A simple design substrate-integrated waveguide horn antenna with reduced back lobe

ABSTRACT

A simple technique to design stable gain and low back lobe substrate-integrated waveguide (SIW) horn antenna is proposed. Matching is achieved by placing a metallised via in a specific distance from the aperture of the horn. The proposed design method is based on the analytical equivalent circuit that derived for the impedance of the antenna aperture and the matching metallic via in SIW. The aperture impedance and metallic via in SIW are studied and design curves are extracted for a specified substrate. Also, to reach a directive pattern and reduce the back lobe of the antenna, some chokes are used on the aperture of the horn. The effect of chokes on some parameters such as power flow and radiation pattern, the front to back ratio (FBR), side lobe level (SLL) and increasing directivity of the antenna is reported. The measurement results confirm simulation, appropriately. The proposed structure has high compactness due to the matching technique and design. The proposed SIW horn has compact dimensions as 18.7 * 23.34*7.62 mm (0.93 * 1.16 * 0.37 λ₀) and the measured gain of the horn is about 5.5 dB at 15 GHz and bandwidth of six percent.     

Wide-band microstrip antenna with an H-shaped coupling aperture

Theoretical and experimental results of a wide-band planar antenna are presented. This antenna can achieve a wide bandwidth, low cross-polarization levels, and low backward radiation levels. For wide bandwidth and easy integration with active circuits, it uses aperture-coupled stacked square patches. The coupling aperture is an H-shaped aperture. Based on the finite-difference time-domain method, a parametric study of the input impedance of the antenna is presented, and effects of each parameter on the antenna impedance are illustrated. One antenna is also designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of 21.7%. The cross-polarization levels in both E and H planes are better than 23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results of S parameters and radiation patterns are presented and discussed     

Antenna-Pattern Measurement Using Spectrum Analyzer for Systems with Frequency Translation [Measurements Corner]

Pattern measurements using a network analyzer are typically based on measuring the transmission coefficient, S₂₁. When the transmitting and receiving frequencies are different, it is not possible to directly measure the antenna pattern using a network analyzer. In this paper, an antenna-pattern measurement system using a spectrum analyzer, designed to measure the radiation pattern of an antenna with a microwave sampling beamformer (MSBF) structure, is presented. A synthesized oscillator was used as the transmitter in the measurement setup. The instruments were controlled through GPIB by a program specifically designed for the system. High-quality pattern measurements were obtained for several antenna types. The measurement results were verified using HFSS simulations.     

Flush mounted rectangular cavity slot antennas--Theory and design

The loaded rectangular cavity slot antenna is analyzed using variational methods in conjunction with simplified equivalent circuit techniques to derive accurate design guides for efficiency, bandwidth, and resonant frequency. The aperture admittance is computed and the effects of a compound aperture plane iris and of material loading are analyzed. The aperture admittance of all such loaded cavity antennas is proportional tomu_{r},sqrt{mu_{r}/epsilon_{r}}, or1/epsilon_{r}, which characteristic lends to a common method of optimization of|T|^{2}(transmission cofficient). Experimental results include: 1) measurements of aperture field; 2) a comparison of theoretical and experimental value of bandwidth, efficiency, resonant frequency, and beam pattern for several experimental models; and 3) the measurement of the effect of applied dc magnetic field.     

一种基于超表面的方向图可重构天线

为了满足日益增长的对多功能天线的需求,提出了一种基于超表面覆层的低剖面可重构天线. 该天线由三部分组成:矩形蘑菇型超表面覆层,缝隙耦合天线和简单的直流偏置控制电路. 通过分别调整两组PIN开关的工作状态,使得天线辐射表面的电流被改变,进而实现辐射方向图的重构. 通过仿真计算和优化,最终确定了天线的最优结构. 实测结果表明:天线可以在四种不同的状态下工作,其xoz面方向图可以在±30°之间切换;四种工作状态的共享?10 dB阻抗带宽为4.2%. 所提出的天线具有低剖面、高增益、低成本、操作简便等特点.     

