Discrete multiloop, modified multiloop, and plate-loopantennas-multifrequency and wideband VSWR characteristics

Three types of loop antennas are presented: discrete multiloop (ML), modified ML and plate-loop (PL) antennas. The discrete ML and modified ML antennas are composed of N square loops. The N square loops of the modified ML antenna are connected by wires at the loop corners. The PL antenna is regarded as a modified ML antenna with infinite loops (N=∞). The analysis of the discrete ML antenna shows that one of the N loops resonates when its circumference is approximately one wavelength. It follows that the discrete ML antenna has N minima in the frequency response curve of the VSWR. In contrast to the discrete ML antenna, the modified ML has a VSWR with a wide-band frequency response: approximately 16% with N=7, which is more than 2.5 times as wide as that for a single-loop antenna (N=1). Further analysis reveals that the PL antenna has a VSWR bandwidth similar to that of the modified ML antenna. The maximum gain of the PL antenna is approximately 9 dB, which is very close to those of the discrete and modified ML antennas     

Synthesis method for broad-band tapered wire antennas and itsexperimental verification

A method for synthesizing the geometry of extremely broadband tapered wire antennas used as part of a broadband spectrometer for millimeter and submillimeter waves is presented. The antenna is designed to have a nearly constant gain and a low voltage standing-wave ratio (VSWR) over a bandwidth of at least 20:1. After the synthesis, the characteristics of the antenna are analyzed by the moment method using a system of reaction integrals as described by Richmond (1974). An antenna version with resistively loaded ends of the wires has a mean gain of 5.7 dBi and a maximum gain variation of ±1.25 dB. The VSWR is equal to 1.7 over almost the entire frequency range peaking only to 2.6 at the lowest frequency. These theoretical results were verified by measurements in the frequency range from 1 to 18 GHz with a scaled model of the tapered wire antenna     

Bandwidth enhancement of the monopole antenna by using a parasitic normal-mode helix

An innovative monopole antenna coupled with a parasitic normal-mode helix has been designed and studied both experimentally and theoretically. The effects of various dimensions of the monopole and the parasitic helix were investigated extensively. This simple combination can significantly enhance the antenna bandwidth over that of the conventional monopole antenna. It is found that, with suitably chosen antenna dimensions, the VSWR bandwidth (VSWR ≤ 2) of the antenna can be increased to 36%, almost double that of the monopole antenna alone. The far-field pattern of the combined antenna is basically the same as that of the monopole antenna. This antenna is designed to operate at 1.8GHz. The substantially enhanced bandwidth of this simple and small antenna is a useful feature for future mobile communications.     

Monopulse printed circuit dipole array

The design and performance of a monopulse Ku-band planar array is described. The antenna is designed to provide 20 dB sidelobes sum pattern in the azimuth plane and an operating bandwidth of 1 GHz (16.25-17.25 GHz). The voltage standing-wave ratio (VSWR) of this array at the input is less than 2:1 over the bandwidth.     

矩形微带天线的带宽和宽频带技术

本文从空腔模型理论出发,导出了矩形微带天线方向图带宽和阻抗带宽的一组计算公式和曲线,并用实验结果作了验证。归纳和讨论了展宽频带的三条途径和潜力,并提出了简便易行的用枝节匹配与增厚基片相结合的展宽频带技术。已用厚0.05波长的实验单元进行了双枝节匹配,达到了13％的带宽(驻波比不大于2)。     

Mesh antennas for dual polarization

Three mesh antennas, all having an extremely small antenna height of approximately 0.06 wavelength above a ground plane, are presented. First, a mesh antenna excited with a balanced feed is analyzed. It is revealed that the mesh antenna radiates a linearly polarized wave with no cross-polarization component in the principal planes. The radiation mechanism is explained using the current distribution. Second, a mesh antenna excited with an unbalanced feed is analyzed. This antenna shows almost the same radiation characteristics as the mesh antenna with a balanced feed. The frequency bandwidth for a VSWR=2 criterion is evaluated to be approximately 3%. Third, a mesh antenna having two perturbation elements is analyzed. It is found that the antenna acts as a radiation element of circular polarization. The frequency bandwidth for a 3-dB axial ratio criterion is calculated to be approximately 1%. The mesh antennas in the first and second analyses can be used as dual linear polarization elements by appropriately switching the feed. Similarly, the mesh antenna in the third analysis can be used as a dual circular polarization element by switching the feed     

