Y. J. Guo

A Reconfigurable High-Gain Partially Reflecting Surface Antenna

A high-gain partially reflective surface (PRS) antenna with a reconfigurable operating frequency is presented. The operating frequency is electronically tuned by incorporating an array of phase agile reflection cells on a thin substrate above the ground plane of the resonator antenna, where the reflection phase of each cell is controlled by the bias voltage applied to a pair of varactor diodes. The new configuration enables continuous tuning of the antenna from 5.2 GHz to 5.95 GHz using commercially available varactor diodes, thus covering frequencies typically used for WLAN applications. Both the PRS and phase agile cell are analyzed, and theoretical and measured results for gain, tuning range, and radiation patterns of the reconfigurable antenna are described. The effect of the varactor diode series resistance on the performance of the antenna is also reported.

A Pattern Reconfigurable U-Slot Antenna and Its Applications in MIMO Systems

A new compact pattern reconfigurable U-slot antenna is presented. The antenna consists of a U-slot patch and eight shorting posts. Each edge of the square patch is connected to two shorting posts via PIN diodes. By switching between the different states of the PIN diodes, the proposed antenna can operate in either monopolar patch or normal patch mode in similar frequency ranges. Therefore, its radiation pattern can be switched between conical and boresight patterns electrically. In addition, the plane with the maximum power level of the conical pattern can be changed between two orthogonal planes. Owing to a novel design of the switch geometry, the antenna does not need dc bias lines. The measured overlapping impedance bandwidth (|S11| <; -10 dB) of the two modes is 6.6% with a center frequency of 5.32 GHz. The measured radiation patterns agree well with simulated results. The antennas are incorporated in a 2 × 2 multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system to demonstrate the improvement in system capacity. In the real-time MIMO-OFDM channel measurement, it is shown that compared to omnidirectional antennas, the pattern reconfigurable antennas can enhance the system capacity, with 17% improvement in a line-of-sight (LOS) scenario and 12% in a non-LOS (NLOS) scenario at a signal-to-noise ratio (SNR) of 10 dB.

A Frequency Reconfigurable Printed Yagi-Uda Dipole Antenna for Cognitive Radio Applications

A frequency reconfigurable printed Yagi-Uda antenna is presented for cognitive radio applications. A 46% continuous frequency tuning bandwidth is obtained by loading the driver dipole arms and four directors with varactor diodes. This configuration allows a high-gain and an almost constant end-fire pattern to be maintained while the antenna operating frequency is tuned. A parametric study was undertaken considering the inter-director spacing, director length tapering, and reflector geometry. It was found possible over the band that the front-to-back ratio is >; 16 dB, the sidelobe level is <; -14 dB and the cross polarization levels in the principal planes are <; - 15.5 dB. From 1-dB compression point measurements, the maximum input power of the antenna with the present diodes is limited to 17.6 dBm at 700 MHz. This suggests that reconfigurable antennas which use active components should have an IIP3 specification placed on them. The frequency selective feature of the antenna makes it as an attractive user terminal antenna for fixed point-to-multipoint cognitive radio enabled broadband wireless access.

1D-Leaky Wave Antenna Employing Parallel-Plate Waveguide Loaded With PRS and HIS

A new type of one-dimensional leaky-wave antenna (LWA) with independent control of the beam-pointing angle and beamwidth is presented. The antenna is based on a simple structure composed of a bulk parallel-plate waveguide (PPW) loaded with two printed circuit boards (PCBs), each one consisting of an array of printed dipoles. One PCB acts as a partially reflective surface (PRS), and the other grounded PCB behaves as a high impedance surface (HIS). It is shown that an independent control of the leaky-mode phase and leakage rate can be achieved by changing the lengths of the PRS and HIS dipoles, thus resulting in a flexible adjustment of the LWA pointing direction and directivity. The leaky-mode dispersion curves are obtained with a simple Transverse Equivalent Network (TEN), and they are validated with three-dimensional full-wave simulations. Experimental results on fabricated prototypes operating at 15 GHz are reported, demonstrating the versatile and independent control of the LWA performance by changing the PRS and HIS parameters.

