An improved multipactor dynamic model is proposed for studying the multipactor phenomenon on a dielectric surface existing longitudinal RF electric field using Monte Carlo method. The susceptibility curves of the electric field on the surface and the temporal evolution images of the multipactor discharge were obtained and discussed. The power deposited on the dielectric surface by the multipactor was also investigated in terms of an S-band RF dielectric window. The results show that, the longitudinal RF electric field may intensify the single-surface multipactor effect, which is likely detrimental to RF transmission and to result in the dielectric crack.
In this letter, a new miniaturized broadband 3-dB branch-line coupler at the center frequency of 880 MHz is proposed. The proposed coupler is designed by means of integrated miniaturization method, which consists of shunt capacitors, fractal geometry and equivalent miniaturized stubs, to achieve 82% size reduction compared with the referenced coupler. The return loss and isolation are both under -20 dB over a 19% relative bandwidth. The proposed coupler is simulated, fabricated and measured. The measured results agree well with the simulated ones.
A novel 21-35 GHz single-balanced quadruple subharmonic monolithic passive mixer is fabricated using the 0.15 μm GaAs pHEMT process. This mixer consists of a local oscillation (LO) spiral balun and a radio frequency (RF) band pass filter which has an intermediate frequency (IF) extracted feature utilizing a pair of anti-parallel Schottky barrier diode to achieve quadruple subharmonic mixing mechanism. The RF band pass filter formed with an interdigital coupler and a low-pass network is used to reduce the chip dimension while operating at a low frequency band and to improve the isolation between the RF and IF ports with a broadband operation. From the measured results, the mixer exhibits 11.3-15.1 dB conversion loss, 28.8 dB-high RF-to-IF isolation, 40 dB-high LO-to-RF isolation, 60 dB-high 3LO-to-RF isolation over a 21-35 GHz RF bandwidth, and an input 1 dB compression power of 4 dBm. The compact IF extraction circuit supports an IF frequency ranging from DC to 3.1 GHz. The core chip size is only 0.67 × 0.75 mm2.
The efficient design of broadband turnstile junctions compensated with piled-up cylindrical metallic posts is discussed in this contribution. Very high relative bandwidths can be obtained, while maintaining the diameter of the input circular access port lower than the width of the rectangular waveguide ports, thus reducing the number of excited higher order circular waveguide modes. A novel full-wave analysis tool has also been implemented in order to reduce the CPU effort related to the complete design process.
In this paper, a novel double-band integrated antenna for applications in WLAN is presented and studied. Based on the mature dipole theory, radiation elements are printed on the two faces of a low cost FR4 substrate. The two dipoles are designed on the sides of the feedline, which can reduce the impact of each other availably. The distance between the two arms and the width of the arms plays an important role in improving the impedance matching. Furthermore, by folding the arms efficiently, the current distribution of the proposed antenna is extended, and the dimensions of the proposed antenna can be reduced. The size of the designed antenna is just 34mm×24mm×1mm (about 0.27λ×0.19λ×0.008λ, λ is the wavelength relative to the frequency 2.4 GHz). Moreover, the prototype of the antenna is constructed and tested, which shows a good agreement with simulated result. The measured bandwidths, ranging from 2.35 GHz to 2.61 GHz and from 4.7 GHz to 6.0 GHz respectively, are obtained with return loss less than -9.54 dB (about 2:1 VSWR). The proposed antenna covers 2.4/5 GHz WLAN bands, and radiation patterns with good omni- directional radiation in the operating frequency are observed.
In this paper, a planar microstrip UWB monopole antenna with a good band-rejection is presented. By using a pair of arc shaped parasitic elements around the patch, an excellent notched frequency band for rejecting the WLAN band (5--6\,GHz) can be obtained. The arc shaped strips are parametrically studied and the effects of them on the radiation patterns and time domain behaviour of the UWB antenna are investigated.
