Farhad Farzami

Pattern Reconfigurable Printed Dipole Antenna Using Loaded Parasitic Elements

A printed dipole antenna is designed with two parasitic elements loaded by embedded resonators to provide reconfigurable patterns. The embedded resonators in the parasitic elements are loaded by varactor diodes, which change the phase and the transmission coefficient responses of the parasitic elements. This allows the parasitic elements to act as either a director, a reflector, or a neutral element. The proposed printed dipole antenna with two loaded parasitic elements acts as a printed Yagi–Uda antenna. Because the parasitic elements can act as either a director or a reflector, the directed gain can be increased, and the front-to-back ratio (FBR) may be improved up to 42xa0dB. It is also possible to achieve different target FBR if broadcasting is needed in two directions of the boresight. This pattern reshaping can be obtained as quickly as the diodes can change their capacitance. The antenna is designed to operate at 2.4xa0GHz, but this design approach can be applied to other frequency bands. The simulation and measurement results are in good agreement.

A Full-Duplex Bidirectional Amplifier With Low DC Power Consumption Using Tunnel Diodes

A low-power, switchless, full-duplex bidirectional amplifier operating in the 915 MHz (industrial, scientific and medical band) is proposed. It is composed of two identical reflection amplifiers and one 90°, −3 dB branch line coupler (BLC). The reflection amplifiers are designed using low dc power consumption tunnel diodes and provide a measured reflection gain of 13 dB with consumed power of only <inline-formula> <tex-math notation=LaTeX>

Inherent Self-Interference Cancellation for In-Band Full-Duplex Single-Antenna Systems

178~mu text{W}

Reconfigurable Linear/Circular Polarization Rectangular Waveguide Filtenna

</tex-math></inline-formula> for −30 dBm of incident signal power. These reflection amplifiers are integrated with a miniaturized BLC to form a bidirectional amplifier that provides 9 dB of measured transmission gain and 22 dB of measured return loss.

Ultra-low power reflection amplifier using tunnel diode for RFID applications

We propose a new analog self-interference cancellation (SIC) technique for in-band full-duplex transmission in single-antenna systems. We use an RF circulator to separate transmitted (Tx) and received (Rx) signals. Instead of estimating the SI signals and subtracting them from the Rx signals, we use the inherent secondary SI signals at the circulator, reflected by the antenna, to cancel the primary SI signals leaked from the Tx port to the Rx port. We modified the frequency response of the secondary SI signals using a reconfigurable impedance mismatched terminal (IMT) circuit, which consists of two varactor diodes at the antenna port. We can also adjust the frequency band and the bandwidth by controlling the varactor diodes bias voltages. The IMT adjustability makes it robust to antenna input impedance variations and fabrication errors. We analyze and fabricate a prototype of the proposed technique at 2.45 GHz. We achieved more than 40-dB cancellation over 65 MHz of bandwidth. Our technique is independent of the RF circulator and antenna type and it can be applied to any frequency band. It is also very relevant to small mobile devices because it provides a simple and low-power and low-cost adjustable analog SIC technique.

Reconfigurable Dual-Band Bidirectional Reflection Amplifier With Applications in Van Atta Array

We introduce a new reconfigurable linear polarization and circular polarization (CP) antenna, based on a rectangular waveguide (RWG) and a novel reconfigurable polarizer. The polarizer consists of two orthogonal apertures. The apertures transform the linear polarization of the dominant mode of the RWG antenna to CP. Each of these apertures is loaded by a p-i-n diode to alter its electrical length. This length difference provides the phase rotation needed to obtain CP. The signal polarization of the antenna can be selected by changing the applied bias voltage of p-i-n diodes as right-handed (RH)/left-handed (LH) CP. We can also achieve linear polarization if both diodes are ON or OFF. The reconfigurable polarizer acts as a bandpass filter, since the apertures can be considered as complementary electrically small resonators. This self-filtering capability is useful for reduction out of band noise in a communication system such as satellite links. The proposed antenna is designed to operate at 2.65 GHz, but the same approach can be applied to other frequency bands. The measurement results show a very good RH/LHCP and they are in good agreement with simulations.

A power-efficient implementation of in-band full-duplex communication system (ReflectFX)

To increase backscatter efficiency and communication range in RFID systems, we propose an ultra-low power reflection amplifier using a tunnel diode. We measured the input impedance of a tunnel diode and used a compact matching circuit to provide the desired input impedance at 890 MHz for the RFID UHF band. The proposed circuit is designed to be free from oscillations to avoid Signal to Noise Ratio (SNR) degradation. This reflection amplifier consumes 0.2 mW DC power at bias voltage of 200 mV, making it an ideal candidate to amplify backscattered electromagnetic field in RFID transceivers. The gain of the proposed reflection amplifier is 17 dB for the incident power of −30 dBm. The fabricated circuit size is 20×25 mm² (0.06λ<inf>0</inf> × 0.075λ<inf>0</inf>) on a substrate with ε<inf>r</inf> = 3 and h = 0.762 mm. The measurement and simulation are in a good agreement.

Detection and imaging of cracks in reinforced concrete structures using RF tomography: Quadratic forward model approach

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 an FET transistor and two p-i-n 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 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 (<inline-formula> <tex-math notation=LaTeX>

SAT-C: An Efficient Control Strategy for Assembly of Heterogeneous Stress-Engineered MEMS Microrobots

{S} _{21}

Efficient constant-time addressing scheme for parallel-controlled assembly of stress-engineered MEMS microrobots

</tex-math></inline-formula> and <inline-formula> <tex-math notation=LaTeX>