In this paper, two planar diplexers using dual-mode resonators are designed, which have achieved significant size miniaturization. The first diplexer is made of a simple single dual-mode resonator as a square cavity in the substrate integrated waveguide technology. The two degenerate modes with 90° rotation are perturbed by the placement of metallic via and CPW lines as input and output ports. A prototype model of this diplexer is designed and fabricated in the X-band. Its simulation results and measurement data agree very well. An isolation of 22 dB is achieved between two ports, which is quite suitable for receiving systems. For the improvement of isolation and bandwidth, the degree of structure is increased, whereby dual-mode resonators are used to connect the channel filters to the input port. Those types of channel filters are used which generate a transmission zero in the frequency band of the other channel. The isolation and bandwidth of the diplexer have been improved significantly, where its size is much smaller than the common diplexers.
We have studied the instability of electrostatic ion-cyclotron waves in collisional magnetized two-ion component plasma (light positive K+ ions and heavy positive Cs+ ions). An ion beam propagating through collisional magnetized plasma containing electrons and two positive ion components drives electrostatic ion cyclotron (EIC) waves to instability via Cerenkov interaction. Analytical expressions & numerical calculations have been carried out for the frequency and growth rate of ion cyclotron waves for two EIC wave modes for existing experimental parameters, and it is found that the unstable mode frequency does not depend on electron collision frequency, while the growth rate is increased linearly with the electron collision frequency. Moreover, as the light ion concentration is increased, the frequency of the heavy ion mode moves closer to its gyrofrequency. Similarly, the frequency of the light ion mode approaches the light ion cyclotron frequency as the heavy ion concentration is increased. It is also found that the normalized unstable mode frequencies remains unchanged with electron collision frequencies, while the growth rate is increased linearly with the electron collision frequencies. In addition, the unstable mode frequencies are found to be dependent on the magnetic field strengths.
In this paper, a compact microstrip fed ultra-wideband antenna with a band notch characteristic is presented. The proposed antenna consists of two tridents and two uneven split ring resonators. The overall size of the antenna is 26 mm × 24 mm × 1.53 mm. By adding the uneven split ring resonators to the dual trident ultra-wideband antenna, a band notch of 5.05 GHz to 5.9 GHz is achieved. The band notch is adjusted by the size and the split locations of the resonators. CST microwave studios software was used to simulate the design. The measured |S11| (dB) pass band and notch band agree with the simulation within the frequency band from 3.65 GHz to 12.85 GHz.
In this paper, a dual-band circularly polarized (CP) patch antenna with left-hand circular polarization (LHCP) in the lower band and right-hand circular polarization (RHCP) in the higher band is proposed. On the basis of aperture coupled feed, the dual-band circular polarizations are achieved by adopting two rectangular patches with different rotation angles on the front and back of a substrate. A good agreement between the simulated and measured results is obtained. The 10-dB impedance bandwidths and 3 dB Axial Ratio (AR) bandwidths are 18.4% (1.93-2.32 GHz) and 3.2% (2.14-2.21 GHz) in the lower band and 12.4% (2.58-2.92 GHz) and 1.7% (2.84-2.89 GHz) in the higher band, respectively. The proposed antenna with its simple structure, compact size and excellent performanceprovides a reference forcommunication system applications.
This paper presents a method for improving Angle-of-Arrival estimation accuracy in multipath environments using a sliding antenna array consisting of only two antennas. The proposed method is then experimentally validated by means of a dual channel Software-Defined Radio receiver and a wireless microphone.
In this paper, a novel wideband single-feed circularly polarized patch antenna is presented. The antenna consists of an L-shaped probe, four parasitic patches perpendicular to the probe, and a planar reflector. By modifying the structure of the patches, two orthogonal radiation modes are created to realize the circular polarization in the broadside direction. This antenna exhibits a wide impedance bandwidth of 82.4% from 2 GHz to 4.8 GHz for the voltage standing wave ratio (VSWR) ≤ 2 and a 3-dB axial ratio (AR) bandwidth of 56.2% from 2.11 GHz to 3.77 GHz, over which the antenna gains vary from 5.7 dBic to 9.7 dBic. The measured results agree well with the simulated ones.
Covariance matrix adaptation evolutionary strategy algorithm is applied to optimize a dielectric loaded microstrip patch antenna. The optimization process performance is enhanced by not considering the symmetrical factor of the antenna structure. The antenna is optimized to work for IEEE 802.11a WLAN 5-6 GHz band. Experimental measurements have also been performed to validate the performance of the proposed antenna.
This paper presents an analytical solution for capacitance and characteristic impedance of CPW with defected structures (CPW_DS) in signal line. The first category of incomplete elliptic integrals F(φ, k) is employed for calculation, and the capacitance and characteristic impedance of CPW_GS in signal line are first time achieved by the analytical solution. FEM simulation results are used toverify the results of analytical solution,which shows a good agreement. All calculations are completed in software Wolfram Mathematica, and CPW structures are simulated in software HFSS.
A new method of electrodynamic analysis of gyrotropic (isotropic and anisotropic) media is developed. This method is based on the scalar representation of Maxwell's equations corresponding to 4×4- matrix formulation and coupling equations for gyrotropic medium in the Drude's form. It is utilized by solving the wave equations of second and fourth order, followed by cross-linking the fields at the boundary. The obtained results are experimentally verified by their good matching with the popular benchmark data, such as quartz rotatory power and in comparison with a known standard parameter of an optical element, such as λ/4-plate. This method simply summarizes the polarimetric and ellipsometric calculations.
A novel ultra-wideband (UWB) coupled-line coupler with an operating frequency band from 2 to 22 GHz is presented in this article. The proposed coupler is composed of six coupled-line sections. The continuous zigzag capacitive compensation (CZCC) technology is used to broaden the operation frequency band, which also significantly enhances the isolation and return losses of the coupler. The coupler is built on a multilayer circuit structure. In order to improve the design accuracy of the three-dimensional circuit structure, the combination simulation of EM simulator and circuit simulator are employed. The simulated and measured results of the UWB 10 dB asymmetric directional coupler are presented and discussed, which demonstrate that it is practical to achieve good performances in such a circuit structure.
A broadband circularly polarized planar antenna based on a quarter-mode substrate integrated cylindrical cavity subarray is presented in this communication. It is composed of two layers: a quarter-mode substrate integrated cylindrical Cavity (QMSICC) subarray and the feeding network comprised of three Wilkinson power dividers. The measured 10-dB return loss and 3-dB axial ratio bandwidths at the center frequency 5.2 GHz are 40% and 25.5%, respectively. The gain measured for right-hand circular polarization (RHCP) is 4.6 dBi at 5.2 GHz. And it will be used in WLAN operating at 5.2 GHz.
Underestimation of path loss when planning the deployment of 802.11n APs can lead to coverage gaps and user dissatisfaction. The use of Free Space Path Loss modelling can sometimes lead to underestimation of path loss in urban environments when the effect of small scale fading is not considered. A field experiment was conducted with the aim to investigate the applicability of the ITU-R P.1141-7 Recommendation in path loss estimation of 802.11n signals in an urban environment in Malaysia. The results showed that Section 4.3 of ITU-R P.1411-7 can estimate the path loss of 802.11n signals with very low error margins of between 0 dB and 5 dB for transmitter receiver distances of 50 m and more. At these distances, the average difference of path loss estimation between FSPL and measured path loss is approximately 18 dB. The study concludes that 802.11n APs may need to be placed at closer proximities than previously assumed if FSPL is used to model the path loss. This is to ensure that targeted traffic is actually offloaded; coverage gaps are reduced; user satisfaction is improved.
A novel four-element multiple input multiple output (MIMO) antenna system for LTE 2300 and 2.45 GHz ISM applications is presented. The total size of the proposed MIMO antenna system is 34 mm×18 mm, and the whole antenna system has a wide working bandwidth of 350 MHz (2.19-2.54 GHz). The measured isolation between antenna elements is higher than 15 dB with a close edge-to-edge separation of 0.03λ. Correlation coefficient of the MIMO antenna system is lower than 0.12, which can meet the requirements of 4G wireless systems.
