Compact microstrip resonant cell

: analysis and applications

Abstract

In recent years, Photonic Band Gap (PBG) materials have drawn significant attention to microwave engineering due to their band-stop and slow-wave characteristics, which can be exploited for rejecting unwanted frequency and passive components size reduction. One-dimensional microstrip PBG cells, which exhibit remarkable slow-wave and band-stop characteristics within a single unit have been proposed. The unit possesses the same features of the PBG structure, except that it is not a periodic structure, and is called a Compact Microstrip Resonating Cell (CMRC). This thesis presents some new achievements in the study of the CMRC structure and its applications. Initially, equivalent circuits both in lumped and distributive parameters are proposed to model the CMRC. The lumped equivalent circuit consists of only capacitors and inductors, which is concise and it provides a simple explanation for the resonating band-stop mechanism of the CMRC. The distributive equivalent circuit consists of microstrip components such as microstrip lines, step discontinuities, cross-junction, T-junctions, tapered lines and coupling gaps. All of these components can be calculated by existing closed form equations, which make it possible to design and optimize the CMRC easily without using time consuming numerical simulation. Secondly, a transistor oscillator incorporating the CMRC as its terminating resonance is proposed. Adjusting the dimensions of the cell enables the phase of the fundamental frequency and the second harmonic to be constructive and destructive feedback, respectively, at the input port of the oscillator. The output power of the proposed CMRC oscillator is 13.6 dBm with 26.2 dB rejection of the second harmonic, outperforming the conventional microstrip termination with a 40 % size reduction. Next, a 4th sub-harmonic (SH) mixer exploiting four open/short stubs is introduced. Then, a millimeter-wave (35 GHz) 4th SH 4-open/short-stub mixer is designed and measured. The conversion loss is less than 15 dB within 2.4 GHz bandwidth. The minimum loss is 11.5 dB at the center frequency. After two of the stubs are replaced with two CMRC in-line stubs, the SH mixer not only reduces its size but also improves its performance. At 35 GHz, the conversion loss can be as low as 6.6 dB with 5 GHz of 3-dB bandwidth. The conversion loss in the whole Ka-band (26.5 to 40 GHz) is less than 16 dB. Besides, a microstrip bandpass filter using a CMRC as the resonator is proposed. The filter has the features of compact size, low-insertion loss, sharp-rejection and narrow-band. Experimental results show that the filter only has 1.3 dB and 1.5 dB insertion losses when using the symmetrical and asymmetrical CMRC resonators respectively. The effects of varying the length of the resonator to the notch frequencies of the filter have been studied. Furthermore, due to the CMRC characteristic, the size of this filter is only 0.1λg by 0.29λg, where λg is the guided wavelength at the center frequency of the pass band. The proposed filters have been verified by simulation and measurement with good agreement. In addition, a wide bandwidth UWB bandpass filter using a single stub with CMRC is also proposed. It entails the design concept of stub-tapped half-wavelength line resonator which provides three transmission poles in the passband and two transmission zeros at the high and low rejection bands. The two stubs are replaced by a single dual-band stub and the parallel coupled-line structures are meandered, leading to a compact size of 0.26λg by 0.32λg. Lastly, a millimeter-wave communication sub-system has been designed with the proposed mixer and the design procedures will be shown in detail. The system consists of mixer, LNA, filter, local oscillator, antennas and baseband. It can be used to transmit multimedia signals from one location to another. Waveguide technique will be applied to the system since it provides good shielding to the surrounding environment and reduces the transmission loss in the system integration.

Date of Award	15 Feb 2007
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Chi Hou CHAN (Supervisor)