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on-time of elements can be controlled by using CPLD accurately [41, 42], but to synthesize a new antenna pattern, by realizing a new set of on-time sequence, the CPLD must be reprogrammed by completely erasing the previous set of on-time values. In contrast, the proposed VAS-QOT needs a simple circuitry as shown in Figure 13, where the new set of on-time sequences according to the need can be obtained simply by altering the appropriate binary input sequence to the selected inputs of the multiplexers. Thus, by fabricating the QTM in integrated circuit (IC) or by using some discrete components on a printed circuit board (PCB), TMAA

Introduction of the additional degree of freedom "time" provides flexibility in synthesizing antenna array patterns and overcomes the shortfalls of realizing the patterns through conventional array synthesis methods. Among the different time-

consisting of a pulse generator, simple tapped delay line with equal delay at each tap output, flip-flops, and multiplexers. This circuit can be implemented in either an integrated circuit (IC) form or in a printed circuit board and can be used as a discrete component to generate different patterns. However, as far as the nonuniform period modulation is concerned, the function of the quantized time modulator (QTM) circuit needs to be investigated, specifically to time modulate the elements with multiple frequencies which need accommodation of multiple PLLs in

approaches, complexity in the switching circuit increases as per the sequence, VAS, pulse shifting, BOTS, SOTS, and NPM, respectively, while their performance in synthesizing low SLL power patterns with suppressed SBL follows the reverse order. Thus, for a time-modulation approach, the improved performance in terms of the capability of synthesizing low side lobe power patterns by suppressing harmonic signal level is obtained at the cost of complex switching mechanism. However, due to the advancement in the semiconductor technology, availability of highspeed semiconductor switches makes it possible to realize such complex switching mechanism by writing simple program code in complex programmable logic

In all the time-modulation approaches except NPM, for the desired power pattern, optimization algorithm is required to determine the proper set of on-time sequence. The construction of suitable cost function with multiple objectives such as narrow beamwidth; low values of SLL and SBL, etc.; and the selection of

corresponding weighting factors plays an important role to achieve the best possible power patterns. This chapter gives a brief fundamental insight toward all this issues.

This work is financially supported by the Ministry of Electronics and Information Technology (MeitY), Govt. of India, under Visvesvaraya Young Faculty Fellowship of Visvesvaraya Ph.D. scheme (Grant No. PhD-MLA-4(29)/ 2015-2016) and DST-SERB project ref. file number EEQ/2016/00836, dated

modulation strategies, QAS can be realized through a simple digital circuit

the circuit for the multiple frequencies. Regarding other time-modulation

switching can be done easily.

Advances in Array Optimization

9. Conclusions

devices (CPLDs).

Acknowledgements

January 17, 2017.

30

Sujit Kumar Mandal\*, Ananya Mukherjee, Sujoy Mandal and Tanmoy Das Microwave and Antenna Research Laboratory, Department of Electronics and Communication Engineering, National Institute of Technology Durgapur, Durgapur, West Bengal, India

\*Address all correspondence to: skmandal2006@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
