Three bent waveguides are proposed and investigated, two for circular waveguide TM₀₁ mode transmission and one for coaxial TEM mode transimission. For high power-handling capacity, all of them are over-mode waveguides. In the bend, circular or coaxial waveguides transmitting only sector waveguide TE₁₁ modes are split into several same sector waveguides by metal plates and metal rod. Those sector waveguides are grouped by their lengths. Different lengths of sector waveguides mean there are phase differences of the TE₁₁ modes after bending. Due to requirements of mode conversion, the phase difference regulated by radii of circular waveguide and metal rod must be 2nπ, n = 0, 1, 2…. Since the phase difference is independent of bend radius, the radius could be as small as possible. One of the prototypes is experimented, and the test result of the VSWR shows that simulation has good match with experiment. Insertion loss is 0.2 dB at 8.4 GHz, which proves the feasibility of the prototype.

A wideband interdigital capacitor (WIDC) is proposed and verified. By short interconnecting the open ends of interval fingers with microstrip lines etched on PCB bottom layer, the spurious spikes that limit the bandwidth of conventional interdigital capacitor (IDC) are eliminated. The bandwidth and capacitance of IDC increase more than 2800% and 100%, respectively.

In this paper, we propose a direction-of-arrival (DOA) estimation algorithm under unknown mutual coupling with a sparselinear array (SLA). We employ an SLA composed of two uniform linear arrays (ULA), and the element spacing of one of the subarrays is large enough to neglect the effect of the mutual coupling (MC). The forth-order-cumulants (FOCs) of the received data from partial elements of the first subarray and all elements of the second subarrayare exploitedto construct an extended FOC matrix. Then, the DOAs of incident signals are estimated by dealing with the FOC matrix. The array aperture is extended greatly due to the sparsestructure. Hence, the proposed method shows much better performance than some classical blind DOA estimation methods in accuracy and resolution. We also proposed some simulation results to prove the effectiveness of our method.

In this paper, a microstrip lowpass filter with -3 dB cutoff frequency of 3.8 GHz consisting of two cascaded resonators with flabelliform patches and two symmetric suppressing cells is proposed. To design the filter, the impact of each transmission line on the frequency response is determined by extracting the equations of the insertion loss (S21) and return loss (S11) on the basis of the equivalent LC circuit of the main resonance cell and the cascaded structure. The designed filter is constructed and tested, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss close to zero and an acceptable suppression level of -30 dB from 4.47 to 25.17 GHz are achieved. Furthermore, a flat insertion loss in the passband and a low return loss (-23.02 dB) in the stopband can prove desired in-band and out-band frequency response.

In the field of radar target detection, vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM) has drawn great attention in recent years because of its prospect to improve the capacity of information acquisition. As a typical vortex EM wave, the high-order Bessel vortex beam (HOBVB) has the properties of non-diffraction propagation, small central spot diameter, good direction, and long propagation distance. This study investigates the scattering of non-diffracting HOBVB by radar targets. The mathematical description of the electromagnetic field components of the arbitrarily incident HOBVB are given. The surface integral equations for solving the scattering problems involving typical radar targets are established. The effects by OAM intrinsic mode characteristics on the radar scattering cross section are simulated. This investigation is expected to provide useful guidance for revealing EM scattering mechanism in the OAM domain.

In this paper, a horizontally polarized (HP) omnidirectional antenna array with a broadband characteristic is presented. The proposed antenna consists of a circular array based on four planar arc dual-dipole structures, a wideband 1-to-4 feeding network with baluns, four reflectors and twelve directors. The arc dual-dipoles with four etched slots are introduced to obtain the broadband characteristic. By using twelve directors in front of the dipoles, the gain variation in the horizontal plane is improved. In addition, the reflector elements are able to improve the gain for the middle frequency band. With the concept, a prototype antenna with an overall size of 0.66λ_L × 0.66λ_L × 0.01λ_L (λ_L× is the free-space wavelength at the lowest frequency) is fabricated and measured. The designed antenna exhibits a relative impedance bandwidth of 98.3% (1.245-3.652 GHz) for |S₁₁|<-10 dB. The HP omnidirectional patterns provide a gain variation less than 3.0 dB over the frequency band 1.245-3.519 GHz (95.5%). Within the impedance bandwidth, the cross-polarization level is lower than -20 dB in the horizontal plane.

In this paper a compact wideband aperture coupled microstrip patch antenna (MPA) with impedance bandwidth of 26.3% is designed. Size reduction of the radiating element and the slot in the ground plane is achieved by incorporating an interdigital capacitor (IDC) in the patch and a complementary split ring resonator (CSRR) close to the slot which offers composite right/left-hand (CRLH) antenna. An interdigital capacitor in the patch acts as series left-hand component, and the slot together with the CSRR in the ground plane acts as a left-hand parallel inductor. By this technique, the patch and slot dimensions compared with the initial designed antenna are reduced about 26.2% and 30.2%, respectively. Through cutting CSRRs with different arrangements in the ground plane, a dual frequency band antenna is designed. Finally, a compact wideband circularly-polarized (CP) MPA is proposed through imposing various perturbations in the current route in the ground plane of the antenna. The maximum gain and the impedance bandwidth of the designed CP antenna are 8.4 dBi and 25%, respectively. Two designed antennas are fabricated and tested. The measurement results confirm the simulation ones.