A new method is introduced to construct a slab that has electric fields with propagation properties which are equivalent to a fractional-space wave equation in two-coordinate system. While its magnetic fields have propagation properties which are equivalent to the complementary fractional-space wave equation. Analytical forms for the reflection and transmission coefficients of this slab are derived. Results of these reflection and transmission coefficients show that such quasi-fractional-space slab has spatial and frequency selectivity properties.
This paper presents the design and implementation of a compact 2.4/5.2-GHz rat-race coupler on a glass substrate. Due to the low-loss substrate and thick metal layers, the process provides high-Q capacitors and inductors, and therefore the lumped rat-race coupler is practical. The coupler consists of three bandpass and one bandstop networks to achieve dual-band operations. The measured insertion losses at 2.4 GHz and 5.2 GHz are less than 2.7 dB and 1.9 dB, respectively. The measured return losses at the frequencies of interest are better than 20 dB. Moreover, the phase imbalances at the in-phase and anti-phase output ports are less than 3.9o and 4o at 2.4 GHz and 5.2 GHz, respectively. The chip size including all testing pads is merely 2.87 × 2.1 mm2 which is comparable to on-chip levels.
A new double arrow head defected ground structure (DGS) with centered etched ellipse is proposed for designing a multilayer low pass filter (LPF) with wide rejection band and low insertion loss in the stop-band. The prototype LPF consists of three double arrow head DGS with centered etched ellipse in the ground plane and compensated capacitor on the top layer of a 30×40 mm2 Roger RT/Duroid5880 substrate having relative permittivity (εr) of 2.2 and thickness of 0.78 mm. The cutoff frequency is equal to 1.07 GHz .The prototype LPF is then realized as multilayer structure to enhance the filter response and reduce its size. The size reduction of the proposed multi-layer LPF is about 26% more than the conventional one. The proposed filter has been fabricated and measured. Good agreement is achieved between the simulated and measured results. The filter presents the advantages of compact size; low insertion loss and high out-band suppression. Finally, the multilayer LPF is transformed to band pass filter (BPF) using J-inverter method.
Folded wire load antennas with matching network are designed by using optimization algorithms. The loads are parallel capacitor/inductor/resistor circuits that are adjusted by means of Differential Evolution (DE) optimizers to maximize bandwidth and the matching networks. The measured voltage standing-wave ratio (VSWR) of the load folded dipoles confirms broadband performance and agrees with data obtained from moment method computations. Antennas having bandwidth ratio of 2.5 : 1, with measured VSWR less than 3.5, meets the requirement.
As studied by Jaulent in 1982, the inverse problem of lossy electric transmission lines is closely related to the inverse scattering of Zakharov-Shabat equations with two potential functions. Focusing on the numerical solution of this inverse scattering problem, we develop a fast one-shot algorithm based on the Gelfand-Levitan-Marchenko equations and on some differential equations derived from the Zakharov-Shabat equations. Compared to existing results, this new algorithm is computationally more efficient. It is then applied to the synthesis of non uniform lossy electric transmission lines.
This paper applies a meshless method based on radial basis function (RBF) collocation to solve three-dimensional scalar Helmholtz equation in rectangular coordinates and analyze the eigenvalues of spherical resonant cavity. The boundary conditions of spherical cavity are deduced. The RBF interpolation method and the collocation procedure are applied to the Helmholtz and boundary condition equations, and their discretization matrix formulations are obtained. The eigenvalues of spherical resonant cavity with natural conformal node distribution are computed by the proposed method. Their results are agreement with the analytic solution.
The system of Maxwell equations with an initial condition in a vacuum is solved in a cylindrical coordinate system. It derives the cylindrical transverse electromagnetic wave mode in which the electric field and magnetic field are not in phase. Such electromagnetic wave can generate and exist in actual application, and there is no violation of the law of conservation of energy during the electromagnetic field interchanges.
