Sharif Digital Repository

Variation of the input driving power can cause in some varactor and BJT frequency multipliers parametric instability. If parametric oscillations are present in the circuit, output phase noise of the multiplier degrades remarkably in some specific driving levels. Phase noise of the varactor and BJT multiplier is calculated by the conversion matrix method using generalized nodal analysis. By the conversion method the phase noise degradation can be predicted precisely. In the calculation of phase noise the effect of the noise sources that are modulated by the large signal drive and the conversion of components of the internal noise sources of the device to the output spectrum due to circuit... 

In this thesis, it is shown that by detuning the array peripheral elements, without using phase shifters, and locking the array to the common frequency there exists a phase difference between two adjacent elements which is constant along the array and is proportional to the amount of free running frequency detuning. By changing free running frequency and therefore resultant phase difference, one can control the array beam direction. Linear, ring, hexagonal and triangular array configurations have been analyzed so far. In this work we endeavor to explore a circular planar array with weak coupling. The aim is to yield an analytical relationship to determine the free running frequency of each... 

In this thesis a substrate integrated waveguide (SIW) filter is designed and constructed using the contour integral method. A substrate integrated waveguide can overcome the drawbacks of regular waveguides, namely bulkiness, high costs and the difficulty to be integrated with other elements in high frequencies. In planar structures with arbitrary shapes where green’s functions aren’t available, we can use the contour integral method to construct the impedance matrix. Because the SIW structure supports TEn0¬ modes, we can consider SIW as a planar structure and thus use the contour integral method. Regular filter structures are usually analyzed using the FEM method (with HFSS) or the FIT... 

In this thesis, a modified method based on frequency discriminator technique is presented for measuring phase noise of microwave oscillators. In the proposed method, the phase shifter is omitted. In contrast, a 90° hybrid with one more channel containing a phase detector, and an LNA is added to the measurement setup. It can be said that an I/Q phase noise detection has been developed. With the proposed method, tuning of the variable phase shifter is not needed anymore. Therefore, the measurement is done automatically and as a result the measurement time is decreased. Beside the wideband property of the new technique, another considerable advantage is that the method is theoretically self... 

In this thesis interferometric method is used in the frequency discriminator based on classic delay line technique for phase noise measurement of microwave oscillators at X-band. In this method no reference oscillator is needed for phase noise measurement. Beacause of carrier suppression, we can use low noise amplifier in linear regimeandthereforethe added noise to the phase detector, is reduced and the sensitivity of the system is improved consequently. Moreover cross correlation method isapplied to improve the sensitivity of classic delay line frequency discriminator technique. It has been shown that up to 15 dB improvement is achievable at far from carrier offsets.
 

Oscillators in microwave communication systems play very important role. Therefore, designing an oscillator with a good performance, influences the final performance of the system. One of the parameters that determine the performance of an oscillator is the phase noise. This parameter in systems that have a large number of adjacent frequency channels, is causing many problems. Therefore, designing an oscillator with low phase noise improves the entire system performance.
Microwave oscillator phase noise is influenced by various factors, which one of the most important is the resonator. In microwave applications cavities have small sizes, thus it is difficult to use of them. Thus, in... 

Ultralow phase noise microwave oscillators with high stability are one of the key components required for many applications. With recent advances in ultrapure microwave oscillators, optoelectronic oscillators (OEOs) culminated in the state-of-the-art ultralow phase noise microwave oscillators. In this thesis, a nonlinear analytical approach is used to predict the main oscillation mode power and spurious levels in ultrapure microwave OEOs. Our analytical predictions are verified by numerical simulations and experimental data. Performance of an intensity-modulation direct-detection (IMDD) microwave photonic link (MWPL) operating under nonlinear conditions when its input consists of a sum of... 

E-plane waveguide filters are good choices due to highly manfacturing accuracy in Q-band microwave devices.To increase the attenuation slop or selectivity of such filters one need to synthesis transmission zeros with cross coupled resonators.With this method for constanst degree and return loss, attenuation slop increases in comparison to direct coupled resonators.
In this thesis we designed and fabricated a Q-band 4th degree filter,with center frequency at 42.1746 GHz and bandwidth of 350 MHz with two transmission zeros. Results of simulations and measurments are given in chapters 3 and 5.
Microwave filters using coupled resonators are important components in microwave systems.... 

Modern microwave and wireless communications systems are too complex today to permit the complete simulation of the nonlinear behavior at the transistor level of description. This problem presents a significant productivity bottleneck for design engineers. At the bridge between the transistor circuit and the multichip module or RF integrated circuit (RFIC) we use “behavioral models” to describe the nonlinear circuit blocks or ICs in the system. The behavioral models are simplified models of the essential nonlinear behavior of the complex sub-circuits; this simplification means that these models will execute more quickly, and use much less memory than if an entire complex subsystem was... 

Ridge gap waveguide is a new technology with low loss and high power handling capability in millimeter wave(mm-wave) frequencies. In this technology there is no need for electrical connection between the constitutive parts and using dielectric material as a substrate. This thesis focuses on the capabilities of this technology in realization of devices used in communication systems at the mm-wave frequency. Novel devices based on this technology have been designed, fabricated and tested. The main goal of the thesis is realization of the whole RF front end of a communication system in Ka band based on this technology. So at first step, a ridge gap waveguide transmission line is evaluated and a... 

