performance is described in terms of its principal E-
and H-plane patterns. The E-plane is defined as “the plane
containing the electric field vector and the direction of
maximum radiation,” and the H-plane as “the plane containing
the magnetic-field vector and the direction of maximum
radiation.” Radiation plots are most often shown in either the
plane of the axis of the antenna “E-plane” or the plane
perpendicular to the axis “H-plane”.
The principal objective is to show a radiation plot that is
representative of a complete 360 degrees
in either the “E-plane” or “H-plane”. In the case of highly
directional antennas, the radiation pattern is similar to a
flashlight beam. Patterns are usually referenced to the outer
edge of the plot which is the maximum gain of the antenna.
Radiation pattern determine important antenna characteristics
directly from the plot.
IV. RESULTS:
Design antenna has diameter of 250mm and axial length
300mm at 6.93GHz frequency which met all the
specifications. After the fabrication and testing of this conical
horn antenna obtained results are:
Gain: 20db gain
VSWR: 1.2
Beam-width: 100
at both planar
Radiation patterns: Antenna radiation patterns or plots show
a quick picture of the overall antenna response.
(a) The co-planar radiation pattern for the conical horn
antenna receiving vertical polarization.
(a)
(b)
Fig.5.co-.polar and rectangular radiation patternplot for
vertical polarization at 6.93GHz
(b) The co-polarization radiation pattern of conical horn
antenna receiving horizontal polarization.
(a)

4. (b)
Fig.6.co-polar and rectangular radiation pattern plot for
horizontal polarisation at 6.93GHz
V. Conclusions:
From above testing and measurements it is concluded that the
designed low cost conical horn antenna is having all desired
specification which are high gain and directivity, suppressed
side lobes, VSWR less than 2 over the full band. It can be
used for ground based applications in microwave radiometer.
The narrow beam-width and low side lobes of radiation
pattern show the successful designing of conical horn antenna.
Due to its equal and narrow radiation patterns in both E-plane
and H-plane, high gain and directivity is obtained at high
frequency.
REFERENCES:
[1] Calla, O.P.N.Application of microwave Remote Sensing
[2] Constantine. A. Balanis, "Antenna Theory Analysis &
Design", John Wiley, & Sons INC, Third Edition
[4]Brian Kidney,”Horn antennas” Engineering,98 16 –
Antennas 2001.
[3] Kirpal Singh, Ajay Siwach, Loveline Kaur “Advancement
in designing wide band Horn Antenna”,IJETT,2013.
[5] Thomas A Milligan, "Modem Antenna Design", John
Wiley & Sons INC, Second Edition.