Coaxial Feed Line Research Articles

Design of Dual-Band MIMO Antenna with High Isolation for WLAN Mobile Terminal

In this paper, we propose a dual-band multiple-input multiple-output (MIMO) antenna with high isolation for WLAN applications (2.45 GHz and 5.2 GHz). The proposed antenna is composed of a mobile communication terminal board, eight radiators, a coaxial feed line, and slots for isolation. The measured −10 dB impedance bandwidths are 10.1% (2.35 GHz to 2.6 GHz) and 3.85% (5.1 GHz to 5.3 GHz) at each frequency band. The proposed four-element MIMO antenna has an isolation of better than 35 dB at 2.45 GHz and 45 dB at 5.2 GHz between each element. The antenna gain is 3.2 dBi at 2.45 GHz and 4.2 dBi at 5.2 GHz.

Design of Dual-Band MIMO Antenna with High Isolation for WLAN Mobile Terminal

In this paper, we propose a dual-band multiple-input multiple-output (MIMO) antenna with high isolation for WLAN applications (2.45 GHz and 5.2 GHz). The proposed antenna is composed of a mobile communication terminal board, eight radiators, a coaxial feed line, and slots for isolation. The measured -10 dB impedance bandwidths are 10.1% (2.35 GHz to 2.6 GHz) and 3.85% (5.1 GHz to 5.3 GHz) at each frequency band. The proposed four-element MIMO antenna has an isolation of better than 35 dB at 2.45 GHz and 45 dB at 5.2 GHz between each element. The antenna gain is 3.2 dBi at 2.45 GHz and 4.2 dBi at 5.2 GHz.

Investigations on a Novel Folded Ring Resonator Antenna With Multiband Characteristics

A novel loop antenna based on the volumetric folded ring resonator (FRR) structure is proposed. It is shown that the FRR antenna can be represented by an equivalent circuit model for approximate analysis with sufficient accuracy. Two practical implementations are presented: The first version is a single FRR antenna embedded in a dielectric substrate and excited by a 50 coaxial feed line. Parametric studies of the structural parameters are presented showing three resonances that can be impedance matched achieving positive gain. In the second implementation, the FRR is embedded in a slotted ground plane for improved matching and radiation performance. Two bands, one at 3.6 GHz and another between 4.75 GHz and 5.8 GHz, are matched to better than S11 = -10 dB and maintain a constant 2.5 dBi gain with >; 90% radiation efficiency. The simulated reflection coefficient and gain radiation patterns agree well with measurements.

COPLANAR PRINTED MONOPOLE ANTENNA USING COAXIAL FEEDLINE FOR DTV APPLICATION

This article presents a coplanar printed monopole antenna for digital television (DTV) in the UHF band (470{862MHz) application. The antenna structure consists of a meander loop monopole for radiation, a step-shaped ground plane for impedance matching, and a 50-› mini coaxial feedline for excitation. The meander loop monopole and step-shaped ground plane are printed on the same side of a substrate with an area of 15 £ 170mm 2 . The measured impedance bandwidth for 2.5:1 voltage standing wave ratio (VSWR) is 550MHz (465{1015MHz, 74%), covering the DTV band. In addition, the proposed antenna shows a real reception performance on a notebook computer. The reception results for audio and video signals exhibit stable characteristics.

External-Excitation Curl Antenna

A strip curl antenna is investigated for obtaining a circularly-polarized (CP) tilted beam. This curl is excited through a strip line (called the excitation line) that connects the curl arm to a coaxial feed line. The antenna structure has the following features: a small circumference not exceeding two wavelengths and a small antenna height of less than 0.42 wavelength. The antenna arm is printed on a dielectric hollow cylinder, leading to a robust structure. The investigation reveals that an external excitation for the curl using a straight line (ST-line) is more effective for generating a tilted beam than an internal excitation. It is found that the axial ratio of the radiation field from the external-excitation curl is improved by transforming the ST-line into a wound line (WD-line). It is also found that a modification to the end area of the WD-line leads to an almost constant input impedance (50 ohms). Note that these results are demonstrated for the Ku-band (from 11.7 GHz to 12.75 GHz, 8.6% bandwidth).