Phase noise is one factor determining the quality of radar and telecommunication systems. Oscillators play an important role in system phase noise, as a signal generator for information modulation. Due to the greater impact of flicker noise at near carrier frequency than other types of phase noise sources, its reduction will greatly impact the phase noise of the telecommunication system. In this research, the simulation of phase noise and flicker noise of an oscillator with various types of bias circuit methods, such as bias with two independent sources, self-bias, improved self-bias, active bias, and low-frequency feedback, has been done. Then, a microwave dielectric resonator oscillator... 

Microwave and millimeter wave engineering are now crucial to modern life. This field has developed as a result of its applications in non-destructive testing, communications, radars, imaging, and medicine. Oscillators generate the reference frequency in all of these applications, therefore utilizing an appropriate oscillator may have a significant influence on the performance and even the additional expenses of a microwave system. Phase noise is an example of an oscillator’s characteristic that is especially crucial. This characteristic results in a number of limitations in the system’s final performance. For instance, the phase noise of the local oscillator will be one of the causes of... 

In an operational IFM receiver, there is usually a limiting amplifier in front of the power divider, delay line, and phase correlator. The limiting amplifier can improve the sensitivity of the receiver by providing RF gain to process weak input signals. In general, a signal must reach the limiting level in order to be processed by the receiver. It is important to notice that a limiting amplifier can be used only at the input of an IFM receiver. It should not be used in other kinds of receivers because the limiting amplifier will generate intermodulation products when overlapping signals are present. Since an IFM receiver only reads one signal at a time, the limiting amplifier will not... 

Modern communication systems,while demanding high power efficiency, suffer from the inherent nonlinearty effects. Such a problem becomes more critical in LEO satellites, in which there are fundamental power limitations. Considering that the main source of nonlinear effects are power amplifiers, one of the most common methods to improve signal quality in a transmitter, meanwhile maintaining power efficiency, is to utilize linearization techniques for power amplifiers. This project consists of two parts. The first is to design and fabricate a power amplifier for the desired frequency (2.4 GHz) and power requirements (3 W). The other is design and fabrication of a linearizer and matching it to... 

Phase noise is one of the most important parameters in communication systems especially in receivers. Implementation of low phase noise oscillators has always been important.One of the most important parameters in reducing the phase noise of the oscillator is the quality factor of the cavity used in its structure. As a result, increasing the quality factor of the cavity can reduce the oscillation phase noise. Cylindrical waveguides in higher order modes have a higher quality factor than the main modes of excitement. As a result, this property can be used to increase the quality factor of the cavity and reduce the phase noise of the oscillator. This will increase the size of the cavity. The... 

High power, broadband amplifiers at microwave and millimeter wave frequencies are needed for military and civilian applications. High power, broadband, high linearity, low noise, high efficiency and graceful degradation on failure are among the most important features in amplifier design. Solid state and vacuum tube devices have many disadvantages. A promising solution has been spatial power combining technique. Spatial power combining is a method of coherently combining the power of many amplifying devices using free space as the power dividing/combining medium within a guided wave structure in contrast to traditional circuit based amplifiers. This thesis presents the design and fabrication... 

Modern broadband microwave and millimeter-wave systems often struggle with excessive pass band ripple and negative gain slopes due to the loss of transmission lines such as coaxial cables, or ripples in the gain characteristic of broadband amplifiers. The common solution for this problem is using a gain equalizer to compensate for the intrinsic pass band variation with some extra loss in the band of interest in return.Designed equalizers often have a constant slope in their bandwidth. However, having ripples in pass band or in other words slope changing in some parts of the band is one of the issues that designers should deal with. In this thesis, after reviewing the previous works on the... 

For decades Crystal Oscillators (XO) have been the unequaled references for stable and low noise frequency sources. This leadership is due to their high Q-factor. The resonant frequency of such crystal resonator is inversely proportional to the thickness of the quartz disk (the resonant cavity) and is today limited , by physical manufacturing constraints , to about 150 MHz . in order to avoid such limitation , the solution is to start with an oscillator at higher fundamental frequency. SAW technology on quartz offers this opportunity . with SAW the resonant cavity size is not linked to the thickness of the substrate and resonant frequencies up to the GHz range are achievable. In this thesis... 

Low noise oscillator design has always been an important subject. Oscillators aren’t usually applicable in free-run mode. Thermal instability and high phase noise level near the carrier frequency are some of the reasons which makes the oscillator not to be used in free-run mode. Using the oscillator in a phase locked loop overcomes the mentioned problems. The oscillator considered in this project, uses a SAW resonator(1GHz). Low phase noise level at far carrier offsets, is the main feature of this oscillator. However, the near carrier phase noise isn’t good enough. Consequently, using a phase locked loop, we lock the oscillator to a low noise and stable source in order to increasing thermal... 

Phase noise is one of the important parameters in telecommunication systems and its measurement has always been considered. Digital phase noise measurement methods have a simpler implementation and calibration than analog types. Also, in digital methods, amplitude noise and phase noise can be separated and measured both at the same time. Comparing the phase noise of two oscillators with different frequencies is another major advantage of digital methods. The sensitivity of digital methods is limited to the noise of their analog-to-digital converters. Cross-correlation technique is used to reduce the minimum measurable level of phase noise. This method reduces the internal noise of the...