In this paper, dispersion characteristics of the partial H-plane waveguides are theoretically investigated by applying Galerkin's method in Fourier domain. By extracting the dyadic Green's functions of the structure and satisfying the boundary conditions along the longitudinal slit, propagation constant and consequently, the fields in the structure are obtained. It is seen than propagation constant not only depends on the waveguide dimensions, but also on the location and dimension of the slit. A significant feature of the structure is that its first and second propagation modes can be separately controlled which is very useful in designing single-mode and multi-mode filters. Two examples are given which in the first one, the parameters of the structure are assigned in such a way the first and second cut off frequencies are at f=3.1 GHz and f=6.2 GHz respectively, but in the second example, first and second modes are degenerate. The validity of the method is confirmed by comparing our results with ones from others.
In this paper, a high selectivity quadruple-mode bandpass filter (BPF) with source-load coupling is proposed. This filter uses two short-circuited stubloaded stepped-impedance resonators (SIRs) which have the same type but different size. Two SIRs can generate four operating modes, which can be approximately adjusted individually. Owing to the special design of the filter, the coupling of two resonators is weak. In each resonator, the even-mode frequency can be flexibly controlled by changing the length of the short stub, whereas the odd-mode one remains stationary. Due to the source-load coupling, two transmission zeros are close to the cut-off frequencies of the passband, which leads to high selectivity. Simulated results show that central frequency is 2.27 GHz with 3-dB fractional bandwidth of 22.9%. The measured and simulated results are well complied with each other.
A compact ultra-wideband (UWB) bandpass filter (BPF) with simultaneous narrow notched band and out-of-band performance improvement is presented. The UWB BPF is built up using the hybrid microstrip and coplanar waveguide (CPW) structure. By employing split-ring resonator (SRR) defected on the lower plane, the narrow notched band was introduced. The center and bandwidth of the notched band can be controlled by adjusting the length and width of the SRRs. A novel cross-shape patch is constructed to implement transmission zeros in the upper out-of-band so as to suppress the spurious passband. The measured results show that insertion loss is less than 1.7 dB, the return loss is more than 13 dB and the variation of group delay is less than 0.2 ns. Furthermore, the width of narrow notched band is about 0.15 GHz and the attenuation is more than 18 dB at the center frequency of 5.76 GHz. The upper stopband is up to 15.2 GHz with rejection greater than 20 dB.
A new design of dual-band antenna for DCS/ PCS/ UMTS/ WLAN/ WiMAX applications is proposed. Using two metamaterials omega-shaped structures, a good impedance matching the dual-band mode is obtained. The proposed prototype antenna is fabricated on a 1.5mm thick FR4 epoxy substrate with a relative dielectric permittivity εr= 4.4, and loss tangent tanσ = 0.02. Good monopole-like radiation patterns and antenna gains over the operating bands have also been observed. Effects of each omega particle on the antenna performance and their coupling are all examined and discussed.
The present paper is a work on fluorescent tube performing the function of a monopole plasma antenna. In the construction, the needed power supply to the fluorescent tube is controlled by an IC 555 timer. In the experiments the supply frequency varies from 25 Hz to 200 Hz. By using a vector network analyzer it is shown that the persistence of plasma developed inside the tube persists for longer duration with increase in supply frequency. It is also found that the stability of resonant frequency increases with the increase in frequency of the AC power supply measured up to 200 Hz. Result shows that the effective part of a fluorescent tube functioning as Monopole plasma antenna is about 60% of the total length of the tube.
In this letter, a modified broadband 90° phase shifter is proposed. By using a dentate microstrip and a patterned ground plane, an extremely tight coupling can be obtained, and consequently a constant phase shift over a wide bandwidth can be achieved. To verify the proposed idea, a topology is implemented, the measured results of a phase difference of 90 ± 5° in 79.5% bandwidth, better than 10 dB return loss across the whole operating band, are also given. The measurement results agree well with the full-wave electromagnetic simulated responses.
In this paper, we present a frequency tunable antenna suitable for Digital Video Broadcasting Handheld applications. Due to the narrow operating frequency band of the antenna derived from a monopole coupled loop antenna, a tuning system has been proposed to sweep the narrow band on a large frequency range in order to cover the DVB-H frequency bandwidth [470-702] MHz. We provide results of this antenna mounted on a circuit board simulating a terminal handset.
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