A distributed-feedback antenna oscillator

In this paper, a new design of the active transmitting antenna array, called the distributed-feedback antenna oscillator, is proposed. The active array is formed by serially connecting several unit cells to a closed loop. Each unit cell contains an amplifier and a two-port antenna, with an overall insertion gain larger than 0 dB and a phase delay equal to a multiple of 360°. The signal traveling on the loop is amplified and radiated in each unit cell. The radiation fields from all the antennas are then combined in free space. A four-element feedback antenna oscillator operating at 10 GHz is demonstrated by using two-port aperture-coupled microstrip antennas. Simulation results show that multiple oscillation modes with different frequencies and different radiation beams may be excited in the antenna oscillator. By experiment, it is found that each oscillation mode can be built by tuning the biases of the oscillator. The measured radiation pattern for each mode agrees very well with the predicted one. For a single-mode operation with a broadside pattern, bandstop filters of a simple geometry are designed and embedded in the oscillator to suppress the unwanted oscillation modes. Finally, the influence of the bias condition on the radiation power of the single-mode oscillator is investigated     

A radiometric antenna gain calibration method

A radiometric method is presented for measuring the power gain of a microwave antenna. It is particularly applicable to horns with gains in the range 20-45 dB, and an absolute uncertainty (3sigma) of less than 0.1 dB is achievable in favorable cases. An absorbing screen with a circular aperture is placed in the far-field of the test antenna. The diameter of the aperture is chosen to subtend an angle much smaller than the main lobe of the radiation pattern of the test antenna. Then two sheets of microwave absorber (one at ambient temperature and the other cooled to the boiling point of liquid nitrogen) are alternately placed first behind the screen aperture and then, for normalization, across the aperture of the test horn. The ratio of the antenna temperature differences measured with a sensitive microwave radiometer is proportional to the effective antenna solid angle, and thus its directivity. Corrections must be applied for near-field effects, diffraction at the screen aperture, partial resolution of the screen aperture by the main lobe of the test antenna pattern, and ohmic losses. A comparison of black disk measurements using a large conical horn at 86 GHz with theoretical calculations confirms the accuracy of this gain calibration technique.     

一种用于机载SAR的UHF波段超宽带天线

介绍了一种结构简单可用于机载SAR的UHF波段超宽带天线。该天线由两个加特殊反射板的偶板子及一个超宽带功分器组成，通过等效电路与HFSS仿真设计相结合的设计方法，使得该天线在52％的带宽内驻波比小于1．5，同时适当压缩天线的H面波束宽度，提高了天线的增益。     

Broadband printed circularly-polarised aperture antenna array for millimetre-wave gigabit applications

A simple and successful design of a printed aperture antenna array is presented in view of high-speed millimetre-wave wireless access applications. The antenna element design is based on a broadband travelling- wave aperture antenna for circularly-polarised radiation. For the antenna array design, the sequential rotation scheme is employed for improving the co-polarised gain and axial ratio. The presented antenna array is designed in the 40?48 GHz band and implemented with a 5mil-thick RT/Duroid-5880 PCB. Promising performances are achieved, including a return loss (,10 dB) bandwidth of 32%, an axial ratio (,3 dB) bandwidth of 25%, and a co-polarised gain (flatness , 3 dB) bandwidth of 32% with a maximum gain of 11dBic.     

一种加载超表面结构的宽带天线设计北大核心CSCD

文中通过加载超表面(Metasurface,MTS)的方式设计了一款超表面的宽带微带天线,将传统的矩形辐射贴片替换成超表面结构,提高了微带天线的电性能。天线通过共面波导的阶梯型孔径馈电。超表面印刷在介质板顶面,而介质板底面为共面波导馈电电路,从而增加了超表面与底层馈电孔径之间的耦合。超表面和阶梯型的孔径共同作用,使天线获得了较宽的阻抗带宽。文中设计的天线结构简单,外形紧凑。该天线的-10 dB相对阻抗带宽约为56.4%(7~12.5 GHz),覆盖整个X波段,主辐射方向偏离法向30°。实验测试结果与仿真结果吻合较好,为军事领域中的侦查和探测以及超宽带短距离室内定位中的天线设计提供了思路。     

Backscattering-Based Measurement of Reactive Antenna Input Impedance

A scattering technique for measuring reactive antenna input impedance is described. The antenna scattering is measured with three different loads: an open circuit, a conjugate match, and a reactive match. The load reactances tune the antenna into resonance at the measurement band. Theory and error considerations are presented, as well as measurement results of two ultra high frequency radio frequency identification antennas. The measurements were performed in a gigahertz transverse electromagnetic mode cell. The measured impedances are within about 10% of the simulated values for a dipole-like antenna. The results of a planar inverted-F antenna are somewhat more complex, but also supported by the presented simulations and the coaxial impedance measurement results.     