Frequency Steerable Two Dimensional Focusing Using Rectilinear Leaky-Wave Lenses

The concept of frequency steerable two-dimensional electromagnetic focusing by using a tapered leaky-wave line source embedded in a parallel-plate medium is presented. Accurate expressions for analyzing the focusing pattern of a rectilinear leaky-wave lens (LWL) from its constituent leaky-mode tapered propagation constant are described. The influence of the main LWL structural parameters on the synthesis of the focusing pattern is discussed. The ability to generate frequency steerable focusing patterns has been demonstrated by means of an example involving a LWL in hybrid waveguide printed-circuit technology and the results are validated by a commercial full-wave solver.

Electronic Full-Space Scanning With 1-D Fabry–Pérot LWA Using Electromagnetic Band-Gap

A novel mechanism to obtain full-space electronic scanning from a half-space scanning one-dimensional (1-D) Fabry-Pérot (FP) leaky-wave antenna (LWA) is proposed and experimentally demonstrated in this letter. By using a central feed that divides the structure into two independently controlled leaky lines, one each side, and making use of the electromagnetic band-gap (EBG) region of the FP resonator, the antenna can be electronically tuned to operate in three different regimes: backward scanning, forward scanning, and broadside radiation. Leaky-mode dispersion theory and experimental results of a fabricated prototype demonstrate a continuous electronic scanning from -25° to +25° at 5.5 GHz.

Frequency Switchable Printed Yagi-Uda Dipole Sub-Array for Base Station Antennas

A frequency switchable printed Yagi-Uda dipole sub-array is proposed as an array element for base station antennas. The sub-array consists of four Yagi-Uda dipole elements loaded with PIN diodes. The electrical lengths of the director and driven dipole elements can be changed by controlling the PIN diodes states so that the sub-array can operate in two different frequency bands. The impedance bandwidth (|S11|≤ -10dB) is measured to be 4.9% and 12.9% in the lower (from 2.39 to 2.51 GHz) and higher band (from 3.18 to 3.62 GHz), respectively. The measured gain of the sub-array is 9.2 and 11.9 dBi at 2.44 and 3.4 GHz, respectively. The end-fire fan-beam pattern is obtained across the two operation bands, which makes the antenna element suitable for base station application with frequency reconfigurablity.

Rectilinear Leaky-Wave Antennas With Broad Beam Patterns Using Hybrid Printed-Circuit Waveguides

A theoretical study on the design of broadbeam leaky-wave antennas (LWAs) of uniform type and rectilinear geometry is presented. A new broadbeam LWA structure based on the hybrid printed-circuit waveguide is proposed, which allows for the necessary flexible and independent control of the leaky-wave phase and leakage constants. The study shows that both the real and virtual focus LWAs can be synthesized in a simple manner by tapering the printed-slot along the LWA properly, but the real focus LWA is preferred in practice. Practical issues concerning the tapering of these LWA are investigated, including the tuning of the radiation pattern asymmetry level and beamwidth, the control of the ripple level inside the broad radiated main beam, and the frequency response of the broadbeam LWA. The paper provides new insight and guidance for the design of this type of LWAs.

Efficient Synthesis of 1-D Fabry–Perot Antennas With Low Sidelobe Levels

A novel technique for the efficient synthesis of one-dimensional (1-D) Fabry-Perot leaky-wave antennas with low sidelobe levels is described. It is based on the study of the reflection characteristics presented by the two periodic surfaces that form the cavity. The synthesis technique avoids the search for modal solutions in the complex plane, which is typically needed to characterize the dispersion of the leaky modes associated with the antenna geometry. Instead, it involves the solution of two simple equations, so that the desired aperture distribution (amplitude and phase) can be directly synthesized. Numerical and experimental results show that the method can be used to efficiently synthesize 1-D Fabry-Perot low sidelobe leaky-wave antennas for any desired scanning angle.