A very low spurious frequency doubler for wireless communication systems is proposed. The key to this technique is to change the input signal into a rectangular wave, which effectively suppresses the fundamental frequency and the odd harmonic components. The desired to undesired signal ratio (D/U) is better than 50 dBc at the desired output frequency of 1.1 GHz. The proposed doubler eliminates the need for the band-pass filters which occupy a large part of the radio frequency (RF) module. High order multipliers easily are fabricated with this method. In this paper, a quadrupler is also described.

The Finite-Difference Time-Domain (FDTD) method has been applied to study the scattering characteristics of Fabry-Perot cavities with infinite planar periodic surfaces. Periodic Boundary Conditions (PBC) are used to reduce the analysis to one unit periodic volume. Both dielectric and metallic losses are included in the algorithm using a frequency dependent formalism. This technique is used to study the frequency response of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors. These cavities are assumed to be illuminated by a normally incident plane wave. After a detailed description of the algorithm, we show theoretically the separate effects of dielectric and metal losses on the transmission coefficient of such cavities. We compare also simulation results to measurements, in the 60 GHz band, of resonant frequencies and Q factors of cavities with various mesh parameters.

This paper suggests a new type of 180-degree 3 dB hybrid, which consists of a cylindrical cavity and four E-plane rectangular waveguides radially coupled with it, and shows that good hybrid properties are realized by modifying the positions of the four input/output waveguides and the radius of the cylindrical cavity that are determined by the field distribution of the TE111 resonant mode. Moreover, a method of broadening the bandwidth with additional impedance steps is described. The present hybrid is marked by simple structure, and hence is useful for applications at millimeter wave frequencies and to high-power microwave systems. Experimental verification is additionally shown.

High-temperature superconductor (HTS) receiving filter subsystem for mobile telecommunication base station has been developed. An 11-pole HTS filter using YBa2Cu3O7-δ (YBCO) thin films and a low noise amplifier were cooled to 70 K by a small cryocooler. Total noise figure of this subsystem was measured to be 0.5 dB. Furthermore the effect of using the subsystem in the receiver front-end of Code Division Multiple Access (CDMA) cellular base station was investigated. The transmitting power reduction of handy terminal was estimated to be about 35%.

Design of circularly polarized active antennas of dual-fed square patch type is given, and spatial power combining and phased array operation of the antennas have been successfully achieved. In a phased array experiment of the arrays with two and three active antennas by the method of varying their free-running oscillation frequencies, we obtained the scan angles from -12 to +13 and those from -13 to +13, respectively, and good axial ratios together with high spatial power-combining efficiencies.

This paper describes a multibeam antenna which uses switched parasitic and switched active elements to obtain multiple simultaneous directional beams that can be steered in azimuth. A 13 element monopole multibeam array has been optimised for gain and front to back ratio. Results from numerical simulation and measurements in an anechoic chamber are presented. The 13 element array can achieve up to three beams simultaneously with a minimum gain over 360 azimuthal coverage of 1.2 dB less than the maximum gain. Located on a ground plane with diameter of 2λ at 1.5 GHz, the maximum elevation angle was 20.2 with -3 dB vertical beamwidth of 88.

A cavity-backed two-element rectangular loop slot antenna for circular polarization is presented and investigated by using the generalized network formulation based on the equivalence principle. By applying the method of moments, the magnetic current including the effect of the cavity is obtained for a thin rectangular loop slot. Two short-circuiting points are introduced on the slots to get circular polarization and symmetrical radiation pattern. The axial ratio bandwidth (3 dB) with VSWR (2) reaches 7.6%. The measured and computed results are in good agreement.

Microstrip leaky-wave antenna fed by an aperture-coupled microstrip operating at K-band is presented. Using the aperture-coupled microstrip as a feeding structure can fully exploit the wideband characteristic of the microstrip leaky-wave antenna. The dimensions of the antenna are obtained from the calculation of the propagation characteristics. Measurement shows a bandwidth of 22% for VSWR < 2:1 and a peak power gain of 12 dBi at 22 GHz for one element. Four-element array is developed with a gain of 18.7 dBi and the frequency-scanning feature is exhibited. The waveguide model is verified by measuring the 3-D radiation pattern of the microstrip leaky-wave array.

