Loss-budget versus comprehensive analysis of gain loss for microwave reflector antennas

Microwave reflector antennas are often analyzed by utilizing a loss-budget technique in which the gain degradations due to various perturbations are individually analyzed and then added together to yield a total antenna gain loss. The comprehensive analysis technique described shows that the loss-budget technique may yield erroneous results since it fails to take into account the possible interrelations of the perturbations.     

Millimeter-wave range for the quick evaluation of large reflector antennas with complex feeds

An automated millimeter-wave antenna range capable of measuring primary-feed structure patterns and transferring this data to a mainframe computer for secondary pattern computation is described. Its applicability to the rapid evaluation of complex feed structures as used in a Cassegrain antenna is illustrated. An example of a reflector antenna analysis is compared to a measured pattern.     

Loss in gain and boresight crosspolarisation in reflector antennas with surface errors

Isolation and loss in gain measurements on reflector antennas with surface errors are revealed. An expression for the probability density of isolation is given in terms of the r.m.s. error. The cumulative distribution function is also discussed. The loss in gain distribution is discussed and related to crosspolar isolation.     

Coaxial feeds for high aperture efficiency and low spillover of paraboloidal reflector antennas

Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H11modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of100degto160deg. Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.     

Wideband folded shorted patch antenna with low profile

The design and measurement of a low-profile folded patch antenna with a short-circuited element are presented. By introducing dual-resonance, a significantly improved bandwidth of almost 30% for S ₁₁<-10 dB, which ranges from 1.48 to 1.99 GHz, is achieved, while the total profile of the proposed antenna is kept at a very low level of 0.046 lambda₀ only. The impedance matching, radiation patterns and gain curve are measured and illustrated. This antenna is easy to fabricate and its performance is less susceptible to manufacturing errors. Owing to its wideband and low-profile characteristics, it is highly suitable for applications in mobile communication systems, such as PCS, DECT and PHS     

Millimeter-wave indoor radio channel with artificial reflector

Experiments of 94-GHz millimeter-wave propagation were carried out in indoor channels, where the propagation path loss and multipath fading are investigated. The results show that the path-loss exponents in the line-of-sight (LOS) and obstructed (OBS) channel are 1.2-1.8 and 3.6-4.1, respectively. The received power of the OBS path is attenuated significantly as compared with that of the LOS path, thereby requiring an additional link-budget margin as well as battery power. In this paper, the use of an artificial reflector is also suggested under OBS conditions in order to avoid significant propagation loss, and then, a comparative study is conducted     

A novel horn radiator with high aperture efficiency and low cross-polarization and applications in arrays and multibeam reflector antennas

A step horn structure is presented that yields about 90% aperture efficiency with low cross-polar radiation. It is found that for obtaining high aperture efficiency, the horn aperture should consist of only the TE/sub z/ type of modes in appropriate amplitudes and phases. The desired TE/sub z/ modes are produced using multiple steps in the horn walls. The distances between the steps are critical to suppress the undesired TM/sub z/ modes. Radiation characteristics of high efficiency circular and square horns are presented and potential applications of such high efficiency horns are discussed.     

Crosspolarisation and gain reduction due to sand or dust on microwave reflector antennas

A model describing the effect of a sand/dust accretion on the aperture field and gain of a reflector antenna is checked experimentally and extended to predict enhanced crosspolarisation. The largest effects theoretically occur for accretion layers that are uniformly thick but only cover part of the reflector.     

Investigation of low profile, conformable, dielectric resonator antennas

An experimental investigation studied a cylindrical dielectric resonator antenna placed in a conducting well. Both the resonant frequency and input impedance increased as the wells became smaller, but the radiation patterns remained essentially unchanged. Resonators with smaller height-to-diameter ratios showed these effects to a lesser degree.     

基于超表面的低剖面高增益圆极化天线

提出了一种基于缝隙耦合超材料表面的低剖面圆极化高增益天线,该天线由一个超材料表面和一个微带缝隙天线紧贴着组成.通过改变超表面切角的大小来产生圆极化波,同时还可以提高天线增益和拓宽阻抗带宽.为了验证仿真结果,制作和测量了一个大小为1λ×1λ×0.067λ(在10 GHz处)的样本天线,仿真和测量结果显示出良好的一致性.结...     

Circularly-polarised four rhombic loop antennas with high gain and broad beam

A four rhombic loop antenna for circular polarisation is proposed. This antenna has a high gain of about 9.7 dBi and a broad beam of more than 130° half power beam width. Four parasitic loops are added inside the original four loops to increase the axis ratio bandwidth. A broadband balun is incorporated into the antenna for impedance matching. Details of the antenna design and experimental results are presented.     

