Feeding Coaxial Cable Research Articles

An efficient hybrid method for analyzing the coupling response of microstrip antenna system

This paper presents an efficient hybrid method consisting of Lorentz reciprocity theorem, finite-difference-time-domain (FDTD) method, thin wire model, transmission line (TL) equations and transfer impedance model, which can be utilized to analyze the system-level transient responses of the microstrip antenna system with antenna, metallic enclosures, braided shielded cable, and lumped element, when illuminated by an external electromagnetic pulse (EMP). In order to avoid over-fine mesh generation and repeated modeling of the antenna in multiple simulations, Lorentz reciprocity theorem is employed to extract an equivalent source model of antenna coupling, thereby improving the computational efficiency. Then, the transfer impedance model and thin wire model are incorporated into the FDTD-TL method efficiently to deal with the back-door coupling through the shielding layer of feeding coaxial cable. Finally, the hybrid FDTD method combined with the extracted equivalent source of antenna coupling is utilized to solve the coupling responses of the whole antenna system. The results of numerical simulation are verified by comparing with the simulation results of CST CS. Then, considering the influence of different incident conditions of external EMP, the characteristics of the coupling response of the system are analyzed. The obtained coupling response information demonstrate that the proposed method is available for further designing electromagnetic protection of the inner circuits of the microstrip antenna system against the impact of external EMP.

Study on a broadband new structure dipole‐shaped circularly polarized antenna

AbstractA broadband, circularly polarized (CP), new structure, dipole‐shaped antenna is proposed in this article. The antenna is composed of dipole‐shaped patch, FR4 substrate, ground and feeding coaxial cable. A double‐printed semicircular ring is utilized to feed the radiator. An optimized antenna with an oversize of 0.42λ0 × 0.42λ0 × 0.136λ0 0.75 × 0.75λ0 × 0.15λ0 (at 1.32 GHz) is designed and measured. The measured results show that the proposed antenna yields an impedance bandwidth (IBW) of 36.8%(1.24–1.8 GHz), a 3‐dB axial‐ratio (AR) bandwidth of 24%(1.32–1.68 GHz), and an average gain of 9.1 dBic in the operating frequency band.

Helical Torsion Coaxial Cable for Dual-Band Shared-Aperture Antenna Array Decoupling

Direct connection between coaxial cables and antenna radiators is one of the most popular and simplest approaches for antenna excitation. In dual-band shared-aperture antenna arrays that operate in higher and lower frequency bands, feeding coaxial cables of the higher band antenna array will inevitably introduce electromagnetic coupling in the lower band antenna arrays. The cross-band coupling will further lead to radiation pattern distortion, gain decrease, and impedance mismatching in the lower band antennas. Instead of using conventional straight coaxial cable feedings, this article proposes to decouple the unwanted cross-band coupling with a novel helical torsion coaxial cable design. The helical torsion feeding (HTF) coaxial cables are investigated from equivalent circuit analysis and full-wave simulation. The analysis results demonstrate that the HTF coaxial cable possesses open-circuit characteristic in the operation band of the lower band antenna. Through this design, the cross-band coupling is effectively suppressed at 0.69 GHz. The effectiveness of the approach is then demonstrated in a dual-band shared-aperture antenna array. Both the simulated and measured results validate the proposed design. The proposed decoupling method will find applications in compact multiband 5G MIMO antenna array developments.

Compact Endfire Coupled-Mode Patch Antenna With Vertical Polarization

Coupled-mode patch antenna (CMPA) is able to reform the beam by manipulating the phase of the fringing fields at the edges. In this paper, a method is proposed to realize endfire radiation with vertical polarization based on the concept of CMPA. Besides the phase controlled by the coupling, the asymmetric feeding introduces additional phase shift to one of the radiation slots, which makes the beam pointing to the forward endfire direction within the whole band. The ground of the antenna is truncated to be the same size of the top patch, which eliminates the undesired effect of the ground edge and ensures the symmetric patterns pointing around endfire direction. The size of the antenna itself is only $0.26\lambda _{0} \times 0.44\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the center operating frequency. In order to block the unwanted common mode current outside the feeding coaxial cable, a quarter-wavelength balun is applied in the implementation. The fabricated antenna sample has highly selective two-pole $S_{11}$ response with center frequency of 2.41 GHz and 10 dB fractional bandwidth of 2.5%. The simulated and measured patterns confirm the endfire radiation of the proposed antenna. The measured 3 dB bandwidth of realized gain at forward endfire is 2.5% at center frequency of 2.41 GHz, where the realized gain is 2.8 dBi and the front-to-back (F/B) ratio is 17.1 dB. The proposed endfire antenna with vertical polarization has the advantages of its inexpensive and friendly fabrication, compact and simple configuration, and high selectivity.

