An adaptive impedance tuning circuit (AITC) is used to compensate for the impedance between the arbitrary load impedance and the characteristic impedance of interest. An AITC is required for correct and accurate load impedance measurements. A new type of mismatch measurement circuit that measures the arbitrary load impedance more accurately is proposed and its performance against existing methods is compared. The proposed circuit exhibits a significant performance improvement compared with the conventional method, and it could be applied to different communication systems that have a variety of input signal strengths.Introduction: In an electrical system, maximum power transfer between a load and a source is achieved when impedances of the load and the source are matched with respect to each other, which minimises reflection losses between the load and the source. In RF communication, the characteristic impedance of the front end is substantially constant, but the antenna impedance varies considerably with frequency and external circumstances. One way to solve this problem is to use an adaptive matching circuit instead of a fixed matching circuit. To correctly apply an adaptive impedance tuning circuit (AITC), accurate measurement of the load impedance is required. To respond rapidly to the continuously changing circumstances, a method for calculating the load impedance directly without iteration is a more efficient way than a method with iterations [1]. This Letter details a load impedance measurement method using a sectioned λ/4 transmission line (TL) without iterative calculations. The sectioned-TL-based method and theory has been presented in several papers [2,3]. According to [2], the TL should be divided into several parts, and each part must be measured, so this technique requires complex calculations. In addition, this technique is difficult to implement. The technique in [3] is simplified to a three-point measurement on a λ/4 TL; however, the calculation method for selecting the exact results is not presented.This Letter presents a calculation method for directly measuring the load impedance by only measuring the voltages at three points on the λ/4 TL without iteration, and suggests a selection algorithm for determining the exact measurement values from several calculated load impedances. In addition, a new type of mismatch measurement circuit is proposed. This novel circuit measures the arbitrary load impedance more accurately by using a high-impedance sampling TL and sampling capacitors. By comparing the performance with the conventional method that uses coupling resistors, the superior performance of the proposed circuit is demonstrated.
In this study, a compact, low-power 2D phase comparison direction finder was designed and fabricated. For the design of the directionfinding (DF) receiver, a 2D phase comparison DF equation was derived from the structure of four uniformly arranged antennas, and the main design parameters were derived from the receiver’s system parameters. Based on the derived DF equations and design parameters, a DF receiver was designed, and a direction finder was fabricated. A comparison of the fabricated direction finder to a simulation model showed that its performance was comparable to the simulated performance and satisfied the system parameters. Moreover, a comparison of the theoretical, simulated, and actual injection and radiation DF precision showed that the fabricated direction finder had performance consistent with that indicated by the theoretical and simulation results and DF precision within 0.5°.
This article proposes the design of a four‐element array antenna for the accurate direction of arrival (DOA) estimation of Global Positioning System (GPS) interference signals. The proposed array antenna has four individual antenna elements, and each element consists of a radiating patch on the upper layer and a feeding loop on the lower layer. The patch and loop are intentionally designed in a circular shape to obtain the symmetric current distributions on the radiators. The feeding loop is directly connected by two output ports of an external hybrid chip coupler, and the radiating patch is then electromagnetically coupled by near‐fields of the feeding loop. This feeding mechanism in the proposed structure allows for a more uniform current and H‐field distribution for phase characteristics of the radiation that are close to the ideal isotropic radiators in the azimuth angle. In addition, the high‐dielectric ceramic substrate is adopted to minimize the physical height of the antenna for the phase characteristics of the radiation close to the ideal isotropic radiators in elevation angles. To validate that the phase characteristics are similar to those of an ideal radiator, the DOA estimation performances are observed using a dual‐axis interferometry. The results demonstrate that the proposed four‐element array antenna with phase difference characteristics similar to those of an ideal radiator is suitable for the accurate DOA estimation of GPS interference signals.
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