Sharif Digital Repository

This article presents a novel dual-band transmission line (TL), consisting of a multibranch stub, which can provide equal unwrapped phases at two different frequencies. The frequency ratio can be close to one without any significant degradation in the device performance. Besides, the bandwidth of the proposed line can be manipulated at both frequencies by adjusting the design parameters. The behavior of the structure over the frequency bands is investigated theoretically, and the design procedure and relations are derived. The simulation and measurement results of a quarter-wavelength open-ended stub and a branch-line coupler (BLC) are presented and compared to verify the performance of the... 

A novel N-path filter using a complex impedance is designed to replace the frontend SAW filters in receivers with on-chip bandpass filters. It is demonstrated that the center frequency of the filter can be tuned solely by changing the value of some capacitances without the need to change the clock frequency. In addition, thanks to the use of smaller capacitors, the silicon area is reduced compared to similar designs. The high-Q bandpass filter is realized utilizing two gyrators and an arrangement of four baseband capacitors with NMOS switches, driven by 4-phase 25% duty cycle clock signals. This paper also analyzes the performance of the proposed filter against imperfections such as thermal... 

This paper describes the design procedure and measurement results of a single-layer low-cost, and wideband frequency scanning antenna, which exhibits a nearly symmetrical beam-steering around broadside direction. The measured antenna bandwidth ranges from 27.5 to 40 GHz, which covers most of the Ka-band. In addition, the antenna main beam scans from − 52° to + 42° as the frequency sweeps from 27.5 to 36.5 GHz, showing 94° beam-steering range. At the center frequency of 32 GHz, the beam points to the broadside direction. The measured radiation patterns verify that the beam-pointing error is less than 2° over the scanning range. Furthermore, the measured gain for a 10-cell structure with 6-cm... 

Quarter-wavelength superconducting spiral resonators have been used to realize a coplanar waveguide bandpass filter and bandstop filter around the center frequency of 6 GHz. These compact coplanar waveguide filters have been made from 300-nm-thick NbTiN thin film on a 525-μm-thick silicon substrate. The bandpass filter is a six-pole Chebyshev filter with two zero transmissions due to nonadjacent coupling in its structure. Accurately microfabricated air-bridges have been used to suppress the undesired slot-line mode in this filter. The bandstop filter is a very simple two-pole structure that used wire bonding to suppress the slot-line mode. Measurements have been done at a temperature of 4.2... 

A four stage LC-ring oscillator is presented. Eight different phases are generated in which there in 45 degrees phase difference between consecutive outputs and direction of phases is defined. Nmos capacitors in parallel with constant capacitors are used for coupling between stages. The control voltage is applied to Pmos varactors to adjust the oscillation frequency. The advantages of this structure are the rather small inductors size, low power consumption, and tuning curve linearity. The proposed structure is simulated in 0.18um CMOS technology. Power consumption for each stage is 4.8mW from a 1.8B supply. The proposed VCO has a phase noise of -121dBc/Hz at 1MHz offset from the center... 

This paper presents two integrated concurrent dual-band class-J power amplifiers (PAs) in AlGaAs-InGaAs pHEMT technology. Design flexibility of class-J space is employed to explore the availability of a dual-band PA where the center frequency of the second band is twice the center frequency of the first band (f2=2f1). The theoretical formulations are developed for f2=2f1 case, for which it is not feasible to obtain high efficiencies using class-F-1, class-F, and other high-efficiency modes. A proof of concept 5/10-GHz class-J PA is manufactured in a 0.1- μm GaAs pHEMT technology. The proposed PA delivers 26.9- and 26-dBm output power with peak power added efficiencies (PAEs) of 49% and 46%... 

In this paper, we present a detailed analytical approach to obtain the channel capacity of optical space-division multiplexing (SDM) systems. To this aim, the nonlinearity effects of optical fiber are modeled as additive white Gaussian noise (GN) process, and accordingly a closed-form formula is derived for SDM capacity. Furthermore, we extend our result to a more generalized case, which includes different bandwidth, center frequency, and transmission powers. © 2017 IEEE  

A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed...