Title: Bearing measurement device for a portable attack warning radar

Description: BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to bearing measurements devices for psuedorandom noise radar systems.

2. Description of the Prior Art

Ordinary antenna systems require drive motors to enable the systems to cover 360.degree.. The present invention obtains range tracking and angle measurement information in a manner such that no mechanical motion of the antenna will be necessary, thus eliminating the need for antenna drive motors and, also, eliminating clutter modulation by a scanning antenna pattern. The latter feature provides for maximum sub-clutter visibility through velocity discrimination. Velocity measurement will be accomplished by bandpass filtering the doppler spectrum in a number of contiguous channels.

SUMMARY OF THE INVENTION

The invention includes a pair of oppositely facing receiving antennas and a pair of oppositely facing transmitting antennas. The pairs of antennas are located orthogonally with respect to each other. A phase modulated constant wave source is fed into each of the two transmit antennas with a different P-N Code to each transmit antenna. The receiving antenna signals are homodyned by the unmodulated constant wave source. The resulting coded video is amplified and compared in two correlators, one having a delayed version of the code transmitted by one of the transmitting antennas and the other correlator having a delayed version of the code transmitted by the other transmitting antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the system; and

FIG. 2 is a schematic view of the four identical antennas and the range which they each cover.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Bearing measurement in this system is obtained by a combination of antenna pattern shape and P-N code modulation. In FIG. 2 is shown the antenna coverage required by the radar showing 360.degree. coverage. The implementation of this pattern is a composite of the pattern of four identical antennas mounted as shown in FIG. 2. The azimuthal pattern of each antenna covers 180.degree. and thus the patterns of adjacent antennas overlap in a full quadrant. By alternating the function of the antennas (transmit-receive) as shown in FIG. 2, a target present in quadrant I would be received in antenna R.sub.1 from illumination by energy transmitted from antenna T.sub.1. If the signal received in R.sub.1 had been the result of energy transmitted from antenna T.sub.2 the target would have had to be located in quadrant IV. Greater angle resolution can be obtained by comparing the amplitude of return in adjacent quadrants. For example octant resolution is obtained from the logic that a signal seen in both quadrants I and IV must be the result of a target present at an angle between the defined quadrant angles (i.e. segment A). This octant logic resolution is the result of a simple decision as to whether or not a target signal exists in a given quadrant. Resolution to within 2.degree. may be obtained using the difference in amplitude present in adjacent quadrants, a common direction-finding technique. The antenna also has a coverage from the horizon to an elevation angle of 60.degree..

Shown in FIG. 1 is a constant wave oscillator which provides both the transmit and receive local oscillator signal. A separate binary phase modulator associated with each transmit antenna imparts a different pseudonoise code to the radiation of transmit antenna T.sub.1 than to transmit antenna T.sub.2. The receive antenna signals are homodyned by the unmodulated constant wave source. The resulting coded video is amplified by wide band, low noise, video amplifiers. Each receiver video is then compared in two decorrelators, one decorrelator having a delayed version of the code transmitted by antenna T.sub.1 and the other decorrelator having the delayed version of the code transmitted by antenna T.sub.2. Since the two codes are either completely orthogonal or at least orthogonal over the range of interest the quadrant I correlator will produce an output only when the signal received from antenna R.sub.1 has the "P-N Code I" encoded on it. This identifies the signal as having been transmitted from transmit antenna T.sub.1. The decorrelator of quadrant IV will produce a signal, again received from antenna R.sub.2, only when the received signal is encoded with the code transmitted from antenna T.sub.2.
Other info:


Inventors: Magorian, William Ray (China Lake, CA, US)

Application Number: 351727
Filing Date: 1973-04-16
Publication_date: 1976-05-11
Assignee: The United States of America as represented by the Secretary of the Navy (Washington, DC)
Primary Class(es): 342/147 342/189, 342/378
Other Classes:
US Patent Ref:

2929056	Mar, 1960	Page	343/16.
2965898	Dec, 1960	Lewis	343/16.
3300768	Jan, 1967	Bystrom et al.	343/5.
3689750	Sep, 1972	Esser	343/100.

Other Refs:
Primary Examiner: Hubler, Malcolm F.
Assistant Examiner:
Attorney: Sciascia; R. S., Miller; Roy