Previously reported staggered double vane (SDV) slow wave structure (SWS) traveling wave tube (TWT) gave electron efficiency as low as 3.4% at 220 GHz, which needs to be improved. One easy method to improve the electron efficiency and the output power is to reuse the spent electron beam energy, by resynchronizing electron velocity to the phase velocity of the terahertz (THz) signal at the second section of the TWT. In this article, we have modified the pitch of the SWS to realize the tapered phase velocity, which is for the first time to our knowledge applied to the SDV SWS at 220 GHz. By varying the geometry configuration, an optimized structure of tapered pitch SWS has been successfully developed. The results reported in this paper show a significant improvement of the output power, gain and electron efficiency. At 220 GHz, the output power has increased by about 65% with respect to the previous reported value reaching 111 W, and the electron efficiency has improved from 3.4% to 5.6%. In order to simplify the microfabrication process, an input/output coupler with E-plane bending has been designed, which can be fabricated by using only one mask UV-LIGA process.

This paper presents an ultra-compact filtering integrated antenna for GPS (1.57 GHz) and LTE (2.65 GHz) applications. The antenna comprises integration between dual composite right/left-handed antenna and band stop filter in one platform. The whole integrated antenna size is only 30×28.5 mm². Compared to conventional antenna with the same dimensions, the proposed antenna is only 6.5% at GPS band and 16.5% at LTE band. The deign procedures of individual antennas, bandstop filter and the filtering integrated antennas are explained in details. The full wave simulations supporting the design procedures and experimental measurements for all introduced components are introduced with good agreement. Finally, as a consequence of the proposed antenna ultra small size and its filtering capability, the antenna is a good candidate for implanted antenna applications.

In this paper, a magnetically tunable metamaterial is proposed and studied. The metamaterial is based on the combination of ferrite sheets and dielectric rods. The tunable property is originated from the ferromagnetic resonance and electric response of dielectric rods. The retrieved electromagnetic parameters and transmission characteristic showed that by simultaneously inspiring the ferromagnetic resonance and electric resonance, composite metamaterial can possess double-negative band in the resonant state. Moreover, this band was tunable by adjusting applied magnetic fields. The simulations and experiments verified that the composite metamaterial clearly displayed a tunable feature. The proposed method is simple in designing tunable metamaterials.

Polarization converters based on metamaterial have broad application in imaging, sensing and communication from microwave to optical frequency. However, its performance is limited by single function and narrowband. In this paper, a new type of polarization converter based on square loop shaped metamaterial has been presented. It works in the reflection mode to achieve broadband polarization conversion for both circular and x/y linear polarization waves. The incident linearly polarized wave will be converted to its cross-polarized state with a polarization conversion ratio (PCR) lager than 0.9 in two distinct broad frequency ranges; on the other hand, circularly polarized wave will be reflected to its co-polarized state efficiently in the same spectrum regimes. Good agreements have been observed for both simulation and measurement results. This work offers a further step in developing high performance multi-function microwave or optical devices.

Two single-layer X/Ku dual-band dual-polarization reflectarray antennas of different sizes with double parallel dipole elements are presented. Elements of the two bands are set to two orthogonal linear polarizations and placed in interlaced grid. The proposed reflectarrays operate in two frequency-bands within X-band centered at 10 GHz and Ku-band centered at 13.58 GHz. The smaller size reflectarray with elements arranged in a 13×13 grid for X-band and in a 12×12 grid for Ku-band is designed and simulated first. Based on the excellent dual-band performance of the small size reflectarray, then a larger size prototype has been designed, manufactured and measured. Measured results demonstrate the maximum gain of 28.54 dB with 50.93% radiation efficiency at 10 GHz and 31.06 dB with 51.34% radiation efficiency at 13.58 GHz, which show desirable dual-band dual-polarization radiation performance.

An unequal power divider which features quasi-arbitrary output phase difference is proposed in this paper. The circuit consists of four microstrip lines and a resister. By the even- and odd-mode analysis technique, the closed-form design equations of this structure are derived. The characteristic impedances, electrical length and bandwidth variations with power division ratio and phase difference are analyzed. For proving its validity, a prototype with this proposed structure is designed and implemented at 1 GHz. The results of simulation and measurement show that the pro-posed power divider can effectively produce two outputs with controllable power division and phase difference.

In this work, a novel family of Finite Airy array beams have been produced by an optical Airy transform system illuminated by Gaussian Array beams. Based on the generalized Huygens- Fresnel integral, an analytical expression is developed to describe the pattern properties of the beam generated at the output plan of the optical system. The well-known Finite Airy beam generated from the fundamental Gaussian beam using an optical Airy transform system is deduced, here, as a particular case of the main result of the actual study. Numerical calculations are performed to show the possibility to create a multitude of Finite Airy array beams with controllable parameters depending on the number of beamlets, the distance between the adjacent modules and the positions and orientations of the beamlets.

Security detection is becoming extremely important with the growing threat of terrorism in recent years. An effective millimeter-wave (mmw) holographic imaging system is presented in this paper, which can be applied in nondestructive detection such as security detection in airport or other public locations. The imaging algorithm is an extension of the work before as it takes the decay of the amplitude with range into account. The experiment result of an imaging system working at 28-33 GHz frequencies indicates good quality of the algorithm.

