Millimetre and submillimetre wave antenna design using ray tracing

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Aki Karttunen Name of the doctoral dissertation Millimetre and submillimetre wave antenna design using ray tracing Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 127/2013 Field of research Radio Engineering Manuscript submitted 6 June 2013 Date of the defence 10 September 2013 Permission to publish granted (date) 13 August 2013 Language English Monograph Article dissertation (summary + original articles) Abstract The millimetre and submillimetre wave frequency ranges have many current and potential applications for example in satellite technology and telecommunications. Electrically large antennas are needed in several applications, e.g., in order to achieve high antenna gain with a narrow beam. Reflector and lens antennas, with all dimensions large compared to the wavelength, are commonly designed using ray tracing. Ray tracing is based on a high frequency approximation of Maxwell’s equations. The main advantage of ray tracing is the decreased computational effort as compared to more accurate full-wave methods. In this thesis, ray tracing is used in both synthesis and simulation of electrically large antennas. In the first part of this thesis, a 650 GHz dual reflector feed system (DRFS) is designed, tested, and used in a hologram-based compact antenna test range (CATR). The DRFS provides shaped illumination that simplifies the hologram manufacturing. A ray-tracing based numerical synthesis method is used to design the 650 GHz DRFS. It is tested with antenna measurements prior to the compact range measurements. The designed DRFS is used successfully in a full scale compact range, in which a 1.5-m antenna is tested at 650 GHz. In the second part of this thesis, several beam-steering integrated lens antennas (ILAs) are designed with ray-tracing simulations. Antenna prototypes are designed, fabricated, and tested at 77 GHz with antenna measurements. Electrical beam steering is demonstrated with integrated feed arrays and switching networks. Also, beam-steering properties of ILAs with a wide range of different lens permittivities and feed element directivities are studied with raytracing simulations. Lens shapes are developed for improvement of the beam properties at large beam-steering angles. With a low permittivity ILA, an intermediate eccentricity, compared to those of the conventional hemispherical and elliptical lenses, is found to have smaller scan loss and lower side-lobes with large beam-steering angles of about 30°. Placing the feeds on a spherical surface of an extended hemispherical ILA is found to result in a beam shape and gain that remain nearly constant at beam-steering angles up to about 25°. A typical disadvantage of a beam-steering ILA is the increase of the internal reflections with the increase of the feed offset. It is shown that the extension of a low permittivity extended hemispherical ILA can be shaped to significantly reduce the internal reflections. It is also shown that it is possible to design an integrated lens antenna with low reflection loss (< 1 dB), for moderate beam-steering angles (< 15°), with any lens permittivity and with any feed element directivity. The reduction of internal reflections is based on the selection of the original ellipse radius larger than the final lens radius and designing the shape of the extension for minimal reflections.The millimetre and submillimetre wave frequency ranges have many current and potential applications for example in satellite technology and telecommunications. Electrically large antennas are needed in several applications, e.g., in order to achieve high antenna gain with a narrow beam. Reflector and lens antennas, with all dimensions large compared to the wavelength, are commonly designed using ray tracing. Ray tracing is based on a high frequency approximation of Maxwell’s equations. The main advantage of ray tracing is the decreased computational effort as compared to more accurate full-wave methods. In this thesis, ray tracing is used in both synthesis and simulation of electrically large antennas. In the first part of this thesis, a 650 GHz dual reflector feed system (DRFS) is designed, tested, and used in a hologram-based compact antenna test range (CATR). The DRFS provides shaped illumination that simplifies the hologram manufacturing. A ray-tracing based numerical synthesis method is used to design the 650 GHz DRFS. It is tested with antenna measurements prior to the compact range measurements. The designed DRFS is used successfully in a full scale compact range, in which a 1.5-m antenna is tested at 650 GHz. In the second part of this thesis, several beam-steering integrated lens antennas (ILAs) are designed with ray-tracing simulations. Antenna prototypes are designed, fabricated, and tested at 77 GHz with antenna measurements. Electrical beam steering is demonstrated with integrated feed arrays and switching networks. Also, beam-steering properties of ILAs with a wide range of different lens permittivities and feed element directivities are studied with raytracing simulations. Lens shapes are developed for improvement of the beam properties at large beam-steering angles. With a low permittivity ILA, an intermediate eccentricity, compared to those of the conventional hemispherical and elliptical lenses, is found to have smaller scan loss and lower side-lobes with large beam-steering angles of about 30°. Placing the feeds on a spherical surface of an extended hemispherical ILA is found to result in a beam shape and gain that remain nearly constant at beam-steering angles up to about 25°. A typical disadvantage of a beam-steering ILA is the increase of the internal reflections with the increase of the feed offset. It is shown that the extension of a low permittivity extended hemispherical ILA can be shaped to significantly reduce the internal reflections. It is also shown that it is possible to design an integrated lens antenna with low reflection loss (< 1 dB), for moderate beam-steering angles (< 15°), with any lens permittivity and with any feed element directivity. The reduction of internal reflections is based on the selection of the original ellipse radius larger than the final lens radius and designing the shape of the extension for minimal reflections.