Design and Verification of Antennas for Tomographic Radar Systems in the Frequency Range 76–81 GHz
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Typ
Examensarbete för masterexamen
Program
Publicerad
2020
Författare
RAHAMTULLA, WAFA PATHAN
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Microwave tomography is an imaging technique used to construct 3D images of the
object under test using the principle of radar. Antennas in such systems are
designed to obtain specific radiation characteristics to transmit and receive the
signals. Antennas utilized for the purpose of radar generally radiate a fan shaped
beam with high directivity in one plane and a wide beam in the orthogonal plane.
This thesis project focuses on the design, simulation, fabrication and
characterization of antennas which will be integrated with a tomographic radar
system being developed for noninvasive material characterization in the frequency
range 76–81 GHz. The motive behind developing the antennas is that
commercially available antennas do not satisfy the specifications.
The background theory of antennas is introduced and critical antenna parameters
are identified. The design of the prototypes is based on specifications derived from
the application. Two types of antennas – horn antenna and patch antenna array
are designed as they each satisfy different system requirements more competently.
The antennas are modelled according to the calculated approximate dimensions
and simulated using finite element method simulations in ANSYS HFSS. In
addition, optimization of different parameters is carried out to achieve the best
antenna performance while fulfilling the system conditions.
The horn antenna was fabricated through 3D metal printing using two materials
(steel and brass). The steel horn antenna has a half power beamwidth (HPBW) of
9.0° in the H-plane and 64.5° in the E-plane and a gain of 16 dB whereas the brass
horn possesses a HPBW of 8.5° in the H-plane and 60.0° in the E-plane with a gain
of 17.5 dB. Both the horn antennas cover the intended frequency range of 76–81
GHz. The second prototype produced is the patch antenna array with two variants
differing in the size between the single patch elements. A HPBW of 17.0° in the
E-plane and 60.0° in the H-plane with a gain of 14.4 dB was obtained for d=0.5 g
variant. For d=1.5 g spacing, the HPBW was 6.5° in the E-plane and 63.0° in the
H-plane with a gain of 12.9 dB. The bandwidth covered by each is 2.2 GHz and 3.89
GHz, respectively. Analysis of the results and comparison with the specifications
show that the horn antenna and d=1.5 g spacing patch antenna array satisfy the
system specifications. The variant with d=0.5 g partially satisfies the requirements
and can be used in applications with size restrictions as it 50% less in length.
The tomographic radar system was simulated by considering one case of a
transmitting and a receiving antenna with a glass slab. Increasing the distance of
the glass from the transmitting antenna reduced the reflections. The glass
produced the same effect as placing a lens in front of the antenna. The beam
undergoes refraction at the air-glass boundary and bends towards the normal. The
opposite effect takes place when the beam exits the glass.
The developed antennas can be utilized in different applications such as
tomographic radar systems, medical and security applications which require the
antennas to possess the specified radiation characteristics and operate over the
frequency range 76–81 GHz.
Beskrivning
Ämne/nyckelord
Antennas , RF , RADAR , FEM simulations , microwave engineering