In earlier time, we proposed a flat LHM-based hyperthermia scheme for conformal hyperthermia of a large superficial tumor. It is demonstrated that in this scheme by de-ploying multiple microwave sources in a specific array to shape the heating zone and properly setting the source-to-lens distance or phases of sources to adjust the inclination of heating zone, a heating zone better fit to large superficial tumor can be generated. In this paper, we propose a new hyperthermia scheme based on a cylindrical LHM lens which would be more maneuverable for tumors located in tissues with curved surface. It is shown that the same way adopted in the flat LHM-based scheme can be used in this new scheme to acquire desired heating zone for better fitting to tumor region. And larger critical source intervals defined in this new applicator greatly relax the restriction to the size of practical antennas applied in this scheme.

In this paper, a compact filtering power divider (PD) based on half mode substrate integrated waveguide (HMSIW) is presented. The proposed structure is realized by etching slots on the top layer of the HMSIW PD. Accordingly, two resonators are embedded in each patch, as a second order filter. The slots dimensions are obtained by the relationship between them and the extracted external quality factor and coupling coefficient. A good agreement between the simulated and measured results is reported. The measured 3 dB fractional bandwidth is 25% (6.3-8.1 GHz). The maximum insertion loss is 0.9 dB, and the return loss is above 20 dB in the passband. This design has the advantages of low insertion loss, improved out-of-band rejection, compact size, controllable bandwidth, and high selectivity.

In this study, we present an implementation of Ultra wide band (UWB) Koch Snowflake antenna for Radio Frequency Identification (RFID) applications. The compact antenna, based on the Koch Snowflake shape, is fed by coplanar waveguide (CPW) and microstrip line with an overall size of 31x27x1.6 mm³. The simulation analysis is performed by CST Microwave Studio and compared with HFSS software. The antenna design exhibits a very wide operating bandwidth of 13 GHz (3.4-16.4 GHz) and 11 GHz (3.5-14.577 GHz) with return loss better than 10 dB for microstrip line antenna and CPW antenna respectively. A prototype of CPW and microstrip antenna was fabricated on an FR4 substrate and measured. Simulated and measured results are in close agreement. The small size of the antenna and the obtained results show that the proposed antenna is an excellent candidate for UWB-RFID localization system applications.

The improvement of Terahertz (THz) antenna requires efficient (nano)materials to operate within the millimeter wave and THz spectrum. In this paper, doped graphene is used to improve the performance of two types of patch antennas, a rectangular and an elliptical antenna. The surface conductivity of conventional (non-doped) graphene is first modeled prior to the design and simulation of the two graphene based antennas in an electromagnetic solver. Next, different graphene models and their corresponding surface conductivities are computed based on different bias voltages or chemical doping. These configurations are then benchmarked against a similar antenna based on conventional metallic (copper) conductor to quantify their levels of performance improvement. The graphene based antennas showed significant improvements for most parameters of antenna than that of the conventional antenna. Besides that, the higher chemical potentials resulting from higher biasing voltages also resulted in this trend. Finally, the elliptical patch graphene antenna indicated better reflection performance, radiation efficiency and gain than a rectangular patch operating at the same resonant frequency.

A novel family of fractal curves is proposed which provides the designer a systematic way of miniaturizing the microwave components with the freedom of choosing among form factor, design complexity and achieved miniaturization. The proposed fractal curve is characterized by two integer values m and n. The m value determines the form factor of the fractal while n value governs the iteration number. The equations governing the geometry of fractals are also presented. The proposed fractal is characterized for miniaturization by designing a printed monopole antenna for various values of m and n. The results from the full wave simulations and experiments are analysed and explained. The effect of fractal on reducing the resonant frequency is quantified by an equation based on its physical interpretation. Based on this analysis, saturation point for miniaturization is established. The curves being symmetric around a straight line, distortionless radiation patterns are seen.

A novel probe-fed single-layer circularly polarized (CP) truncated microstrip antenna with enhanced CP bandwidth and gain is presented in this paper. The axial ratio (AR) bandwidth is broadened by loading with a circle of truncated square parasitical patches. Parameter analysis is made to investigate the effect of the loading structures on the AR property. For comparisons, both the unloaded and loaded truncated patch antennas with the same size are designed, fabricated and measured. The measurement results show that by adding the parasitical patches, the -10 dB impedance bandwidth was increased from 0.98 GHz (15.9%) to 1.42 GHz (21.5%), among which the 3-dB RHCP AR bandwidth has been increased from 200 MHz (3.3% at the center frequency of 6.04 GHz) to 780 MHz (12.6% at the center frequency of 6.19 GHz). The gain enhancement is about 0.5 dB~1.5 dB around the operating frequency range, and the maximum gain of the proposed antenna is about 9.1 dB. With the advantages of simple structure, wide CP bandwidth and considerable gain property, this antenna has potential application in wireless communications.

