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. AbstractAn optical time delay network (OTDN) for time delay steering of phased arrays of various sizes is projected. The approach involves integrated optic switches and sections of optical waveguide for time delays. An example phased array radar is defined. The impact of time delay network performance parameters such as insertion loss, network switch isolation and triple transit effects on radar system performance such as noise figure, dynamic range, phase and amplitude linearity and sidelobe levels is analyzed. Performance levels needed within the optical time delay network to meet projected radar system requirements are identified. TIME DELAY NETWORK CONFIGURATIONSPhotonic based programmable time delay circuits with microwave inputs and outputs could be directly applied to active element arrays to achieve wideband time delay operation.A variety of integrated optic circuit architectures have been studied, including parallel and serial line layouts as illustrated in Figure 1 . Either architecture can incorporate on-off or routing switches. A binary serial architecture like Figure 1(a) has been selected as a baseline for current developments. Companion papers"2 describe the photonics and semiconductor design approaches and the microwave impedance matching circuit designs being explored.Selection of this architecture was based on a study of future active element radars and phased arrays. Phase steering works fine for small arrays or narrow instantaneous bandwidth applications, but time delay is needed in large arrays with wide bandwidth waveforms. Since the neal need for time delay is large arrays, large delays are required.Delay line increments can be selected based on a step scan approach, providing the exact delays to steer the beam in, for example, one-half beamwidth steps. Alternately, delay increments can be selected based on approximating continuoils scan with granularity small enough so sidelobes and beam pointing errors are acceptable. The step scan approach results in simpler network, with fewer delay increments, for small arrays; but the continuous scan approach is simpler for large arrays. Hence, the continuous scan has been selected. a) SERIAL ARCHITECTURE RF IN __ flfl LASER V DIODE OPTICAL SWITCHES RF Ot.ff PHOTO-DIODE DETECTOR b) PARALLEL ARCHITECTURE DETECTOR GM001237 Figure 1 . Delay Network Architecture.Table I shows the delay requirements for small to large arrays covering the 2 to 4 GHz frequency band with continuous scan. Time delay granularity corresponds to 5.65 degrees peak O-8194-0868-9/92/$4.OO SPIE Vol. 1 703 (1992) I 545 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx