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This thesis work presents a new harmonic suppression technique for microstrip patch antennas. Harmonic suppression in active integrated antennas is known as an effective method to improve the efficiency of amplifiers in transmitter side. In the proposed design, the antenna works as the radiating element and, at the same time, as the tuning load for the amplifier circuit that is directly matched to the antenna. The proposed active antenna architecture is easy to fabricate and is symmetric, so it can be conveniently mass-produced and designed to have circular polarization, which is preferred in many applications such as satellite communications. The antenna simulations were performed using Ansoft High Frequency System Simulator (HFSS) and all amplifier design steps were simulated by Advanced Design System (ADS). The final prototypes of the linearly polarized active integrated antenna and the circularly polarized active integrated antenna were fabricated using a circuit board milling machine. The antenna radiation pattern was measured inside Utah State University's anechoic chamber and the results were satisfactory. Power measurements for the amplifiers' performance were carried out inside the chamber and calculated by using the Friis transmission equation. It is seen that a significant improvement in the efficiency is achieved compared to the reference antenna without harmonic suppression. Based on the success in the single element active antenna design, the thesis also presents a feasibility of applying the active integrated antenna in array configuration, in particular, in scanning array design to yield a low-profile, low-cost alternative to the parabolic antenna transmitter of satellite communication systems.

This dissertation contains two significant investigations. One is the development of the broadband microwave bandpass filters with high out-of-band performance. The other is the development of low-loss hybrids. These researches are parts of the National Aeronautic and Space Administrator (NASA)s mission to explore the universe. The former is focused on the techniques used in microstrip line bandpass filter design that help achieving both low in-band insertion loss and high out-of-band attenuation level. Moreover, these filters achieve very broadband out-of-band attenuation bandwidth. These techniques are related to the improvement of stepped impedance resonators, coupling between resonators and effective methods to allocate transmission zeros to suppress filters out-of-band spurious responses. The later is focused on the techniques used in planar magic-T designs such that the developed magic-T obtains high isolation between port E (difference port) and port H (sum port). Moreover, it obtains low-loss and broadband characteristics. These techniques are related to the development of the low-loss broadband microstrip-toslotline (MS-to-SL transition and the magic-T with a highly symmetric structure. The theoretical analysis and experimental measurements have been performed. The experimental results of both the filter and magic-T researches show significant improvement over their prior state-of-the-art designs by number of magnitude. The designs also reduce fabrication complexity.