Antenna phased array

Another important difference between bistatic and monostatic radar is that a directional receive antenna must scan at a non uniform rate to follow the position of the transmitted signal through space, a process known as pulse chasing. This can be very challenging for designs based upon mechanical scanning and hence an alternative is to use one or more electronically agile beams as in phased array radar. Such phased array antennas can be expensive and in some applications will prohibit the use of the bistatic technique. 

Applications that have received attention, and the material properties that enable them, are shown in Figure 27.1. These applications are reviewed in detail in Waser and Ramesh. Decoupling capacitors and filters on semiconductor chips, packages, and polymer substrates (e.g., embedded passives ) utilize planar or low aspect ratio oxide films. These films, with thicknesses of 0.1 to 1 J,m, are readily prepared by CSD. Because capacitance density is a key consideration, high-permittivity materials are of interest. These needs may be met by morpho-tropic phase boundary PZT materials, BST, and BTZ (BaTi03-BaZr03) solid solutions. Phase shifters (for phase array antennas) and tunable resonator and filter applications are also enabled by these materials because their effective permittivity exhibits a dependence on the direct current (DC) bias voltage, an effect called tunability. 

C. Antenna. The antenna is used to make a transition from a guided wave (from the transmission line) to a radiated electromagnetic wave. The design of the antenna is influenced by many factors such as size, frequency, and electrical impedance. Antennas are normally of two types - omnidirectional and directional. The omnidirectional antennas are element type antennas such as monopoles or dipoles. The directional are horn-type antennas, parabolic dish type antennas such as a satellite communications antenna (SATCOM), or a phased-array antenna which can emit many beams at once. The characteristics of the antenna are a very important aspect of hazard evaluation. 

These studies are often spurred by the government s need to transmit growing amounts of voice, data, and video information through space systems, or to assess whether new technologies have made it possible to do so. To begin such a communications system study, analytical models in the CDC are updated to account for technical advances such as phased array antennas, lightweight centralized... 

A tapered periodic surface (TPS) is an array of wire or slot type elements with element sizes and interelement spacings that vary as a function of position over the array. Many different appUcations of TPS come to mind. Most of these applications involve a smooth electrical transition to terminate the finite edge of an FSS or phased array. A TPS could also be used to transition from one FSS design to another in a radome with multiband window areas. Another application is as a building block for broad band and low side lobe antenna designs. Tapered Periodic Surfaces exhibit two fundamental properties ... 

K. A. Shubert and B. A. Munk, Matching Properties of Arbitrarily Large Dielectric Covered Phased Arrays, IEEE Trans. Antennas Propag., Vol. AP-31, January 1983, pp. 54-59. 

V. Galindo, Finite Arrays, Edge Effects, and Aperiodic Arrays, in Theory and Analysis of Phased Array Antennas, N. Amitay, V. Galindo, and C. P. Wu, eds., WUey-Interscience, New York, 1972, Chapter 8. 

D. M. Pozar, Analysis of Finite Phased Arrays of Printed Dipoles, IEEE Trans. Antennas and Propag., Vol. AP-33, October 1985, pp. 1045-1053. 

R. C. Hansen, Phased Array Antennas, John Wiley and Sons, New York, 1998. 

H. A. Wheeler, Simple Relations Derived from a Phased Array Antenna Made of an Infinite Current Sheet, IEEE Trans. Antennas Propag., AP-13(4), 506-514, July 1965. 

One of the attractive features of the Opto-VLSI-based tunable time delay architecture is its ability to generate multiple RF delays without the need for RF splitters. Furthermore, the amplitude weight of each generated RF delay sample can simultaneously be controlled. This architecture offers excellent flexibility in applications such as phased-array null steering because multiple true-time RF delays for each antenna element can simultaneously be synthesized using computer generated holograms. 

Opto-VLSI-based tunable beamformerfor microwave phased-array antenna... 

The requirements for future phased array antenna beamformers include (i) the ability to perform wideband signal processing, (ii) short reaction time, (iii) small footprint (small size and light weight), (iv) increased coverage range and increased resolution, (v) reliability and maintainability, and (vi) low cost. 

Photonics-based broadband phased-array antenna beamformers have been extensively investigated over the last decade for applications ranging from modern microwave radar to wireless communication systems. A broadband phased-array antenna requires the generation of variable true-time delays at each antenna element to realize beam or null steering. Several approaches have been adopted to realise tunable true-time delay units, including the use of in-... 

Broadband null-steering beamformers are much more difficult to realise than beam-steering beamformers. Theoretical analysis of broadband null steering of phased-array antennas shows multiple variable true-time delays are needed for each antenna element, while only one variable true-time delay for an antenna element is required for broadband beam steering. An N-element smart antenna can synthesise (N-1) nulls only, and this requires the beamformer to simultaneously generate (2n-1-1) delayed versions of the RF signal received by the antenna. 

Fig. 10(a) shows a typical N-element phased-array antenna architecture, whose array factor (or directional response) is given by (Zmuda et ah, 1998) ... 

Without loss of generality, considering a 4-element phased array antenna, with its main lobe at an angle 0 and nulls located along angular coordinates, 6i, 02, and 63, the array factor... 

From Eq. (11), it can be observed that for a 4-element phased array antennas, = 7 delay taps need to be generated by the true time delay unit in order to synthesis three nulls, and that the time delays required to be synthesized are ... 

Generally, for an N-element broadband phased array, the synthesis of (N-1) broadband nulls can be achieved if the beamformer of the antenna can adaptively generate and combine (2 -1 -1) delayed versions of the RF signals received by the antenna elements, as illustrated in Fig. 10(b). 

Fig. 10. (a) Typical phased-array antenna architecture, (b) Phased array antenna architecture for broadband null steering. 

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