Chung Tse Michael Wu

Maximally Flat Negative Group-Delay Circuit: A Microwave Transversal Filter Approach

A comprehensive method to synthesize negative group delay (NGD) in the microwave regime with a maximally flat response is proposed in this paper. This method is based on transversal-filter topologies; it will be shown that by choosing proper coupling coefficients of each tap of a transversal filter, we can realize NGDs with maximally flat characteristics at the output of the transversal filter. The desired coefficients to realize maximally flat NGDs with various amount of group delay are analytically derived and tabulated in this paper. Furthermore, the results are verified experimentally through microwave transversal-filter approaches in both passive and active ways using multi-section asymmetric directional couplers and distributed amplifiers.

A Dual-Purpose Reconfigurable Negative Group Delay Circuit Based on Distributed Amplifiers

In this letter, a novel reconfigurable negative group delay distributed amplifier (NGD-DA) circuit is proposed. This NGD-DA offers a new method to realize negative group delay. By properly choosing the gain coefficient of each tap for the DA, we can synthesize the negative group delay at the reverse port of the DA in the frequency band of interest, while maintaining a flat gain at the forward port; this results in a dual-purpose DA. Moreover, the proposed NGD-DA is reconfigurable; the phase response at the reverse port can be simply controlled by adjusting the tap gain coefficients, and therefore the bandwidth as well as the amount of negative group delay can be manipulated. The proposed active NGD circuit is validated through theoretical explanation and experimental results.

A re-radiating CRLH-transmission line leaky wave antenna using distributed amplifiers

In this paper, a re-radiating CRLH-transmission line leaky wave antenna using distributed amplifier structure is proposed. The active leaky wave antenna consists of four FETs and two CRLH-transmission lines separately connected to gate and drain side of the FETs, which serve as two leaky wave antennas. The gate side CRLH-transmission line operates as a receiving antenna. The signal received by the antenna will then travel to each unit-cell and be amplified through the FETs. The amplified signal then goes to the drain side CRLH-transmission line, which operates as a transmitting antenna, and will be re-radiated. Furthermore, if the two CRLH leaky wave antennas are designed to be identical, the radiated beam will be directed in the same angle but opposite direction that the incident wave arrived and can operate as a repeater or transponder. In addition, this leaky wave antenna can also perform as a high-gain frequency dependent beam-scanning antenna if properly excited from one port. A 24-cell prototype demonstrates the proposed leaky wave antenna, performing both re-radiating and beam scanning functionality.

Ring-Resonator-Inspired Power Recycling Scheme for Gain-Enhanced Distributed Amplifier-Based CRLH-Transmission Line Leaky Wave Antennas

We propose a novel power recycling scheme for distributed amplifiers (DAs) integrated with composite-right/left handed transmission line leaky wave antennas (LWAs). This new type of power recycling scheme is essentially inspired by a ring-resonator. By forming a closed-loop on the drain side LWA of the DA, we create the ring-resonator that is actively coupled by the DA from the gate line and hence can obtain a substantial gain enhancement compared to the one directly terminated without the loop. Such enhancement fluctuates with respect to the frequency. At the resonant frequencies of the closed-loop ring-resonator, the enhancement reaches a maximum. The phenomenon will be explained and derived theoretically in detail, and then validated through the real implementation.

A Compact Single Radiator CRLH-Inspired Circularly Polarized Leaky-Wave Antenna Based on Substrate-Integrated Waveguide

A circularly polarized (CP) CRLH-inspired leaky-wave antenna (LWA) based on substrate-integrated waveguide (SIW) and microstrip delay line is presented. The unit-cell of the proposed periodic antenna consists of two conventional CRLH SIW cells and two quarterwavelength microstrip lines. The interdigital slots on the CRLH SIW are rotated at +45° and -45° with respect to the wave propagation direction and separated by 90° to create circular polarization. Utilizing the microstrip line instead of the SIW delay section, the total size of the live unit-cell antenna is reduced by 24.4% in comparison to the previous single radiator CP LWA. Furthermore, microstrip lines provide improved matching for broadside radiation as well as better CP purity. The unitcell characteristics are investigated in detail through dispersion and Bloch impedance analysis. In addition, space harmonic analysis is carried out to explain the radiation mechanism of the proposed antenna. The proposed CRLH-inspired SIW CP antenna operates from 4.2 to 4.85 GHz and frequency scans from -25° to 26° along the elevation angle. Axial ratio is maintained below 3 dB throughout the operating frequency. The measured results show good agreement with the simulated results.