Development of new network standards leads to the use of bulky base station antennas. Their wide surfaces are not compatible with integration constraints in urban areas. As the antenna is composed of a high number of radiating elements, reducing the surface of each element is a way to reduce the antenna surface. Compact radiating element would allow integration of several antennas on the initial surface. In this paper, a new compact antenna is designed in order to obtain up to four antennas at the place of one. The antenna gain and horizontal Half Power Beamwidth (HPBW) should be maintained. The size reduction is obtained by dielectric embedding. In order to determine the dielectric characteristics in which the antenna must be immersed, a theoretical model is proposed in this paper. Simulations and measurements are provided to show the evolution of the antenna's performances in order to achieve manufacturer's specifications.

A scattering problem for two semi-infinite rectangular waveguides coupling through a narrow slot cut in the common end wall of the two waveguides is solved. The slot is partially filled with a dissipative or perfect dielectric insert. A mathematical model based on continuity of tangential components of magnetic field vectors on both surfaces of the diaphragm in the coupling waveguides is proposed. The magnetic field in the slot is represented by a set of slot eigenwaves. The electrical field distribution function is used as a basis function in the Galerkin's procedure allowing to find unknown amplitude coefficients. Simulation and experimental measurement have been carried out. Dependences of scattering parameters upon the wavelength were studied for various geometric parameters, insert position in the slot, and insert material permittivity and losses. A good agreement between simulation results and experimental data is obtained. It was shown that an estimate of the insert permittivity and losses can be done for unknown materials using experimental and simulated data.

We investigate the efficiency of a metasurface supporting spoof plasmons to control the electro-magnetic emission of a radiating element. The three-dimensional metasurface is made of an array of metallic grounded rods, and it is used as the substrate of a printed antenna. Such a substrate provides a transmission band at low frequencies, corresponding to spoof plasmon propagation, and a total electromagnetic band gap above the cut-off frequency. We show how an efficient and directive emission with low side-lobe levels and backward radiation can be obtained when the operating frequency of the antenna is considered in the band gap. The role of the spoof plasmons is further demonstrated by tuning the transmission band at the operating frequency. The proposed meta-substrate is an original and efficient alternative to reshape the emission of electromagnetic sources.

A compact Ultra Wideband (UWB) antenna with Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN) with dual band-notched characteristics is presented in this article. The antenna design parameters have been optimized by the High Frequency Structural Simulator (HFSS) and CST Microwave Studio to be in contact with biological breast tissues over 3-13 GHz frequency range with dual band-notched characteristics. The proposed antenna is a polygon printed on a low dielectric FR4 substrate fed by a 50-Ω feed line and a partial ground plane in other side. The results exhibit that the proposed antenna shows a wide bandwidth covering from 3 GHz to at least 13 GHz with VSWR<2 and observing band elimination of WiMAX and WLAN bands. The proposed UWB antenna has omnidirectional radiation patterns with a gain variation of 0.5 dBi to 5.2 dBi and low distortion group delay less than 1 ns over the operating frequency range. The simulation and the measurement results show a good agreement. And good ultra-wideband linear transmission performance has been achieved in time domain with a compact dimension of 28×20 mm².

Magnetically coupled resonant wireless power transfer (WPT) has been employed in many applications, including wireless charging of portable electronic devices, electric vehicles， etc. However, the power transfer efficiency (PTE) decreases sharply due to divergence of magnetic field. Electromagnetic (EM) metamaterial (MM) can control the direction of magnetic fields due to its nega-tive effective permeability. In this paper, MMs with negative effective permeability at radio frequencies (RF) are applied to a WPT system operating at around 16.30 MHz for improvement of PTE. This ul-tra-thin and assembled planar MM structure consists of a single-sided periodic array of the capaci-tively loaded split ring resonators (CLSRRs). Both simulation and experiment are performed to cha-racterize the WPT system with and without MMs. The results indicate that the contribution of high PTE is due to the property of negative effective permeability. By integrating MM in the WPT system, the experimental results verify that the measured PTE with one and two MM slabs have respectively 10% and 17% improvement compared to the case without MM. The measured PTEs of the system at different transmission distances are also investigated. Finally, the proposed MM slabs are applied in a more practical WPT system (with a light bulb load) to reveal its effects. The results verify the efficiency improvement by the realized power received the load.

This paper presents a new implementation of a millimeter wave heterodyne receiver based on six-port technology. The six-port circuit is designed using three hybrid couplers H-90º and a new ring power divider. For the characterization of the circuit, several six-port two-port measurement configurations were designed and fabricated on the same wafer along with calibration standards. The new six-port architecture evaluation based on qi points location demonstrates wideband performances and high coupled-port phase and amplitude balance in the 57-65 GHz frequency band. The six-port model based on S-parameter measurements is then implemented in ADS software, for realistic advanced simulation systems of a short-range 60 GHz wireless link. The millimeter wave frequency conversion is performed using a six-port down-converter. The second frequency conversion uses conventional means due to the low IF frequency value. The demodulation results of a V-band QPSK signal for high data rate from 100 to 1000 MBits/s are presented and discussed. The results of the Bit Error Rate (BER) analysis demonstrate that the proposed architecture can be successfully used for high speed wireless link transmission at 60 GHz.