Efficiency Measurement of Connected Arrays Using the Improved Wheeler Cap Method

Abstract

We present a method for measuring antenna efficiency of connected arrays. The method is a modified version of the improved Wheeler cap (IWC) method where the antenna under test (AUT) is electrically connected to two walls of the Wheeler Cap which simulates array connection. Theoretical analyses based on plane wave and cylindrical wave problems and numerical simulations using HFSS and FEKO are presented to establish accuracy estimates for the method. Close attention will be made in comparing two data collection techniques: frequency sweeping versus wall shifting. Finally, we discuss an apparatus for efficiency measurement of a 1-D connected array and the measurement results.

Post-processing accuracy enhancement of the improved Wheeler cap for wideband antenna efficiency measurements

“…With wallshifting, only one of the six walls of the short-circuited waveguide moves between successive frequency points: wall-shifting satisfies Thal's constant-conductance condition [13], [14]. On the other hand, frequency-sweeping changes the wavelength: this is equivalent with all six walls of the waveguide moving simultaneously.…”

“…On the other hand, frequency-sweeping changes the wavelength: this is equivalent with all six walls of the waveguide moving simultaneously. The recorded data still produce a circle on the Smith chart, but that circle does not always lie on a constant conductance circle [14]. On the above basis, the hypothesis was formulated that the accuracy of the frequency-swept IWC can be enhanced by the following transformation:…”

“…Investing in knowledge society through the European Social Fund. are: (i) Resistance/conductance comparison according to the original WCap concept [1], (ii) McKinzie's S 11 rotation on the Smith chart [3], (iii) the improved Wheeler cap (IWC) [4], [5], [7]- [11], [13], [14], which is the subject of this work, (iv) the assumption of radiating AUT inside the WCap [6], (v) the complementary Q-factor method (CQFM) [2], [15], and (vi) the equivalent-circuit WCap [12], [16]. All six PPMs require the absence of natural cavity resonances.…”

“…The original Improved Wheeler Cap (IWC) [4], [11], [14] is implemented with variable-geometry cavities ("wall-shifting"), which require precise manufacturing to secure shielding and avoid leakage. Geissler et al [5] simplified the process by replacing wall-shifting with frequency-sweeping, making the IWC applicable to fixed-geometry cavities, which are easier and cheaper to build.…”