Mai T. Ngo

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.

Clear-air backscatter from the lower atmosphere using a high-power, millimeter wave radar

This paper presents our clear-air backscattering observations from the lower atmosphere using the high power, high resolution WARLOC millimeter wave (94 GHz) radar developed at the Naval Research Laboratory (NRL) [1]. With a peak power of 70 kW and a 62-dB gain antenna, the WARLOC radar offers more than 30 dB higher sensitivity than typical weather radars at this frequency. In addition, the radar provides unprecedented high range and spatial resolution with the 50-cm range resolution and a beam width of less than 0.1 degrees, respectively. The radar is currently located at the NRLpsilas Chesapeake Bay Detachment (CBD) facility, on the western shore of the Chesapeake Bay, Maryland, providing observations eastward across the bay. The unique capabilities of the WARLOC radar have opened up new opportunities in atmospheric research. In this paper, characteristics of clear-air backscatter will be presented. Radar cross sections as a function of temperature and height will be discussed. These observations will be related to phenomena such as clear-air turbulence and convective eddies.

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.

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.