Investigations on microwave balanced components : novel filters and active integrated antennas

Abstract

High integration and complex environment has been the main feature of modern microwave systems. Thus, there is not only a high-level of electromagnetic interaction between circuit nodes and crosstalk from substrate coupling between components, but also the interference from space. Therefore, the balanced circuit technology has become more and more important in the modern communication systems because of their good common-mode rejection capability. However, for a long time, the balanced circuit suffers the problems such as high cost and devices matching for components in dual channels. With the development of IC technology, these problems can be easily solved. In various balanced components, the balanced bandpass filters and the balanced active integrated antennas (AIAs) are very important. Hence, this dissertation concentrates on the study of these two kinds of balanced circuits. Theory, design and applications are included in this dissertation. The work can be divided into five parts. The first three parts are about balanced bandpass filter, while the next two parts are about balanced AIAs. In the first part, center-loaded uniform impedance resonators are introduced based on the investigation of half-wavelength transmission-line resonators. It is found that the common-mode suppression can be made independent of the differential-mode response in the balanced filter, making use of the center-loaded half-wavelength resonators. This is very important to simplify the design and tuning processes of the balanced filters. Making use of this feature, the resonator is not only utilized to design the balanced single-band bandpass filter but also the balanced dual-band bandpass one. To demonstrate the design ideas, one single-band and two dual-band balanced filters are presented. The experimental results agree well to the theoretical predictions and simulations. In part two, a half-wave length SIR loaded by a capacitor or a resistor is introduced and theoretically analyzed. It is found that the capacitor can minimize the common-mode external quality factor, and the resistor can reduce the common-mode unloaded quality factor. With the use of this property, the common-mode response can be suppressed, whereas the differential-mode response is almost unaffected. To demonstrate the design idea, one balanced dual-band bandpass filter operating at 2.4 and 5 GHz and another balanced single-band bandpass filter with a wide stopband are designed. The experiment results show high common-mode suppression. And high selectivity is obtained by using cross coupling scheme. Subsequently, other three techniques for balanced bandpass filter are proposed. First, source-load coupling is utilized in balanced bandpass filter to get controllable common-mode transmission zero, with which the common-mode suppression inside the differential-mode passband can be greatly improved. Then, coupled stepped-impedance resonators are used to implement a balanced dual-band bandpass filter without the loaded lumped elements. Finally, a balanced bandpass filter based on double-sided parallel-strip line (DSPSL) is presented. The difference between balanced bandpass filters based on the DSPSL and microstrip line is that the DSPSL is one kind of balanced transmission line, which has the inherent feature of immunity to common-mode noise. Following the DSPSL balanced bandpass filter is a balanced voltage-controlled integrated antenna oscillator (VCIAO), which integrates a DSPSL-based differential voltage-controlled oscillator (VCO) with DSPSL-fed quasi-Yagi antenna. The quasi-Yagi antenna is used not only as the radiating element, but also as the output power combiner and the resonating load of the differential VCO without any matching circuits or transition between them. The two sub-oscillators of the VCO on the opposite sides of the substrate share a common quarter wavelength DSPSL resonator and a common inserted ground plane, which also works as the reflecting element for the quasi-Yagi antenna. Due to the differential output of the proposed VCO, the cross polarization of the proposed VCIAO is suppressed to a great extent in the entire tunable frequency range. Finally, a singly balanced integrated antenna mixer (IAM) has been constructed. The proposed IAM integrated a quarter-wavelength hybrid coupler, a DSPSL-fed quasi-Yasi antenna, and two mixer diodes together. The hybrid coupler based on the DSPSL with an inserted conductor plane, which can be directly connected to the DSPSL-fed quasi-Yagi antenna, is theoretically analyzed and simulated. The measurement results of the whole IAM show good isolation and radiation patterns.