Implicit beam angle control for a frequency scanning radar system

Claim 3

The invention set forth in claim 1, further defined in that said predetermined increment of phase change is 2 pi radians.

Claim 4

The invention set forth in claim 2 further defined in that said transmission line is defined as an extended path waveguide transmission line.

Claim 5

In a frequency-scanning radar which includes an antenna array having successive radiating elements energized from corresponding successive points along a first extended path waveguide transmission line to produce a radiated beam having a pointing angle as a function of frequency of microwave energy providing excitation for said array, the combinatioN comprising: a microwave generator for producing said microwave energy in the frequency band of interest, said generator being frequency controllable in response to stepped variable frequency-controlling signals; a second extended path waveguide transmission line connected to receive energy at its input from said microwave generator; said second transmission line being a plurality of wavelengths in electrical length of said second transmission line further being such that a frequency change therein sufficient to produce an overall output phase change equal to 2 pi radians is the same frequency change which, applied to said first transmission line, produces a predetermined increment of beam pointing angle change from said antenna array; programming means for generating and applying said variable frequency-controlling signals to said microwave generator for producing a predetermined pattern of successive stepped frequency variations of said microwave energy, each of said frequency steps corresponding substantially to a discrete beam-pointing angle; and means for comparing the phase of energy from the input of said second transmission line with the output thereof to produce a correction control signal as a function of phase difference between said input and said output, and for applying said correction control signal to said microwave generator for modifying said microwave generator frequency to tend to produce phase coincidence between said second transmission line input and output.

Claim 6

In a frequency-scanning radar which includes an antenna array having successive radiating elements energized from corresponding successive points along a first extended path waveguide transmission line to produce a radiated beam having a pointing angle as a function of frequency of microwave energy providing excitation for said array, the combinatioN comprising: a microwave generator for producing said microwave energy in the frequency band of interest, said generator being frequency controllable in response to stepped variable frequency-controlling signals; a second extended path waveguide transmission line connected to receive energy at its input from said microwave generator; said second transmission line being a plurality of wavelengths in electrical length of said second transmission line further being such that a frequency change therein sufficient to produce an overall output phase change equal to 2 pi radians is the same frequency change which, applied to said first transmission line, produces a predetermined increment of beam pointing angle change from said antenna array; programming means for generating and applying said variable frequency-controlling signals to said microwave generator for producing a predetermined pattern of successive stepped frequency variations of said microwave energy, each of said frequency steps corresponding substantially to a discrete beam-pointing angle; and means for comparing the phase of energy from the input of said second transmission line with the output thereof to produce a correction control signal as a function of phase difference between said input and said output, and for applying said correction control signal to said microwave generator for modifying said microwave generator frequency to tend to produce phase coincidence between said second transmission line input and output.

Claim 7

The invention set forth in claim 4 further defined in that said first and second extended path waveguide transmission lines are in thermal communication with each other, thereby to substantially eliminate any change of said beam pointing angle corresponding to a discrete frequency of said microwave generator as a function of temperature.

Claim 8

The invention set forth in claim 5 further defined in that said microwave generator is a backward wave oscillator having a helix operable as a frequency-controlling element, said frequency controlling signals comprise a staircase voltage from said programming means, and means are included for mixing said staircase voltage and said correction control signal to form a composite control signal and for applying said composite signal to said helix to control the frequency of said backward wave oscillator.

Claim 9

The invention set forth in claim 5 further defined in that said means for comparing the phase of energy to produce a correction control signal as a function of phase difference comprises a Magic T hybrid having its inputs connected on each to the input and output ends of said second transmission line and the outputs of said Magic T are separately detected and amplitude compared to produce said correction control signal in bipolar form.

Claim 10

The invention set forth in claim 7 further defined in that a controllable phase shifter is inserted in series between said second transmission line output and the corresponding one of said Magic T inputs, thereby to introduce an offset in said radiated beam-pointing angle as a function of frequency.

Claim 11

The invention set forth in claim 8 further defined in that said phase shifter is defined as being electrically controllable over an angle not exceeding 2 pi radians whereby said beam-pointing angle may be varied by a preselected fraction of a beam width by controlling said phase shifter in the period between successive occurrences of said successive stepped frequency variations of said microwave energy.

Claim 12

The invention set forth in claim 4 in which said first and second extended path transmission lines are defined as serpentine waveguides folded to provide an extended electrical length per unit of overall length.