Wondered if anyone has come across phased array antennas that use different functions of phase shift vs. frequency. There is a lot of literature with true time delays that give a linear phase shift vs. Freq but what if the phase shift vs. freq was an exponential function.
Is there any advantage/disadvantage to the beam squint or sidelobes of a phased array system if we could vary the phase vs. freq in an exponential (or other type of function) relationship instead of a linear one. Is the linear relationship always the best one?
If you want a single beam direction across all frequencies, then you are talking about true time delay steering. Phase shifters approximate true time delay for narrow band signals. As you point out, a true time delay is a linear frequency-dependent phase shift. This is a simple Fourier Transform property, and far-field antenna patterns are essentially the Fourier Transform of the aperture illumination.
Looking at it the other way, if you have something other than a linear frequency-dependent phase shift for each element, then you will have different beam patterns for different frequencies. The question is then "Is this useful?" That is, is it useful to have different frequencies pointed in different directions? We could possibly conjure a scenario where this might be useful, but I will leave this for someone else to comment on.
Some desired design features can be provided in antenna arrays using nonlinear phase vs. frequency or nonlinear phase vs. aperture or both. For example, beam broadening, special shaped radiation patterns, etc.
Thanks for the answers.
The special shaped radiation patterns is an interesting one. Please let me know if you come across any papers where this has been applied.
Some references for beam broadening and shaping with nonlinear phase tapers:
Irwin D. Olin, Flat-Top Sector Beams Using Only Array Element Phase Weighting: A Metaheuristic Optimization Approach , Naval Research Laboratory Report, NRL/FR/5303--12-10,227, 2012.
J. Clayton Kerce, George C. Brown, and Mark A. Mitchell, Phase-Only Transmit Beam Broadening for Improved Radar Search Performance, 2007 IEEE Radar Conference, pp.451-456.
A few more for nonlinear phase vs. frequency things to build broadband and other beamformers:
Ch. 5 Frequency Invariant Beamforming in "Wideband beamforming : concepts and techniques " by Wei Liu & Stephan Weiss, Wiley, 2010.
https://www.researchgate.net/publication/202253391_Concept_of_Microwave_Electronic_Steered_Array_using_Analogue_FIR-Filter
Also google "Finite Impulse Response (FIR) beamformer"
Conference Paper Concept of Microwave Electronic Steered Array using Analogue...
- Badges
- Science topic