Millimeter-wave and terahertz integrated circuit antennas

A comprehensive review of integrated circuit antennas suitable for millimeter and terahertz applications is presented. A great deal of research was done on integrated circuit antennas in the last decade, and many of the problems associated with electrically thick dielectric substrates, such as substrate modes and poor radiation patterns, have been understood and solved. Several antennas, such as the integrated horn antenna, the dielectric-filled parabola, the Fresnel plate antenna, the dual-slot antenna, and the log-periodic and spiral antennas on extended hemispherical lenses, which have resulted in excellent performance at millimeter-wave frequencies, are covered in detail. A review of the efficiency definitions used with planar antennas is included     

A small dipole-fed resonant reflector antenna with high efficiency, low cross polarization, and low sidelobes

The computer-aided optimization of a small five-wavelength diameter reflector antenna with a center-supported dipole-disk feed is described. The primary radiation is controlled by using a patented beamforming ring to give low cross polarization and low sidelobes due to spillover. The efficiency is maximized by controlling and taking advantage of the multiple reflections between the feed and the reflector. This has inspired the name "resonant reflector antenna." The gain from the feed reflector resonances is so large that it compensates almost completely for the about 1 dB loss due to center blockage of the aperture.     

Cylindrical and three-dimensional corner reflector antennas

Two reflector antennas are proposed. The first is constructed by adding a cylindrical reflecting surface of suitable radius to theV-shaped corner reflector antenna. The feeding element is a half-wavelength dipole. The resulting cylindrical corner reflector provided a 2 dB increase in gain, minimum sidelobe level, low input reactance, and uncritical dependence of performance on frequency. The second antenna is constructed by adding a cylindrical surface to the three-dimensional corner reflector. This extension provided an increase in gain of at least 6.5 dB, an input resistance compatible with the commercially available 50- or75-Omegacoaxial cables, low input reactance, and uncritical dependence of performance on frequency. A grid-type cylindrical corner reflector antenna, and a three-dimensional corner reflector antenna with a cylindrical subsurface of finite reflecting surfaces were designed, and the measured input impedances, gains, and field patterns showed excellent agreement with the theoretical results for both antennas.     

Dielectric waveguide filter with low profile and low-insertion loss

A novel type of dielectric waveguide filter has been developed for future mobile communications. The filter is characterized by planar input/output terminals as well as a practical low-profile structure. Fabricated filters, a three-pole with 2.5-mm height and a two-pole with 0.6-mm height, exhibit low-insertion losses of 0.8 and 1.3 dB, respectively, for the bandwidth of 200 MHz at 5.8-GHz center frequency     

Jacobi-Bessel analysis of reflector antennas with elliptical apertures

Although many reflector antennas possess circular projected apertures, there are recent satellite and ground antenna applications for which it is desirable to employ reflectors with elliptical apertures. Here a modification of the Jacobi-Bessel expansion is presented for the diffraction analysis of reflectors with elliptical apertures. A comparative study is also performed between this modified Jacobi-Bessel algorithm and the one which uses the Jacobi-Bessel expansion over a circumscribing circular region. Numerical results are presented for offset reflectors with elliptical and circular apertures and the improved convergence properties of the modified algorithm are highlighted.     

Gaussian beam optical systems with high gain or high loss media

Coherent electromagnetic wave amplifiers with non-negligible gain per wavelength are included in the Gaussian beam matrix formalism and a procedure is developed for propagating Gaussian beams in optical systems that may include unsaturated amplifiers and similar absorbers. Standard formulas for beam spotsize and radius of curvature in a uniform medium are generalized in a new way to include gain or loss. An asymmetric focal shift and a potentially infinite spotsize are predicted. These dramatic effects are interpreted physically     

Design and analysis of multiple-beam reflector antennas

Simplified design and analysis equations are presented for multiple-beam reflector antennas based on the Gaussian-beam analysis of the primary and secondary patterns. The derived equations are useful for the quick design and performance analysis in terms of the coverage-area directivity and the inter-beam isolation of multiple-beam antenna systems. Results of the analysis given in this paper agree well with rigorous computations based on physical-optics analysis of the reflector-antenna radiation patterns. Extension of the analysis to multiple-beam lens antennas, and to shaped/contoured-beam antennas, is also presented     

Millimeter-wave imaging using FET detectors integrated with printed circuit antennas

The application of field effect transistor (FET) detectors integrated with planar twin dipole microstrip antennas to millimeter-wave imaging has been demonstrated. Circuits were configured as practical heterodyne mixers, as elements in a 2×3 element planar focal plane array for imaging, and as receivers in frequency modulated (FM) radars for three-dimensional imaging, at 63 GHz. These experiments show that quasioptical circuits, using conventional present-day FETs and simple printed circuit construction, can be applied usefully in the millimeter-wave region.