Yu-Xiong Cao

Broad-band orthomode transducers

The design and test results of a quad-ridged waveguide L-band orthomode transducer (OMT) for radio telescope are presented. This OMT achieves satisfactory performance using relatively short length compared with other same kind of designs. Measurements of the system in the frequency range 1-4GHz agree well with simulation results. The broad-band return loss and cross-polarization behavior is given where the OMT used is measured in conjunction with a wideband scalar horn.

A Combined Model With Electrothermal Coupling and Electromagnetic Simulation for Microwave Multifinger InP-Based DHBTs

This paper presents a combined model with electrothermal coupling and electromagnetic (EM) simulation for multifinger InP-based double heterojunction bipolar transistors (DHBTs). The electrothermal coupling effect, which occurs in multifinger InP DHBTs, is characterized based on 3-D thermal simulation. In addition, EM simulation technique is presented to account for the distributed effect of interconnection of the fingers and their surroundings. A large-signal model for single-finger DHBTs is implemented as a seven-port symbolically defined device, which accounts for several physical phenomena, including the self-heating effect, Kirk effect, current blocking effect, mobile charge modulation of the base-collector capacitance, and velocity field modulation in the transit time. The combined model implemented in Agilent-ADS is verified by comparing the simulated and measured data in dc small-signal S-parameters and large-signal microwave power characteristic. This approach allows a simple method to analyze and predict microwave multifinger InP DHBTs for power amplifier circuit design using commonly available computer-aided design tools such as Agilent-ADS.

A W-band two-stage cascode amplifier with gain of 25.7 dB

A W-band two-stage amplifier MMIC has been developed using a fully passivated 2 ? 20 ?m gate-width and 0.15 ?m gate-length InP-based high electron mobility transistor (HEMT) technology. The two-stage amplifier has been realized in combination with a coplanar waveguide technique and cascode topology, thus leading to a compact chip-size of 1.85 ? 0.932 mm2 and an excellent small-signal gain of 25.7 dB at 106 GHz. Additionally, an inter-digital coupling capacitor blocks low-frequency signal, thereby enhancing the stability of the amplifier. The successful design of the two-stage amplifier MMIC indicates that InP HEMT technology has a great potential for W-band applications.

An improved VBIC model for InP DHBTs

An emprical model is established for InP/InGaAs DHBTs based on the VBIC model. The heterojunction barrier and current blocking effect are considered in the current expressions. And new empirical models for transit time and collector capacitance are proposed by considering the voltage and current dependence. The excellent fitting results show that the improved model has better accuracy than the conventional VBIC model.

A 20-dB gain W-band InP DHBT power amplifier

A two-stage double heterojunction bipolar transistor (DHBT) power MMIC fabricated in InP technology is realized using coplanar waveguide structure. The output cell unit consists of four parallel cascode fingers. Sixteen fingers are at output stage from which the power is combined. Broad-band, low-loss matching networks lead to high gain and high combining efficiency. The chip area is 1.5×1.7 mm2. Measurements show that small signal gain is above 20 dB over 75.5 GHz ~ 84.5 GHz frequency band. Simulated saturated power is 19.7 dBm @ 89 GHz and the actual output power is to be measured once the W-band power source arrive.

A W-band two-stage cascode amplifier with small-signal gain of 25.7 dB

A W-band two-stage amplifier MMIC has been developed using a InP-based high electron mobility transistor (HEMT) technology. The two-stage amplifier has been realized in combination with coplanar waveguide topology and cascode transistors, thus leading to a compact chip-size of 1.85 mm×0.932 mm and an excellent small-signal gain of 25.7 dB at 106 GHz. The successful design of the two-stage amplifier MMIC indicates the InP HEMT technology has a great potential for W-band applications.

A physical model for scaling and optimizing layers structure of InGaAs/InP double heterojunction bipolar transistors based on hydrodynamic simulation

Currently the most popular HBTs model are unscalable and cannot be used for device structure optimization which must primarily be calibrated with already fabricated and measured devices. To overcome the problem, a physical model for scaling and optimizing layers structure of InGaAs/InP double heterojunction bipolar transistors (DHBTs) based on hydrodynamic simulation is developed in this paper.