A bottom-feed omni-directional circularly polarized antenna array

AbstractA bottom-feed omni-directional CP (circularly polarized) antenna array is proposed in this letter. The antenna array is composed of four elements (two printed ZPS (zero-phase-shift) line loops and two half-wavelength dipoles). The four elements are fed with the same phase and amplitude. The ZPS line loops provide the horizontal polarization while the dipoles provide the vertical polarization. Therefore, omni-directional circular polarization is formed in the far field. The feeding network consists of a 1–4 T-shaped power divider formed by parallel strip lines. In order to balance the amplitude of the feeding coaxial cable, the structure is used in the bottom to transfer parallel strip line to micro-strip line. Besides, the loops and the dipoles are placed on the different side of the network to guarantee the omni-directional radiation property. The measured impedance bandwidth of the fabricated antenna is 0.13 GHz (2.40–2.53 GHz) and the measured maximum CP gain at 2.45 GHz is 4.8 dBic.

Parameter optimization for the three-frequency feed for the mirror antenna of the non-linear radar

Analyzed below is a radiating structure represented by a flat self-complementary three-sector structure fed by three segments of the microstrip line and located above the stepped metal screen, and to be used as an exciter for the non-linear radar antenna. When proper matching with the feeding coaxial cable is achieved, results of the numerical simulation proved that the antenna can provide near-circular polarization of radiation at the probing signal frequency, and linear polarization at the second and third harmonics of this signal.

Tools for Attacking Tumors: Performance Comparison of Triaxial, Choke Dipole, and Balun-Free Base-Fed Monopole Antennas for Microwave Ablation

Microwave ablation (MWA) is a promising therapeutic technique that uses minimally invasive interstitial antennas for heating tumors to cytotoxic temperatures [1], [2]. Over the years, numerous MWA antennas have been reported in the literature (e.g., [3]-[15]). MWA antenna designs typically use coaxial cable feed lines to deliver the microwave energy to the active part of the antenna. Due to the unbalanced nature of coaxial cables, current can flow on the outer surface of the outer conductor. If not appropriately suppressed, this current can cause unwanted heating of healthy tissue along the antenna?s insertion path. Moreover, in such situations, the input impedance of the antenna becomes dependent on the insertion depth.

A plug’n’play WiFi surface-mount dual-loop antenna

Abstract We present the design, modelling and characterization in the 2.4 GHz band of a B-shaped antenna consisting of a dual circular loop over a conductor plane. The proposed design is intrinsically unbalanced and features a very good match to a 50 Ω line at resonance, which makes our device essentially plug’n’play for a coaxial cable feed. Another interesting property of the proposed antenna is its simplicity of construction. The antenna has been modelled using the moment method. A prototype resonant at 2.4 GHz has been built and we have measured its impedance in this spectral region. The radiation pattern and the gain at resonance have also been characterized and the device has been shown to provide 6.31 dBi gain. The overall properties of the device make it an excellent option to provide WiFi connectivity when required in open hardware implementations.

Antenna for Ultrawideband Channel Sounding

A novel compact antenna for ultrawideband channel sounding is presented. The antenna is composed of a symmetrical biconical antenna modified by adding a cylinder and a ring to each cone. A feeding coaxial cable is employed during the simulations in order to evaluate and reduce its impact on the antenna performance. The optimized antenna demonstrates S $_{11}$ below $-$ 10 dB and a stable omnidirectional radiation pattern robust against the cable effect over the frequency band 1.5–41 GHz despite its compactness (the maximum electrical dimension is of 0.29 $\lambda _{\rm max}$ , where $\lambda _{\rm max}$ is the free-space wavelength at the lowest frequency of operation). A prototype of the antenna is fabricated and tested. The simulated and measured S $_{11}$ are in a good agreement. Measured radiation patterns confirm the pattern stability in terms of the direction of maximum radiation and 3-dB beamwidth.

