Sungjoon Lim

Metamaterial-based electronically controlled transmission-line structure as a novel leaky-wave antenna with tunable radiation angle and beamwidth

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is, in essence, a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift keying transmission link and successful recovery of the baseband data is demonstrated.

Electronically scanned composite right/left handed microstrip leaky-wave antenna

A novel electronically scanned periodic microstrip leaky-wave (LW) antenna based on the concept of composite right/left-handed (CRLH) metamaterials is presented. This antenna includes varactors modulating the capacitive loading of the unit cell and therefore the propagation constant of the structure, which results in voltage scanning of the radiated beam. An accurate circuit model is proposed. The antenna is demonstrated experimentally to exhibit continuous scanning in the dominant mode from backward to forward angles. The scanning range is from -10/spl deg/ at 35 V to +7.5/spl deg/ at 0 V, and broadside occurs at 9 V, at the fixed frequency of 3.23 GHz.

Adaptive power controllable retrodirective array system for wireless sensor server applications

An adaptive power controllable retrodirective array system is presented. It is able to conserve battery power in an idle mode and wake up only when it needs to operate, extending the array systems lifetime. One application of this technology is for use as wireless sensor servers, which act as a relay point between wireless sensors and remote data collectors. The proposed retrodirective array is fabricated and tested at 5.8 GHz and uses an integrated rectenna and an analog switch, which controls a battery power source. When an RF signal is received by the antenna array, it is split between a rectenna and receiver (RX), where most power is sent to a rectenna. The collected dc voltage wakes up the system by activating a switch connected to a battery and the RX. When there is no interrogation, the switch turns off. Furthermore, the second and third harmonic rejection characteristic of a circular sector antenna is introduced so that it makes the system simpler by eliminating a low-pass filter in the rectenna. For the phase-conjugation retrodirective array, second subharmonic mixers are used by employing antiparallel diode pairs, which enables avoiding expensive high-frequency oscillators. It is experimentally demonstrated that the retrodirective array system with the proposed power management can retransmit the received signal toward the source when the received power is greater than -8.5dBm. Application of the retrodirective array system as a multifunctional RX array is also investigated.

Electronically-controlled metamaterial-based transmission line as a continuous-scanning leaky-wave antenna

An electronically-controlled metamaterial-based transmission line (TL) is demonstrated for the first time and applied to a continuous-scanning leaky-wave (LW) antenna. This transmission line is a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. The CRLH structure is rigorously analyzed in terms of the equivalent circuit models and dispersion diagrams. The TL behaviour is verified by way of its application as a LW antenna which is experimentally demonstrated. The antenna, operated at the fixed frequency of 3.1 GHz, exhibits the capability of continuous scanning from backward to forward angles over a range of 77/spl deg/ (from -41/spl deg/ to +36/spl deg/), with efficient broadside radiation, by varying the varactors bias voltages from 15V to 0V (5V at broadside).

60-GHz Retrodirective Array System with Efficient Power Management

In this paper, a 60-GHz retrodirective array system is proposed with an efficient power management. The system consists of three sections; a retrodirective array, a local oscillator (LO), and a power management. For efficient battery operation of the retrodirective array, the power management circuit controls the power of the LO by way of a rectenna technology. While there is no interrogating signal, it is initially in a sleeping mode where the system is off with extremely low power. When it is interrogated by an RF signal, the system is awaken and starts consuming full power. The proposed idea is experimentally demonstrated. When the received power density is larger than 0.013 mW/cm 2, the system turns on and starts working as a retrodirective array

Novel arbitrary angle leaky-wave reflector using heterodyne mixing

A novel leaky-wave reflector using heterodyne mixing is proposed and demonstrated experimentally. This reflector uses a unique antenna element and is capable of reflecting an incoming signal to any arbitrary angle by controlling an LO frequency in real time. It may be fully integrated and refined for several commercial and military applications.

Adaptive Power Controllable Retrodirective Array System for Portable Battery-Operated Applications

An adaptive power controllable retrodirective array system is presented for a portable applications. The proposed system is able to turn on only when it needs to operate so that it can avoid wasting battery power in idle mode. This power management is accomplished by employing a rectenna and an analog switch into a battery-operated system. When an RF signal is received by an antenna, it is divided into a rectenna and a receiver, where most power is sent to a rectenna through a 15-dB coupler. The converted DC power from a rectenna wakes up the system by activating a switch connected to a battery and the receiver. When there is no interrogation, a switch becomes off. An output voltage is twice increased by a voltage doubler and added up by connecting in series. The 2 n d and 3 r d harmonic rejection characteristic of a circular sector antenna is introduced so that it makes the system simpler by eliminating a low-pass filter (LPF) in the rectenna. For the phase-conjugation retrodirective array, 2 n d sub-harmonic mixers are used by employing anti-parallel diode pairs (APDPs), which enables to avoid the expensive high frequency oscillators. It is experimentally demonstrated that the retrodirective array system with the proposed power management can retransmit the received signal toward the source when the received power density is over 0.057 mW/cm 2 .

Novel reconfigurable leaky-wave aperture with tunable directivity

This paper presents a novel reconfigurable aperture using leaky-wave radiation with tunable directivity. This property is achieved by controlling the wave propagation in a metamaterial based structure. The wave can be made a fast wave (radiation) or slow wave (guidance) in different sections of the structure by changing bias voltages of varactor diodes loaded on the aperture. Thus, the radiation aperture size is reconfigurable in electronic manner, so that beamwidth is also tunable. The proposed idea is experimentally demonstrated at a fixed frequency, 2.6 GHz. A slow wave factor (SWF) is plotted from a measured phase of S21. Comparing with the complete structure in a fast wave region, a half-power beam-width (HPBW) is increased from 58deg to 90deg in the case that a half of structure is in a fast wave region and the other is in a slow wave region