Method and apparatus for using signal doppler change to resolve long baseline interferometer ambiguous phase change measurements for locating a radar emitter

A method for locating a radar emitter by using a long baseline interferometer (LBI) and for resolving ambiguous differential phase measurements made by said LBI, comprising the steps of:

• forming the LBI baseline between two antennas having a common field of view,
• measuring the signal angle-of-arrival (AOA) induced phase difference on the baseline,
• measuring emitter signal carrier frequency,
• calculating a difference value between the frequency values measured in two different dwells,
• dividing said difference by the frequency by the frequency measured in the earlier of said two dwells to yield a normalized frequency value,
• multiplying said frequency difference and normalized frequency values producing a first value corresponding to the differential of the cosine of the signal AOA,
• multiplying the ambiguous phase difference measured on the LBI baseline by a scaling factor derived from measured emitter frequency and baseline length to yield a second value corresponding to the differential of the cosine of the signal AOA,
• comprising said first and second differential values and adjusting the value of said second differential value by properly scaled positive or negative integers until the absolute value of the difference between said first and second values is less that .pi. thereby resolving phase ambiguity and
• using the value resulting from said comparing and adjusting step to locate the radar emitter.

A method for locating a radar emitter by using a long baseline interferometer (LBI) and for resolving ambiguous differential phase measurements made by said LBI, comprising the steps of:

• forming the LBI baseline between two antennas having a common field of view,
• measuring the signal angle-of-arrival (AOA) induced phase difference on the baseline,
• measuring emitter pulse time-of-arrival (TOA)
• extracting from TOA values a periodic event representing an invariant time interval at the radar or an inter-pulse repetition of pulse patterns in the radar signal referred to as t.sub.po at the radar and t.sub.p at the observer,
• calculating a difference between inverse values of t.sub.p between two dwells forming a pulse repetition frequency estimate f.sub.prf and dividing this result by a f.sub.prf estimate in the earlier dwell of the two being used for determining a phase difference value,
• multiplying said differenced and normalized f.sub.prf values by a scaling factor derived from the observer's speed producing a first differential value of the cosine of the signal AOA,
• multiplying an ambiguous phase difference measured on the LBI baseline by a scaling factor derived from measured emitter frequency and baseline length producing a second differential value of the cosine of the signal AOA
• comparing said first and second differential values and adjusting said second differential value by the addition of properly scaled positive or negative integer values until the absolute value of the difference between the two measurements has a value less than .pi. thereby resolving phase ambiguity and
• using the value resulting from said comparing and adjusting step to locate the radar emitter.