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CW or FM CW radar performance is dependant on the isolation between the transmitter and receiver. The sensitivity of FM-CW radar is limited by the noise accompanying the transmitter signal which leaks into the receiver. Although advances have been made in reducing the AM and FM noise generated by high power CW transmitters, the noise is usually of sufficient magnitude compared with the echo signal...
An analytical study of the early-time surface current density induced on a perfectly conducting circular cylinder excited by a parallel line source carrying a δ-function current has been carried out. Expressions of the current density for both the shadow and the illuminated region are obtained. Numerical results are presented to illustrate the variation of the surface current density with time for...
Circularly polarized antennas are commonly designed using two different approaches: 1) by shaping the geometry, and 2) by dual excitation of linearly polarized antennas. The most common antennas of the first type are the helical antennas, where the radiation is due to a circulating electric current on the conducting wire of the antenna. The geometry of the antenna controls the polarization and as...
In designing a microstrip phased array (MSA-array) shown in Fig.1, it is important to estimate the influence of mutual coupling between microstrip antennas(MSA)(1). In this paper, we investigate the effect of mutual coupling on the radiation pattern of the antenna. After calculating the coupling, the experimental patterns are compared to the calculated ones. From these results, it is shown that the...
Passive and active y-junction dielectric waveguides have been the subject of extensive theoretical and experimental investigations, in view of their potential applications as power dividers, switches, modulators, TE-TM mode splitters etc. in integrated optical circuits. However, multibranch waveguides with more than two branches have received much less attention.
The generation of Intermodulation interference by nonlinear conduction mechanisms in normally passive hardware components can lead to severe degradation in the performance of muiticarrier communication systems in satellites, space probes and ground-based systems. If a common path for closely-spaced high power transmit and sensitive receive bands can not be avoided in the system, it is very difficult...
The maturing of MMIC technology opens up many interesting options in the design of ground and space segment antennas. Using MMIC components in direct radiating arrays or array fed reflector antennas makes it possible to implement multiple beams and reconfigurability that would be impractical to implement using a passive array. Distribution of amplification implies transmit beam forming at low power...
Expressions are presented for the input admittance and the current distribution along a linear antenna without restrictions on either the length or the thickness. These expressions which are based on Hurd's Wiener-Hopf type analysis, are used to find the characteristics of short as well as thick antennas. It is found that although using one term of the solution asymptotic series produces accurate...
A single-wire spiral antenna backed by a small ground plane is proposed as an element which is capable of radiating a circularly polarized wave. The current distribution of the antenna element and the ground plane is numerically analyzed using the moment method. On the basis of the current distribution, the radiation characteristics are evaluated.
The paper develops an explicit formula for the surface current on the basis of self-consistent field and current investigation at an interface of two different media. The concept of the transverse-longitudinal decomposition of an arbitrary field within a homogeneous medium is used to achieve the purpose.
Several methods for array pattern nulling with control of phase-only are discussed in some papers. Now, a more effective method for phase-only nulling is proposed in this paper. It is seen that the method of calculating the phases for minimized weight perturbation in the least square sense is given, with attention focused on the computation of the beam space coefficients.
A new type of broadband miniature antenna consists of helical dipole folded by central conductor is presented in this paper. Besides a brief analysis, the experimental results show the good performances of wider bandwidth (25%–40%), higher input impedance(about 200 Ohms), and flexible for designing, it is suitable to be used as both mobile vertical antenna and excitor of Yagi antenna.
Recent study related to electromagnetic-pulse (IMP) and electromagnetic interference (EMI) has caused a strong need to develop an isotropic broadband antenna. One such antenna, which, has been used, is a dipole with, tapered resistive loading in order to support traveling wave on antenna. [11]
A microstrip patch antenna has a simple geometry which is normally etched on a dielectric substrate to form a resonant cavity over the ground plane. Depending on the size of the patch various TMmn modes resonate in the cavity and the radiation occurs due to the fringing field at the patch edge. Because they are highly resonant structures their bandwidth is small and operation in a wider band or multiple...
Geostationary satellites providing services in the UHF and lower microwave bands have been proposed which use large deployable reflectors with array feeds to form several simultaneous beams. If conventional horn antennas are used in such a feed the mass and volume may be excessive.
Microstrip and slot antennas are often used in aerospace vehicles because of their advantages of simplicity in construction, lightweight and their ability to conform to the shape of the space-borne structures. In practice, a large number of aerospace bodies or their significantly scattering portions can be conveniently approximated by Quadric Surfaces of Revolution (QUASORs) or Quadric Cylinders (QUACYLs)...
Waveguide y-junction circulator in a microwave ferrite device whose structure is simple and whose size is small. It finds many applications. It is especially broadband. There is a metal step in such circulators to reduce junction height and to obtain the necessary impedance transformation. In 1975 Helszajn stated how to obtain a n=2 Chebyehev response characteristics with such junctions [1]. But his...
Without the dielectric substrate, a microwave integrated circuit is equivalent to a complex linear antenna (passive or active) backed by a ground plane. The “MIC-Antenna”. fortunately, does not have significant radiation due to its small size.
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