Phaseless Characterization of Broadband Antennas

Abstract

Abstract-A new efficient method for broadband antenna characterization from phaseless acquisitions in the frequencydomain is presented. The phase-retrieval technique is based on an extrapolation of the off-axis indirect holography. In common with the conventional approach, the power of the interferometric field of the antenna under test and a reference antenna, whose field is known in advance, as well as the power of the antenna under test alone, is measured at the desired frequencies. Nevertheless, the phase retrieval is accomplished independently at each spatial point by filtering in the time-domain rather than in the k-space. Thus, the dependency of the phase retrieval on the position accuracy is reduced and it can be accomplished simultaneously at all frequencies without resorting to iterative schemes. Moreover, it yields a less dense sampling and a phase retrieval algorithm not dependent on the geometry of the acquisition. The method is illustrated with a numerical example in the W -band as well as with two near-field measurement examples in the Ka-and W -bands.

Indirect Off-Axis Holography for Antenna Metrology

“…In order to obtain the FF pattern of the AUT, both tangential fields are needed [1] and, thus, the process has to be repeated after turning the AUT 90 ∘ to acquire the other component [23]. Second, for the sake of simplicity, the offset of the reference antenna has only been introduced in the x-axis (as shown in Figure 1) without loss of generality.…”

“…The technique consists in the removal of the autocorrelation terms of the hologram prior to the filtering process and can be implemented by means of two different approaches. First of them requires an extra measurement to characterize the amplitude of E aut (the amplitude of E ref is a priori known) [21,23,29,30,39]. Second approach, commonly known as opposite-phase holography [28,40], introduces a hybrid-T component in the setup, which provides simultaneously the complete hologram in the sum port and the autocorrelation terms in the difference port.…”

“…As in conventional indirect off-axis holography, the reference antenna has to be previously known in amplitude and phase, also all the components of the setup, mainly the AUT, must be broadband; otherwise their time responses will be spread and may cause overlapping in the spectrum of the recorded hologram [23].…”

“…This kind of technique is popular because they involve minor changes in the measurement setup, nevertheless they can suffer from stagnation and their convergence is strongly related to the first guess solution. On the other hand, and belonging to noniterative techniques, most of the interferometric approaches [5,[20][21][22][23] rely on the use of a reference field, previously known in amplitude and phase, used to interfere the field of the AUT and allowing an easy and iteration-free phase retrieval by means of a filtering process in the spectral domain.…”

“…Novel techniques that allow for the use of synthesized reference waves with mechanical phase shifts [5,30] will be introduced in Section 3. A new efficient method for amplitude-only characterization of broadband antennas [23] compatible with nonredundant sampling techniques [31] will be described in Section 4. Finally, main conclusions regarding the advantages and disadvantages of the proposed methods will be drawn in Section 5.…”