Main Radiation Direction Research Articles

On the impact of downward-directed human voice radiation on ground reflections

Previous studies on vertical or full-spherical directivity patterns of the human voice showed that the human voice has a slightly downward main radiation direction over a wide frequency range. This paper investigates the phoneme-dependencies of human voice radiation in the vertical plane and analyzes to what extent these characteristics affect the ground reflection and the sound incidence at a listener position. The results show that for most phonemes and below 800 Hz, the ground reflection is stronger than the direct sound component because of the downward-directed main radiation. On the contrary, between 800 Hz and 1.6 kHz, the main radiation direction is upward, probably mainly due to diffraction and reflections from the shoulders and the torso.

Double-Periodic Patch-Loaded Spoof Surface Plasmon Polariton Leaky-Wave Antennas With Suppressed Open-Stop Band Effects

A leaky-wave antenna (LWA) based on split-ring-shaped spoof surface plasmon polaritons (SSPPs) is designed, simulated, and measured. We proposed a double-periodic patch-loaded method to suppress the open-stop band (OSB) effect and introduced an SSPP power divider with a 180° phase shift for the anti-phase excitation to enhance the gain in the main radiation direction of the antenna. Both methods are analyzed and verified. The investigated results show that both S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> are less than -10 dB in 7-11 GHz and no bulge is observed around the broadside radiation frequency of 10 GHz, demonstrating good OSB suppression (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> < -26 dB, S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> < -45 dB). Furthermore, the LWA also demonstrates good performances with a wide-angle (-48° to +15°), high scanning rate (1.57°/%), high gain (10 dBi), and high average efficiency (97%). This work provides a new way to realize efficient OSB suppression for LWA designs.

Dual‐metasurface‐based wideband antenna

A dual metasurface-based wideband antenna is proposed herein. The antenna is fed through the stepped aperture of a coplanar waveguide. One layer of the metasurface is printed directly above the aperture, where the other layer is printed on the dielectric plate and placed above the antenna. The antenna bandwidth is significantly improved by the high-order modes excited by the double-layer metasurface. The proposed antenna is simple and compact. The − 10 dB relative impedance bandwidth of the proposed antenna is approximately 95.6% (4.8–13.6 GHz), and the main radiation direction deviates from the normal direction by 30°. The proposed antenna has an ultra-wideband (UWB), which facilitates short-range indoor UWB positioning.

Wideband and high-order microwave vortex-beam launcher based on spoof surface plasmon polaritons

The electromagnetic vortex carrying orbital angular momentum (OAM), which is first studied at optical frequency, has begun to attract widespread attention in the field of radio-frequency/microwave. However, for the OAM mode generated by traditional single antennas, there are problems such as low order and narrow bandwidth, and complex structures such as dual-fed networks may be required. In this paper, based on spoof surface plasmon polariton (SSPP) mode leaky-wave antenna, a single-port traveling-wave ring is proposed to radiate high-order OAM modes working near the cut-off frequency of SSPP state. The achieved 12-order OAM mode within 9.1–10.1 GHz (relative bandwidth of 10.4%) has the main radiation direction close to the antenna surface, forming a plane spiral OAM (PSOAM) wave, which reduces the requirements for mode purity in practical applications. This SSPP ring using periodic units as radiating elements can be an effective radiator for broadband and large-capacity OAM multiplexing communications. The structural characteristics of single feed contribute to the integration of microwave circuits.

Wideband and High-Gain Wearable Antenna Array with Specific Absorption Rate Suppression

In this paper, a wideband and high-gain antenna array with specific absorption rate suppression is presented. By adopting the wideband monopole antenna array and the uniplanar compact electromagnetic band gap (UC-EBG) structure, the proposed wearable antenna array can realize a high gain of 11.8–13.6 dBi within the operating band of 4.5–6.5 GHz. The sidelobe level of the proposed wearable antenna array is less than −12 dB, and the cross polarization in the main radiation direction is less than −35 dB. Benefiting from the UC-EBG design, the specific absorption rate is suppressed effectively, guaranteeing the safety of the proposed antenna array to the human body. The proposed antenna array is processed and tested, and the measurement results show good agreement with the simulation results.