In this paper, a parallel Higher-order FDTD (HO-FDTD) algorithm is described. Moreover, a novel implementation of convolution PML (CPML) is presented for the HO-FDTD method. A printed microstrip patch antenna is designed to analyze the feasibility of the parallel algorithm and the absorbing performance of the CPML. Moreover, the proposed algorithm is used to deal with the large-scale computational model of the vaulted tunnel. The simulation results show that the adopted parallel strategy is feasible. and the CPML performs well in the HO-FDTD scheme.

Design of a compact Substrate Integrated Waveguide (SIW) transmission line is presented in this paper. The main parameters of SIW were parametrically studied, and nal designed component was fabricated and measured, which showed very good matching (near 90%) with simulations, demonstrating significant miniaturization factor. The miniaturization was done using Half-Mode (HM) and Slow-Wave (SW) principles together. It was found that the HM-SW method for SIW miniaturization reduced the SIW surface area with a remarkable factor value (70%) while maintaining acceptable characteristics compared to the original SIW. In fact, HM technique reduced 40% the lateral dimension of the SIW, and using the SW technique allowed 30% of size reduction added to the HM principle. Furthermore, a proper microstrip to HM-SW-SIW tapered transition was designed, which showed a return loss decrease between 3 dB and 7.5 dB, as well as facilitating measurement. On the other hand, the proposed transmission line could lead to a size reduction of 30% compared to the HM-SIW miniaturization technique. The HM-SW-SIW transmission line concept presented in this paper can be used to design other compact SIW components such as bandpass filters, couplers, and power divider.

In this paper, a lowpass filter with -3 dB cut-off frequency of 1.69 GHz employing modified hairpin resonator with long straight slots is designed. In the first step, to design the primary resonator, the open stubs of a conventional hairpin resonator are folded inside its free area, which results in a smaller occupied area and an improved frequency response. Next, to control the scattering parameters, asymmetric coupled lines with slots are utilized instead of symmetric open-stubs of the primary resonance cell. In each step, the impact of the employed microstrip transmission lines on the scattering parameters of the designed resonator is determined by extracting the equations of the insertion loss (S21) and return loss (S11) on the basis of their equivalent LC circuit. Finally, by using two modified resonators with slots which are placed symmetrically around (Y) axis, a sharp transition band (264 dB/GHz) and wide stopband from 1.78GHz to 10GHz with a suppressing level of -20 dB are obtained. The overall circuit size is 0.140λg×0.076 λg, which indicates a small circuit size. The proposed lowpass filter has a high figure of merit equal to 72032.

This paper presents the design and analysis of a planar pattern reconfigurable antenna for WLAN applications. The proposed design makes use of four Vee dipoles placed around a center input probe. The directional beam generated can be reconfigured to any one of the four directions in the azimuth plane. The antenna pattern can be controlled by means of switches provided to connect the Vee dipoles to the input port. The design and analysis of the parameters show the scalability of the design to adapt to any frequency of choice. To validate the concept, an antenna is designed for the WLAN frequency of 5.3 GHz， and a prototype is fabricated. The measured results match closely to that of simulated results. The gain provided by the antenna is noted as 7.5 dBi. The planar structure and simple design of the antenna enable this antenna to be useful for modern pattern reconfigurable communication systems.

A novel design of frequency reconfigurable Fabry-Pérot cavity antenna is presented. The superstrate of the antenna is a reconfigurable partially reflecting surface with PIN diodes on it. A dual-band patch antenna is used as the radiator of the antenna. Through changing the states of diodes, the partially reflecting surface can present different reflection phases, so the working frequency of the antenna can be tuned. The operation of frequency reconfiguration and the design method of the antenna are described exhaustively. A prototype antenna is fabricated and measured. The measured results show that the antenna can realize 13.1 dB gain at 4.6 GHz and 17.1 dB gain at 5.5 GHz with impedance bandwidths of 3.3% and 4.7%, respectively. Good agreement between the simulated and measured results is achieved, which proves the correctness of the design method. Besides, this method can also be used to design Fabry-Pérot cavity antenna working at other frequencies.

A miniaturized monopole-like slot antenna with improved un-roundness of H-plane radiation patterns at higher frequency response for ultra-wideband application is presented and discussed. With the monopole-like slot antenna structure, wide working band (3.21-16.3 GHz) is obtained within a limited physical size (21×21.5×1.6 mm3). By modifying the structure of the proposed antenna, such as etching a quarter of a circular slot at the corner of the ground plane and a trapezoidal slot in the radiating patch, the un-roundness of H-plane radiation patterns is reduced by 5 dB in high-frequency band. Measured results show that it has a bandwidth from 3.2 GHz to 17.52 GHz, which are in good agreement with simulations.