Magnetic-Current-Loop-Induced Electric Dipole Antenna Based on Substrate Integrated Waveguide Cavity

In this letter, a novel dipole antenna based on substrate integrated waveguides (SIWs) is presented. The dipole antenna radiates through the equivalent magnetic current loops on the top and bottom annular ring slot that is excited by the fundamental mode of the SIW cavity. Therefore, the proposed dipole possesses a vertical polarization perpendicular to the metallic plane. Moreover, thanks to normal electric field, the proposed dipole is less affected by the ground plane size and surrounding metal. The proposed antenna topology provides a very easy way to realize vertical dipole antenna by just using planar circuits and is promising to be used as a fundamental element to realize antenna arrays.

Negative group delay circuit based on a multisection asymmetrical directional coupler

In this paper, we present a novel passive negative group delay (NGD) circuit based on directional couplers. By cascading several directional couplers with appropriate coupling coefficients, we are able to synthesize negative group delay with a broad bandwidth at the coupled port of the multisection directional coupler. Unlike conventional NGD circuits that use bandstop structures with lumped elements, such as inductors and capacitors, to realize negative group delay, the proposed design provides a fully distributed realization of NGD circuit. Therefore, this novel NGD circuit is very promising to be integrated into high frequency designs.

Dual-fed distributed amplifier-based CRLH-leaky wave antenna for gain-enhanced power combining

A ring-resonator-inspired distributed amplifier (DA)-based composite right/left-handed (CRLH) leaky wave antenna (LWA) with dual-fed configuration is proposed in this paper. Compared with the conventional single-fed structure, the radiating power of the DA-based LWA can be further increased twice as much theoretically by using the dual-fed scheme.

Microwave Gas Sensor based on Graphene-loaded Substrate Integrated Waveguide Cavity Resonator

In this paper, novel microwave gas sensors based on graphene-loaded substrate integrated waveguide (SIW) cavity resonators are presented. Two SIW-based cavity resonators, a ring-slot resonator and a complementary split ring resonator (CSRR), are fabricated and coated with chemical vapor deposited (CVD)-grown graphene. The fabricated graphene contains a layer of polymethyl methacrylate (PMMA) on its top. The graphene sheets exhibit high sensitivity to various kinds of polar and non-polar gases. When polar gas contacts the graphene sheet, it will donate or receive electrons, thereby changing its conductance. The SIW cavities thus perform a resonant frequency shift from the perturbation of electron exchange. In the experiment, a frequency shift of 59 MHz and 157 MHz for the SIW ring-slot resonator and CSRR, respectively, can be observed after pure ammonia gas is injected into a closed chamber filled with air at standard atmospheric pressure and temperature. This work demonstrates a very simple and efficient gas sensing scheme in the microwave regime. The proposed devices are promising to be further integrated with RF front-ends, providing a low cost and high sensitive gas sensing and environmental monitoring solution.

Self-biased self-oscillating mixing receiver using metamaterial-based SIW dual-band antenna

In this paper, a novel receiver consisting of both “self-biased” and “self-oscillating mixing” schemes is proposed. The receiver is self-biased since it does not require an external DC bias from a power supply but rather the DC voltage is provided through the rectifier branch of the receiver, which converts the received RF power to DC; the receiver is also integrated with a self-oscillating mixer so that it does not require an external LO source that is usually necessary in a mixer circuit. Moreover, a composite right/left-handed (CRLH) metamaterial based substrate-integrated-waveguide (SIW) dual-band antenna is equipped in the receiver: the lower band (2.2GHz) is used to wirelessly provide power to the system and the higher band (5.77GHz) can be used to send information.