Hongming An

A novel measurement technique for amplifier-type active antennas

A novel technique is proposed for the measurements of the transducer power gain and noise figure of the amplifier embedded in a receiving active antenna, where the direct measurements with traditional techniques are impossible. The bandwidth of the active antenna can be also determined with this technique. The good agreement between the measurements and calculations of a number of active receiving microstrip antennas shows the validity of the measurement technique. This makes it possible to characterize all the performance of receiving active antennas.<<ETX>>

Analytical and experimental investigations of aperture coupled unidirectional dielectric radiator arrays (UDRA)

Experimental and analytical investigations of unidirectional dielectric radiator arrays (UDRA) are presented for the first time. Attractive electrical performance due to the use of nonradiating dielectric waveguide (NRD) structures is demonstrated. A numerical model based on a cavity-resonator approximation is developed for prediction of radiation properties of the UDRAs. Good agreement between measurements and calculations shows the validity of the modeling approach. On the other hand, the feed technique for the UDRA by microstrip line and coupling-aperture is experimentally investigated. Measurement results show high coupling and radiation efficiencies of the proposed excitation method. Such a circuit configuration allows the combination of planar millimeter-wave M(H)MICs and NRD components in one system for the best use of different technologies.

A 50:1 bandwidth cost-effective coupler with sliced coaxial cable

A 20 dB 50:1 bandwidth, extremely low-cost coupler with sliced coaxial cable is reported in this paper. The proposed coupler consists of two shaped coaxial cables with adequate sliced linear-tapered cuts and soldered together. It has excellent performance in terms of low VSWR, good isolation, excellent EMI shielding, ultrawide coupling bandwidth, and high power handling capability. Good agreement between measurements and calculations on one hand shows the excellent performance of the coupler, and on the other hand validates the design procedure.

Spectral-domain analysis of radiating cylindrical dielectric resonator for wireless communications [WLANs]

A novel class of leaky-mode cylindrical dielectric resonators including mounting holder and radial-step has been recently proposed as a feed structure for omnidirectional antennas that are suitable for wireless communication systems. In this work, a spectral-domain modeling is developed and used for analysis of these composite cylindrical dielectric resonators considering single and double radiating slots. The dielectric resonators are bounded between two parallel conducting plates so that leaky-wave propagation takes place under some electrical and geometrical conditions. Results and discussion are focused on the properties of low-order leaky TM-modes. Influences of various structural parameters on resonant frequency and quality factor of leaky dielectric resonators are presented in detail. A set of experiments are made to verify the proposed theoretical approach.

Radiation pattern prediction of the unidirectional dielectric radiator (UDR)

The authors present a theoretical prediction of the radiation patterns of the unidirectional dielectric radiator (UDR) using a cavity approximation. The antenna structure is first modeled as an NRD resonator, and the electromagnetic fields at the radiating aperture of the antenna structure are then determined and used to calculate the radiation fields and the radiation patterns of the antenna. The validity of the analysis is confirmed by the measurement results.<<ETX>>

A novel leaky-mode cylindrical dielectric resonator used as feeds of omnidirectional antenna for wireless communications

This paper presents a novel leaky-mode cylindrical dielectric resonator including mounting holder and radial-step, which can be used as feeds of a class of omnidirectional antennas suitable for wireless communication systems. An enhanced spectral domain (SDA) approach is extended to determining resonant properties of the proposed resonator. Numerical results are focused on low-order leaky TM-mode properties. The effects of different structural parameters on resonant frequencies and quality factors are studied in detail. Theoretical results are verified by experiments.<<ETX>>

A novel microwave omnidirectional antenna for wireless communications

A novel microwave omnidirectional antenna is proposed in this paper for wireless communications. This antenna is constructed with cavity-restrained multi-stacked dielectric disks. Vertical polarized omnidirectional radiation patterns are obtained from radiative ring slots in the side wall of dielectric-metal cavities operating on TM/sub 01/spl delta// mode. High omnidirectional gain is realized with stacked cavities with multi-radiative slots. Ring slots between the adjacent cavities are used to enhance the excitation of the desired radiating mode in phase, which actually eliminates the feed network. A special technique is adopted for excitation of the antenna from coaxial line, with which very good matching is achieved. This type of antennas could be ideal for the base or center stations for wireless and indoor communications. Experimental results of a prototype of the antennas working at 12.6 GHz is given to demonstrate the great potentials for wireless applications.

Broadband Active Microstrip Antennas

The concept of combining active devices with radiating elements for broadband active antenna design was proposed. An active microstrip transmit antenna was realized by using two sided structure and single-ended one-stage amplifier configuration. A 24 percent bandwidth, which is about 6 time that of the passive patch, was achieved both in terms of active reflection coefficient and flat gain of radiation, and about 9dB extra gain was obtained in the working band. The results are attractive for broadband MIC active array design and probably the same concept can be used in broadband MMIC applications such as in radar and satellite communication.

A novel type of low-cost high performance coaxial cable coupler

A new type of extremely low-cost, high-performance couplers is presented in this paper. The proposed coupler consists of two U-curved coaxial cables with proper cuts on the bottom of the curves and soldered together. It has excellent performance in terms of high directivity, low VSWR, very good isolation, excellent EMI shielding, moderate and wide coupling bandwidth, and high power handling capabilty. Detailed analysis of the coupler is carried out for the first time. Some very useful properties of this kind of couplers are found. Strong couplings such as 3-dB can be easily realized with two tandem connected coupler of low coupling coefficients. We have successfully realized a 11-dB coupler with return loss of ¿30 dB and directivity of higher than 32 dB (maximum 42 dB), for example. Good agreement between measurements and calculations on one hand shows the excellent performance of the coupler, and on the other hand validates the design procedure.

Experimental study of cavity-backed dielectric disk and ring omnidirectional antennas for indoor wireless communications

The performance of a new type of cavity backed disk and ring dielectric antennas is experimentally investigated. The suitability of its application in microwave/millimeter wave indoor wireless communications is discussed in terms of return loss, bandwidth, gain and radiation patterns.