Leaky NRD guide fed microwave planar antenna

A novel and unique application of leaky waveguides as feeding systems for microwave planar antennas is presented. A new leaky nonradiative dielectric (NRD) guide based on a grating structure is proposed, and a planar array slot antenna using this leaky waveguide is constructed and measured at 23 GHz.<>     

Leaky wave antenna based on image NRD guide with staircase-shapeddielectric slab

A leaky wave antenna based on the use of an asymmetric image nonradiative dielectric (NRD) guide has been studied experimentally. By using a staircase-shaped image NRD guide, the gain bandwidth of the antenna becomes three times that of a leaky wave antenna using an ordinary image NRD guide. Moreover, this antenna employs a flared horn in the NRD guide which makes the H-plane beamwidth controllable     

用区域分解法分析基于NRD波导结构的漏波天线

提出了利用区域分解结合频域有限差分法,分析基于NRD波导结构的漏波天线。用区域分解法将原问题分解为若干子问题,大大缩小稀疏矩阵的规模,从而使得求解大尺寸问题成为可能。文中首先介绍了区域分解法在分析三维电磁问题中的实现,并计算了典型结构金属块的散射问题,用于验证算法的正确性;最后分析了一种基于NRD波导结构的漏波天线,并与实验值进行了比较,说明了方法的有效性。同时还给出了一种能够有效改善该天线性能的改进型漏波天线结构的分析结果。     

The sun as a test source for boresight calibration of microwave antennas

Although the diameter of the sun at microwavelengths is a little over half a degree, the sun can be used for establishing, say between 3 and 30 cm, the pointing corrections (boresight calibration) of microwave antennas, with high precision. There is, however, a discrepancy between the position of the microwave sun on any given day and the position of the center of the solar disc as tabulated in [16]. Over the period 1966-1969 this discrepancy had an rms value of 1.6' east-west and 1.2' north-south and a range of 11.4' east-west and 9.2' north-south. These conclusions are based on sun maps, made at 9.1 cm with an antenna having a beamwidth of approximately 3', which are published regularly. From such a map the microwave centroid can be determined with an error less than 1'. In the absence of such a map, the centroid can be estimated to within 2' or slightly better by taking account of optical data such as sunspots or plages. The correction on any one day is strongly correlated with that of the day before, but the correlation is small after about 5 days. The correlation returns in part after 27 days.     

A new leaky NRD guide based on a grating structure

Analysis and experiment of a new leaky nrd guide based on a grating structure is described. Analysis employs a mode coupling procedure which yields highly accurate results while presenting the advantage of simplicity and ease of manipulation. Numerical values for the phase and leakage constants are presented and the role of each grating parameter is assessed. Theoretical results are compared with experimental data for different geometric and constitutive parameters and reasonable agreement between them is obtained.     

A Systematic Investigation on Leaky Characteristics for NRD Guide with Arbitrary Profile of Cross-Section

The leaky characteristics of the NRD guide with arbitarary profile of cross section are systematically studied by a method which combines staircase approximation with multimode network theory and mode-matching procedure. Emphasis is laid on the investigation of the effect of the different profile dimensions on the leakage characteristics of the NRD guide. Extensive numerical results are given to establish useful guidelines for the design of some new types of NRD guide leaky wave antennas.     

Investigation of planar antennas for submillimeter receivers

A frequency-scaled model of a tapered slot antenna has been investigated. The antenna consists of a dielectric substrate which serves as a carrier for a tapered slotline. The width and the shape of the slotline and the dimensions of the substrate (including the value of the permittivity) have been varied to investigate the radiation patterns. The result is a planar antenna with a symmetrical beam in the E and H planes and a beam efficiency of almost 50%. The substrate thickness is the most important limiting factor for scaling the model to submillimeter frequencies. Taking away parts of the dielectric substrate in the front area of the antenna allows a relatively large substrate thickness. The variations of the half-power beam width versus slot parameters, versus the dielectric thickness of the substrate, and versus the length and the width of the substate are presented. In addition the beam efficiency has been measured for various frequencies, and the radiation pattern has been calculated for comparison     

A new planar feed for slot spiral antennas

A new planar, wideband feed for a slot spiral antenna is presented and tested at VHF frequencies. Radiation pattern measurements are presented to demonstrate the performance and usefulness of this feed. In contrast to most traditional printed spiral antenna designs, the one presented here incorporates a completely planar balun and feed, making it more attractive for conformal applications     

Virtual array synthesis method for planar array antennas

A new array antenna synthesis method, which we call the virtual array synthesis method, is presented. In this method, the excitation values of a virtual array are synthesized using some known synthesis method. The geometry of the virtual array can be chosen so that there will be a suitable synthesis method for that geometry and the synthesis of the virtual array can be done accurately enough. In the synthesis method presented, the excitation values of the virtual array are transformed into the excitation values of the actual array geometry. Matrix operations are simple and large arrays can be easily synthesized     

A new technique for planar array antennas synthesis

A novel technique, conceived and baptized the immunity tactic will be presented in this paper. As one will see, we classify the technique under the stochastic processes while governed by deterministic rules. This technique was greatly inspired by the immune activity, which has the tendency to eliminate the strange bodies and to preserve the self-organism. The analogy with the synthesis will be as follows:

• Elimination of all the weak solutions.

