As the microwave wireless communication systems growing rapidly, microstrip planar ceramic filters attract many attentions because of the advantages of small size, low cost, easy fabrication, higher performance and easy integration. In this thesis, several kinds of bandpass filters are designed for different operating purposes. First, two kinds of dual-mode bandpass filters are designed for 2.4 GHz wideband with the T-shaped I/O arranging in a straight way for easy integration. Second, the hook-coupling and insert-coupling structures are adopted for series connecting of the stepped-impedance resonator structures, and 2.4/5.2 GHz dual-band filtering properties could be achieved. Third, two open-loop rectangular ring resonators and U-shaped I/O are designed for 2.4/5.2 GHz dual-band bandpass filters with deep transmission zeros. The quarter wavelength stubs and groove structures are used for enhancing deep transmission zeros between two passband and ripples of the second passband, respectively. Fourth, the parallel positioned resonators with phase difference method are used to design the dual-band (1.23/2.4 GHz) and quad-band (1.23/2.4/3.5/5.2 GHz) bandpass filter with asymmetrical bandwidths and transmission zeros. In the thesis, high quality Al2O3 ceramic substrates are used to fabricate different kinds of bandpass filters for pattern minimization and low losses. The electromagnetic simulators, HFSS and IE3D, were used to adjust and optimize the associated parameters. The printing method was used to fabricate the proposed bandpass filters, which did not need using the FeCl3 to etch the Cu plate from the surface of Duroid or the FR4 substrates. The proposed filters are measured by Agilent-N5230A with the SMA connectors welding. Finally, the simulated and measured results of proposed bandpass filters are in good agreement.

Today's microwave circuits, whether for communication, radar, or testing systems, need compact tunable microwave filters. Since different microwave circuit applications have radically different size, power, insertion loss, rejection, vibration, and thermal requirements, new filter technologies with different balances between these requirements are always desirable. Negative Refractive Index (NRI) transmission media was discovered 10 years ago with the unique property of negative phase propagation. A literature review was conducted to identify potential NRI methods for filters and other devices, but no NRI tunable filters were found. To address this gap, a family of tunable NRI bandpass filters was simulated and constructed successfully using end-coupled zeroth order resonators. Tuning was accomplished by controlling the negative phase length of the NRI sections with varactors. The resulting L-band filters exhibited a 25-40 percent tunable range, no higher order resonances, and required only one fourth the length of a coupled-line filter constructed from traditional 180 degree microstrip resonators.

This thesis proposes an analytical method to synthesize bandpass filter with multiple transmission zeros. By using the six pre-determined parameters including two reflection zeros, two matching quality factors, and two transmission zeros, the method can exactly synthesize the corresponding prototype of second-order coupled-resonator bandpass filter. The synthesized filters not only can provide two pre-determined transmission zeros in the lower and upper side of the passband, but also can generate an extra transmission zero in the stopband. This thesis presents the prototypes of the bandpass filter and the methods of synthesis in detail. Finally this thesis implements compact LTCC bandpass filters by using the proposed synthesis method for 3.5 GHz WiMAX applications.

Bandpass sigma-delta modulators combine oversampling and noise shaping to get very high resolution in a limited bandwidth. They are widely used in applications that require narrowband high-resolution conversion at high frequencies. In recent years interests have been seen in wireless system and software radio using sigma-delta modulators to digitize signals near the front end of radio receivers. Such applications necessitate clocking the modulators at a high frequency (MHz or above). Therefore a loop filter is required in continuous-time circuits (e.g., using transconductors and integrators) rather than discretetime circuits (e.g., using switched capacitors) where the maximum clocking rate is limited by the bandwidth of Opamp, switch’s speed and settling-time of the circuitry. In this work, the design of a CMOS fourth-order bandpass sigma-delta modulator clocking at 500 MHz for direct conversion of narrowband signals at 125 MHz is presented. A new calibration scheme is proposed for the best signal-to-noise-distortion-ratio (SNDR) of the modulator. The continuous-time loop filter is based on Gm-C resonators. A novel transconductance amplifier has been developed with high linearity at high frequency. Qfactor of filter is enhanced by tunable negative impedance which cancels the finite output impendence of OTA. The fourth-order modulator is implemented using 0.35 mm triplemetal standard analog CMOS technology. Postlayout simulation in CADENCE demonstrates that the modulator achieves a SNDR of 50 dB (~8 bit) performance over a 1 MHz bandwidth. The modulator’s power consumption is 302 mW from supply power of ± 1.65V.

In this thesis two different research topics are undertaken, both in the area of compact RF/microwave circuits design. The first topic involves the design of a compact circularly polarized (CP) slot-ring antenna. A study of several compact CP microstrip and slotline antennas reported in the past has been carried out. In this research, a method of reducing the size of a printed slot-ring antenna is proposed. The reduction in size is achieved by introducing meandered-slot sections in the ring. Circular polarization is achieved by introducing an asymmetry, also a meandered-slot section, and feeding the antenna at an angle of 45o from the asymmetry using a microstrip feed line. The minimum axial ratio of 0.4 dB is obtained at 2.46 GHz, which is the operating frequency of the antenna. The size of the proposed antenna is reduced by about 50% compared to a conventional CP slot-ring antenna and it displays a CP bandwidth of about 2.5%. The simulated and measured results are presented, and they are in good agreement. The small size of the antenna makes it very suitable for use in modern RF/microwave wireless systems which require compact, low cost, and high performance circuits. Moreover, its CP behavior makes it more attractive for applications such as satellite communications. The second topic in the thesis involves the design of a compact microstrip bandpass filter using triangular open-loop resonators. A new compact three-pole microstrip bandpass filter using four triangular open-loop resonators is presented. A fourth resonator is placed to provide cross-coupling in the structure which gives a better skirt rejection. The measured pass-band center frequency is 2.85 GHz. The filter demonstrates about 7% bandwidth with insertion loss of less than 1 dB in the passband, a return loss of greater than 15 dB and out-of-band rejection of greater than 30 dB. The simulated and measured results are in good agreement. The proposed filter is very attractive for use in modern wireless systems which require bandpass filters having compact size, low insertion loss, high selectivity, and good out-of-band rejection.

