Optimization of microstrip feed geometry for prime focus reflectorantennas

The radiation characteristics of a circular microstrip antenna are studied numerically. Surface integral equations are used to formulate the problem from the boundary conditions and moment methods are used to reduce the integral equations to a matrix equation. An analytic method is used to design a microstrip feed and to achieve symmetric radiation patterns with low cross polarization and backlobe levels. The backlobe level is reduced by adding a quarter-wavelength choke to the side wall or the ground plane of the antenna and the bandwidth is improved by stacking two layers. The performance of the feed with the reflector antenna is also considered. One of the feeds was fabricated and tested. Satisfactory agreement between the computed results and the measurement data was obtained. The microstrip feed has a very small size which should reduce its blockage of the reflector aperture     

An annular-ring microstrip antenna fed by a co-planar feed circuitfor mobile satellite communication use

A new configuration of circularly polarized annular-ring microstrip antenna (ARMSA) fed by a branch-line hybrid coupler placed at the inner part of the ARMSA and its design method using an equivalent circuit are presented. Since the ARMSA has a narrow bandwidth and high-input impedance, a parasitic element placed above the ARMSA is employed for not only obtaining a broadband characteristic, but decreasing the input impedance down to 50 Ω. A hybrid coupler to generate circular polarization, therefore, can be connected to the co-planar space of the ARMSA directly without a large-size matching circuit and a very low profile and simple structure can be achieved. The ARMSA is excited at the TM₂₁ mode to produce a conical pattern, which has a high gain in a low-elevation angle for mobile satellite communications. An effective design method using the equivalent circuit is indicated and, as a result, it is obvious that a broadband characteristic is obtained when each resonant frequency of the ARMSA and parasitic element is identical. Experimental results in the L-band showed satisfactory characteristics for vehicle antennas     

Cavity backed microstrip patch array feed for multiple beamapplications

Multiple beam antennas use reflectors with several feeds at offset locations in the focal plane. The complete feed array tends to be bulky and heavy, hence, to alleviate this, microstrip patch arrays have been used as feed elements. However, a power division circuit becomes necessary for the patches which increases losses. A patch array backed by a cylindrical cavity is proposed which eliminates this lossy circuit. An additional feature is that the beamwidths in various planes may be controlled to a certain extent by varying the interelement spacing. The test results of the proposed feed are presented and discussed; the feed seems suitable for use in multiple-beam applications     

A statistical model for a land mobile satellite link

A statistical model for a land mobile satellite link is described. The model assumes that the amplitude of the line-of-sight component under foliage attenuation (shadowing) is lognormally distributed and the received multipath interference has a Rayleigh distribution. Expressions for the level crossing rate and average fade duration are given. Comparison between results calculated from the model and from measurements show reasonably good agreement. The model should be useful for designing communications systems and for simulating propagation effects in the laboratory.     

A frequency scanning satellite system for land mobile communications

A frequency scanning system for mobile applications has been assessed for a European mission at L-band. Feasibility evaluations, electrical design and analysis have been performed for both the antenna and the entire repeater. Efforts have also been made to solve accommodation, thermal and mechanical problems, so as to demonstrate the actual feasibility of the frequency scanning concept in user-oriented applications. The very promising results obtained are presented in this paper.     

A study of microstrip array antennas with the feed network

The radiation and losses in microstrip antennas with a corporate feed network are studied. A surface current approach is applied in which the electrical currents in the feed lines are modeled as in ideal transmission lines. The free-space radiation and the surface-wave excitation of typical segments in printed feed networks are studied. A four-element array antenna with its printed feed network is analyzed and predicted radiation patterns, directivity, and gain are presented and compared with experimental results. The gain and directivity of large arrays of 16, 64, 256 and 1024 elements are calculated and measurements in the frequency range of 10 to 35 GHz are reported     

Reed-Solomon codes for land mobile satellite channels

The performance of Reed-Solomon codes is determined for land mobile satellite communications where a shadowed Rician channel model is used. An effective coding/interleaving scheme is proposed which uses the multipath fading and shadowing statistics of the channel.<>     

Analysis of a microstrip array and feed network

An analysis technique for a microstrip array is presented. The array elements and mutual coupling between elements are analyzed by a method of moments (MM) solution of the exact integral equation. The combination of the microstrip array elements, plus the microstrip transmission line feed network is analyzed using a generalized Thévenin theorem. The method is applied to the specific problem of the series fed microstrip array.     

Circularly polarised microstrip antenna array using proximitycoupled feed

A 2×2 circularly polarised (CP) microstrip antenna array using a proximity coupled feed and sequential rotation is described. As compared with a previously presented single-element circularly polarised microstrip antenna with a cross-slot, the new array achieves a much wider impedance bandwidth of 11.18% and has an axial ratio bandwidth of 4.1%. The return loss, radiation patterns and axial ratio of the antenna array were measured and are presented     

卫星移动通信中的电扫描阵列天线

90年代以来，卫星移动通信发展异常迅速。许多科研组织都对移动地面站中的电扫描阵列天线进行了研究。介绍了目前已经开发并应用于卫星移动通信的几种电扫描阵列天线及其技术细节。     