Broadband tapered microstrip leaky-wave antenna

This study proposes a novel scheme based on the characteristics of leaky-wave antennas for the empirical design of broadband tapered microstrip leaky-wave antennas. This scheme can explain and approximately model the radiation characteristics of a linearly tapered leaky-wave microstrip antenna. A broadband feeding structure that uses the balanced and the inverted balanced microstrip lines to form a pair of broadband baluns is also presented. The measured return loss of the inverted balanced microstrip lines has a VSWR/spl les/2 from dc to 18.6 GHz and that of the back-to-back feeding structures has a VSWR/spl les/2 from 2.2 to 18.6 GHz. This feeding structure can be used to feed a broadband planar leaky-wave antenna with a fixed mainbeam that uses the tapered microstrip structure. The measured bandwidth of the antenna for a VSWR/spl les/2 exceeds 2.3:1.     

Wide-band sleeve-cage and sleeve-helical antennas

A sleeve-cage monopole has parasitic wire elements that form a sleeve around the driven cage antenna. Appropriate placement and dimensions of the wire parasites lead to bandwidth enhancement. Genetic algorithms and an integral equation solver are employed to determine the position and lengths of the parasitic wires in order to minimize voltage standing wave ratio (VSWR) over a band. The cage is replaced by a normal-mode quadrifilar helix for height reduction and the resulting structure is referred to as a sleeve helix. Measured VSWR and input impedance data are in good agreement with computed data. A fabricated sleeve-cage monopole has a bandwidth ratio of 4.4:1 and a sleeve helix has a bandwidth ratio of 3.5:1 for measured VSWR less than 3.5.     

Bandwidth enhancement of a microstrip-line-fed printed wide-slotantenna

Printed wide-slot antennas fed by a microstrip line with a fork-like tuning stub for bandwidth enhancement are proposed and experimentally investigated. Both the impedance and radiation characteristics of this antenna are studied. Experimental results indicate that a 1:1.5 VSWR bandwidth of 1 GHz is achieved at operating frequencies around 2 GHz, which is nearly ten times that of a conventional microstrip-line-fed printed wide-slot antenna. It also achieved a 2-dB gain bandwidth of at least 0.5 GHz     

Dual polarized stacked SSFIP array antenna in C-band for beam-pointing

This paper presents the design and development of a wideband dual polarized planar array antenna of 4 × 6 elements in C-band with a centre frequency of 5.3?GHz. The radiating element is of stacked strip slot foam inverted patch (SSFIP) configuration. The complex excitation coefficients of the antenna have been chosen in order to achieve a fixed beam-pointing by 10° and side-lobe level better than ?15?dB. The array antenna offers a VSWR bandwidth of 20% for a VSWR ratio of 2:1. The simulated and measured antenna parameters are presented.     

Tilted- and axial-beam formation by a single-arm rectangular spiralantenna with compact dielectric substrate and conducting plane

A single-arm rectangular spiral antenna is analyzed using the finite-difference time-domain method. The spiral is printed on a finite-size dielectric substrate backed by a finite-size conducting plane. Both the substrate and conducting planes are square with a side length L of less than 0.6λ₀ (λ₀: wavelength in free space). The radiation pattern is dependent on the outermost arm peripheral length C. The spiral whose peripheral length is within 2λ_gg (λ_g: the guided wavelength of the current) radiates a tilted beam of circular polarization. When the peripheral length is decreased to λ_gg, the spiral radiates an axial beam. The axial beam has a wide half-power beam width of approximately 102° (for L≈0.369λ₀) with a gain of approximately 6.7 dB. The axial beam shows a 15% frequency bandwidth for a 3 dB axial ratio criterion. Over this bandwidth, the voltage standing-wave ratio (VSWR) is less than two, as desired. The experimental results for the radiation pattern, gain, axial ratio, and VSWR are also presented     

