Design and Verification of Antennas for Tomographic Radar Systems in the Frequency Range 76–81 GHz
Examensarbete för masterexamen
RAHAMTULLA, WAFA PATHAN
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.
Antennas , RF , RADAR , FEM simulations , microwave engineering