Thin-film slot-array receiving antennas fed by coplanar waveguide (CPW) were fabricated on fused quartz substrates, and the antenna properties were investigated at 700 GHz. It was confirmed that the transmission efficiency of CPW was 0.83/λm, and the rate of radiated power from a slot antenna was 0.5 at 700 GHz. The fabricated antennas worked as expected from the theory based on the transmission line model, and the two-dimensional 83 slot-array antenna fed by CPW increased the power gain by 11 dB over a single-slot antenna. The power gain of the antenna was 13 dBi and the aperture efficiency was 40% when the 700 GHz-submillimeter wave was irradiated through the substrate.

There is currently a need for development of a new frequency band to enable creation of next-generation mobile communication systems. Of the potential bands, the 3 GHz and over microwave band holds the greatest promise. Experimental studies on the delay characteristics of multipath propagation must be conducted in order to achieve high-speed transmission in the microwave band. We have developed a system for measuring the microwave broadband propagation delay profile over 100 MHz spread bandwidths in the 3, 8 and 15 GHz bands. Our experiments confirmed system performances of 20-ns resolution, 40-µs maximum measurable delay, relative amplitude error of within 3 dB and dynamic range of over 60 dB. We used our system to measure delay profiles on an urban area with line of sight, particularly, in terms of the effects of mobile antenna height. Typical examples are presented. Analysis showed that delay spreads increased with transmit/receive distance and decreased with the higher antenna height.

This paper presents a novel full-band optoelectronic system extending the capabilities of vector network measurements to the millimeter-wave regime both in small and large signal analysis. The design of the measurement system is made with an emphasis on its practicability for real-world applications using all 1.55-µm-wavelength-based photonic technology. We demonstrate the performance of this network analyzer by measuring the 2-port S-parameters of a HEMT device. The accuracy of the results is also shown by comparing them with conventional 50-GHz electronic measurements. The transit frequency of the active device of over 100 GHz is directly measured for the first time to our knowledge.

In microwave hyperthermia for cancer therapy, two power feeding techniques can be utilized: incoherent and coherent operations. In the incoherent operation, not-synchronized microwave power is fed into each array element, whereas the coherent operation is achieved by feeding synchronized microwave to the array elements. The authors have been studying the coaxial-slot antenna for interstitial microwave hyperthermia. The antenna is usually employed as an array applicator inserting several antennas into the tissue to generate large heating area. So far we have examined the control of the heating pattern by feeding techniques in order to obtain more uniform and enlarged heating region. Particularly, `tip-heating,' which means sufficient heating at the area near the tip of the applicator, is significant not to damage surrounding normal tissue in interstitial hyperthermia. In this paper, two feeding techniques are combined and calculated temperature distributions in a hexagonal array applicator are examined by solving Pennes bioheat transfer equation by finite difference method. As a result, in the coherent feeding, large heating area was obtained, while better tip-heating was achieved in the incoherent feeding. Moreover, an instance of sequential combination of two feeding techniques is depicted. In this case, temperature distribution had both characteristics of large heating area and tip-heating, therefore the ability of the control of heating characteristics by sequential combination of the coherent and the incoherent feedings was presented.

If a four-port network is terminated by arbitrary impedances, the conventional methods for even- and/or odd-mode excitation analyses are not available because no symmetry planes exist. Under these conditions, two types of new design equations for asymmetric 3-dB branch-line hybrids are reported. To make sure that the derived design equations are correct and adaptable, simulations were performed under assumed ideal conditions for one type of asymmetric 3-dB branch-line hybrid and a uniplanar branch-line hybrid terminated by 50 Ω, 41.6 Ω, 55.6 Ω and 62.5 Ω was fabricated and measured for another type of asymmetric 3-dB branch-line hybrid.