• Preservation of the best solution.

Some biologic immunity operators will be borrowed and adapted to our technique, which remain governed by deterministic rules to avoid any destabilization.     

Modified T-shaped planar monopole antennas for multiband operation

In this paper, we propose a novel modified T-shaped planar monopole antenna in that two asymmetric horizontal strips are used as additional resonators to produce the lower and upper resonant modes. As a result, a dual-band antenna for covering 2.4- and 5-GHz wireless local area network (WLAN) bands is implemented. In order to expand the lower band, a multiband antenna for covering the digital communications systems, personal communications systems, Universal Mobile Telecommunications Systems, and 2.4/5-GHz WLAN bands is also developed. Prototypes of the multiband antenna have been successfully implemented. Good omnidirectional radiation in the desired frequency bands has been achieved. The proposed multiband antenna with relatively low profile is very suitable for multiband mobile communication systems.     

一种多波束面阵天线的分析与设计

介绍了二维多波束天线的特点和实现二维多波束的几种方法，针对空馈的Rotman透镜推导出了由它馈电的平面天线阵的相位计算公式及设计方法，在此基础上成功地实现了空馈透镜的平面天线阵样机，并给出了相应的测试结果。     

Plane-wave characterization of antennas close to a planar interface

The plane-wave scattering matrix is used to characterize antennas that are located just above a planar interface that separates two media. The plane-wave transmitting spectrum for the field radiated downward into the lower medium is expressed directly in terms of the current distribution of the transmitting antenna. The transmitting spectrum for a reciprocal antenna determines the plane-wave receiving spectrum for the field that propagates upward in the lower medium. A measurement procedure is discussed for determining the plane-wave transmitting and receiving spectra from measurements with a probe that is located in the lower medium.     

Bird-proof feed-horn windows for microwave radio system antennas

Window units constructed from multiple dielectric plates offer means for combating bird damage to antenna feed horns on microwave radio systems. The need for such devices on Australian systems is increasing as routes are extended into the drier regions of the country. Measurements show that the antenna electrical characteristics are not appreciably altered by the new window units.     

A New Leaky Waveguide for Millimeter Waves Using Nonradiative Dielectric (NRD) Waveguide-Part I: Accurate Theory

An almost-rigorous analysis is presented for a new leaky waveguide of simple configuration based on a recent nonradiative modification of H guide suitable for millimeter wavelengths, The analysis employs a transverse equivalent network that yields a dispersion relation in closed form, and contains some interesting and subtle features. Numerical values are presented for the phase and leakage constants in terms of the different geometric parameters and the dielectric constant comparisons with measurements are made in the companion paper, part II.     

Triple band planar inverted F antennas for handheld devices

Two novel triple band planar inverted F antennas (PIFAs) are presented. The first antenna is realised by housing a dual frequency L-shaped spur line loaded PIFA element within the lower resonance PIFA element. The second antenna is realised by embedding two single element PIFAs within a quarter-wave patch. For both antennas, an isolation of better than -15 dB between the feed ports and a good agreement between simulation and measurement results was obtained     

Command preprocessor for radio telescopes and microwave antennas

The LQG (linear-quadratic-Gaussian) controllers, designed for the NASA Deep Space Network antennas, have small tracking errors and are resistant to wind disturbances. However, they induce limit cycling during antenna-slewing operations and target acquisition. The cycling is caused by the violation of the antenna's rate and acceleration limits. This problem can be avoided by introduction of a command that does not exceed the limits. The command preprocessor, presented, generates a command that is equal to the original command if the latter does not exceed the limits, and that varies with the maximum (or minimum) allowable rate and acceleration if the limits are met or exceeded. The preprocessor is comparatively simple, since it requires knowledge of the command at only the current and the previous instants of time, while the other known preprocessor requires knowledge of the terminal state and the acquisition time. Analysis and field tests of the preprocessor are presented. The dynamics of the preprocessor itself, and of the antenna with the preprocessor, are illustrated with the antenna's measured responses to typical commands     

A New Leaky Waveguide for Millimeter Waves Using Nonradiative Dielectric (NRD) Waveguide-Part II: Comparison with Experiments

Accurate measurements were taken of the leakage constant of a leaky-wave structure based on nonradiative dielectric (NRD) waveguide in order to verify the theory derived in the companion paper, part I. Although the structure is intended for millimeter-wave use, measurements were made on a model scaled to X band (lambda = 3 cm) to improve the accuracy of the experimental results. The measurements were taken by probing the electric near field strength along the longitudinal direction. Comparisons with accurate theoretical data are presented for different frequencies and geometrical parameters, and very good agreement is found between the measurements and the theory.     

Trapped image guide leaky-wave antennas for millimeter wave applications

A leaky-wave antenna is developed from a novel dielectric waveguide for millimeter wave applications. Design formulas and data are provided, and measured and computed results are presented for a prototype model.