Merrill Skolnik

Role of radar in microwaves

Radar has been highly influenced by the technology of microwaves, and likewise the development of microwaves has been significantly affected by the needs of radar. This paper addresses the relation between the two. It begins by briefly describing the introduction of microwave radar in World War II that was a major factor in the Allies achieving success in air defense and antisubmarine warfare. Microwave radar developments during and after the war are reviewed, along with a listing of current military and civilian applications. The dependence of modern radar on digital processing (with clock rates at microwave frequencies), high-power transmitters, and sophisticated antennas is discussed. The paper concludes by mentioning possible future directions for radar, and briefly describes two examples of future radar system opportunities. These are the ubiquitous radar and high-power transportable millimeter-wave radar based on the gyroklystron amplifier. The message is that microwaves and radar have mutually benefited from one another and that radar still offers many opportunities for microwave engineers to demonstrate their ingenuity and creativity.

Senrad: an advanced wideband air-surveillance radar

The generic characteristics and performance of an experimental long-range air-surveillance radar, known at the Naval Research Laboratory as Senrad, is described. Its distinguishing feature is that it can operate with simultaneous transmissions over a very wide bandwidth-from 850 to 1400 MHz. The technology and type of experimental radar equipment employed are discussed and examples are given of its performance capabilities obtained by means of very wideband operation. The unusually wide bandwidth of this radar allows 1) improved detection and tracking performance because of the absence of the nulls that are common in the antenna elevation radiation-pattern of a single-frequency radar; 2) moving target indication (MTI) without loss of targets due to blind speeds and without the need for multiple PRFs (pulse repetition frequencies); 3) accurate height finding with a fan-beam radar by taking advantage of the multipath time difference as a function of target height; 4) a form of limited target recognition based on high range-resolution; and 5) a reduction of the effectiveness of electronic countermeasures that can seriously degrade more narrowband radars.

Ultrawideband microwave-radar conceptual design

This paper outlines the special considerations that characterize the design of an UWB radar for the detection of low-altitude missiles over the sea. It discusses the factors which enter into the choice of frequency, and the selection of the transmitter, antenna, and receiver. Reviewed are signal processing issues concerning detection of UWB signals in noise and clutter, nondoppler MTI based on the pulse-to-pulse change in range due to target motion, measurement of target height based on multipath time delay, and target recognition. As the investigation progressed, the authors became disappointed with the available UWB technology, but encouraged about the potential advantages of UWB for this application. The chief limitation of UWB radar that must be overcome before applications are viable is its poor electromagnetic compatibility (EMC). >

Attributes of the ubiquitous phased array radar

This paper reviews the concept and properties of a ubiquitous radar, one that looks everywhere all the time. The receiving antenna of a ubiquitous radar consists of contiguous directive beams covering the same region as the wide beam (quasi-isotropic) transmitting antenna. Such a radar has the important advantage of performing multiple radar functions simultaneously without the serious limitations of a conventional phased array radar that has to perform its multiples functions sequentially, one at a time. Briefly described are the general characteristics of such a radar, its advantages, and several of its potential applications. The digital beam-forming ubiquitous radar is a method for achieving significant radar capabilities not readily available with conventional radar architectures.

Improvements for air-surveillance radar

Both a near-term and a far-term radar concept for improved air-surveillance are described. The near-term concept is based on operating simultaneously with multiple frequencies over two radar bands to obtain the benefits of more uniform coverage in elevation, improved target detection, improved automatic tracking, target height-finding without the need for a 3D antenna, elementary target recognition, and other attributes that result from operating over a very wide band. The far-term concept is based on operating an air-surveillance radar with a very wide bandwidth as in the near-term approach, but with an architecture quite different from that used in current air-surveillance radars. This radar looks everywhere all the time with a number of fixed directive receiving beams and an omnidirectional transmitting beam. The spatial, temporal, and spectral domains are used along with digital beamforming and digital signal processing to allow this ubiquitous radar to perform multiple functions in parallel with variable data rates and without time sharing so as to achieve simultaneous weapon control and surveillance, reduced susceptibility to intercept, and other capabilities difficult to obtain with conventional analog beamforming methods.

An Empirical Formula for the Radar Cross Section of Ships at Grazing Incidence

From a collection of measurements of the radar cross section of ships at grazing incidence, an empirical formula is presented that relates cross section to radar frequency and ship displacement.

An ultrawideband microwave-radar conceptual design

The paper outlines the special considerations that characterize the design of an UWB radar for the detection of low altitude missiles over the sea. It discusses the factors which enter into the choice of frequency, and the selection of the transmitter, antenna, and receiver. Reviewed are signal processing issues concerning detection of UWB signals in noise and clutter, non-Doppler MTI based on the pulse-to-pulse change in range due to target motion, measurement of target height based on multipath time delay, and target recognition. The chief limitation of UWB radar that must be overcome before applications are viable is its poor electromagnetic compatibility (EMC).

The radar antenna—Circa 1995

Abstract This paper reviews some of the current interests in radar antennas, including work conducted at the U.S. Naval Research Laboratory. Almost all types of antennas have been used in radar, but it is the phased array which has received the most attention in recent years, especially for military applications. Methods for making phased arrays more affordable are discussed, as well as the potential of ferroelectric phased arrays, diode lens arrays (Radant antenna), agile plasma mirror, phased arrays employing fiber optics, and antennas for ultra-wideband radar. Also briefly mentioned are several areas where further radar antenna development might be indicated.

Radar detection of gas seepage associated with oil and gas deposits

The use of a simple X-band radar for the location of underground oil and natural gas deposits based on the seepage of gas into the atmosphere is discussed. The validity of the original explanation offered by others is questioned and it is suggested that the observed radar echoes may be due to the effect of turbulence induced in the atmosphere by the seeping gases. >

Status of ultrawideband (UWB) radar and its technology

UWB radar is of interest because of its highly successful application to ground probing radar and to the challenge of working in an area which requires technology different from more conventional narrowband (NB) radar. The status of UWB technology is examined, and differences between UWB and NB radar are discussed with reference to the transient nature of target scattering, dispersive propagation effects, antenna effects, transmitters, and signal processing.<<ETX>>