Radiation Efficiency Improvement of a Balanced Miniature IFA-Inspired Circular Antenna

The radiation efficiency improvement of an electrically small antenna is presented. We consider a balanced miniature inverted-F-antenna-inspired circular antenna whose radius is ${{\mathbf \lambda }}/28$ at 433 MHz and radiation efficiency is 30%. By modifying the antenna strip width, we identify, by electromagnetic simulations, an antenna radiation efficiency improvement up to 53% while keeping its overall dimension and general structure identical. Then, we confirm the antenna performances improvement by radiation efficiency measurements performed inside a large anechoic chamber and using the gain pattern integration technique. An optical fiber link is used to avoid possible perturbation due to the feeding coaxial cable. The radiation efficiency improvement, confirmed by experimentation, is of major interest for ultranarrowband antennas for which the radiation efficiency is the most critical parameter. This efficiency improvement is discussed in light of the fundamental limits of miniature antennas.

Electrically Small Folded Dipole Antenna for HF and Low-VHF Bands

A novel, highly miniaturized, lightweight antenna operating at the low-VHF band is presented. Earlier studies on an extremely short HF monopole antenna consisting of two in-phase vertical elements face an inevitable issue regarding an unbalanced coaxial cable feed due to the very small ground plane . To resolve this problem, as well as to achieve higher bandwidth, we introduce an electrically small folded dipole version of the same antenna having a fully balanced structure. The overall dimension and total mass of the proposed antenna are $10 \times 10 \times 15 ~\hbox{cm}^3$ . ( $0.013{\lambda _0} \times 0.013{\lambda _0} \times 0.02{\lambda _0}$ at 40 MHz) and 98 g, respectively. The gain and pattern of the fabricated antenna are measured in an elevated range that is in nearly free-space conditions. Measurements are shown to be in good agreement with the design predictions from simulation.

Radiation Pattern Measurement of a Low-Profile Wearable Antenna Using an Optical Fibre and a Solid Anthropomorphic Phantom

This paper presents a study into radiation pattern measurements of an electrically small dielectric resonator antenna (DRA) operating between 2.4 and 2.5 GHz in the industrial, scientific and medical (ISM) radio band for body-centric wireless communication applications. To eliminate the distortion of the radiation pattern associated with the unwanted radiation from a metallic coaxial cable feeding the antenna we have replaced it with a fibre optic feed and an electro-optical (EO) transducer. The optical signal is then converted back to RF using an Opto-Electric Field Sensor (OEFS) system. To ensure traceable measurements of the radiation pattern performance of the wearable antenna a generic head and torso solid anthropomorphic phantom model has been employed. Furthermore, to illustrate the benefits of the method, numerical simulations of the co-polar and cross-polar H-plane radiation patterns at 2.4, 2.45, and 2.5 GHz are compared with the measured results obtained using: (i) an optical fibre; and (ii) a metallic coaxial cable.

Impedance and Radiation Measurement Methodology for Ultra Miniature Antennas

This paper presents new measurement methodologies for ultra-miniature antennas. A first one is dedicated to the impedance measurement and the second one to the radiation measurement. Both methods are detailed focusing on an ultra-compact antenna design at 2.4 GHz, whose electrical dimensions, including the ground plane, are λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /25×λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /25×λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /62.5. Given the very small antenna size compared to the wavelength, measurements by means of conventional coaxial cable can affect the characterization results. The issues related to the use of a feeding coaxial cable in both simulation and prototype measurements are first discussed. Then, specific methods to deduce the isolated antenna properties are proposed. Both methodologies rely on the use of electromagnetic simulation to compensate perturbations introduced by the measuring device.