Tunable Bandpass-to-Bandstop Quasi-Yagi–Uda Antenna With Sum and Difference Radiation Patterns

A design of the double-element E-plane quasi-Yagi–Uda antenna is proposed offering two different radiation patterns and reconfigurable bandpass-to-bandstop frequency-tunable responses. The double-element antenna covers a wide frequency range that is exploited for the realization of the tunable operation modes. This is achieved by the integration of a pair of bandpass-to-bandstop filters, each of which can be reconfigured using two varactor diodes and one p-i-n diode. The p-i-n diode serves the function of switching between bandpass and bandstop states, and the varactors facilitate the frequency tunability for both states of operation. The bandpass filter provides a continuous frequency tuning function with a minimum rolloff rate of 57 dB/GHz and out-of-band transmission coefficient −1 dB. Importantly, the reconfigurable filtering functionality of the two-element antenna is preserved when fed by a wideband hybrid coupler to produce both the sum and difference radiation patterns. To obtain a high beam symmetry, the antenna elements are fed by the difference ( $\Delta $ ) signal to produce the directive radiation pattern and they are fed by the sum ( $\Sigma $ ) port to produce the null in the main radiation direction. The experimental results validate this concept with a measured tunability of 50.0% for the bandpass state and 50.4% for the bandstop state.

Research on the distribution of aerodynamic noises of high-speed trains

This paper established a computational model for the aerodynamic noise of a high-speed train with 3-train formation including 3 bodies, 6 bogies, 2 windshields and 1 pantograph system. Based on Lighthill acoustic theory, this paper adopted large eddy simulation (LES) and FW-H model to conduct numerical simulation for the aerodynamic noise of high-speed trains and analyzed the distribution of aerodynamic flow behavior and noises of the whole train. Researched results showed that the main aerodynamic noise sources of high-speed trains were in pantograph, pantograph region, streamlined region of head train, bogies, bogie region, windshield region, air conditioning and other regions. Pantograph head, junction of upper arm and lower arm, and chassis region were main aerodynamic noise sources of pantograph. Compared with other 5 bogies, bogie at the first end of head train was main aerodynamic noise source. In addition, vortex shedding and fluid separation were main reasons for the aerodynamic noise of high-speed trains. When the high-speed train ran at the speed of 300 km/h and 400 km/h, the main energy of the whole train focused on the range of 1000 Hz-4000 Hz. Aerodynamic noises were broadband noises in the analyzed frequency domain. At the longitudinal observation point which was 25 m away from the center line of track and 25 m away from the nose tip of head train, the total noise sound pressure level reached up to maximum values 96.5 dBA and 101.4 dBA, respectively. Compared with inflow, wake flow had a greater influence on the aerodynamic noise around high-speed trains. The main radiation direction of pantograph aerodynamic noises was the left and right sides of pantograph head. In addition, the main radiation energy of pantograph aerodynamic noises was in mid-high frequency. In the part of high frequency, pantograph head made the greatest contribution to aerodynamic noises in the far field.

A Multidirectional Pattern-Reconfigurable Patch Antenna With CSRR on the Ground

A pattern-reconfigurable patch antenna with nine beam directions based on the complementary split-ring resonator (CSRR) loaded ground is proposed. The antenna consists of a coaxial feed rectangular patch on the top layer and a ground plane loaded with four CSRRs on the bottom layer. Two p-i-n diodes are installed on the stub of every CSRR. By changing the states of the p-i-n diodes, the main radiation direction can be switched both in the E-plane and H-plane. The operation principle of the beam switching by loading CSRRs on the ground is discussed. The prototype is fabricated with p-i-n diodes and bias circuit. The measured common impedance bandwidth of |S 11 | less than -10 dB is from 2.42 to 2.48 GHz. The 3-dB beamwidth covers the elevation angles from 0° to more than 60° and full azimuth angles. The antenna has a compact size of 0.82 λ 0 × 0.78 λ 0 , which has the potential to be used in the array design.

Analysis of mode radiation characteristics in a non-magnetized cold plasma column

The electromagnetic surface waves which propagate along a non-magnetized cold plasma column have a great value in the application of plasma antenna. In this paper, the dispersion properties, the transmission power distributions, and the radiation patterns for these electromagnetic surface waves which have lower frequencies than the electron plasma frequency are analyzed numerically. Based on Helmholtz equation, the specific expression of dispersion equation is derivedby the field matching method, then the exact values of complex axial wave vector kz under different wave frequencies are obtained by solving the transcendental dispersion relation. Using the specific value of kz obtained above, the exact expressions of transmission power profile in the plasma column and field profiles in the three regions, i.e., plasma, dielectric, and free space are derived, respectively. Finally, based on the complex form of electric conductivity that is derived from the Boltzmann-Vlasov equation with Krook term and the complex axial wave vector kz obtained above, the influence of the parameter pea/c on phase property, and the dependence of radiation pattern and transmission power profile on wave frequency of the non-magnetized cold plasma column in a cylindrical dielectric tube system are analyzed. The results show that the electron plasma frequency has a significant influence on the phase property, which is evidently confirmed by the fact that the propagation velocities of the three modes m=0, m=1 and m=2 are all near to the light speed when the value of parameter pea/c gradually increases. Meanwhile, through the investigation of the radiation patterns for the three modes, an important conclusion is that the radiation pattern has evident dependence on wave frequency. While the radiation direction of the main lobe is in the axial direction for the m=1 mode, the m1 modes each have an angle between the radiation direction of the main lobe and the axial direction, this crucial conclusion is in good agreement with the theoretical calculation results obtained from other researcher. Further, we find that with the increase of wave frequency, the angle between the main lobe radiation direction and the axial direction turns smaller for each of m=0 and m=2 modes, and the width of main lobe gradually narrows for each of all modes, and the amplitude of the first side lobe becomes notable for each of m=0 and m=2 modes and ignorable for the m=1 mode. Also, the transmission power increases as the wave frequency increases for each of all modes. These theoretical calculation results provide a detailed theoretical reference for the designing of plasma stealth and high-precision requirements of plasma antenna design, and giving a comprehensive optimization guidance for the modulation of plasma antenna.