Bandwidth and band-broadening of a rectangular microstrip antenna

Based on the cavity model theory, a set of simple formulas and graphs for calculating both the radiation pattern bandwidth and the impedance bandwidth of a rectangular microstrip antenna are presented with experimental verification. Three kinds of approaches to broaden the bandwidth and their potentiality are reviewed and discussed. A simple broadband technique by means of combination of stub-matching and increasing the antenna thickness is developed. An experimental element with the thickness of 0.05 wavelength is matched by using two stubs, while the input VSWR is measured to be less than 2:1 over a 13% bandwidth.     

Elliptical planar monopole antenna with extremely wide bandwidth

A planar monopole antenna with an extremely wide bandwidth is introduced, which is composed of an elliptical monopole patch and a trapeziform ground plane, both printed on the same side of a substrate, and is fed by a tapered CPW feeder in the middle of the ground plane. The simulated and experimental results demonstrate that this antenna achieves a ratio impedance bandwidth of 21.6:1 for VSWR/spl les/2, and exhibits a nearly omnidirectional radiation pattern, while its area is only about 0.19/spl lambda//sub l//spl times/0.16/spl lambda//sub l/ where /spl lambda//sub l/ is the wavelength of the lowest operating frequency.     

Broad-band single-patch circularly polarized microstrip antennawith dual capacitively coupled feeds

New design of a circular microstrip antenna with dual capacitively coupled feeds for broad-band circular polarization radiation is presented. The dual feeds are with a small top-loaded disk and are connected to a Wilkinson power divider with a 90° phase shift between its two output feedlines. The radiating circular patch, printed on a thin substrate, is supported by nonconducting posts on a conducting ground plane and is excited capacitively through the dual feeds. With a distance less than 10% times the center operating wavelength between the circular patch and the ground plane, the present proposed antenna can provide an impedance bandwidth (VSWR ⩽2) of about 49% and a 3-dB axial-ratio bandwidth of about 35%. The antenna gain bandwidth, defined to be within 1-dB gain variation in the axial-ratio bandwidth, is as large as 28%, with the antenna gain level at about 7.0 dBi     

Multiple meander strip monopole antenna

A novel multiple meander strip monopole antenna is presented. By iteratively meandering the vertical strip, compactness and broadband characteristics for the monopole antenna were achieved simultaneously. The designed monopole antenna with a radiation element volume of 14/spl times/14/spl times/14 mm/sup 3/ has the measured bandwidth ratio of 3.87:1, from 2.83 to 10.96 GHz for VSWR/spl les/2, with fairly frequency-insensitive omni-directional radiation characteristics.     

Single-feed circularly polarized microstrip ring antenna and arrays

An analysis is presented for a microstrip-feed proximity-coupled ring antenna and a four-element array. Interactions between the embedded microstrip feed and the radiating element(s) are rigorously included. Results demonstrate that circular polarization of both senses can be achieved with a ring antenna with proper design of two inner stubs located at angles of ±45° with respect to the feedline. Theory and experiment demonstrate an axial ratio 3-dB bandwidth of 1% and the voltage standing wave ratio (VSWR) <2 bandwidth of 6.1%. The axial ratio bandwidth is typical for a microstrip antenna with perturbations, while the VSWR bandwidth is larger than for the circular or rectangular patch with perturbations. A mutual coupling study between two elements shows that the axial ratio is less than 2 dB for interelement spacing greater than 0.55λ_eff, while the VSWR <2 for all spacings considered. A comparison between theory and experiment is provided for a 2×2 element array. The benefits of sequentially rotating the antenna elements in an array environment are presented. The axial ratio and VSWR bandwidths are both increased to 6.1% and 18% for a four-element array. A single-element antenna with two orthogonal feeds to provide both senses of polarization is demonstrated. The ring antenna is small (D/λ₀=0.325), the substrate thickness is thin (H/λ₀~0.035), and the microstrip feed produces a completely planar antenna system, which is compatible with microwave and millimeter integrated circuits (MICs), and monolithic microwave integrated circuits (MMICs)     

