Farhad Farzami

Reconfigurable Bidirectional Amplifier

We designed a reconfigurable dual band reflection amplifier with operation frequency bands over 1.8 GHz and/or 2.4 GHz.

Tunable TLs Based on SIW Loaded by VLESRRs

Wave propagation in single layer substrate integrated waveguides (SIWs) loaded by embedded split ring resonators (ESRRs) is discussed theoretically and experimentally

SIW Miniaturizing by Using ESRR

A substrate integrated waveguide (SIW) loaded by embedded Split Ring Resonators (SRRs) with transversal negative effective permeability is proposed.

Full-Duplex Communication System (ReflectFX)

We propose a power-efficient implementation for ReflectFX, an in-band full-duplex wireless communication system.

Tunable SIW Loaded by VLCSRR

Two substrate integrated waveguides (SIW) loaded by a new single metamaterial (MTM) cell are discussed theoretically and experimentally.

SIW Loaded by 3D-ESRR

A substrate integrated waveguide (SIW) loaded by three-dimensional embedded split ring resonators (3-DESRRs) is discussed theoretically and experimentally.
Reconfigurable Dual Band Bidirectional Reflection Amplifier with Applications in Van Atta Array
We designed a reconfigurable dual band reflection amplifier with operation frequency bands over 1.8 GHz and/or 2.4 GHz. This one-port amplifier boosts the reflected signal over either of these two frequency bands or both as a dual band reflection amplifier. The amplifier circuit consists of a FET transistor and two PIN diodes which act as switches to form a reconfigurable system. The measured reflection gains at single 1.8 GHz and 2.4 GHz frequency bands are 17.6 dB and 16.75 dB respectively. The dual band operation frequency shows 11.2 dB and 15 dB gain at 1.8 GHz and 2.4 GHz, respectively. Then, we realized a bidirectional amplifier using a dual band -3 dB 90 Branch Line Coupler (BLC) integrated with two of the proposed reconfigurable reflection amplifiers. This bidirectional amplifier is a two-port bilateral amplifier. The measured reflection gains show at least 10 dB transmission gains (S21 and S12) at operation frequency bands. The proposed reconfigurable bidirectional amplifier is then used in a dual band Van Atta array. The proposed active retrodirective system outperformed passive Van Atta array by 5 dB gain with only half the number of antenna elements. Each component is investigated analytically and analyzed by Advanced Design System (ADS). Fabricated circuits are measured and show a good agreement with simulations.
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Experimental Realization of Tunable Transmission Lines Based on Single Layer SIWs Loaded by Embedded SRRs
Wave propagation in single layer substrate integrated waveguides (SIWs) loaded by embedded split ring resonators (ESRRs) is discussed theoretically and experimentally. It is shown that the loaded SIW can support a backward-wave passband below the cutoff frequency (fc) of the host SIW or a stopband will appear above fc if the effective transversal permeability is negative. In addition, varactor-loaded ESSRs (VLESRRs) can show resonance frequency agility through a variable reverse bias voltage applied to the varactors. Next, VLESRRs are loaded in SIWs to realize transmission lines (TLs) with either tunable passbands (stopbands) below (above) fc of the host SIWs. Both cases are considered in this paper. First, an SIW with fc = 7GHz is loaded by five VLESRRs showing a tunable passband below the cutoff from 1.5 to 4GHz. Second, an SIW with fc = 1.9GHz and five VLESRRs is discussed where a tunable stopband is achieved above fc from 2 to 4 GHz. In both cases, the reverse bias voltage applied to the varactors varies from 0 to 20V. Finally, two fabricated prototypes are provided for each case to validate the analysis. The measured and simulated results are in good agreement.
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Design and Modeling of a Miniaturized SIW Using Embedded SRRs
A substrate integrated waveguide (SIW) loaded by embedded split ring resonators (SRRs) with transversal negative effective permeability is proposed. It is shown that the structure can support propagation of backward waves below cut off frequency. Therefore the width of the SIW structure can be considered less than half a wavelength at the cut off frequency, which means that the SIW structure is miniaturized. In this paper, design and modeling of a miniaturized SIW structure is proposed. An experimental SIW loaded with double embedded SRRs in 4.75 GHz frequency band has been designed, fabricated and tested. The measured and simulated results show a passband for backward waves below the cutoff frequency. It is also shown that the phase at a certain frequency in the backward passband increases as the physical length of the loaded SIW is increased (opposite to forward wave propagation), which proves that backward waves propagate below the cut off frequency.
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A Power-Efficient Implementation of In-Band Full-Duplex Communication System (ReflectFX)
We propose a power-efficient implementation for ReflectFX, an in-band full-duplex wireless communication system. ReflectFX is based on backscatter modulation where the electromagnetic waves are modulated and reflected by the same antenna that receives them.With ReflectFX, the end-user receives self-interference free signals. At the end-user receiver, we use a bi-directional amplifier to amplify the reflected wave while providing sufficient power at the end-user demodulator. The bidirectional amplifier consists of two identical reflection amplifier using negative resistance and a 90, -3dB branch line coupler (BLC). A phase shifter circuit, which consists of four microstrip transmission lines, has been used to apply QPSK modulation to the reflected power. The designed ReflectFX end-user circuit, with power consumption of only 90 µW, provides 17 dB and 16.8 dB reflection and transfer gains, respectively.
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A Tunable Transmission Line based on an SIW Loaded by a New Single-Cell Metamaterial
Two substrate integrated waveguides (SIW) loaded by a new single metamaterial (MTM) cell are discussed theoretically and experimentally. The first MTM-loaded SIW shows a passband-like response with balanced backward- and forward-wave passbands below and above the cutoff frequency of the host SIW, respectively. The MTM-SIW structure is then slightly manipulated and two varactor diodes are added to achieve frequency agility. The resulting varactor-loaded transmission line (TL) shows tunable transmission bands whose frequency characteristics can be controlled continuously by varying the reverse bias voltage applied to the varactors. The two MTM-SIW TLs are discussed based on the study of a Composite Right/Left Handed (CRLH) MTM-based SIW considering the dispersion diagrams and the equivalent circuits. Finally, prototypes of the former and the varactor-loaded MTM-SIW TL are fabricated and tested. The measured results are in good agreement with those obtained by the simulation and analysis.
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Substrate Integrated Waveguide Loaded by 3-D Embedded Split Ring Resonators
A substrate integrated waveguide (SIW) loaded by three-dimensional embedded split ring resonators (3-DESRRs) is discussed theoretically and experimentally. The 3-DESRR structure which has proved to be an alternative magnetic metamaterial resonator for SIW structures is able to provide negative transversal
permeability if excited properly. The 3-DESRR loaded SIW shows a bandpass-like response as an effect of loading the 3-DESRRs in the SIW. The lower and upper band edges of the resulting Transmission Line (TL) are determined by the SIW cutoff (fc) and the resonance frequency of the 3-DESRRs, respectively. Finally, a prototype of the proposed 3-DESRR loaded SIW TL is fabricated and tested. The measured results are in good agreement with those obtained by theory and simulation.

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