This work presents a planar handset antenna having a small size 47×15×0.8mm3 and providing four wide operating bands of at least 698-960, 1710-2690, 3100-3900 and 5150-5850 MHz for the 11-band LTE700/GSM850/900, GSM1800/1900/UMTS/LTE2300/LTE2500, WiMAX 3.5GHz/ 5.4GHz, WLAN 5.8GHz. The multi-broadband antenna consists of Br-1, Br-2, Br-3, C-Strip and Ground plane. The structure is analyzed by S11 and surface current distribution. The simulated and measured results agree well. The gain of the proposed antenna is 1.51-4.12dBi, and the radiation efficiency is about 75%-94%.
In Geosynchronous earth orbit synthetic aperture radar (GEO SAR) working system, the radar signal travelling through the atmosphere is sensitive to the ionosphere. One of the effects is the Faraday rotation under geomagnetic field, which is similar to the phenomenon when the signal traveling through a ferrite medium. So based on the theoretical inference, we semi-physically simulate Faraday rotation of the ionosphere with that of the ferrite in the ground, which is one of the experiments of the ground railway prototype testing for GEO SAR system. The measurements of a mountain without ionospheric Faraday rotation and under the equivalent Faraday rotation of ionosphere are given experimentally. Imaging studies show that the influence of the ionosphere Faraday rotation on the distributed targets imaging is not visually obvious. Our work provides experimental basis for the GEO SAR to successfully image on the satellite.
A novel wideband horizontally polarized omnidirectional antenna (HPOA) with an electrical conductor reflector is proposed for the 4th generation (4G) Long Term Evolution (LTE) applications. The proposed antenna consists of four pairs of printed dipoles distributed on the front and back of the substrate, and a star-shape patch integrated with stepped parallel strip lines constitutes a balun for the unbalance-balance transition from the coax feeding to the antenna. Both simulated and measured reflection coefficients (S11) demonstrate a wide -10 dB impedance bandwidth of 39.6%, from 1.82 to 2.72 GHz. This band covers PCS, UMTS, LTE 2300, LTE 2500, WLAN and Bluetooth bands. The presented antenna has a peak gain of 3.2 and 4.0 dBi at 1.95 and 2.48 GHz, respectively, and an omnidirectional radiation pattern in E-plane. HPOA may be suitable for ceiling-mounted indoor 4G applications.
The one-step leapfrog hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method for lossy media is presented. By adopting the Crank-Nicolson and Peaceman-Rachford schemes, the derived method involves calculations of the lossy terms at two different time steps. Different from the original HIEFDTD method, the proposed method can also be considered as a second order perturbation of the conventional FDTD method. To verify the effectiveness of the proposed method, numerical experiments are performed by using different FDTD methods. It is shown that the proposed method can be more efficient than the conventional HIE-FDTD method with almost the same accuracy.
An off-grid direction-of-arrival (DOA) estimation method that utilizes a sparse array covariance matrix is proposed. In this method, the array covariance matrix is sparsely represented in the form of a vector and then modified to become an off-grid DOA estimation model according to the first-order Taylor series. By solving for the two sparse vectors in the resulting array covariance matrix, the off-grid DOA estimation can thus be achieved. We present an alternating iterative algorithm that exploits the alternating update of a convex optimization problem and a least-squares problem to solve for these two sparse vectors. Our method also extends the aperture. The effectiveness and efficiency of the proposed method are demonstrated in the simulation results.
A wideband antenna with band notch function using electromagnetic bandgap (EBG) structure is proposed. The antenna is capable of reconfiguring up to three band notch operation. Three EBGs are aligned underneath the feed line of the wideband antenna. The transmission lines over EBGs unit cells perform as a band stop filter. A switch is placed on each of the EBG structure, which enables the reconfigurable band stop operation. The simulated and measured reflection coefficients, together with the radiation patterns, are shown to demonstrate the performance of the antenna.
A dual-band and ±45° dual-polarized antenna is proposed for 2G/3G mobile communications in this paper. The proposed antenna consists of five elements for the lower band and ten elements for the upper band. Results for a single element and antenna array are presented. The front-to-back ratio is from 25 dB to 30 dB, and the axial cross polarization ratio is from 19 dB to 22 dB in a single low band unit. The dual-band array achieves a bandwidth of 15.7% (820-960 MHz) for the lower band and a bandwidth of 23.7% (1710-2170 MHz) for the upper band, covering the frequency bands required by 2G/3G systems. Simulation results show that the gains for antenna array are 15.7 dBi for the lower band and 19.1 dBi for the upper band, which is suitable for base stations applications.