Zhenghe Feng

A novel compact electromagnetic-bandgap (EBG) structure and its applications for microwave circuits

A novel electromagnetic-bandgap (EBG) structure in a fork-like shape is investigated. This structure has an extremely compact size. A comparison has been carried out between the new structure and the conventional mushroom-like EBG structure. Simulations and experimental results have verified that the area of the fork-like structure is less than 40% of the latter. The presented structure also provides an additional degree of freedom to adjust the bandgap position, which is applied to design a novel reconfigurable multiband EBG structure. Several application examples have been demonstrated, including a double-element microstrip antenna array with low mutual coupling, notch-type antenna duplexer, and steerable array with a linearly discrete beamsteering of 20/spl deg/ in steps of 10/spl deg/ at 2.468 GHz.

Design and Linearization of Concurrent Dual-Band Doherty Power Amplifier With Frequency-Dependent Power Ranges

A design methodology for a concurrent dual-band Doherty power amplifier (PA) with frequency-dependent backoff power ranges is presented in this paper. Based on a dual-band T-shaped network and a coupled line network, different dual-band components needed in Doherty PA topology, including a 3-dB branch-line coupler, an offset line, and a quarter-wavelength transformer, are developed. Two prototypes with balanced and imbalanced backoff power range modes are implemented to verify the feasibility. Continuous wave signal test results show that the proposed dual-band PA successfully achieves a power-added efficiency of 33% and 30% at the 6-dB backoff point from the saturated output power at 880 and 1960 MHz, respectively. To meet linearity requirements, the PA nonlinear behavior is characterized by using digital multitone signals, which categorize the distortions of a concurrent dual-band PA into intermodulation and cross-modulation. Finally, a 2-D digital predistortion technique is used to compensate for the nonlinearity of PA in dual bands. Two two-tone signals are applied to the dual bands for linearization, and the experimental results show that this technique achieves improvements of better than 19.1 and 24.6 dB for the intermodulation and cross-modulation in the dual bands, respectively.

A Dual-Polarization Slot Antenna Using a Compact CPW Feeding Structure

A dual-polarization coplanar waveguide (CPW)-fed slot antenna is proposed in this letter. By exploiting the even and odd modes of a CPW structure, two orthogonal polarizations can be excited in a slot aperture by the same feeding CPW, which results in a compact dual-polarization antenna design with very good isolation between the ports. The -10-dB reflection coefficient bandwidths of two polarizations are 670 MHz (27.9%) for one polarization and 850 MHz (35.4%) for the other, and the isolation between the two ports in the WLAN band is better than -32.6 dB. The radiation pattern and efficiency of the proposed antenna are also measured, and radiation pattern data are compared with simulation results.

A Compact Hepta-Band Loop-Inverted F Reconfigurable Antenna for Mobile Phone

A folded loop-inverted F reconfigurable antenna for mobile phone applications is designed and the obtained results are discussed in this communication. It is shown that loop antenna mode and an inverted F antenna (IFA) mode are controlled by only one p-i-n diodes with simple bias circuit. The impedance can be matched by adopting a matching bridge for both the loop and IFA modes. In a compact volume of 60 × 5 × 5 mm3, the proposed antenna operates in hepta-band, including GSM850, GSM900, GPS, DCS, PCS, UMTS and WLAN, with the return loss lower than 6 dB. A prototype of the proposed antenna is fabricated, measured, and obtained results including return loss, efficiency and gain, are presented.

Axial Ratio Bandwidth Enhancement of 60-GHz Substrate Integrated Waveguide-Fed Circularly Polarized LTCC Antenna Array

A substrate integrated waveguide (SIW)-fed circularly polarized (CP) antenna array with a broad bandwidth of axial ratio (AR) is presented for 60-GHz wireless personal area networks (WPAN) applications. The widened AR bandwidth of an antenna element is achieved by positioning a slot-coupled rotated strip above a slot cut onto the broadwall of an SIW. A 4 × 4 antenna array is designed and fabricated using low temperature cofired ceramic (LTCC) technology. A metal-topped via fence is introduced around the strip to reduce the mutual coupling between the elements of the array. The measured results show that the AR bandwidth is more than 7 GHz. A stable boresight gain is greater than 12.5 dBic across the desired bandwidth of 57-64 GHz.

