G. Linde

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.

WARLOC: A high-power coherent 94 GHz radar

This paper describes the development of a high-power, coherent radar system at W-band and discusses potential applications of radars with this new capability. Previous radars in this frequency band were limited by available power-amplifier technology to about 500 W of average power; WARLOC radar represents an increase in power, by 20 times, over previous coherent radars at 94 GHz. This performance improvement is possible due to the development of a gyroklystron amplifier specifically for this and future radars in this frequency band. The gyroklystron amplifier tubes deliver 100 kW peak power and 10 kW of average power at a center frequency of approximately 94 GHz. Other novel features of this radar include the use of highly overmoded waveguides and rotary joints for the transmission of power from the final power amplifier (FPA) to the antenna, and a high-power quasi-optical duplexer. The system uses a relatively large 1.8 m diameter (580-wavelength) Cassegrain antenna, which required the development of an antenna with an rms surface accuracy of 0.0025 in, to obtain long-range detection and identification of small objects. Test data show an antenna gain of 62.5 dB, confirming that the needed surface accuracy was achieved. Two mobile shelters house the radar system, permitting relocation to various test sites. WARLOC is presently operational at the Naval Research Laboratorys Chesapeake Bay Detachment facility, Maryland. It is being employed in radar imaging of airborne and surface objects, and in the scientific study of propagation effects and atmospheric physics phenomena.

High-power millimeter-wave transmitter for the NRL WARLOC radar

High power millimeter wave instrumentation radars have a number of important applications ranging from defense missions to basic scientific studies At the Naval Research Laboratory, a new high power 94 GHz radar named WARLOC has been developed. This radar employs a high power gyro-klystron as the final power amplifier and was developed during 1996-2001. The WARLOC radar has been integrated as a transportable system, using the 100 kW peak, 10 kW average power gyro-klystron amplifier, a low-loss transmission line, a quasioptical duplexer, and a Cassegrain antenna. The transmitter operation and waveguide system is the subject of this paper.

The structure of turbulence in clouds measured by a high power 94 GHz radar

The Naval Research Laboratory (NRL) has recently developed a 3–10 kW average, 80 kW peak power 94 GHz radar with scanning capability, WARLOC (W Band Advanced Radar for Low Observable Control). This radar is powered by a gyroklystron developed by a team led by NRL. One application has been to image clouds. New capabilities of WARLOC include imaging with greatly improved sensitivity and detail as well as the ability to detect much lower cloud returns. At short scale lengths (∼10 m), the cloud reflectivity has a speckle pattern indicating that it is governed at least in part by stochastic processes. Here WARLOC is used to measure correlation functions and turbulence spectra in clouds. In the inertial range, the Kolmogorov prediction for the correlation function index (2/3) agrees well with the data, but the assumption of isotropy does not. Furthermore, for longer scale lengths, the fluctuations appear to be wave like in the vertical direction, but not in the horizontal direction.

WARLOC: a high-power millimeter-wave radar

A high-power, coherent, W-band (94 GHz) millimeter-wave radar has been developed at the Naval Research Laboratory. The radar employs a 100 kW peak power, 10 kW average power gyroklystron as the final power amplifier, an overmoded transmission line system, and a quasioptical duplexer, together with a 6 foot Cassegrain antenna, a four-channel receiver, and state-of-the-art signal processing. Developed as a research radar for the investigation of tactical Navy radar applications in the millimeter wave band, additional radar measurement studies include cloud physics, propagation, and forward and backscatter studies.

Exploration of the lower atmosphere with millimeter-wave radar

Abstract : With the high peak power and large antenna gain of the WARLOC W-band (94 GHz) radar, clear-air radar returns from the lower atmosphere, which have no visible underlying scattering mechanism, have been observed. Due to their close resemblance to classical sea spikes from the sea surface scatter, the unknown phenomena are being referred to as air spikes. In this paper, a brief description of the high power WARLOC radar and preliminary observations of radar returns from air spikes are presented. Characteristics of air spikes in terms of height distribution, velocity response, volume density distribution, radar cross section, and spatial extent are discussed.

Cloud Imaging Using the NRL WARLOC Radar

The Naval Research Laboratory has recently developed a 3–10 kW average, 80 kW peak power 94 GHz radar with scanning capability, WARLOC. This radar is powered by a gyroklystron developed by a team led by NRL. One application has been to image clouds. New capabilities of WARLOC include imaging with greatly improved sensitivity and detail as well as the ability to detect much lower strength cloud returns. Here we show how pulse averaging enhances the sensitivity of WARLOC. Since the available power is so high, it can be used in moderate rain to both measure the rainfall rate and to image the cloud above the rain.

An Interleaved-Trace Time-Compression Radar Display

Detection information from conventional surveillance radars is frequently presented in the form of a display known as the plan position indicator map. In this display, new data are displayed while data from previous scans fade from the display. Target blips typically persist for several scans, making possible operator integration or correlation. However, the noise from previous scans often masks signals from small moving targets. To avoid the loss in signal-to-noise ratio caused by the addition of noise to signal plus noise, a digital signal processing display unit has been designed and is presented here.

Gyroklystron‐Powered WARLOC Radar

A high‐power, coherent, W‐band (94 GHz) millimeter‐wave radar has been developed at the Naval Research Laboratory. This radar, named WARLOC, employs a 100 kW peak power, 10 kW average power gyro‐klystron as the final power amplifier, an overmoded transmission line system, and a quasi‐optical duplexer, together with a high gain antenna, four‐channel receiver, and state‐of‐the‐art signal processing. The gyro‐amplifiers and the implementation in the WARLOC radar will be described.