The grid array antenna

Attention is called to the grid array as a possible useful antenna design for UHF clear air radars. This type of antenna integrates radiating elements and the feed network into a single structure so that a fairly large array can be driven from a single feed point. Figures are given which demonstrate the basic principle of the grid array, which are adapted from Conti et al. (1981). Conductors are arranged above a ground plane in a repeating, staggered array of connected rectangles. Each rectangular element is approximately one by one-half wavelength in size. The currents on the conductors at resonance is indicated. The grid array illustrated can be expanded in both vertical and horizontal directions about the feed point by adding additional rectangular conductors. The design eliminates the feed network and would provide a thin, panel-like antenna that could be easily built and transported

Low-altitude coverage of ST radars

Clear air ST (stratosphere troposphere) radars are now widely used for atmospheric research and wind profiling. Most attention to date has been directed toward extending the altitude coverage as high as possible. It is also desirable to extend the coverage as low as possible. Any improvement in the low altitude coverage of existing wind profiling radars would be useful. The approximate lower limits of some existing ST radars are listed and what set these limits are briefly examined

Review of specific antenna configurations: An estimate of cost and performance versus frequency for a simple (10 Lambda)-2 clear-air radar antenna array

The building of operational clear air radar wind profilers is discussed. The choice of operating frequency and antenna configuration for these profilers is examined. The cost and performance of a (10 lambda) 2 antenna array versus operating frequency over the range 30 to 400 MHz is compared. To simplify the comparison the array beam will be fixed and the array will be uniformly fed. Yagi and coaxial collinear (COCO) cable antennas are compared, although other configurations may be competitive. It is assumed that the array is driven by a typical 50 kW peak power, 1 kW average, power transmitter located at the array edge when calculating feedline power handling requirements and when system performance is compared. For this comparison an array aperture of (10 lambda) 2 was chosen since a one way beam width of 5 deg or less is desirable to limit beam spreading effects

Design considerations for high-power VHF radar transceivers: Phase matching long coaxial cables using a cable radar

The Poker Flat 49.92-MHz MST radar uses 64 phase-controlled transmitters in individual shelters distributed throughout the antenna array. Phase control is accomplished by sampling the transmitted pulse at the directional coupler of each transmitter and sending the sample pulse back to a phase-control unit. This method requires phase matching 64 long (256 meter) coaxial cables (RG-213) to within several electrical degrees. Tests with a time domain reflectometer showed that attenuation of high frequency components in the long RG-213 cable rounded the leading edge of the reflected pulse so that the cables could only be measured to within 50 cm (about 45 deg at 49.92 MHz). Another measurement technique using a vector voltmeter to compare forward and reflected phase required a directional coupler with unattainable directivity. Several other techniques were also found lacking, primarily because of loss in the long RG-213 cables. At this point it was realized that what was needed was a simple version of the phase-coherent clear-air radar, i.e., a cable radar. The design and operation of this cable are described

Design considerations for high-power VHF radar transceivers: The Poker Flat MST radar phase control system

Sixty-four separate 50-kW peak-power transmitters are distributed throughout the 200 x 200 meter Poker Flat MST radar antenna array. The relative phase of each transmitter is automatically controlled by a 64-channel unit located in the main building at the edge of the antenna. The phase control unit is described. In operation the RF pulse from a transmitter coupler is power divided and compared with the phase reference in a mixer. The mixer output is low-pass filtered and sampled near the center of the resulting video pulse by an amplifying sample-and-hold integrated circuit. Phase control is effected by maintaining the mixer output pulse near zero volts by amplifying the sample-and-hold output which then drives the voltage-controlled phase shifter in the direction to null the mixer output. The voltage-controlled shifter achieves over 360 deg phase shift in the range from 0.7 to 24 volts. When the voltage into the shifter tracks to either voltage limit the wrap-around control resets the voltage so that the shifter is always operating within its control range

Design considerations for high-power VHF radar transceivers: Distributed versus single large transmitter

The factors which enter into the choice of using a single large transmitter versus a number of smaller units in clear-air radar systems are examined. Feedline economics, ease of repair and spare part costs, operating strategy, vulnerability to catastrophic failure, and phase control requirements are considered

The NOAA TOGA antenna array

The Aeronomy Laboratory recently installed a 100 x 100 meter array antenna with limited beam steering on Christmas Island as a part of the TOGA (Tropical Ocean and Global Atmosphere) program. The array and the associated beam steering and indicating hardware are described

Capabilities and limitations of existing MST radars: Poker Flat

Designed as a prototype system to continuously monitor the atmosphere up to approximately 100 km, the Poker Flat MST radar began operating in 1979 at a relatively low sensitivity. In almost continuous operation since then, the system is steadily increasing in sensitivity to its ultimate design characteristics. Current and final parameters are listed. The advantages of its modular design, which uses 64 transmitting modules distributed through the 200 mx 200 m antenna array include: easy maintenance, beam switching using very low power switching, air cooled transmitting tubes, lower feedline costs, and no moving parts. Continuous, uninterrupted operation ( 4 years) and less man-made interference because of the remote location) are other assets. Most disadvantages are related to its not-yet-finished status, climate, moose excursions, and operating expenses

The Ponape ST radar

In May, 1984, a 50-MHz ST radar was installed on the island of Ponape in the western equatorial Pacific (7 deg N, 158 deg E) by the Aeronomy Laboratory of NOAA. The radar consists of a 100 m x 100 m array with a single, vertically directed, beam and is initially transmitting micro sec. (2.25 km) pulses. The radar is operating continuously, with Doppler spectra being recorded at approximately 1 1/2 minute intervals and sent to Boulder for later analysis. One of the principal goals of the radar is to measure vertical motions in the troposphere and lower stratosphere at a location which is within the intertropical convergence zone during part of the year. First results, during generally fair weather conditions, show detectable echoes up to about 21 km with the tropopause at 17-18 km. Once daily balloon soundings are available locally from a NOAA Weather Service Office on the island, it is planned that this radar will be joined in the coming year by two others with oblique as well as vertical beams on two yet-to-be-selected equatorial islands as part of the TOGA (Tropical Oceans Global Atmosphere) program

A modified Fresnel scattering model for the parameterization of Fresnel returns, part 2.3A

A modified Fresnel scatter model is presented and the revised model is compared with observations from the Poker Flat, Alaska, radar, the SOUSY radar and the Jimcamarca radar. The modifications to the original model have been made to better account for the pulse width dependence and height dependence of backscattered power observed at vertical incidence at lower VHF. Vertical profiles of backscattered power calculated using the revised model and routine radiosonde data show good agreement with observed backscattered power profiles. Relative comparisons of backscattered power using climatological data for the model agree fairly well with observed backscattered power profiles from Poker Flat, Jicamarca, and SOUSY