Recently, it has been increased the illegal usage of the minimized electronic device such as small disk, minimal camera, hidden listening device, and hidden bomb composed of IC chip made by semi-conductor. Many countries including the United States have been studied and developed steadily Non-Linear Junction Detector (NLJD) system for solving this problem. The NLJD system performance are mainly determined by antenna gain and transmission power. However, this system must have terribly limited power due to exposure restriction of electromagnetic wave for human body. Thus, it was absolutely required the NLJD system with high gain antenna to search the small hidden device.
This thesis presents a design of circular polarization antenna for the NLJD system with high detecting ability. In order to minimize the power reduction by reflected polarization wave from the hidden device, a circular polarization antenna has been mainly used for the NLJD system application. Because antenna for this system has to operate in one transmitting frequency band and two receiving frequency bands, wide bandwidth antenna has been required and researched.
In chapter 2, a circular polarization antenna design for the NLJD system used at the fixed gate was presented. In order to obtain for broad bandwidth, the CPW (Co-Planar Waveguide) feeding method is considered in this design. For realization the circular polarization, the axial ratio was controlled by inserting a 45° inclined slot and by cutting an edge of the radiating patch. Measurement results of return loss, bandwidth, axial ratio, polarization pattern and gain are agreed well with their simulation results at interested frequency band of 2.4∼2.44 GHz, 4.84∼4.92 GHz, and 7.28∼7.32 GHz.
In chapter 3, a spiral antenna design for the portable NLJD system was described. To realize the broadband antenna design, the optimization of the number of spiral turns by iterative calculation was considered. In order to realize high directivity and high gain of the proposed antenna, the cavity wall and the metal cap which is located on back of ground plane were also considered in design. Measurement results of return loss for VSWR 2:1 at interested frequency band were observed reasonable agreement with prediction. Measured axial ratio was observed 3 dB below and agreed well with simulation results. The measured gains of the proposed spiral antenna with the RHCP (Right Hand Circular Polarization) were also observed 6.84 dBi above at 2.44 GHz of the transmitting frequency, and 8.96 dBi at 4.88 GHz and 10.85 dBi at 7.32 GHz of the receiving frequency.
The conclusion of this thesis was summarized in chapter 4.