Planar Image-Reject Bow-Tie Antenna With Gain Enhancement for Superheterodyne Applications

A planar bow-tie antenna loaded with open stubs is proposed to realize image rejection and gain enhancement for superheterodyne applications. The loading open stubs are two open-circuit double-sided parallel-strip lines symmetrically connected to the feedline of a planar bow-tie antenna, which functions as a bandstop filter in frequency band lower than the operating frequency to reject image interference and simultaneously as a reflector across the operating frequency band to enhance the antenna gain. Simulated results show that the realized gain of the proposed antenna in the main radiation direction is suppressed by 25 dB at the image frequency and is enhanced by about 3 dB at the operating frequency compared to that of an unloaded antenna. Good agreements between the simulated and the measured results have been observed.

PLANAR DOUBLE-SIDED PRINTED QUASI-YAGI ANTENNA WITH ENHANCED IMPEDANCE BANDWIDTH AND REDUCED SIZE FOR WIDEBAND WIRELESS APPLICATIONS

A compact wideband planar double-sided printed quasi-Yagi antenna is presented. This paper focuses on the feasibility of substituting conventional balun for microstrip-to-slotline transition balun to achieve wider bandwidth and relatively smaller size. The proposed antenna, consisting of a feeding balun, a concave arc-shaped reflector, a modified driver with stacked structure and two directors, is designed and fabricated. Good agreement between simulated and measured results is observed. Simulation and measurement results reveal that the proposed antenna can provide an impedance bandwidth of nearly 100% (2.02-6.05 GHz). Additionally, within the impedance bandwidth, the radiation pattern of the proposed antenna has front-to-back (F/B) ratios ranging from 10.1 dB to 19.1 dB, cross-polarization levels in the main radiation direction from 19.8 dB to 36.2 dB and gains from 3.4 dBi to 7.4 dBi.

Analysis of radiation performances of plasma sheet antenna

A novel concept of plasma sheet antennas is presented in this paper, and the radiation performances of plasma sheet antennas are investigated in detail. Firstly, a model of planar plasma antenna (PPA) fed by a microstrip line is developed, and its reflection coefficient is computed by the JE convolution finite-difference time-domain method and compared with that of the metallic patch antenna. It is found that the design of PPA can learn from the theory of the metallic patch antenna, and the impedance matching and reconstruction of resonant frequency can be expediently realized by adjusting the parameters of plasma. Then the PPA is mounted on a metallic cylindrical surface, and the reflection coefficient of the conformal plasma antenna (CPA) is also computed. At the same time, the influence of conformal cylinder radius on the reflection coefficient is also analyzed. Finally, the radiation pattern of a CPA is given, the results show that the pattern agrees well with the one of PPA in the main radiation direction, but its side lobe level has deteriorated significantly.

Dual‐polarised cavity‐backed annular slot antenna of compact structure

A unidirectional dual-polarised antenna is presented, by applying a cavity-backed annular slot and two mutually perpendicular microstrip feed lines. To improve the isolation between two ports of the designed antenna, a pair of conductor strips is introduced at the opposite side of the feed lines and a metal cylinder into the cavity centre. Aimed at 2.4 GHz wireless local area network systems, a prototype antenna has been fabricated based on the FR4 substrate. The measured results show that an isolation value of over 33 dB can be attained and the co-polarised level is 30 dB larger than the cross-polarised in the main radiation direction. In addition to compact structure, the operating band with about 5 dBi antenna gain indicates the proposed antenna is suitable for indoor multiple-input–multiple-output (MIMO) base station systems.

