Zhenchao Yang

III-nitride transistors with capacitively coupled contacts

AlGaN∕GaN heterostructure field-effect transistor design using capacitively coupled contacts (C3HFET) is presented. Insulated-gate [C3 metal-oxide-semiconductor HFET (C3MOSHFET)] has also been realized. The capacitively coupled source, gate, and drain of C3 device do not require annealed Ohmic contacts and can be fabricated using gate alignment-free technology. For typical AlGaN∕GaN heterostructures, the equivalent contact resistance of C3 transistors is below 0.6Ωmm. In rf-control applications, the C3HFET and especially the C3MOSHFET have much higher operating rf powers as compared to HFETs. C3 design is instrumental for studying the two-dimensional electron gas transport in other wide band gap heterostructures such as AlN∕GaN, diamond, etc., where Ohmic contact fabrication is difficult.

Dual-Circular-Polarized High-Efficiency Antenna for Ku-Band Satellite Communication

A multilayer dual-port dual-circularly-polarized (CP) antenna was designed for Ku-band operation. The design is based on a truncated corner square-ring slot configuration with planar multilayer circuit board technology. High isolation is achieved between orthogonal ports while maintaining axial ratio lower than 3 dB for both senses of circular polarization. Highly efficient dual-CP operation makes this design attractive as a building block for passive and active array feeds for reflector antennas used in satellite communication applications.

Multiband Dual-Polarization High-Efficiency Array Feed for Ku/Reverse-Band Satellite Communications

A dual-band dual-polarized planar passive phased array feed was designed and simulated, with four highly isolated ports and polarizations. The feed design provides an important feasibility demonstration for the deployment of a satellite transponder that transmits a downlink signal at 17.3-17.8 GHz, referred to as reverse band (RB), in the same orbital slot as an existing Ku-band satellite. The design utilizes a multilayer printed circuit board (PCB) to separate the complex feed distribution networks required for the four-port antenna. Simulation results indicate that the feed receives signals in dual linear polarization at Ku-band and dual circular polarization at RB with isolation between all ports better than 20 dB. With the feed illuminating a reflector antenna, the aperture illumination and radiation efficiencies are approximately 70% and 80%, respectively, for all ports, representing one of the most complex yet efficient reported planar array feed designs in the literature.

A planar passive dual band array feed antenna for Ku band satellite communication terminals

A planar passive array feed antenna for bidirectional Ku band satellite communication was designed, fabricated and measured. The feed antenna achieved 50 dB isolation between transmit and receive ports across the transmitting band. An on-reflector test was conducted by mounting the array feed with external low noise amplifier and block downconverter (LNB) on a 90 cm dish to verify the feed radiation efficiency and illumination pattern. The measured signal to noise ratio (SNR) with the planar feed including loss in test connectors was within 2 dB of that of a commercial horn feed.

Effect of mutual coupling on the sensitivity of dual polarized receivers in satellite communications

Dual circular polarization (CP) services are growing in popularity in satellite communications applications. Ground terminals with linearly polarized dish antenna feeds routinely achieve high port isolation between polarizations, but dual CP feeds suffer from higher coupling between ports associated with orthogonal polarizations, particularly for planar microstrip antennas used in electronically beamsteered phased arrays and array feeds. To enable optimal design of CP feeds for satellite ground terminal receivers, an analysis of the effect of mutual coupling on the sensitivity of dual polarized receivers was used to obtain a quantitative relationship between coupling and receiver sensitivity.

Improved Antenna Efficiency Measurement Uncertainty in a Reverberation Chamber at Millimeter-Wave Frequencies

We provide results of antenna radiation and total radiation efficiency at millimeter-wave frequencies gathered with a new open-ended waveguide-plate method that is compared to a well-known two-antenna method. The new method yields improved uncertainty in antenna efficiency measurements. Both methods are based on use of a reverberation chamber. Measurement results are compared to numerical simulations and good agreement (~3% maximum difference) is achieved. Before performing the efficiency measurements, the chamber configuration was assessed with respect to the Rician

A high radiation efficiency microstrip array feed for Ku band satellite communication

K

High-Efficiency Stacked Shorted Annular Patch Antenna Feed for Ku-Band Satellite Communications

-factor, number of uncorrelated paddle orientations, and coherence bandwidth. We calculated the uncertainty using the NIST microwave uncertainty framework capable of performing parallel sensitivity and Monte Carlo analyses. The framework enables us to capture and propagate the uncertainties in the S-parameter measurements to the final efficiency result. The expanded uncertainty that we achieved for these antenna efficiency measurements is 2.60%.

Jones matrix and S-parameter analysis using an equivalent circuit model for intrinsically dual circularly polarized microstrip antennas

For satellite communications terminals, the radiation efficiencies typically achieved by microstrip antennas (MSA) are inadequate. To realize more efficient planar antennas for this application, the dependence of radiation efficiency on two key parameters, substrate relative dielectric constant and thickness, was investigated, and substrate selection guidelines were developed for high radiation efficiency antenna design. Based on the selected substrate, two types of MSA array feeds for Ku band satellite communication were designed, simulated, fabricated and measured for radiation efficiency comparison. One of the MSA arrays achieved a radiation efficiency of 93% at 12 GHz, which is among the best reported efficiencies for this frequency and class of antennas.

Optical electric field sensor sensitivity direction rerouting and enhancement using a passive integrated dipole antenna

Reflector-based satellite communication (SatCom) terminals require high sensitivity to minimize overall antenna size, and in view of their simplicity and high radiation efficiency, horn antennas are used almost exclusively as reflector feeds. As these terminals become more complex, smaller and more compact feeds that can be directly integrated with microstrip circuits are desirable. Standard microstrip antennas (MSAs) have unacceptably low radiation efficiency for use as reflector feeds. We show that the stacked shorted annular patch (SSAP) can be used as a replacement for horn feeds and achieves higher radiation and spillover efficiencies than conventional patch antennas due to the absence of distribution networks and dielectric substrates. Using a half-wavelength stacked patch as a director realizes a pattern that achieves high illumination efficiency with standard parabolic reflector geometries. Simulation and measurements show that the compact SSAP may be the first reported nonwaveguide feed antenna to achieve sensitivity comparable to that of a conventional horn feed.