Microstrip Yagi array antenna for mobile satellite vehicleapplication

A novel antenna structure formed by combining the Yagi-Uda array concept and the microstrip radiator technique is discussed. This antenna, called the microstrip Yagi array, has been developed for the mobile satellite (MSAT) system as a low-profile, low-cost, and mechanically steered medium-gain land-vehicle antenna. With the antenna's active patches (driven elements) and parasitic patches (reflector and director elements) located on the same horizontal plane, the main beam of the array can be tilted, by the effect of mutual coupling, in the elevation direction providing optimal coverage for users in the continental United States. Because the parasitic patches are not connected to any of the lossy RF power distributing circuit the antenna is an efficient radiating system. With the complete monopulse beamforming and power distributing circuits etched on a single thin stripline board underneath the microstrip Yagi array, the overall L -band antenna system has achieved a very low profile for vehicle rooftop mounting, as well as a low manufacturing cost. Experimental results demonstrate the performance of this antenna     

Efficient estimators for the land mobile satellite channel

A novel class of adpative Kalman channel estimators (AKCEs) for low-data-rate signalling via the land mobile satellite (LMS) channel is presented in this paper. The proposed technique is based on a scheme known as the ‘parallel processing algorithm’ and assumes a discrete Gauss–Markov extension of the LMS channel model. Three different approaches compared against the non-adaptive filter show an improved estimation error variance under various environmental conditions. Trading off computational complexity and performance, the derived maximum a posteriori (MAP) approach has been found to be best applicable. © 1998 John Wiley & Sons, Ltd.     

A comparison of data modulation techniques for land mobile satellite channels

Several modulation schemes for transmitting data over land mobile satellite channels are compared using a Monte Carlo simulation. Schemes under consideration include differentially detected minimum shift keying (DMSK), differentially detected filtered offset quadrature phase shift keying (DOQPSK), and coherently detected binary phase shift keying with transparent tone-in-band processing (BPSK-TTIB). The transmission of data to and from a mobile radio, which is also capable of operating as an amplitude companded single sideband radio, is the application considered here. The nominal bit rate is 2400 bit/s, while the nominal channel spacing is 5 kHz. DOQPSK with nonredundant single-error correction (SEC) is shown to be a promising candidate. It is capable of outperforming DMSK with SEC by more than 1 dB. Techniques that send a reference signal along with a PSK signal and then perform coherent detection, such as BPSK-TTIB, are also shown to be inferior to DOQPSK with SEC for the class of channels considered here.     

New simple feed network for an array module of four microstrip elements

A simple microstripline feed network for an array module comprising four microstrip elements is described. The advantages and disadvantages of the network are discussed as well as a theoretical explanation for the radiation characteristics of array modules using the network.     

一种天线馈源用宽带孔径耦合层叠微带贴片阵的设计

介绍了一种宽带孔径耦合层叠微带辐射单元的工作原理,着重分析了该辐射单元主要结构尺寸对其阻抗带宽的影响。该辐射单元阻抗带宽（VSWR≤2：1）在S波段达到了30％以上。作为某抛物反射面天线的馈源,由4个该辐射单元组成四单元微带贴片天线阵后,其性能满足天线系统要求。     

A C/I advantageous satellite system configuration for land mobile applications

A satellite system based on the frequency scanning concept has been recently assessed for L‐band land mobile communications. The study – promototed by ESA/ESTEC for an European application mission – has reached an advanced electrical design phase. The selected configuration is particularly advantageous in terms of Carrier‐to‐Intermodulation ratio (C/I) performance, which constitutes a requirement of key‐importance in the envisaged user applications. The advantage in C/I is due to the proper choice of the on‐board transmitter configuration, which adopts power module pairs where the overall power demand is evenly distributed. The consequent improved C/I is then achievable at both transmitter and radiated far field level. The present paper aims a contribution to the design methodology of frequency scanning satellite systems, by joining two key‐aspects: in fact an analytical approach is proposed to demonstrate the C/I advantage achievable through frequency scanning satellite systems and the methodology is applied to a concrete example, the ESA/ESTEC system, whose feasibility has been fully proved in previous studies. The analysis is performed both at transmitter level and in the far field. The main results achieved are hereinafter presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ionospheric effects on satellite land mobile systems

Satellite-ground radio systems are now so sensitive that ionospheric changes can disrupt their performance. This paper discusses some satellite-to-ground propagation problems in the UHF and L bands caused by the Earth's ionosphere. Such problems include signal time delay, signal dispersion, Faraday rotation, and scintillation.     

一种 K 频段宽带双极化滤波喇叭天线设计

提出了一种新型结构Ku波段矩形滤波波导缝隙阵列天线的设计方法,该阵列天线的滤波特性由嵌入在矩形波导中的“之”形金属杆实现. 通过分析“之”形矩形波导滤波结构的等效电路和带阻滤波特性,设计了一个滤波波导缝隙阵列天线. 实测结果表明,该滤波波导缝隙阵列天线–15 dB阻抗带宽约为6.8%（12.06～12.91 GHz）,覆盖Ku波段卫星通信的下行频段（12.25～12.75 GHz）,带内增益为13.5～14.4 dBi,交叉极化电平低于–38 dB,且在Ku波段卫星通信的上行频段（14.0～14.5 GHz）具有超过29.8 dB的带外抑制.     

UHF频段陆地卫星移动通信业务多径效应测量

UHF测段陆地卫星移动业务多径实验于1999年6月至8月间利用日本GMS140E气象卫星为信标,分别在河南郑州至开封高速公路、林州至上党方向公路以及石家庄至阳泉高速公路段进行。地面接收系统和数据处理设备安置于汽车上。此项实验的目的是为地面卫星移动通信系统的设计提供重要的信道参数。本文给出了不同环境下多径效应的累计分布特性以及相应的预测模型。