Realization of dual-frequency and wide-band VSWR performances usingnormal-model helical and inverted-F antennas

The effects of parasitic elements on the voltage standing wave ratios (VSWR's) of two antennas are investigated. First, a parasitic monopole is used for a normal-mode helical antenna. The VSWR investigation shows that dual-frequency operation is obtained by the parasitic element effects. The dual-frequency operation is revealed as a function of monopole position above a ground plane (monopole height). As the monopole height decreases, the separation of a higher resonance frequency f_H from a lower resonance frequency f_L increases. For a monopole length of L_MP≈0.4λ_HX , where λ_HX is the resonance wavelength of the helix, the frequency bandwidth for a VSWR=2 criterion is 12.5% in the lower frequency f_L region and 5.2% in the higher frequency f _H region, with a frequency separation ratio of f_H/f_L=2.14. Secondly, L-figured parasitic elements are used for an inverted-F antenna (IFA). The parasitic elements improve the VSWR performance. The frequency bandwidth for a VSWR=2 criterion is approximately two times as wide as that of the single IFA. It is also found that bending the horizontal sections of the IFA and parasitic elements contributes to reducing the antenna size while not significantly deteriorating the VSWR bandwidth. The radiation patterns are also presented and discussed     

An interdigitated printed antenna for PC card applications

A quarter-wavelength diversity patch configuration for the 2.4-GHz ISM band PC card application is reported. The structure is based on partly interdigitation of two quarter wavelength separated patches through a set of fingers for achieving the required space diversity on single side printed substrate with an easy matching on 50 Ω, high cross-polarization and within a given maximum space of 30 mm×50 mm. Measured antenna patterns for the developed structure are the same as for a classical patch and the bandwidth for a VSWR less than two is 2% with a maximum gain of 1.5 dB. This antenna has been incorporated in a high-speed wireless LAN PC card system     

Frequency independent microstrip stacked antenna

The advancement of technological development in the microstrip antenna and its applications in diverse areas, have given rise to the need for a frequency agile and frequency independent microstrip antenna which could be used for the same range of frequencies without altering the system. Requirements of such nature could be met by log periodic antenna. However, in the present endeavour a frequency independent microstrip stacked antenna consisting of nine elements operating in the S-band (2.000–4.000GHz) has been proposed. The developed antenna has been experimentally tested over an achievable band of frequencies from 3.200 to 3.920GHz. The antenna performance has characteristics like E-plane radiation patterns. The 3dB beamwidth, radiated power and VSWR show very similar behaviour for the different frequencies of operation obtainable in the S-band. The coaxial-fed microstrip stacked antenna provides an operational bandwidth of approximately 23%, i.e. 3.200GHz to 3.920GHz. The VSWR for the entire operational band is around 2 whereas the gain for the antenna is found to vary from 4.00 to 8.36dB. The 3dB beamwidth has been found to fluctuate between 16.8° and 23.5°. The designed antenna can be well suited for the practical broadband applications.     

Design and realization of GA-optimized wire monopole and matching network with 20:1 bandwidth

This paper presents the successful design and physical realization of broadband loaded wire monopoles with matching networks. The loads are parallel inductor/resistor circuits that are adjusted by means of genetic algorithm (GA) optimizers to maximize bandwidth, and the matching networks are transmission-line transformers. The micro-GA is shown to be more convenient and efficient for optimizing these loaded antenna systems than is the simple-GA. The measured voltage standing-wave ratio (VSWR) of the loaded antennas confirm broadband performance and agree with data obtained from moment method computations. Antennas having bandwidth ratios of 12.6 : 1 and 18 : 1, with measured VSWR less than 3.5 and calculated system gain greater than -4.5 dBi, are presented. Finally, an antenna system is given that has measured VSWR less than 3.0 and calculated system gain greater than -3.2 dBi over a 20 : 1 band.