Xuexia Zhang

L-band circular polarization microstrip antenna based on the narrow-slot fractal method

The resonant frequencies of traditional Koch island fractal patch antennas and their narrow-slot counterparts are investigated. The simulation shows that at the stage of higher than the first iteration, the narrow-slot fractal patch antenna has a better effect in decreasing the resonant frequency and reducing the antenna dimension, and this is partly due to its higher performance in increasing the effective electrical length. By applying this new method, the antenna dimension can be reduced by 62% but still has a proper radiation pattern.

A broadband patch antenna array for wireless LANs

A comparison between the proposed patch-array and a common patch-array without parasitic elements is carried out. It is proved that the proposed patch array has a 2.13 dB higher gain than the common patch-array. Also, the patch array has a broader E-plane beam width relative to the Yagi antenna, which is useful in the application of wireless LAN, as a multiple of terminals may be distributed in a wide angular range.

Dual frequency double-branch printed inverted-F antenna

Introduction The antennas with inverted-F structure are widely used for mobile handsets. Generally speaking, any radiating pole (such as conducting wire, strip, patch) with grounded point can be described as some kind of Invert F structure. This very compact and low-cost structure can be derived many type antennas for wireless applications. In [1][2], the PIFA is printed on the circuit board. The planar structure has extremely low profile and is more conveniently to be integrated with circuit, compared with other type IFA. Recently, the double branches printed IFA structure has been presented to broaden bandwidth in [3], where the end of radiating arm is bifurcated. The bifurcation structure is equivalent to perturbation adding into the radiating structure. In this paper, the double branches structure is further developed and the dual frequency DB-PIFA (Double-Branch Printed Inverted-F Antenna) prototype is firstly proposed.

Study of horn NRD leaky-wave antenna

A coupled transverse equivalent network considering both TE/sup z/ and TM/sup z/ waves was proposed by Sanchez and Oliner (1984). On the basis of this equivalent circuit, the complex propagation constant of a horn nonradiative dielectric (NRD) waveguide leaky-wave antenna is obtained, and the theoretical results are verified by experiment. The study was motivated by the idea of using the horn to enhance the gain of an NRD leaky-wave antenna.<<ETX>>

Application of cryogenic tuning technique in an HTS filter

This paper describes a method for tuning an HTS filter at the cryogenic temperature. Sonnet software was used for simulating the distribution of current density. Dielectric tuning screws were used to regulate the redistribution of electromagnetic field, so that the response characteristics of the filter can be improved. For matching the designed result, this technique allows correcting the deviation caused by fabrication processing and non uniformity of substrate thickness and dielectric constant. 9-pole forward-coupling microstrip filter as a sample shows its response characteristics before and after tuning. The tuning result showed better performance than simulation. The insertion loss and return loss were improved and the center frequency shift towards the low end after tuning

Phase matching technique for HTS filter-cryogenic LNA subsystem

A novel kind of phase matching technique for improving the reflection loss performance of HTS filter subsystems is proposed. The basic principle is that excellent performance is obtained by realizing the inverse phase relationship of the HTS filters S/sub 22/ parameter and the cryogenic LNAs S/sub 11/ parameter at those frequencies where poor S/sub 11/-peaks of the HTS filter exist. We applied this technique to an HTS filter subsystem for 800 MHz wireless communication. Simulation and test results are presented, and it has been proved that this technique is not only effective but also easy to apply and low cost.

Characteristics of low noise 800MHz amplifier at cryogenic temperature

Low noise amplifiers (LNA) have been designed and developed with high performance at cryogenic temperature in CDMA superconducting receiver front end. The low noise amplifier has been characterized at liquid nitrogen temperatures. The frequency band is in the range from 780MHz to 880MHz using Agilent PHEMT which has low noise figure at cryogenic temperatures. The components were implemented with lumped elements, which can make the LNA for the miniaturization and reduce the load consumption of the cooler. In the frequency band of operation at 60K, the achieved noise figure (NF) is within 0. 3 dB from the minimum NF of a single transistor, the power gain is about 17 dB, flat is within 1 dB, the maximum input VSWR/sub in/ and output VSWR/sub out/ are lower than 1.3 individually.

A low profile monopole antenna using a dumbbell EBG structure

A low profile monopole antenna with a novel DEBG structure has been realized. The DEBG structure is equivalent to a magnetic wall around 5.2 GHz. When the antenna works within 4.9-5.15 GHz it can be placed above the DEBG ground only 1.5 mm high. The gain has been improved by 6.5 dB and 5.7 dB in H plane and E plane. The power capacity can be improved while the gain enhancement remained by insertion of a superstrate.

A novel low profile slot-multi-layer patch antenna

We present a novel type slot-multi-layer (SML) patch antenna in which the air-substrate topological structure is used to preserve the relatively thinner profile characteristic (/spl les/0.14/spl lambda/) and also to keep the broad width ( /spl ges/30%). The total operating bandwidth (VSWR<2) of this type of antenna can easily cover from 2.1 GHz to 4.4 GHz.

The current distribution of high-Tc superconducting microstrip lines

In spectral-domain, the complex propagation constants Kxo of microstrip transmission lines with a definite-thickness HTSc strip and the current distributions on the strip are calculated. The key technique is that when the current distribution is calculated, the first coefficient C/sub 0/ must be reasonably supposed as a complex value to consider the effect of the Two-Fluid Model.