Compact Orthomode Transducer Using Single-Ridged Triangular Waveguides

We present a compact L-band orthomode transducer (OMT) with a new waveguide junction consisting of a quad-ridged square waveguide and four single-ridged triangular waveguides. Quad-ridged square and single-ridged triangular waveguides of various sizes were numerically analyzed to estimate the cutoff frequencies and characteristic impedances of the waveguides. An optimum junction structure for the OMT with a low cutoff frequency and specific characteristic impedance was found based on the numerical simulation. The junction has a relatively small size without waveguide branches, and provides good impedance matching with a 50 Ω coaxial feed line. In addition, Klopfenstein and linear tapers were employed to design waveguide ridges for minimizing mismatches at the OMT junction. Measurement showed a bandwidth of about 400 MHz from 1.0 to 1.4 GHz and an isolation level below -40 dB in the frequency range. The cross section of the OMT was reduced to 62% of the standard waveguide cross section, and the total length is only 56 cm (2.24 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) at 1.2 GHz.

A compact, one-piece, metal-plate patch PIFA for 2.4-GHz WLAN operation

A simple, standalone, one-piece patch PIFA operating in the 2.4-GHz WLAN band is introduced. The antenna was first constructed by stamping a rectangular flat plate, which has an area of 10 × 62 mm2, and then bent two times to form a compact patch antenna with dimensions 5 × 10 × 35 mm3. The top patch is of the same width as the antenna ground plane and set 5 mm therein above. The feeding and shorting portions of the antenna are all located on the same, short side of the top patch. This arrangement makes the proposed antenna quite easy to manufacture and also facilitates the feeding-cable soldering. With a low profile of the design and the use of the coaxial-line feed, the antenna was further applied to a wireless LCD TV for the antenna operating frequency and radiation performance analyses. Details of the design prototype are discussed in the article. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26134

THEORETICAL INVESTIGATION OF RECTANGULAR PATCH ANTENNA MINIATURIZATION BASED ON THE DPS-ENG BI-LAYER SUPER-SLOW TM WAVE

The TM0 surface mode in an infinitely long parallel-plate waveguide filled with a double-positive (DPS) and epsilon-negative (ENG) metamaterial bi-layer is studied. With proper constitutive parameters and thicknesses of the two layers, the slow-wave factor (SWF) for such a parallel-plate waveguide can tend to infinity as the frequency decreases. A 2-D cavity based on the DPS-ENG bi-layer waveguide is constructed and studied to evaluate the radiation ability of its corresponding patch antenna. Based on the cavity model analysis of patch antennas, we show that good efficiency for broadside radiation of such a cavity-based rectangular patch antenna can be achieved when one layer of the cavity is shielded (or partially shielded) by PEC boundaries. Taking practical loss and dispersion into consideration, a miniaturized cavity-based rectangular patch antenna is proposed as an example. With the super-slow TM0 surface mode excited in the bi-layer by a simple coaxial line feeding, the antenna has a dimension of only 0.107λ0×0.129λ0×0.045λ0. The patch antenna produces broadside radiation, and fairly good radiation efficiency is achieved. The PEC-Partially-Shielded-ENG-Cavity based rectangular patch antenna with a further miniaturization but reduced radiation efficiency is also discussed. (Less)

TRANSIENT RESPONSES OF SOME ANTENNAS UNDER THE IMPACT OF AN INTENTIONALLY INCIDENT HIGH-POWER ELECTROMAGNETIC PULSE

An improved flnite difierence time domain (FDTD) method is employed for fast capturing transient responses of reconflgurable and multiple-input-multiple-output (MIMO) antennas under the impact of an intentional high-power electromagnetic pulse (EMP) but with difierent waveforms, respectively, where lumped element and sub-cellular thin-wire algorithms and coaxial feed model are integrated together for handling such three-dimensional antennas used for wireless communication. Parametric studies are carried out to show efiects of high-power EMP waveforms, its polarization state and incident direction on the transient coupled voltages on the coaxial feed line and across the diodes, with su-cient information obtained for understanding the interaction between the EMP and the antennas.

