Abstract

Antennas those operating at millimeter-wave (mm-wave) frequencies (30 - 300 GHz) are more advantageous than operating at less than 6 GHz, due to a reduction in antenna physical dimensions, an increase in the data transfer rate, and reduction in latency. However, the electromagnetic waves propagating in free space at mm-wave frequencies experience significant propagation path loss due to the atmospheric absorption and rain attenuation. Therefore, high-gain antennas are preferred to compensate for path loss and to increase the range of wireless communication. Also, transmission lines such as microstrip, and coplanar waveguides incur high radiation losses at mm-wave frequencies. Hence, to minimize losses, a planar waveguide known as a substrate integrated waveguide (SIW) is preferred. Besides, at mm-wave frequencies, circularly polarized (CP) waves are preferred over linearly polarized (LP) waves as these waves reduce multi-path effects at the receiver.

The objectives of this thesis are to design high-gain linearly, and circularly polarized antennas based on SIW at the mm-wave frequency 30 GHz. The proposed antenna models were designed, simulated, and analyzed using CST software. The antenna prototypes were fabricated and measured for the reflection coefficient, gain, and principal plane radiation patterns. In this thesis, we are proposing two single element antennas, a linear to circular wave polarizer, and an array antenna.

At first, we present, a planar, cylindrical sector-substrate integrated waveguide (CS-SIW) narrow slot antenna. The impedance bandwidth of this antenna is 10.87% which is approximately equivalent to 4 GHz of bandwidth at 30 GHz, and the antenna gain ranges from 8.33 to 8.84 dB within the impedance bandwidth. Further, to improve the gain, an engineered substrate is constructed on top of the CS-SIW slot antenna. The impedance bandwidth of the modified antenna is 10.42% - also, the gain ranges from 10.5 to 11.44 dB over the impedance bandwidth, which implies an increase in the gain from 2.1 to 2.7 dB when compared with the gain of CS-SIW slot antenna. Also, we propose a three-layered meander-line polarizer at 30 GHz which transforms linearly polarized waves to circularly polarized waves for the CS-SIW slot antenna.

Lastly, we present, a 1 × 8 CS-SIW slot antenna array with a superstrate to achieve a high-gain LP antenna. The impedance bandwidth of the antenna is 10%. The gain of the array antenna integrated with a superstrate layer varies from 21.35 to 22.95 dB over the impedance bandwidth.