Antenna miniaturization and bandwidth enhancement using a reactive impedance substrate

The concept of a novel reactive impedance surface (RIS) as a substrate for planar antennas, that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna is introduced. Using the exact image formulation for the fields of elementary sources above impedance surfaces, it is shown that a purely reactive impedance plane with a specific surface reactance can minimize the interaction between the elementary source and its image in the RIS substrate. An RIS can be tuned anywhere between perfectly electric and magnetic conductor (PEC and PMC) surfaces offering a property to achieve the optimal bandwidth and miniaturization factor. It is demonstrated that RIS can provide performance superior to PMC when used as substrate for antennas. The RIS substrate is designed utilizing two-dimensional periodic printed metallic patches on a metal-backed high dielectric material. A simplified circuit model describing the physical phenomenon of the periodic surface is developed for simple analysis and design of the RIS substrate. Also a finite-difference time-domain (FDTD) full-wave analysis in conjunction with periodic boundary conditions and perfectly matched layer walls is applied to provide comprehensive study and analysis of complex antennas on such substrates. Examples of different planar antennas including dipole and patch antennas on RIS are considered, and their characteristics are compared with those obtained from the same antennas over PEC and PMC. The simulations compare very well with measured results obtained from a prototype /spl lambda//10 miniaturized patch antenna fabricated on an RIS substrate. This antenna shows measured relative bandwidth, gain, and radiation efficiency of BW=6.7, G=4.5 dBi, and e/sub r/=90, respectively, which constitutes the highest bandwidth, gain, and efficiency for such a small size thin planar antenna.     

Asymmetric dipole antenna suitable for active RFID tags

A novel and simple antenna, which is designed for active RFID tags at 2.45 GHz, is proposed. The antenna, consisting of a short rectangle dipole and a bent 'T' shape monopole, is suitable for direct integration with electronic components such as batteries without significant antenna performance degeneration. Simulation and measurement results show that the proposed antenna provides good gain, excellent bandwidth and omndirectional radiation pattern.     

Analysis of Aperture Field of Circular Groove Guide Horn Antenna by Using FD-TD Method

This paper presents an instance of using FD-TD method to analyze the aperture field of circular groove guide horn antenna. This process is one part of a hybrid method to solve the radiation field of aperture antenna. To verify the calculated aperture field the radiation pattern is computed from it and compared with the measured one. Good agreement is reached.     

Broad-band dual-frequency microstrip patch antenna with modified Sierpinski fractal geometry

A dual-frequency antenna based on the Sierpinski fractal with two parasitic patches to enhance the impedance bandwidth is presented. An electrical circuit model formed by RLC resonators is proposed to learn about the antenna physical behavior and to achieve the dual band operation minimizing a trial-and-error numerical/measurement proofs. The antenna has been designed using a method of moment commercial code and has been experimentally tested, obtaining two bands with a broad bandwidth and similar radiation patterns.     

Compact primary source for W-band reflector antenna

A double slot array antenna pasted on the aperture of a standard WR-10 waveguide is presented. Its compactness and airtightness make it suitable for serving as a primary source for reflector antennas. Compared to a standard WR-10 open-ended waveguide, it acts as a small FSS to provide up to 12 dB return loss enhancement within 9% bandwidth centred on 94 GHz, whereas radiation pattern and gain are similar. Good agreement is found between measured and predicted characteristics between 90 and 100 GHz. A return loss improvement is of particular interest while considering an antenna system with short focal length.     

Folded-type rectangular loop antenna with tunable circuit

A design for a small and tunable loop antenna is presented. This design enables the higher-order mode resonant frequency to become low while keeping the radiation pattern in good shape. The use of a tunable circuit to utilise higher-order mode for bandwidth enhancement has been investigated. The measured and simulated radiation patterns and voltage standing wave ratio are given.     

A Broadband Center-Fed Circular Patch-Ring Antenna With a Monopole Like Radiation Pattern

A center-fed circular microstrip patch antenna with a coupled annular ring is presented. This antenna has a low profile configuration with a monopole like radiation pattern. Compared to the center-fed circular patch antenna (CPA), the proposed antenna has a large bandwidth and similar radiation pattern. The proposed antenna is fabricated and tested. It resonates at 5.8 GHz, the corresponding impedance bandwidth and gain are 12.8% and 5.7 dBi, respectively. Very good agreement between the measurement and simulation for the return loss and radiation patterns is achieved.     

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)。