Low-Profile Multifrequency HF Antenna Design for Coastal Radar Applications

A novel design for an electrically small high-frequency (HF) antenna suitable for coastal radar applications is presented. The principle design objectives were to develop an HF antenna resonant at multiple frequencies that is also compact and easily transportable for deployment to coastal sites and on floating platforms. The compact antenna achieves practical performance values for radiation resistance, bandwidth, and gain while maintaining small values of ka. The design presented in this letter consists of a meandering line antenna composed of helical elements and switchable folded arms. The value of ka ranges down to 0.16 at 5.7 MHz. The antenna is self-resonant at multiple frequencies including 5.7, 16.1, 20.6, and 28.1 MHz for open-circuit mode and 15.1, 18.5, and 26.1 for the short-circuit mode. In all cases, input impedances were easily matched to 50-Ω coaxial feed lines, and the achieved bandwidths ranged from 1% to 12% within the HF band (3-30 MHz). The antenna is 90 cm high with a small ground disk of 60 cm diameter. Simulation results and prototype experimental measurements are presented.

An Efficient FDTD Model for Resistively Loaded Cylindrical Antennas With Coaxial Lines

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A full coarse-grid based finite-difference time-domain (FDTD) model is proposed for an efficient analysis of resistively loaded cylindrical antennas driven by coaxial feed lines. In the case of the electrically thin resistive antenna, the thin-wire approximation is applied to the near fields around the antenna. The resistive antenna is equivalently represented by a series connection of piecewisely lumped resistors along the antenna axis. And the coaxial line is replaced by an equivalent source over the feed aperture of the line. Then the corresponding FDTD update equations make it possible to implement the full coarse-grid model without additional grid refinements for the antenna and the feed line. The transient reflected feed voltage and the input impedance of resistive antennas are calculated numerically and compared with those of a full fine-grid. </para>

Micromachined 38 GHz cavity resonator and filter with rectangular-coaxial feed-lines

Micromachined, multilayer cavity resonators and filters at 38 GHz are demonstrated. Each layer is made of gold-coated silicon, structured by deep reactive etching. Two external coupling structures by coaxial feed lines are proposed to suit the fabrication process. The measured resonator gives an unloaded Q-value of 343 at 38 GHz. Methods to further improve the resonator quality-factors are discussed. The measured insertion loss of the filter is 1.01 dB, the 3 dB bandwidth is from 36.53 to 39.13 GHz, and the return loss is better than −15 dB over the frequency range from 37.0 to 38.6 GHz.

Thin-wire finite-difference time-domain model for insulated and resistively loaded cylindrical antennas driven by coaxial lines

A thin wire-based finite-difference time-domain (FDTD) model for a simple analysis of insulated and resistively loaded cylindrical antennas fed by coaxial lines is proposed. The resistive loading and the coaxial feed line are approximated to equivalent resistors along the antenna axis and the equivalent source over the infinitesimal feed gap, respectively. The effects of the insulation are corrected by employing thin-wire approximation and the boundary condition. A full coarse-grid FDTD algorithm is then implemented without additional grid refinements for the insulation, the resistive loading and the feed line. As a function of insulation properties and resistive loading profiles, the transient reflected feed voltage and the input impedance of antennas are calculated numerically. The validity of the proposed model is proved by comparing it with the results of the full fine-grid FDTD.

Substrate-Integrated Waveguide Ku-Band Cavity-Backed 2 $\,\times\,$2 Microstrip Patch Array Antenna

A Ku-band cavity-backed microstrip patch 2 x 2 antenna array has been implemented using the substrate-integrated waveguide (SIW) technology-a low-cost multilayer printed circuit board (PCB) process. Cavities are emulated using vias, and the patches are fed using microstrip lines that are centrally fed by a shielded coaxial probe feed line. Simple design guidelines for the cavity, patch, and substrate selection are presented. The array was fabricated, and its measured results agreed very well with theoretical predictions and indicated a relatively high efficiency and wide bandwidth of greater than 70% and 9%, respectively.

