High Gain Planar Antenna Structures for Ka-band Applications

Antennas are an essential part of a communication system as they control a coverage area of the signal. The millimeter wave band has the potential to offer numerous radio applications which require the large bandwidth channels. Due to the current cellular subscribers’ demand of higher data rates, even cellular communication is expected to move in millimeter wave communications at Ka band of 26.5 GHz to 40 GHz. However, millimeter waves are sensitive to the high degree of atmospheric and oxygen absorption losses. This challenge of the millimeter wave communication can be tackled by employing high gain antennas. In addition, modern electronic products require compact handheld devices to offer the user-friendly system as well as capture the market. Therefore, planar antenna structures are apt for these communication systems. In this thesis, two antenna structures are presented at the Ka band for millimeter wave communications. Initially, four element patch antenna is presented for high gain in the broadside direction. Patch elements are excited using an aperture coupling from 50Ω microstrip line. Air-gap cavity is used to improve the impedance bandwidth of the design. This structure obtains a relatively moderate impedance bandwidth of 4.6%. The proposed four-element patch antenna exhibits a flat gain over an operating band with 13.8 dB gain at the design frequency. The antenna achieves a wide beamwidth of 700 in H plane. In addition, side lobe levels in E and H planes are -14.5 dB and 23 dB respectively. For the second prototype, an Antipodal Fermi-Linear Tapered Slot Antenna (AFLTSA) is presented to achieve the wide impedance bandwidth with high flat gain for endfire radiation. Substrate Integrated waveguide (SIW) technique is utilized to feed the AFLTSA which reduces insertion losses of the structure. Fermi-Dirac distributed curve in conjunction with a linear curve for a tapered slot increases the coupling of the electric field from a substrate integrated waveguide to the tapered slot. Knife edge rectangular corrugation profile is used at edges of AFLTSA in order to reduce the side lobes and cross polarization levels of radiation pattern. The proposed structure achieves the wide impedance bandwidth to support requirements for high data rate channels. Measurement results from a fabricated prototype exhibit a flat gain over an entire operating frequency band with 16.4 dB gain at 28 GHz. The wide impedance bandwidth is achieved with return loss below 15 dB. Proposed structure has low side lobe levels of -13.9 dB in H plane and -19.5 dB in E plane. In addition, it offers a low cross polarization level of -22 dB