Design and Simulation of a Ka-Band Pattern Reconfigurable Microstrip Patch Antenna

This letter presents a Ka-band(26.5GHz-40GHz) microstrip patch antenna with pattern reconfigurable characteristic. The antenna is provided with five rectangular patches and four RF MEMS (microelectromechanical systems for RF circuits) switches. The central patch and other surrounding patches are connected by the switches. By changing the states of the switches, the antenna can achieve four radiation patterns and it is designed and simulated by using Ansoft HFSS. In addition, the different states are operated at the same centre frequency of 35GHz and the gain of the main radiation direction is about 7.5dB

BROADBAND CPW-FED CIRCULARLY POLARIZED ANTENNA WITH AN IRREGULAR SLOT FOR 2.45 GHZ RFID READER

A coplanar waveguide-fed slot antenna with wideband circular polarization characteristic is presented. The proposed antenna consists of an irregular slot with a stair-shaped edge and an L-shaped feed line. The stair-shaped edge can improve the circular polarization of the antenna. The simulated and measured results show that the antenna has an impedance bandwidth (VSWR < 2) about 1040MHz (42%@2.47GHz) and an axial ratio (AR) bandwidth (AR < 3dB) about 640MHz (25.8%@2.48GHz) for 2.45GHz RFID applications. The RHCP gain in the main radiation direction varies between 2.3dBi and 3.8dBi.

PRINTED TEM HORN ANTENNA FED BY BALANCED MICROSTRIP LINE

In this paper, a new kind of printed TEM horn antenna with high-gain fed by balanced microstrip line is proposed. The radiation part of the antenna (printed on the FR4 epoxy substrate) is composed of two symmetrical triangular metal foil branches fed by balanced microstrip line. The antenna has been simulated by CST MICROWAVE STUDIO r software and the simulated results show that the proposed antenna is a kind of traveling wave antenna. Besides, an equivalent adopted V-shaped antenna model is proposed to describe the radiation characteristic of the antenna. The simulated and measured results indicate that in the frequency ranging from 1.64GHz to 9GHz, the re∞ection coe-cient of the antenna is less than i6dB and in the work frequency band, the average gain value is over 8.2dB. The antenna gain will be improved greatly by extending the length of the dielectric slab appropriately (in the main radiation direction) without in∞uencing the bandwidth. The measured and simulated results have a good consistency. This antenna will have wide application in the UWB fleld.

HIGH POWER ELECTROMAGNETIC TRANSIENT PULSE IN-PHASE SYNTHESIS

PCSS low jitter trigger can reach 65 ps in the condition of high bias electric under the non-liner mode (1-5); high power transient pulse can be gained by virtue of it. The high power transient pulse in-phase characteristic and other tenets are verified by testing axial electric field strength and axial energy density, which is energy per area at the antenna main radiation direction. In the experiment, axial electric field strength and energy density of antenna array measured in different conditions indicate that axial electric field strength is proportional to the number of antenna elements and the energy density is proportional to the square of the number of radiation units, which means the transient electromagnetic pulses could synthesize in phase perfectly.

Membrane supported Yagi–Uda antennae for millimetre-wave applications

This paper addresses for the first time the design, fabrication and 'on wafer' characterisation of membrane supported Yagi-Uda coplanar waveguide fed antenna structures, operating in the 45 GHz frequency range. The antennae were fabricated on 1.4 /spl mu/m thin SiO/sub 2//Si/sub 3/N/sub 4/ membranes obtained by micromachining of high resistivity silicon, using a backside reactive ion etching process. This approach has assured almost free-space operating conditions for the Yagi-Uda antennae and the dry backside etching process has allowed the effect of the bulk silicon wall that supports the membrane in the main radiation direction to be minimised. The design was based on electromagnetic simulations made using the Zeland IE3D software package. The antenna structures, measured 'on wafer', have shown a minimum return loss of 15 dB and a gain of about 7 dBi. Very good agreement has been observed between experimental and simulated results.

Numerical analysis of the horizontal antenna above a lossy ground

AbstractSince the electric field integral equation for the horizontal antenna above a ground contains a kernel of the form δ2/δxδz f (x, z) derived from the vertical Herz potential, its numerical integration is difficult. In this paper, it is shown that this kernel can be transformed to the form δ2/δx2 g(x, z) so that the moment method can easily be introduced without approximation of the kernel by the reflection coefficient method (RCM). Numerical calculations have been performed for the input impedance and the radiation pattern of a half‐wave antenna above a typical lossy ground at 60 MHz in terms of height, relative dielectric constant and conductivity as well as the thickness parameter ω. the resistive part of the computed input impedance agrees almost with the value by the RCM, whereas the discrepancy between two methods increases in the reactance for a fatter antenna if the antenna height is less than about 0.4 times the height. the input impedance vs. the ground conductivity varies abruptly near the transition σ = ωϵ0ϵs from capacitive to conductive nature in the ground. If the height is half wavelength, the H‐plane pattern has the main radiation direction at 62 degrees and hence long‐distance communication is possible by ionospheric reflection. In the case of the ground, about ‐9 dB of the electric field in the maximum direction remains near the zenith and the beam is different from that for perfect conductor cases.