Novel Microstrip Antenna With Rotatable Patch Fed by Coaxial Line for Personal Handy-Phone System Units

An enhanced microstrip antenna is proposed that incorporates a patch that rotates around the inner conductor of the coaxial line or dielectric shaft and a novel coaxial line feeding technique that offers constant electromagnetic coupling. This proposal addresses the disadvantages in our previous patch antenna in which the resonant frequency diverges from the center frequency of the personal handy-phone system (PHS) band and the bandwidth decreases as the patch rotates because of the changing electromagnetic coupling between the patch and microstrip line due to the patch rotation. We verify that this enhanced patch antenna achieves the antenna gain of approximately 0 dBd, which is the same as that of the previously proposed antenna, while suffering no significant gain degradation due to unit inclination over inclination angles from plusmn45deg compared to a conventional quarter-wavelength whip antenna, which experiences a degradation of approximately 2.7 dB. We show that the maximum resonant frequency separation from the center frequency of the PHS band is reduced to 15 MHz from 31.4 MHz of the previous antenna using the novel coaxial line feeding technique. The effective bandwidth needed for PHS is achieved over the inclination angles of -20deg to +40deg. Approximately 93% of the total bandwidth needed for PHS is achieved while the previous microstrip line type achieved only 58% coverage; accordingly, an adequate bandwidth for PHS use is obtained.

Feed models for coax-driven monopole and dipole antennas

A method is presented for accurately modeling a monopole or dipole antenna fed by a coaxial line. The base of the monopole is attached to a conducting plane through which the coaxial feed line extends to the feed. The feed structures considered are easily adaptable to physically rugged forms and are simple to construct. Equivalent models for the three regions of the structure are devised and coupled integral equations for aperture fields and surface currents are formulated to enforce the boundary conditions. Three variations of the feed configuration are discussed and the reflection coefficient of the antenna feed is determined from the data obtained from the solutions of the coupled integral equations. Computed reflection coefficient values are shown to agree well with values measured on laboratory models

Antennas for the next generation of low-frequency radio telescopes

The next generation of large telescopes for radio astronomy at frequencies below 100 MHz will consist of tens of thousands of wide-band dipole-like antennas, each individually instrumented with a receiver and combined using digital signal processing. At these frequencies, the sensitivity of a telescope is limited by Galactic noise, with the result that even simple dipoles can deliver extraordinary useable bandwidth. In this paper the necessary characteristics for these antennas are explained, some bounds on performance are developed, and a few candidate designs are analyzed. It is shown that antenna systems consisting of simple wire dipoles, a 360 K active balun, and a long coaxial feedline can achieve Galactic noise-limited performance over large portions of the range 10-100 MHz. It is further shown that when these antennas are used as elements in a compact array, their Galactic noise-limited characteristics are not significantly affected.

FDTD simulation of a microstrip phased array with a coaxial feed

In the paper, the authors present a novel approach for analysing microstrip patch antennas using the finite difference time domain (FDTD) technique. Specific attention is paid to the issue of modelling the coaxial feed line, using a voltage source with a lumped resistance type of internal impedance. The results of the simulation are found to be in close agreement with those derived by using the method of moments (MoM). The analysis is then extended to the case of planar arrays of microstrip patch antennas. The active element pattern of the patch antenna is first extracted by using the FDTD, which is later used to predict the performance of the planar array. The paper also examines the numerical superefficiency and accuracy of the technique, and discusses its computational complexity.

Comprehensive analysis and simulation of a 1-18 GHz broadband parabolic reflector horn antenna system

A 1-18 GHz parabolic reflector horn antenna system featuring a broadband double ridged primary horn with a coaxial feed line is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not maintain a single main lobe in the direction of the horn axis over the whole frequency range. Instead, at frequencies above 12 GHz the main lobe in the radiation pattern starts to split into four lobes pointing in off-axis directions with a dip of up to 6 dB between them along the center axis. To investigate this phenomenon in detail, a combined method of moments and physical optics approach has been adopted to simulate the complete antenna system.

Narrow flat-plate antenna for 2.4 GHz WLAN operation

A novel flat-plate antenna, obtained by cutting an inverted-L slit in a narrow metal plate or by stamping from a metal sheet, for wireless local area network (WLAN) operation in the 2.4 GHz band (2400–2484 MHz) is presented. The antenna has a simple structure and is easily fed by using a 50 Ω coaxial feed line. A prototype of the proposed antenna with a narrow width of 3 mm is constructed and studied.