Traffic alert and Collision Avoidance System (TCAS) is an airborne system which is designed to provide the service as a last defense equipment for avoiding mid-air collisions between the aircraft. In such airborne systems, where low aerodynamic drag is urgently required, the end-fire antenna is suitable to be used. An effort to develop such an antenna, using microstrip elements, is described in this paper. Here, a Multi-Feed Microstrip Antenna is presented which radiates in the end-fire direction. The proposed antenna is designed in such a way that it can radiate the whole 360° surveillance region of the aircraft. To encapsulate the antenna inside an enclosure, an aerodynamically shaped Radome is also designed and presented in this paper. For designing this antenna model and its Radome, CST Microwave Studio is used here as the EM tool. The performance and other antenna characteristics have been explored from the simulation results followed by the antenna fabrication and measurement. Quite good agreement is achieved between the simulated and measured results. Much better performance characteristics make this proposed antenna a good candidate for this application.

In the present work, a compact size, dual-band antenna is proposed for WLAN/WiMAX/LTE2500/DMB applications. The designed antenna is fed by a 50 Ω coplanar line. The radiating component of the composed antenna consists of radiating strips with half hexagonal and vertical rectangular shapes and square-shaped ground plane which are printed on the same layer. The overall size of the antenna substrate is only 10 x 24 x 1.6 mm3. The simulated and measured results of the proposed antenna show that it operates in the frequency range of 2.5 GHz to 2.75 GHz and 5.0 GHz to 6.7 GHz, respectively.

Optoacoustic imaging (OAI) is an emerging biomedical technique that allows visualization of in-depth tissues by using ultrasonic signals generated by short laser pulses. In this work, the authors combine the optical power of several pulsed high-power diode lasers (HPDLs) at 870 nm and 905 nm to a 7-to-1 675-μm fiber bundle to generate optoacoustic (OA) signals from different mixtures of two gold nanorods solutions with absorbance peak at ~860 nm and ~900 nm, respectively. The pulses produced to generate OA signals are alternated between the two wavelengths by a microcontroller circuit with fast switching (0.5 ms). From the amplitude of the OA signals, the concentrations of the nanoparticles solutions are easily estimated with high accuracy using a fluence model. The results achieved with the proposed system show very good agreement between the concentrations of gold nanorods estimated from measurements and the expected values.

This paper presents an electrically small, low-profile and ultra-wideband antenna with monopole-like radiation type. The antenna is composed of a top-loading hat and two tapered radiation patches on the crossed substrates shorted to the ground. Introducing two tapered radiation patches with the meander loop traces allows for achieving ultra-wideband operation and very low profile simultaneously. In addition, two columns of metal via-holes nested in the crossed substrates can broaden the bandwidth further. The proposed antenna is simulated, fabricated and measured. The measured and simulated results show good agreement and indicate that a measured VSWR lower than 2.0 over 632-3907 MHz (a 144% relative bandwidth) can be accomplished. The antenna has a low profile (0.053 λmin) in height and occupies a small circle of radius 0.078 λmin, where λmin is the free-space wavelength at the lowest frequency. The antenna has a kmin a = 0.59, where kmin is the wavenumber at the lowest frequency of operation. The frequency band covers LTE (0.7 GHz), BDS (1.268 GHz), GPS (1.575 GHz), WIFI (2.5 GHz) and WIMAX (3.5 GHz).

A miniaturized dual-band microstrip antenna has been designed and analyzed for Wireless LAN application. The proposed antenna comprises a 29 × 29mm² radiating patch, fed by a microstrip line on a 1.6mm thick FR4 dielectric material substrate. The antenna measurement illustrates impedance bandwidth of around 10% at 2.4GHz resonance and 6% at 5.5GHz resonance. The measured stable return loss and radiation patterns are presented for the proposed dual-band electrically small microstrip antenna for wireless applications.

The terahertz (THz) compact antenna test range (CATR) detection technology is the foundation of terahertz target recognition technology. It provides an excellent plane wave area which can well meet the far-field condition of antenna pattern and RCS test. Based on the microwave single reflector CATR system that we have designed before, this paper mainly aims at designing a 0.3 THz CATR system and then gives the simulation model of the system errors. After the preparation of the above work, we begin to detect its 0.3 THz band plane wave field, and the final test results can be used for further application.

This paper presents a design and evaluation for a miniaturized ultra-wideband (UWB) printed monopole antenna. The design integrates a UWB printed bell-shaped monopole antenna with a short stub. This antenna improves the matched impedance in the lower frequency band by using the short stub structure. The proposed antenna is formed on a low-cost FR-4 dielectric substrate with the size: 28 x 20 x 1.6 mm³. The designed antenna operates with impedance bandwidth of 3.1~4.0 GHz. The omnidirectional radiation patterns are obtained over the frequency range. Calculation and measurement show that this antenna acquires broadband characteristics covering the required frequency band of UWB system. The proposed antenna is assumed for applying to UWB radar, etc.