Seong-Sik Jeon

High isolation dual-polarized patch antenna using integrated defected ground structure

This letter presents a high isolation dual-frequency orthogonally polarized rectangular patch antenna utilizing microstrip feed line integrated with a defected ground structure (DGS). The demonstrated approach results in a significant improvement in port isolation in comparison to a conventional dual-polarized antenna fed by simple microstrip lines. Measurements show an improvement of 20 dB in port isolation relative to the conventional antenna, operating at 2 and 2.5 GHz. Image impedance of a microstrip line with DGS is controlled by the DGS geometry without modifying the dimension of the line. A 150 /spl Omega/ high impedance line is effectively implemented using a microstrip line with 75 /spl Omega/ line width by incorporating the DGS.

A smart antenna receiver array using a single RF channel and digital beamforming

A new type of smart antenna array receiver with adaptive digital beamforming is proposed. The proposed system offers a drastic reduction in hardware requirements for the smart antenna system through the use of a new Spatial Multiplexing of Local Elements (SMILE) scheme. In this scheme a single element of the array is sequentially connected to signal processing circuitry in order to sample the modulated carrier signal. The sampling rate is higher than the signal bandwidth so the information of the original signal can be fully restored in the post stages using low pass filters. The reconstructed baseband data is then used for adaptive digital beamforming. This system offers an N times reduction in RF hardware for an N element array. A four element prototype is built and discussed, including a new type of array feed network.

Multifunctional microstrip transmission lines integrated with defected ground structure for RF front-end application

This paper presents multifunctional microstrip transmission lines for designing a high port-isolation dual-frequency orthogonally polarized rectangular patch antenna and the antenna-integrated power amplifier. The proposed lines were realized through the integration of defected ground structures (DGSs) with conventional microstrip lines. A spiral-shaped DGS-integrated microstrip line enhances the port isolation of the antenna, while feeding the 2.0-GHz excitation to the antenna and filtering out the 2.5-GHz receiving signal from the other port. High-order harmonic signal suppression of the power amplifier at the 2.5-GHz port was accomplished by the dumbbell-shaped DGS, thereby improving the efficiency of the amplifier. Measurements show an improvement of 20 dB in port isolation and 3% in power-added efficiency relative to an identical RF front-end, but integrated with a conventional patch antenna. An image impedance of the DGS-integrated microstrip lines can be controlled by the integrated DGS geometries. Relatively high-impedances lines, i.e., 150 and 100 /spl Omega/, are effectively implemented using microstrip lines with 75- and 50-/spl Omega/ linewidths by incorporating the spiral- and dumbbell-shaped DGSs, respectively.

A novel smart antenna system implementation for broad-band wireless communications

A novel design of smart antenna system with adaptive beamforming capability is introduced for broad-band wireless communication. To achieve high data throughput of the multi-antenna system, a parallel analog-digital (A/D) signal processing scheme is proposed. The essential idea is to realize the real-time beamforming using heterodyne RF and IF circuitry. The bottleneck of digital signal processor (DSP) I/O and processing speed is thus relieved, while the advanced signal processing capability of the DSP chip is utilized. Based on this idea, a 5.8 GHz smart antenna receiver is implemented. Various experiments are carried out to examine the direction of arrival (DOA) estimation, beam synthesis, and bit error rate (BER) performances of the system. A 20-Mb/s data throughput using binary phase shift keying (BPSK) modulation is demonstrated for this eight-element adaptive array.

Integrated antenna with direct conversion circuitry for broad-band millimeter-wave communications

A compact integrated antenna with direct quadrature conversion circuitry for broad-band millimeter-wave communications is proposed. The conversion circuits include two even-harmonic mixers based on antiparallel diode pairs (APDPs). The equivalent circuit of the APDP derived here provides good agreement with the measured data from 17 to 23 GHz. Overall phase and amplitude imbalance between the in-phase/quadrature (I/Q) output channels are less than 1.2/spl deg/ and 1 dB at IFs of 10 and 100 MHz, respectively. An overall RF power conversion loss of 14.6 dB at the quadrature I/Q channels including the antenna is achieved in the frequency range from 39.75 to 40.25 GHz with a local oscillator (LO) power level of 11.8 dBm. LO leakages at 20 and 40 GHz are -31.5 and -44.8 dBm, respectively. In order to demonstrate the system capabilities for broad-band digital communication, a communication link is built with a pair of the proposed front-ends. Data transmission up to 1 Gb/s data rate for quadrature phase-shift keying modulation is demonstrated.

A novel planar array smart antenna system with hybrid analog-digital beamforming

In this paper, a novel design of a smart antenna system based on hybrid analog-digital beamforming is proposed. The goal of the design is to construct smart antenna beamforming systems with high data rate throughput. The speed bottleneck in DSP I/O congestion is relieved using analog beamforming at the IF frequency, while the advanced signal processing capability of the DSP chip is retained. The data throughput of 20 Mbps for BPSK is reported for an 8-element adaptive array. DOA estimation and the beamforming result based on this new beamforming concept is demonstrated.

Digital wireless sensor server using an adaptive smart-antenna/retrodirective array

A wireless sensor server is developed based on a reconfigurable active smart-antenna/retrodirective array. The system can serve as both a retrodirective array transponder and a smart-antenna receiver simply by changing the frequency of the local oscillator applied to the mixers, enabling it to utilize its hardware best to suit its communication environment. When operating as a direct-conversion receiver, the receiver array successfully demodulates a quaternary phase-shift keying (QPSK) modulated signal with circuit gain of 7 dB, and E/sub b//N/sub 0/ for BER=10/sup -4/ is approximately 12 dB without any error correction. In the retrodirective array mode, the system provides 20 dB circuit gain and 20 dB radio-frequency/intermediate-frequency isolation at the center frequency as well as phase conjugation, exhibiting excellent retrodirectivity. The mixers perform phase conjugation and modulation simultaneously, enabling the transmission of locally stored data. The local data is successfully extracted by an interrogator.

A frequency autonomous retrodirective array transponder

Retrodirective arrays are able to radiate a signal in response to a signal transmitted by an interrogator back toward the transmitter position with no a priori knowledge of the arrival direction. We present a novel architecture that enables the retrodirective array to respond to an interrogator at the same transmitted frequency with no previous knowledge of the transmission frequency. The frequency agile prototype array shows excellent retrodirectivity at various frequencies.

Active quasi-Yagi antenna direct conversion receiver array with digital beamforming

A four-element array single card receiver for indoor wireless applications at C-band is presented. A broadband quasi-Yagi antenna is adopted as the antenna array element due to its broad beamwidth and low mutual coupling characteristics. The integrated receiver circuit uses a multilayer architecture, where RF and baseband circuits are placed above and below the antenna substrate, resulting in a very compact design. Using digital signal processing, the array element patterns are calculated from the four-channel amplitude and phase information of the baseband outputs. An initial test of the integrated receiver shows a scanning range of 70/spl deg/, without the use of any adaptive algorithm.

A broadband beamformer for millimeter-wave systems using sub-band sampling

In this paper, a broadband beamforming system for millimeter-waive systems is proposed. DOA is estimated by sampling only part of signal spectrum, thus the beamformer system does not require high speed sampling rate of A/Ds. In addition, an I/Q vector attenuation scheme was used for the IF weighting process. For the weighting process, a balanced structure of a reflection type variable attenuator was used in order to obtain a linear phase response within 500 MHz bandwidth at IF of 2.75 GHz.