Anomalous leakage current which flows between source and drain in thin film SOI MOSFET's is investigated. It is confirmed that the leakage current is caused by enhanced diffusion of the source/drain dopants along the LOCOS-induced crystal defects. Stress analysis by 2D simulation reveals that thinning a buried-oxide effectively suppresses deformation of an SOI film associated with over-oxidation during LOCOS. It is experimentally confirmed that using a SIMOX substrate which has a thinner buried-oxide causes no noticeable deformation of the SOI film nor anomalous leakage current.

This paper describes a new measurement method of a CD-SEM with nanometer-level precision and good correlation with electrical characteristics for an actual device of ultra-large-scale integration (ULSI). With the decrease in feature size, the pattern to be measured tends to become a curved shape. In order to measure such a pattern within measurement precision on the order of 5 nm, two-dimensional measurement is effective. Here we report a new measurement algorithm featuring that the critical dimension is derived from the value of the area of a measurement pattern. We apply this measurement method to actual device of 64-Mbit DRAM and confirm the reproducibility of 3.6 nm for the gate linewidth measurement, and that of 5.6 nm for the hole diameter measurement. Furthermore, we verify that the measurement values of the gate linewidth have a strong correlation with the threshold voltage and those of the hole diameter also have a strong correlation with the contact resistance, respectively.

In coupled oscillator arrays, it is possible to control the inter-element phase shift up to 180 by free-running frequency distribution based on injection-locking phenomenon. In this paper, a new technique to control the inter-element phase shift electronically up to the maximum extent of 360 is reported. Oscillators are unilaterally coupled to the preceding oscillator through one of the two paths, which differ from each other 180 in electrical length and each includes an amplifier. Turning on the desired amplifier one can control the phase shift either -180 to 0 or 0 to 180. The technique was applied in a three-element oscillator array each coupled to a patch antenna via a round aperture. The radiation beam of the array could be scanned 47 in total.

An ad hoc wireless network is a collection of mobile hosts that self-forming a temporary network without any required intervention of centralized system. In such environment, mobile hosts, which are not within transmission range from each other, require some other intermediate hosts to forward their packets to form a multi-hop communication. In this paper, an ad hoc network is modeled as a graph. Two nodes within the transmission range of each other are connected by an edge. Given a finite set of mobile nodes, a finite set of edges and a new multicast request, the wireless multicast tree problem (WMTP) is to find a multicast tree for the request so that the multicast loss probability is minimized. We prove the WMTP is NP-complete and a heuristic algorithm, called Degree-Based Multicast Routing Algorithm (DBMRA), is proposed. Based on the DBMRA, one algorithm was proposed to establish backup nodes for the multicast tree to improve the reliability. A node is needed to be backup only when it has a high probability to disconnect the multicast tree seriously. The qualification of a node to be backup is subject to a computed threshold, which is determined by a statistic analysis. The theoretical and experimental analyses are presented to characterize the performance of our algorithms.

One effective way to make a large-capacity mobile communication system is to use a microcellular system. One way to do this is to place the base station antennas lower than the surrounding buildings. This result in what is called a street microcellular system. We previously presented basic simulation results evaluating the performance of a different-sized cell combination algorithm (DCC) designed to avoid the problems due to an unbalanced distribution of traffic in street microcellular systems. In this paper, we present the results of simulations evaluating the performance of an improved active different-sized cell combination method (ADCC) that controls the transmission power of each base station.

The transfer function or impulse response of propagation path is one of the most fundamental and most important quantities for equalizing the distortions cased by multipath propagation. In this paper, precise identification of the transfer function of the propagation path under multipath condition is presented. By use of the least-square method, uncertainty due to white noise is sufficiently eliminated.

The onboard antenna beam forming network (BFN) of the next-generation communication satellites must offer multiple beam forming and beam steering. The conventional BFN, which directly controls the array elements, is not suitable for a large-scale array antenna because of the difficulty of BFN control. This paper proposes a new BFN configuration that consists of three/four-way variable power dividers and a Butler matrix (FFT circuit). This BFN can offer continuous beam steering with fewer variable components. By introducing new techniques based upon excluding FFT periods and power evaluations by definite integration, the deviation in beamwidth is reduced by 75% or more and the maximum sidelobe level is improved by 10 dB or more.