With the rapidly progress in the microwave communication systems, miniaturization and performance enhancement have become two main requirements of the microwave devices. Microwave dielectric substrates would be the best choice for these requirements, because high dielectric constant of the substrates would reduce the size of the devices, high quality factor of the substrates would improve the microwave characteristics of the devices, and low temperature coefficient of resonant frequency would reduce the shift of the operating frequencies due to the variation of temperature. As mentioned above, the main research of this dissertation is divided into two parts: microwave dielectric materials and microwave filters. 1. Microwave dielectric materials AB2O6 (A=Mg, Zn; B=Ta, Nb) microwave dielectric ceramics have been developed as the microwave dielectric resonators (DRs) in the past, because the dielectric resonators fabricated by AB2O6 ceramics reveal the good microwave dielectric characteristics. However, the temperature coefficients of resonant frequency of MgTa2O6, MgNb2O6, ZnTa2O6, and ZnNb2O6 ceramics are still not good enough for the applications at the microwave frequency. In addition, MgTa2O6 and ZnTa2O6 ceramics reveal positive temperature coefficients of resonant frequency but the MgNb2O6 and ZnNb2O6 ceramics reveal negative temperature coefficients of resonant frequency. In this study, combining of MgNb2O6 ceramics (with negative temperature coefficients of resonant frequency) and MgTa2O6 ceramics (with positive temperature coefficients of resonant frequency) to form Mg(Ta1-xNbx)2O6 ceramics and combining of ZnNb2O6 ceramics (with negative temperature coefficients of resonant frequency) and ZnTa2O6 ceramics (with positive temperature coefficients of resonant frequency) to form Zn(Ta1-xNbx)2O6 ceramics, which all reveal near-zero temperature coefficients of resonant frequencyand are suitable for the applications of microwave communication devices. The sintering and microwave dielectric characteristics of the Mg(Ta1-xNbx)2O6 and Zn(Ta1-xNbx)2O6 dielectric ceramics are also investigated. 2. Wide-band, dual-band, tri-band, and tetra-band bandpass filters Microwave filters have been widely used in the communication systems. The optimal microwave dielectric characteristics of AB2O6 ceramics developed in this thesis were adopted as the substrates of the filters. The performance of the filters was improved obviously due to the high dielectric constant and high quality factor of the microwave dielectric ceramic substrates. At first, a wide-band and a dual-band (2.45/5.2 GHz) bandpass filters are developed by the combination technique of modified end-coupled microstrip lines and half-wavelength ombination technique will generate three transmission zeros easily in the stop-band to improve the characteristics of the filters. And the next, the tri-band (1.57/2.45/5.2 GHz) bandpass filters are developed by the combination of modified end-coupled microstrip lines, outer-frame structures and half-wavelength U-shaped hairpin resonators. The Defected Grounded Structures (DGS) are add into the ground planes of the tri-band bandpass filters to generate the fourth frequency (3.5 GHz), hence, the tetra-band (1.57/2.45/3.5/5.2 GHz) bandpass filters are accomplished. In addition, due to the uses of the high dielectric constant ceramic substrates and the combination techniques, the size of this tetra-band bandpass filter is only 26.3 mm*9.9 mm. Besides, six deeply transmission zeros are generated in the stop-band to improve the characteristics of the filters (1~7 GHz), all the characteristics of this tetra-band filters (frequency, bandwidth, insertion loss, and stop-band rejection) are suitable for the applications of modern communication systems.

<p>An important component in many communication system is the digital to analog converter. The component is needed in order to convert real world analog quantities to digital quantities which are easier to process. As the market for hand held devices with wireless communication with the outer world has increased new approaches for sharing the frequency spectrum are needed. Therefore it would be interesting to look at the possibility to design an analog to digital converter that, in runtime, can change the frequency band converted, and hence the used standard. This thesis study one of the possibilities to design such an ADC, as a Σ∆ modulator, and more precise the structure called Cascade of resonators with distributed feedback and input (CRFB). The order of the modulator in this study is two.</p>

An important component in many communication system is the digital to analog converter. The component is needed in order to convert real world analog quantities to digital quantities which are easier to process. As the market for hand held devices with wireless communication with the outer world has increased new approaches for sharing the frequency spectrum are needed. Therefore it would be interesting to look at the possibility to design an analog to digital converter that, in runtime, can change the frequency band converted, and hence the used standard. This thesis study one of the possibilities to design such an ADC, as a Σ∆ modulator, and more precise the structure called Cascade of resonators with distributed feedback and input (CRFB). The order of the modulator in this study is two.

No description available.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 48-50)