Ling Tong

IMPEDANCE MEASUREMENTS OF NONUNIFORM TRANSMISSION LINES IN TIME DOMAIN USING AN IMPROVED RECURSIVE MULTIPLE REFLECTION COMPUTATION METHOD

In this paper, a recursive computation method is developed to derive the multiple re∞ections of nonuniform transmission lines. The true impedance proflles of the nonuniform transmission lines are then reconstructed with the help of this method. This method is more e-cient than other algorithm. To validate this method, two nonuniform microstrip lines are designed and measured using Agilent vector network analyzer E8363B from 10MHz to 20GHz with 10MHz interval. The re∞ection coe-cients of these nonuniform microstrip lines in time domain are attained from the scattering parameters using inverse Chirp-Z transform. The reconstructed characteristic impedance proflles of the nonuniform lines are compared with those reconstructed by Izydorczyks algorithm. The agreements of the results illustrate the validity of the recursive multiple re∞ection computation method in this paper.

Measurements of Planar Microwave Circuits Using an Improved Trl Calibration Method

In this paper, an improved TRL (Thru-Re∞ect-Line) calibration method is presented. This method is based on ten-term error model of a two-port vector network analyzer(VNA) measurement system. Eight error terms induced by flxtures as well as two leakage errors are derived directly from the S parameters of the calibration standards measured from the coaxial reference plane without converting S parameters to T parameters. To validate our algorithm, a microstrip device with a via hole and a coplanar waveguide transmission line are fabricated and calibrated using the present TRL calibration method and Engens algorithm, respectively. The magnitudes and phases of S11 and S21 of the devices are compared. The consistency of the de-embedded results with those calibrated by Engens TRL algorithm illustrates the validity of the TRL algorithm in this paper.

Design of a Microstrip-Fed Hexagonal Shape UWB Antenna with Triple Notched Bands

In this paper, a microstrip-fed hexagonal shape ultra-wideband (UWB) monopole antenna with triple notched bands is presented. The antenna consists of a microstrip feed line, a regular hexagonal shape radiation patch with a complementary split ring resonator (CSRR) and a pair of inverted T-shaped conductor-backed planes embedded in the antenna backside. Notched bands can be easily controlled by geometry parameters of the CSRR and conductor-backed planes. The simulated and measured results show that this monopole UWB antenna can offer an operation frequency from 2.93 GHz to 10.04 GHz with −10 dB return loss bandwidth, except three notched bands at 3.31-3.78 GHz, 5.33- 5.77 GHz and 7.24-7.72 GHz for rejecting the WiMAX and downlink of X-band satellite communication system signals. A good agreement between the measured and simulated results is observed. The proposed antenna provides broadband impedance matching, appropriate gain and stable radiation patterns over its operating bandwidth and can be used in wireless UWB applications.

Directional Coupler Using Multi-Stage Coupled Structure Theory

This paper presents a new directional coupler design, which can increase power capacity working with S band. The design concept is based on multi-stage coupled structure. Aim is to increase the size of coupling aperture by reducing the coupling degree of each stage structure. In view of this, multi-stage coupled structure theory is utilized to improve the directivity of directional coupler, coupling flatness and power capacity. According to the derivation of theory, it can be deduced that the sum of the coupling degree of single stage coupling structure is equal to the coupling degree of twostage coupling directional coupler (TSCDC), and the directivity of TSCDC depends on the directivity of the first stage coupling structure. Then, rectangular waveguide two-stage coupled directional coupler is designed and fabricated. The measured results demonstrate fullband from 1.72 to 2.61GHz with coupling flatness 26 dB.

Improved physical model in layered media for via structures

In this paper, the physical model is extended for vias embedded in layered media between two parallel-plate pairs. The effect of this inhomogeneity on signal integrity analysis is crucial, but is rarely studied especially by using the equivalent circuit model. The model presented in this paper is constituted by upper and lower via-to-plane capacitances which are different from each other due to the inhomogeneous dielectrics and equivalent impedance matrix of the parallel-plate cavity with equivalent wave number. The via-to-plate capacitance with layered media is calculated by using cascaded Green’s function with image theory and integral equation method based on partial capacitance, which is the main contribution in this paper. The parallel-plate impedance is calculated by using the cavity resonator method. Transverse resonance method as well as an equivalent approximation method is used for wave number evaluation. For the first time, the circuit model presented in this paper is used for the issue of layered media, which is much simpler with sufficient accuracy up to 20 GHz when compared with analytical method. The model is validated with full-wave simulations.

An improved physic-based model for via structures embedded in layered media

In this paper, an improved physics-based model is introduced for vias embedded in layered media between two parallel-plate pairs. The model is constituted by upper and lower-via-to-plane capacitances and equivalent impedance matrix of the parallel-plate cavity. The via-to-plate capacitance is extracted by Q3D and the parallel-plate impedance is calculated by using the cavity resonator method (CRM) as well as equivalent wave number. For the first time, this circuit model is presented in this paper for the issue of layered media, which is much simpler with sufficient accuracy up to 20GHz when compared with analytical method. The modelis validated with full-wave simulations.

Design, fabricate and test of a new kind of high power microwave directional coupler

In this paper, a new kind of high power microwave directional coupler operating at 1.72GHz to 2.61GHz is presented. To get a directional coupler with very weak coupling but high power capacity, a two-stage coupling strategy is proposed. Multi-holes coupling structure is used for the first coupling stage, and double cross-aperture is used for the second coupling stage. The coupling factors variation trends of these coupling structures can be designed to be opposite. Then a very flat frequency response will be got. The two-stage directional coupler is designed and fabricated. The measurement results show that this directional coupler has a good performance. The deviation of the coupling is smaller than 0.8dB, and this directional coupler can work normally when a 2MW pulse microwave power put in it. The potential peak power capacity of this directional coupler could be much higher.

Design of a microstrip fed spade shape planar monopole antenna for UWB applications

In this paper, a microstrip fed spade shape planar monopole antenna for ultra wideband (UWB) applications is presented. Modified shapes of the lower edge of spade shape patch and the upper edge of ground plane are optimized. The experiment and simulation are well agreement. The proposed antenna provide broadband impedance matching, appropriate gain and stable radiation patterns over its operating bandwidth from 2.8 GHz to 10.95 GHz for a 10 dB return loss and can be used in wireless UWB applications.

Development of a temperature dependent dielectric constant measurement system

In this paper, a dielectric constant measurement system is presented, which can work at different temperatures from room temperature to 200°C. This system is developed based on the theory of NRW algorithm using coaxial line. The calibration standards are also designed for TRL calibration. Temperature distribution is analyzed and optimized carefully using ANSYS thermal analysis to make sure temperature is uniform on the test fixture and is safe enough to connect to Vector Network Analyzer (VNA). Frequency range of this system is from 1GHz to 18GHz.

The study of 2.45 GHz atmospheric microwave plasma generator

Atmospheric pressure microwave plasma has potential been wildly applied to the experiment and industry. But the equipment of the microwave plasma is not easy to control. In order to make it easier to control, we simulated three adjustable parts to figure their effects out. In this paper, we introduced the structure of the microwave plasma generator, and studied the effects of three parts of the structure by simulation, and measured by the Agilent vector network analyzer (VNA) E50618 10MHz-3GHz. From the simulation and the measurement result, we can get some rules and conclusions of the microwave plasma generator.