D. Treves

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. >

Electric surface current model for the analysis of microstrip antennas on cylindrical bodies

An approach to the analysis of microstrip antennas on cylindrical bodies is presented. The printed radiator is replaced by as assumed surface current distribution, and the fields are solved taking into account the presence of the dielectric layer and the metallic cylinder. Calculation takes place in the Fourier domain. The far field, calculated asymptotically from this solution, is used to get the radiation patterns of the wraparound antenna for any dielectric and the half-wavelength patch for \epsilon_{r} = 1 .

Signal, noise, and codes in optical memories

An analysis is given of the effect of additive and multiplicative noise in the data and servo channels of both write -once and magneto -optic recording systems. Electronic (additive) noise is most severe in the magneto -optic data Abstract. An analysis is given of the effect of additive and multiplicative noise in the data and servo channels of both write-once and magneto-optic recording systems. Electronic (additive) noise is most severe in the magneto-optic data channel, and laser noise is of particular concern in both the sum tracking channel and the write-once data channel. In a typical optical memory system, the maximum laser light fluctuation should never exceed 10% of the average light level. I n the differential channel of such a system, the laser noise should be further reduced by another order of magnitude. In the data channel, nonreturn- to-zero (NRZ) encoding has the greatest immunity to noise. Analysis is made of the extent to which the S/N margin is lost when various run-length-limited codes are used, for both additive and multiplicative noise. Subject terms: magneto-optic recording; magneto-optics; optical recording; optical memory.

Effect Of Birefringence On Optical Memory Systems

The effects of birefringence due to substrate and optical components on the sum and difference signals in optical memory systems are studied. A method is presented for calculation in an arbitrary optical system. Computed results are given to elucidate trends for a typical magneto--optic system employing two polrizing beamsplitters and differential detection, and comparison is made with experimental results. The effects of birefringence on the signal--to--noise ratio are discussed.

Radiation patterns of half-wavelength microstrip elements on cylindrical bodies

A method for the analysis of microstrip antennas on cylindrical bodies was developed and described in details [l]. It is based on replacing the printed radiator at the air-dielectric interface by an assumed surface current distribut.ion J8(4, z), derived from transmission-line or cavity type analysis. This approximation is valid as long as radiation is small compared to the stored energy 121. Being a surface current, the source term is introduced only through the boundary conditions. This allowes the description of the fields in each of the regions inside and outside the dielectric as a combination of TM and TE partial fields [3]. Using the cylindrical symmetry, calculation took place in the appropriate Fourier domain, and led to a general expression for the fields in terms of the current for a given set of structure parameters, i.e the cylinder radius a, the dielectric thickness h and the dielectric constant tr. The far field was derived asymptotically from the solution in the Fourier domain.

Conformal arrays of double-sided printed dipoles

Low pmNe printed antennas are an attractive solution for coniormal appiications. This paper presents design and measured results of two X-band conformal arrays of 4 x 4 printed dipoles. The radiating elements were printed on both sides of a thin and flexible substrate and then wraped around a conducting cylinder of small radius (a % 1.5xo) with a honeycomb spacer (a, % 1, k = 0.15Xo) in between. This structure allows for large bandwidth while minimizing surface-wave and network radiation losses [I]. The dipoles orientation is a x i a l for one antenna (Fig. 1) and azimuthal for the second one (Fig. 2). A theory developed for the analysis of printed antennas on cyIiidricaI bodies 121, [3] was used to maximize the directivity in t of the inter-element spacing. The experimental results including: radiation patterns, gains (17-18 dB) and bandwidths (15-20%) show the ability to achieve broadband arrays with gains and patterns in reasonable agreement with theoretical predictions.

A simple microwave interferometer for measuring effective thickness of dielectric slabs

A Michelson-type unequal path interferometer for measuring the effective thickness of dielectric slabs is presented. Due to unequal paths, this interferometer is frequency dependent so that frequency tuning of the source controls the phase difference between the two paths and serves as a phase shifter. FM modulation of the source enables determination of the null point with an electronic sensitivity of 0.02°. High spatial resolution (≃λ/2) is achieved by spacing a suitable horn antenna close to the dielectric surface. Detailed design considerations and experimental results concerning an X-band interferometer are presented.

High Gain Modular Microstrip Antennas

This work extends a modular approach for the design of microstrip arrays to high gain (35 dB) printed antennas. A theoretical study of the gain limitation in single-layer microstrip antennas is compared to experimental results in a set of 16,64,256 and 1024 element arrays.

Near Field Mapping of Microstrip Antennas

An automatic measurement technique for near field mapping of microstrip structures is described. Several field mapping examples indicate that this technique can serve as a diagnostic tool for microstrip antennas.