The paper describes a new type of compact corrugated horn in which an unwanted higher order mode is cancelled at mid-band yielding a performance compatible with a conventional horn three times its length. Simple design equations are presented which enable a fast optimisation routine to be used in order to determine key parameters. Favourable comparison is made between measurements and predictions obtained using a well tried modal matching method.

We have described a novel method of improving the performance of a compact corrugated horn. The horn offers significant performance benefits at mid-band coupled with a band-edge performance at least as good as a standard profiled horn.

A simple and successful design for a variable beamwidth corner reflector antenna is presented. The gain and the -3dB beamwidth of the antenna are predicted using the finite difference time domain (FDTD) method The predicted results are compared with measured data and good agreement is reported.

A design study of the corner reflector antenna is reported, using the finite difference time domain (FDTD) method, which takes account of the finite size of the corner reflector plates. The influence of the geometric parameters on the radiation characteristic is established, and optimum design information is presented. The method has been validated by constructing and measuring an experimental antenna, which gives results in very good agreement with the predictions.

The gridded corner-reflector antenna consists of two lines of metal rods which meet at an angle to form a corner. It is fed by a dipole and is used in situations where a moderate gain is required from a simple antenna, particularly at UHF and low microwave frequencies. This paper uses FDTD to predict the radiation characteristics and shows how the spacing of the rods in the grid influences the gain and front-to-back ratio.

The finite difference time domain (FD-TD) method has been used to study the short backfire antenna which is a compact feed for reflector antennas. A parametric study of a short backfire antenna has been performed which, for the first time, enables an optimum design to be obtained. The computed results have been validated by constructing and measuring an experimental antenna which gave measured results in good agreement with the predictions

The corner reflector antenna consists of two flat conducting plates which meet at an angle to form a corner. It is fed by a dipole, and is used in situations where a moderate gain is required from a simple antenna, particularly at UHF and low microwave frequencies. An array of corner reflector antennas can be used as a base station antenna in mobile communication systems. The antenna was invented over fifty years ago but the number of publications has remained small and most design information relies on experimental studies. Theoretically modelling is difficult due to it being a few wavelengths in size. This paper shows that the finite-difference time-domain (FDTD) method is a good technique for studying the corner reflector antenna with finite length reflecting plates. The accuracy of the FDTD modelling has been verified by comparison with other numerical techniques and by experimental measurements. A parametric study is reported showing how the geometric parameters and the length of the reflecting plates influence the radiation characteristics

Absorbing boundary conditions (ABCs) are needed to surround an antenna and terminate the finite difference time domain spatial domain. The proximity effects of ABCs which are close to the antenna are investigated, and it is shown that specifying the physical distance between an antenna and the ABCs is preferable to specifying the number of cells. Distances of about 0.5λ have been shown to produce good radiation patterns at all observation angles, but larger distances are necessary for accurate prediction of antenna gain. The use of the Berenger perfectly matched layer (PML) allows the amount of free space surrounding a structure to be reduced but incurs a computational penalty depending on the thickness of the PML.

With the widespread availability of relatively powerful computing resources, accurate numerical modelling of electrically small (<5/spl lambda/) antennas has become a useful and viable option. Two of the more widely used methods are the finite difference time domain (FD-TD) method and the method of moments. This paper compares these two methods, specifically comparing the results obtained from the methods for typical cases, highlighting the aspects of the methods which need to be treated with care to obtain accurate results, and comparing the numerical efficiencies.

Two alternative methods of numerical analysis for electrically small antennas (finite difference time domain and method of moments) have been compared for representative problems. It has been found that both are capable of producing accurate predictions of the far field pattern, although it has been found that in some cases the method of moments predictions are sensitive to the way in which the conducting surfaces are gridded. In terms of numerical efficiency, it has been found that whilst the method of moments may require lesser processing times for electrically small antennas, FD-TD analysis becomes increasingly efficient by comparison as the antenna size increases.

The backfire antenna is a compact antenna with good radiation pattern characteristics. The performance compares favourably with horns but the structure of the antenna is much shorter. Applications are as a feed for a reflector or as a single antenna for mobile communications or as an array element. The backfire antenna operates in a resonant mode. This means that no simple theories to predict performance are available and most design data has been obtained from experimental models. The paper reports a study of the short backfire antenna using the finite difference time domain (FD-TD) technique. FD-TD is a powerful computational technique which has enabled a parametric study of the geometry of the antenna to be undertaken. The theory has been verified by an experimental model

The growth of remote sensing by an airborne platform and the use of satellite communication from elliptical orbits indicate the need for a reflector antenna where the beamwidth of the main radiation pattern can be varied dynamically. The requirement is to make the radiated beam spot diameter independent of the antenna platform height and the scan angle. There are various other applications at microwave and millimetre wavelengths where a uniform footprint or precise changes in the beam spot diameter are required, for example, metrology from satellites, fire control radars and military communications. This paper describes a variable beamwidth dual reflector antenna which fulfils their specification. Parametric studies and an experimental verification of the concept are performed.

Antennas are an essential part of every radio system and they have been in use for more than 100 years. The continual growth of radio has steadily increased the types of antennas in use. Hertz used reflector antennas and loops in his classic experiments in the 1880s. Other pioneers, such as Lodge, developed early examples of microwave horns and lenses. The simple monopole wire antenna was crucial to the success of Marconi's first experiments. The indispensable nature of the antenna was recognised even in the early days. This paper surveys the general trends in antenna design over the 100 years of radio. It concentrates on describing early antennas, antennas for mobile communications, antennas for microwave communications and a short review of the methods of antenna design and validation.

The beamwidth of a reflector antenna may be varied by defocusing the feed. The radiation characteristics are studied for both axisymmetric and offset single reflector antennas using both geometric optics for understanding the operation and physical optics for a parametric study. The beamwidth may be increased by over 200% compared to the focused reflector before the main beam bifurcates, but the on-axis gain is reduced. Better performance is obtained with an offset reflector antenna. The study quantifies the limits of beam broadening which can be achieved. Measurements on a 30 GHz experimental antenna show good agreement with theory.

A dielectric lens is integrated into a dielectric loaded horn antenna to produce a high efficiency feed for reflectors. The lens is designed using simple ray theory and analysed using modal matching techniques. Aperture efficiencies of up to 78% are achieved while retaining good crosspolar performance.

The dielectric cone loaded horn consists of a central cone of solid or foam dielectric supported by a second dielectric with a metallised outer layer. The horn has low cross-polarisation over a wide bandwidth and the absence of flanges means better utilisation of the aperture area. The dielectric gives an additional method of controlling the fields in the horn. The authors investigates dielectric loaded horns with a shaped profile. They show that the profiled dielectric horn gives useful control over the performance of the horn. It can be designed in two distinct ways. Either the length of the horn can be kept the same as a linear tapered horn which will give improved electrical performance, or the length (and weight) of the horn can be reduced by comparison with the linear horn, whilst maintaining similar low levels of cross-polarisation

The conical corrugated horn has become the prime choice for use as a feed for high performance reflector antennas in communications, radar and remote sensing systems. This is partly because the radiation characteristics are ideal with good copolar pattern symmetry and low levels of cross polarisation. It is also because corrugated horns can be designed, using a computer, with a high degree of reliability. The paper describes the computer aided design of corrugated horns and discusses the methods used to design horns in terms of their accuracy, reliability and ease of use. The methods of validation are considered and the present position of the CAD of corrugated horns examined