Single‐layer crossed dipole antenna with circular polarization for handheld RFID reader

AbstractA compact circularly polarized coplanar crossed dipole antenna with an unequal length of arms for RFID reader is designed and measured in this paper. It uses two unequal length dipoles connected in parallel to a coaxial cable feed and requires no matching network. The impedance bandwidth of the proposed antenna for S11 &lt;10 dB is about 6.9% and it has a 3‐dB CP bandwidth of about 1.0%. Experimental results and simulations reveal that the proposed antenna features total size of 0.15 λ0 in side of square substrate and 0.005 λ0 in height at the center frequency 924 MHz. In addition to this, the compact antenna is easily to be embedded in the holding box as transmitting antenna in handheld RFID reader. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1172–1176, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25937

Shielded Microstrip Array for 7T Human MR Imaging

The high-frequency transceiver array based on the microstrip transmission line design is a promising technique for ultrahigh field magnetic resonance imaging (MRI) signal excitation and reception. However, with the increase of radio-frequency (RF) channels, the size of the ground plane in each microstrip coil element is usually not sufficient to provide a perfect ground. Consequently, the transceiver array may suffer from cable resonance, lower Q-factors, and imaging quality degradations. In this paper, we present an approach to improving the performance of microstrip transceiver arrays by introducing RF shielding outside the microstrip array and the feeding coaxial cables. This improvement reduced interactions among cables, increased resonance stability, and Q-factors, and thus improved imaging quality. An experimental method was also introduced and utilized for quantitative measurement and evaluation of RF coil resonance stability or "cable resonance" behavior.

Preliminary analysis of the external matching unit for the ICRH system for FAST

The Fusion Advanced Studies Torus (FAST) is a new tokamak machine proposed by the Italian Fusion Association as a Satellite Tokamak for accompanying the ITER programme. A relevant objective of FAST is to study burning plasma issues by simulating the alpha particle dynamics by means of fast ions produced by acceleration of a minority species using an Ion Cyclotron Resonance Heating (ICRH) system. A maximum coupled power of 30 MW is foreseen in the 60–90 MHz frequency range. The load tolerant External Conjugate-T (ECT) concept is being studied to match the low impedance of the launcher to the feeding coaxial cables ( Z 0 = 30 Ω). A preliminary design of the external tuning and matching system has been made and their simulation results are given in the paper.

Investigation Into the Vertical Monopole-Like Radiation Mechanism of a Horizontal Dipole on a Periodic Patch-Loaded Grounded Slab

It was recently demonstrated that a horizontal dipole radiates with a vertical monopole-like radiation pattern when placed near a two-dimensional periodic patch-loaded grounded slab (PLGS). Such a structure has been proposed as a low-profile surface-wave antenna. In this letter, we examine the radiation mechanism of such an antenna. It is indicated in this letter that the vertical monopole-like pattern is generated by the vertical common-mode current flowing on the outside of the coaxial cable feeding the short dipole, and not from the dipole itself. In this manner, the unbalanced horizontal dipole closely resembles a classic T antenna. Furthermore, we examine the propagation characteristics of the surface wave on the PLGS and discuss its contribution to the overall radiation of this antenna. We find that, in the lower frequency range, the PLGS appears insignificant to the antenna radiation. The investigation is carried out by the use of a full wave method-of-moments simulation.

Suppression of Cable Leakage Current for Edge-Fed Printed Dipole UWB Antennas Using Leakage-Blocking Slots

A simple method is presented for suppressing cable leakage current for printed dipole ultrawideband (UWB) antennas using thin leakage-blocking slots. Their effects on VSWR and pattern characteristics are demonstrated by comparing the performances of two identical coplanar waveguide (CPW)-fed printed dipoles except for the presence of the slots. Two thin slots along the feeding CPW trace effectively block a strong leakage current component from flowing over the outer surface of the feeding coaxial cable. While not significantly affecting the antenna's VSWR performance over wide bandwidth, the slots have the effects of increasing the antenna gain in the azimuth plane and reducing the strengths of strong radiation lobes close to the direction of cable attachment especially in the low-frequency range.

Improved Computational Efficiency in the Analysis of Finite Arrays of Thick Microstrip Antennas

A method is proposed that drastically improves the computational efficiency of the spectral-domain method of moments applied to finite arrays of stacked microstrip antennas printed on electrically thick substrates. For that purpose a novel analytical method is proposed to calculate the integrals with infinite boundaries over the asymptotic part of the Green's function in closed form by using the theory of residues. For medium-sized arrays (50-100 elements), a total reduction of CPU time with a factor of 150 was obtained. Electrically thick substrates are taken into account by using a sophisticated model for the feeding coaxial cables that includes an attachment mode to ensure continuity of current at the probe-patch transition. Simulated and measured data of two medium-sized arrays are given. It is shown that the behaviour of edge elements significantly differs from the scan performance of the elements near the centre of the array.