BEAM FORMING NETWORKS ( BFN’s ) EE 525 Antenna Engineering

1. BEAM FORMING NETWORKS(BFN’s)EE 525 Antenna Engineering

2. BFN’s • constrained feeds • space (optical) feeds ------------------------------------------------ • transform feeds(constrained and/or optical)

3. Types of Constrained Feed Systems ● Series feed ● Parallel feed ● True time delay feed ● Multiple beam matrix feed • Butler matrix • Blass matrix

4. Elements of Constrained Feed Systems ● Transmission lines ● Hybrids ● Magic T’s ● Directional couplers ● Coaxial lines ● Striplins

5. Types of Constrained Feeds ● Series feed ● Parallel feed ● True time delay feed ● Multiple beam matrix feed • Butler matrix • Blass matrix

6. Series Feed

7. Parallel Feed

8. True Time Delay Feed

9. True Time Delay Feed • time delay from wavefront to input feed is the same for every path • ● waves via all paths add inphase at the feed point forevery frequency component in the pulse • ●there is no reduction in the peak value of the received pulse • ●time delay = ndsinθ/c • ●not suitable frequency scanning • ●suitable for wideband applications

10. ● is a passive feeding N x N network with beam steering capabilities ● consist of hybrid junctions (or directional couplers) and fixed phase shifters. ●(N/2) log2N hybrids and (N/2) log2 (N – 1) fixed phase shifters are required to form the network. ● hybrids can be either 90° or 180° 3-dB hybrids Butler Matrix Feed System

11. Butler Matrix

12. -distrubutes RF signals to radiating elements -providees orthogonal beamforming Butler Matrix

13. ●multiplebeamforming can beachieved by exciting two ormore beam ports with RFsignals at thesame time. ●two adjacent beams cannot be formed simultaneously as theywilladd up to produce a single beam Butler Matrix

14. - the field amplitudeatthenthoutput element due to unit excitation at the mth beam port -using superposition for an arbitrary inputdistribution f(m)will result in asuperposition of discrete plane wavesweighted by f(m), resulting in theFourier Transform : The Butler Matrix as a Fourier Transformer

15. Butler Matrix

16. Butler Matrix Advantages ● Simple network using few component types easily implemented in stripline or microstrip ● beams generated are of the Woodward-Lawson type with narrow beamwidth, high directivity and are orthogonal ● the ideal Butler matrix is the analog equivalent of the discrete Fourier Transform ● low-loss as minimum insertion loss in hybrids, phase shifters and transmission lines ● Design of large matrices is easy

17. Butler Matrix Disadvantages ● beam-width and beam angle vary with frequency; thus the Butler matrix forms phased-steered beams that squint with frequency ● has a complex interconnection scheme for large matrices

18. employs a set of N antennaarray element transmission lines that intersect a set ofM beam port lines(with directional couplers at each intersection) matrix is terminated with matched loads upper feedline radiatesa broadside beam Feed line tilt angle and propagationconstantsdetermines beam position Blass Matrix Feed Sysyem

19. Blass Matrix

20. Blass Matrix Advantages ● The interconnection layout of the circuit is simple as no crossovers or multilayers are needed ● Time-delayed beams produced do not squint with frequency. ● Shaped beams can be produced by controlling the coupling ratios of the couplers

21. Blass Matrix Disadvantages ● Each coupler on any given feed-line must have a different coupling value >> complicates design !! ● array configuration requires more couplers than the Butler matrix >> greater cost and weight !!

22. Optical (Space) Feeds • Transmission type • Reflection type

23. Space-Fed Arrays • less expensive to construct compared to corporate-fed arrays • suffer from spillover and reflection losses and do not offer good pattern control for sidelobes

24. Optical Feeds - Principal Features • free space exists between the feed(s) and the radiating aperture • aperture distribution is determined mainly by the pattern of the feed. • The larger the FOV, the greater the complexity and the cost of the antenna system.

25. Transmission Type • array elements and phase shifters are connected to an array of pickup elements, illuminated by a feed at a given focal distance • Phase shifters are set to provide the required phase increments.

26. Reflection Type • The concept is the same with the transmission model, except the presence of short circuits behind the phase shifters • amount of required phase shift at each element is half that of the transmission case

27. Transmission & Reflection Types

28. Phased Array With Paraboloid • The reflectarray aperture is placed in the region forward of the focus. • Picks up the converging field andphase-shifts it to refocus on the primary feed(s)

29. Optical Transform Feeds • feed systems in which the input to the feed and the resulting aperture distribution of the array are related by one or more Fourier transforms.

30. Optical Transform Feeds(large lens fed by a small lens)

31. REFERENCES • Lo Y.T. , Lee S.W.,’Antenna Handbook’,Van Nostrand Reinhold,1988, • http://innovexpo.itee.uq.edu.au/2001/projects/s804 113/thesis.pdf • http://www.dcjenn.com/pubs/leeAPS.pdf • Jasic, H., Antenna Engineering Handbook • Johnson, R.C., Jasic H., Antenna Engineering Handbook • Ming H.C., Tsandoulas G.N., A dual-reflector optical feed for wide-band phased arrays, IEEE Transactions on Antennas and Propagation • Mailloux, R.J., Phased Array Antanna Handbook • Hansen, R.C., Phased Array Antennas • Mailloux, R.J., Space Fed Subarrays using a Displaced Feed, Internet