X-BAND CIRCULARLY POLARIZED RECTENNAS FOR MICROWAVE POWER TRANSMISSION APPLICATIONS

Circularly polarized rectennas operating at X-band are studied in this paper. The quasi-square patches fed by aperture coupling are used as the circularly polarized receiving antennas, which are easily matched and integrated with the circuits of rectennas. The double-layer structure not only minimizes the size of the rectennas but also decreases the effects of the circuits on the an- tenna. The receiving elements have broader bandwidth and higher gain than the single-layer patches. Two rectennas operating at 10GHz are designed, fabricated and measured. The voltage of 3.86V on a load of 200? is measured and a high RF-DC conversion efficiency of 75% is obtained at 9.98GHz. It is convenient for this kind of rectennas to form large arrays for high power applications.

Determinations of plasma density and decay time in the hollow cathode discharge by microwave transmission

The microwave （MW） transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge （HCD） in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 1012 cm-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.

Influence of plasma-induced reflected wave variations on microwave transmission characterization of supersonic plasma excited in shock tube

In this work,the theoretical analysis and experiment results investigating the influence of plasma-induced reflected wave variations on microwave transmission characterization are presented.Firstly,an analytical transmission line model for transmission characterization of plasma in shock tube is derived and validated against full-wave simulation.Then,the theoretical analysis of transmission characterization based on a time-dependent reconstruction algorithm that takes into account the variations of reflected wave is presented and the influence of reflection variations under various states of plasma is also investigated.The unusual increase in the amplitude of transmitted wave is theoretically predicted and experimentally demonstrated as well.Finally,the experiment results are also presented to illustrate the effects of reflected wave variations in practical microwave transmission characterization of supersonic plasma excited in shock tube.

A high rectification efficiency Si_(0.14)Ge_(0.72)Sn_(0.14)-Ge_(0.82)Sn_(0.18)-Ge quantum structure n-MOSFET for 2.45 GHz weak energy microwave wireless energy transmission

The design strategy and efficiency optimization of a Ge-based n-type metal-oxide-semiconductor field-effect transistor(n-MOSFET)with a Si_(0.14)Ge_(0.72)Sn_(0.14)-Ge_(0.82)Sn_(0.18)-Ge quantum structure used for 2.45 GHz weak energy microwave wireless energy transmission is reported.The quantum structure combined withδ-doping technology is used to reduce the scattering of the device and improve its electron mobility;at the same time,the generation of surface channels is suppressed by the Si_(0.14)Ge_(0.72)Sn_(0.14) cap layer.By adjusting the threshold voltage of the device to 91 mV,setting the device aspect ratio to 1μm/0.4μm and adopting a novel diode connection method,the rectification efficiency of the device is improved.With simulation by Silvaco TCAD software,good performance is displayed in the transfer and output characteristics.For a simple half-wave rectifier circuit with a load of 1 pf and 20 kΩ,the rectification efficiency of the device can reach 7.14%at an input power of-10 dBm,which is 4.2 times that of a Si MOSFET(with a threshold voltage of 80 mV)under the same conditions;this device shows a better rectification effect than a Si MOSFET in the range of-30 dBm to 6.9 dBm.

An Experimental Research to Study the Microwaves transmission Characteristics of Ablating Material in Arc-Heated Plasma Flow

in this paper, an experimental research the effect of ablating material on the reflection and the transmission of microwaves in arc-heated plasma flow is presented by using the C band microwave measuring system. The results show that the ablating material with accidented surface and its high temperature have remarkably affected the reflection and the transmission of microwaves. The experiment proves that the system has outstanding precision and reliability.

Optimal Design of Aperture Illuminations for Microwave Power Transmission with Annular Collection Areas

This work presents an optimal design method of antenna aperture illumination for microwave power transmission with an annular collection area.The objective is to maximize the ratio of the power radiated on the annular collection area to the total transmitted power.By formulating the aperture amplitude distribution through a summation of a special set of series,the optimal design problem can be reduced to finding the maximum ratio of two real quadratic forms.Based on the theory of matrices,the solution to the formulated optimization problem is to determine the largest characteristic value and its associated characteristic vector.To meet security requirements,the peak radiation levels outside the receiving area are considered to be extra constraints.A hybrid grey wolf optimizer and Nelder–Mead simplex method is developed to deal with this constrained optimization problem.In order to demonstrate the effectiveness of the proposed method,numerical experiments on continuous apertures are conducted;then,discrete arrays of isotropic elements are employed to validate the correctness of the optimized results.Finally,patch arrays are adopted to further verify the validity of the proposed method.

Broadband microwave frequency doubler based on left-handed nonlinear transmission lines

A bandwidth microwave second harmonic generator is successfully designed using composite right/left-handed non- linear transmission lines （CRLH NLTLs） in a GaAs monolithic microwave integrated circuit （MMIC） technology. The structure parameters of CRLH NLTLs, e.g. host transmission line, rectangular spiral inductor, and nonlinear capacitor, have a great impact on the second harmonic performance enhancement in terms of second harmonic frequency, output power, and conversion efficiency. It has been experimentally demonstrated that the second harmonic frequency is deter- mined by the anomalous dispersion of CRLH NLTLs and can be significantly improved by effectively adjusting these structure parameters. A good agreement between the measured and simulated second harmonic performances of Ka-band CRLH NLTLs frequency multipliers is successfully achieved, which further validates the design approach of frequency multipliers on CRLH NLTLs and indicates the potentials of CRLH NLTLs in terms of the generation of microwave and millimeter-wave signal source.

A monolithic distributed phase shifter based on right-handed nonlinear transmission lines at 30 GHz

The epitaxial material, device structure, and corresponding equivalent large signal circuit model of GaAs planar Schottky varactor diode are successfully developed to design and fabricate a monolithic phase shifter, which is based on right-handed nonlinear transmission lines and consists of a coplanar waveguide transmission line and periodically distributed GaAs planar Schottky varactor diode. The distributed-Schottky transmission-line-type phase shifter at a bias voltage greater than 1.5 V presents a continuous 0°–360° differential phase shift over a frequency range from 0 to 33 GHz. It is demonstrated that the minimum insertion loss is about 0.5 dB and that the return loss is less than-10 dB over the frequency band of 0–33 GHz at a reverse bias voltage less than 4.5 V. These excellent characteristics, such as broad differential phase shift, low insertion loss, and return loss, indicate that the proposed phase shifter can entirely be integrated into a phased array radar circuit.

Highly Directional Emission from a Subwavelength Slit in Metal-Dielectric Layered Films

The directional light emission from a single subwavelength slit surrounded by periodic grooves in layered films consisting of Ag and transparent dielectric is analysed numerically by the finite difference time domain method. The results show that the transmission through this structure is strongly confined by the modulation of the dielectric film with grooves on the output side. The role of evanescent waves in this phenomenon is discussed. It is the re-diffraction of the evanescent waves （that are generated by the diffraction of the subwavelength slit） caused by the grooves on the dielectric film that leads to the directional transmission. Some suggestions are given to obtain beaming light with high transmittance.

A low-outgassing-rate carbon fiber array cathode

In this paper, a new carbon fiber based cathode — a low-outgassing-rate carbon fiber array cathode — is investigated experimentally, and the experimental results are compared with those of a polymer velvet cathode. The carbon fiber array cathode is constructed by inserting bunches of carbon fibers into the cylindrical surface of the cathode. In experiment, the diode base pressure is maintained at 1×10^（-2） Pa–2×10^（-2） Pa, and the diode is driven by a compact pulsed power system which can provide a diode voltage of about 100 kV and pulse duration of about 30 ns at a repetition rate of tens of Hz.Real-time pressure data are measured by a magnetron gauge. Under the similar conditions, the experimental results show that the outgassing rate of the carbon fiber array cathode is an order smaller than that of the velvet cathode and that this carbon fiber array cathode has better shot-to-shot stability than the velvet cathode. Hence, this carbon fiber array cathode is demonstrated to be a promising cathode for the radial diode, which can be used in magnetically insulated transmission line oscillator（MILO） and relativistic magnetron（RM）.

Nonreciprocal microwave transmission under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect

Nonreciprocal microwave devices,in which the transmission of waves is non-symmetric between two ports,are indispensable for the manipulation of information processing and communication.In this work,we show the nonreciprocal microwave transmission in a cavity magnonic system under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect.In contrast to the schemes based on the standard phase modulation or magnon Kerr nonlinearity,we find that the joint mechanism enables the nonreciprocal transmission even at low power and makes us obtain a high nonreciprocal isolation ratio.Moreover,when two microwave modes are coupled to the magnon mode via a different coupling strength,the presented strong nonreciprocal response occurs,and it makes the nonreciprocal transmission manipulating by the magnetic field within a large adjustable range possible,which overcomes narrow operating bandwidths.This study may provide promising opportunities to realize nonreciprocal structures for wave transmission.