Takashi Katagi

Resonant frequency and radiation efficiency of meander line antennas

One of the approaches to reducing the size of half-wavelength linear dipole antennas is the meander dipole antenna, where the elements form a meander line. This paper presents a formula for the relationship between the geometrical size and the resonant frequency of the meander line dipole antenna, and a calculation formula for the radiative efficiency is derived from the result. It is shown that the geometrical parameters of the meander line dipole antenna can be determined from the specified radiative efficiency.

A compact broad-band helical antenna with two-wire helix

A new method of increasing the bandwidth of normal-mode helical antennas (NMHA) is proposed. The antenna has length of around 0.1 of the target wavelength, and consists of a helix constructed with two flat wire strips. The method exploits the two current modes of the two-wire design to obtain wideband response. Based on an analysis of the equivalent circuits of the two modes and subsequent optimization of design parameters, a final two-strip NMHA design is proposed that is demonstrated to have a bandwidth of 12% in the 760-MHz band at a voltage standing wave ratio of less than 2.

Radial line planar monopulse antenna

In recent years, mobile satellite communications have been growing rapidly. Monopulse tracking operations for beam pointing to the satellite are often employed for those systems which, in general, require rather severe EIRP and G/T specifications. Thus, the development of a monopulse antenna with a good antenna efficiency is of great interest. A radial line planar monopulse antenna is proposed. An analysis of the probes in a radial line has been carried out which gives an understanding of why the monopulse patterns can be synthesized, and a simple and effective theory is presented about a realization of uniform-aperture field distribution. The antenna has been fabricated and the radiation characteristics have been measured which supports the theory as well as verifies the capability of the antenna for the monopulse tracking operation.

Shaped-beam horn-reflector antennas

A design method for a horn-reflector antenna, which has a beam of arbitrary cross section, is developed. To show the effectiveness of the design theory, the measured data of an electrical model of Japans domestic communications satellite antenna of this type are shown in comparison with calculated results. The design theory is based on geometrical optics, and is applicable not only to a horn-reflector antenna, but also to any reflector antenna. At the first step of the design theory, the shape of the wavefront near the aperture is determined to correspond to desired beam shape. The shape of the reflector is then determined by the law of the optical path.

An improved thinning method for density tapering of planar array antennas

A thinning method is presented to realize the desired aperture distribution in a planar array antenna with elements fixed on an array lattice. In this method elements to be excited are determined by quantizing cumulative weights which are calculated from the desired aperture distribution. At first, this method is applied to density tapering on orthogonal axes of a planar array. Radiation patterns of the planar array determined by this method are compared with those by the desired amplitude distribution, and the results show good coincidence. Next, this method is extended to density tapering on four axes, that is, orthogonal and diagonal axes of a planar array. Moreover, this method is applied to density tapering with multi-amplitude level elements in order to enhance directive gain of thinned array. Lastly, a rectangular planar array was fabricated, and its radiation patterns were measured. Measured results were in good coincidence with calculated ones, and the usefulness of this method was verified.

Beam-shape correction in deployable phased arrays

Deployable phased-array antennas-antennas that are receiving great attention-have a major problem in that they possess the possibility of an incomplete deployment and antenna shape distortion. These effects cause a displacement of the element antenna positions that results in deviation of the phase distribution on the antenna aperture, eventually causing antenna beam deflection. We have investigated how to correct this beam deflection by observing the phased-array antenna from certain directions. There are cases when more than one observation point is necessary to carry out the proposed method depending on the extent of the antenna shape distortion and the number of the points is consulted. This correction method makes it possible to correct the deflection of the main beam and also to determine the displacement of relative element positions.

A built-in correction method of the phase distribution of a phased array antenna

A correction method for the phase distribution of a phased array antenna by the REV (rotated element electric field vector) method using pickup antennas placed at thinned element positions was proposed and tested. The effectiveness of this method for reforming a beam is verified.<<ETX>>

A linear array antenna using bifilar helical elements for mobile satellite communications

In mobile satellite communication systems such as the AMSC/TMI system [Lunsford et al., 1992], circularly polarized omni-directional antennas are attractive for vehicle antennas because any satellite tracking mechanism in the azimuth direction is not necessary for these antennas [Ohmori, 1991]. As one type of omni-directional antenna, a bifilar helical antenna has been proposed [Nakano et al., 1991]. This antenna is convenient owing to its thin diameter. However, this antenna. has a disadvantage that the beam direction in an elevation plane moves according to frequency change. In the present paper, the authors propose a linear array antenna using two bifilar helical antenna elements placed along the helix axis. The capability of reduction of beam direction movement is discussed for this array antenna.<<ETX>>

Front fed offset cassegrain type multibeam antenna

Introduction Large high capacity communication satellites with multibeam antennas are being developed in Japan(l), Ilnited States(2) and so on. The merits of multibeam antenna are ( 1 ) high EW, (2) reuse of frequencies. But in the design of multibeam antenna, one of the most difficult problems to be solved is to obtain the high beam-to-beam isolation. In conventional antennas, for instance Offset Gregorian, the increase of scan angle causes the increase of sidelobe level and scan loss on account of aberration and increase of cross polarization level, so beam-to-beam isolation becomes lower.

Increasing the bandwidth of a two-strip meander-line antenna mounted on a conducting box

A meander-line antenna consisting of two strips (two-strip MLA) is applied to a conducting box as a handset model in order to increase the bandwidth of a built-in antenna. The analysis of an MLA mounted on a conducting box leads to its resonant frequency f/sub r/, and radiation resistance R/sub r/ at f/sub r./ Using the two-strip MLA with balance mode impedance, broadbanding of the antenna in the impedance characteristics is considered.