Polarization Reconfigurable Slot Antenna With a Novel Compact CPW-to-Slotline Transition for WLAN Application

A polarization reconfigurable slot antenna with a novel coplanar waveguide (CPW)-to-slotline transition for wireless local area networks (WLANs) is proposed and tested. The antenna consists of a square slot, a reconfigurable CPW-to-slotline transition, and two p-i-n diodes. No extra matching structure is needed for modes transiting, which makes it much more compact than all reference designs. The -10 dB bandwidths of an antenna with an implemented bias circuit are 610 (25.4%) and 680 MHz (28.3%) for vertical and horizontal polarizations, respectively. The radiation pattern and gain of the proposed antenna are also tested, and the radiation pattern data were compared to simulation results.

Design of a Wideband Horizontally Polarized Omnidirectional Printed Loop Antenna

This letter presents the design of a novel wideband horizontally polarized omnidirectional printed loop antenna. The proposed antenna consists of a loop with periodical capacitive loading and a parallel stripline as an impedance transformer. Periodical capacitive loading is realized by adding interlaced coupling lines at the end of each section. Similarly to mu-zero resonance (MZR) antennas, the periodical capacitive loaded loop antenna proposed in this letter allows current along the loop to remain in phase and uniform. Therefore, it can achieve a horizontally polarized omnidirectional pattern in the far field, like a magnetic dipole antenna, even though the perimeter of the loop is comparable to the operating wavelength. Furthermore, the periodical capacitive loading is also useful to achieve a wide impedance bandwidth. A prototype of the proposed periodical capacitive loaded loop antenna is fabricated and measured. It can provide a wide impedance bandwidth of about 800 MHz (2170-2970 MHz, 31.2%) and a horizontally polarized omnidirectional pattern in the azimuth plane.

Linearization of Concurrent Dual-Band Power Amplifier Based on 2D-DPD Technique

This letter reports a two-dimensional digital predistortion technique to compensate for the nonlinearity of a concurrent dual band PA. Two different multi-carrier WCDMA signals with more than 1 GHz frequency spacing are concurrently employed to drive the PA and verify the linearization performance. Experimental results show that the proposed technique bounds the adjacent channel power ratio to lower than -46 dBc, which is more than 12 dB improvement for both bands concurrently.

Compact Heptaband Reconfigurable Loop Antenna for Mobile Handset

In this letter, an internal folded reconfigurable loop antenna for mobile handset applications is designed, built, and tested. Two operating states with different frequencies are obtained by switching the shorting pins of the loop. The bandwidth of the proposed antenna has been increased by adopting a matching bridge. In a compact volume of 60×5×5 mm3, the proposed antenna operates in heptaband, including GSM850, GSM900, GPS, DCS, PCS, UMTS, and WLAN, with the return loss lower than 6 dB. The efficiency and gain with the p-i-n diodes with their bias circuit are also measured and analyzed.

Compact Azimuthal Omnidirectional Dual-Polarized Antenna Using Highly Isolated Colocated Slots

An omnidirectional dual-polarized antenna with high port isolation is presented for 2.4-GHz wireless local area network (WLAN) applications. The omnidirectional patterns of both vertical and horizontal polarizations in the azimuthal plane are achieved by positioning two orthogonal slots cut onto the walls of a slender columnar cuboid. The overall volume of the proposed antenna is only 83 × 11 × 11mm3 (0.664λ0 × 0.088λ0 × 0.088λ0), with low mutual coupling between two radiating slots. A prototype of the proposed antenna is fabricated and tested. The measured results show that the 10-dB reflection coefficient bandwidths of dual polarizations cover the desired band of 2.4-2.48 GHz and the port isolation is lower than -33.5 dB. Stable gains are greater than 3.17 and 1.19 dBi for vertical and horizontal polarizations, respectively. The diversity performance is also evaluated, including the correlation coefficient, mean effective gain (MEG) ratio, and diversity gain.