This paper presents a technique for designing a dielectric Electronically Steerable Parasitic Array Radiator (Espar) antenna to achieve miniaturization of the conventional Espar antenna. The antenna's size is reduced by immersing the central active element in a dielectric cylinder, mounting the surrounding planar parasitic elements at the circumference of the cylinder, and decreasing the radius of the ground skirt to that of the parasitic elements. An example of a polycarbonate (εr = 2.9 + j0.006) Espar antenna operating at 2.484 GHz is optimised by using a genetic algorithm in conjunction with an FEM-based cost function. The designed antenna generates a half-power beam width of 78and a main lobe that elevates at an angle of only 5from the horizontal plane. The designed antenna is also fabricated and measured. Good agreement between the measurement and simulation results is obtained. We reduce the size of the designed Espar antenna to 1/8 the size of its conventional counterpart while achieving a 12improvement in half-power beam width.

Reactive near field reflection characteristics of commercial RF absorbers are investigated to determine the minimum size of a reactive-field anechoic box necessary for measuring the reactive near field of an ESPAR antenna. The reflectivity of the absorber placed in close proximity to an antenna is inversely proportional to the distance between the antenna and the absorber. For carbon filled urethane foam tapered absorbers, we find that the backscattered reflection characteristics mainly depend on their tapered height rather than the thickness of absorber base. As a result, we show that carbon filled urethane foam pyramidal and wave surface shaped absorbers can be used to make reactive-field anechoic boxes. A prototype of a reactive-field anechoic box is presented and the distance from the absorber to the antenna is reduced to a wavelength. The prototype is verified by comparing its performance with that obtained from a large anechoic chamber.

This paper presents newly developed very small MMIC bandpass filters along with novel positive and negative feedback techniques. In order to maintain the expected Q factor without unwanted oscillations in the positive feedback loop, the unity-coupler principle is proposed to stabilize the constituent amplifier. A prototype bandpass filter is monolithically integrated in a very small area of only 0.1 mm2 on a GaAs substrate. A sharp factor as high as 5.6/1-30 dB is achieved near the frequency range of 1 GHz. The other technique presented in this paper is to achieve the bandpass function without using any positive feedback. This is negative feedback consisting of feedback elements with the unique variable transfer function of b/(1as). A variable bandpass filter based on this design concept is also fabricated in a 1.21.3 mm2 area on a GaAs substrate. It has both a varactor and varistor integrated in the circuit, resulting in an independently controllable center frequency and Q factor. It is shown experimentally that the Q factor is controllable over a remarkable range of 20 to 400 and the center frequency is broader than 100 MHz at the 1 GHz band. By cascading two of the fabricated MMIC chips, a forth-order frequency response is successfully obtained along with a 35-40 dB forward gain and an in-band gain flatness of 0.35 dB.

To reduce the phase noise of MMIC phase-locked oscillators (PLOs), we study the phase noise properties of PLOs given that the oscillator Q factor is relatively low in monolithic circuits. Such PLOs must have wide bandwidth in order to suppress monolithic oscillator noise. Therefore, to reduce MMIC PLO phase noise, the phase noise in the PLO passband has to be decreased. Noise generation by each component of the PLO, and its contribution to the output are discussed with emphasis on experimental estimation and rigorous analysis of the component phase- or baseband-noise. Based on these results, a new loop configuration is proposed for reducing phase noise in the PLO using a low Q-factor oscillator. It is demonstrated experimentally that PLOs based on the new loop exhibit 7 dB lower phase noise than conventional PLOs.

This paper theoretically revisits linear passive two-port systems from the viewpoint of power transfer. Instead of using the conventional S21 magnitude, we propose generalizing the kQ product as a figure of merit for two-port performance evaluation. We explore three examples of power transfer schemes, i.e. inductive, capacitive, and resistive channels. Starting from their voltage-current equations, the kQ formula is analytically derived for each scheme. The resultant formulas look different in appearance but are all physically consistent with ωM/R, which stems from the original definition of kQ product in a primitive transformer. After comprehensively learning from the three examples, we finally extend the theory to a black-box model that represents any kind of power transfer channel. In terms of general two-port Z-parameters, useful mathematical expressions are deduced for the optimum load, input impedance, and maximum power transfer efficiency. We also supplement the theory with helpful graphics that explain how the generalized kQ behaves as a function of the circuit parameters.

A novel sampling comparator circuit is presented for extending the pull-in range of microwave phase-locked oscillators (PLOs). It performs both phase and frequency detection without any frequency dividers, and a GaAs MMIC prototype is developed and tested. The proposed comparator improves the pull-in range by about 10 times more than is possible with conventional sampling phase detectors.

In this paper, performance of a novel interference cancellation technique for the single user detection in a direct-sequence code-division multiple access (DS-CDMA) system has been investigated. This new algorithm is based on the Cycle-and-Add property of PN (Pseudorandom Noise) sequences and can be applied for both synchronous and asynchronous systems. The proposed strategy provides a simple method that can delete interference signals one by one in spite of the power levels of interferences. Therefore, it is possible to overcome the near-far problem (NFP) in a successive manner without using transmit power control (TPC) techniques. The validity of the proposed procedure is corroborated by computer simulations in additive white Gaussian noise (AWGN) and frequency-nonselective fading channels. Performance results indicate that the proposed receiver outperforms the conventional receiver and, in many cases, it does so with a considerable gain.

Higher-order harmonics and distortions generated by nonlinearity of capacitance-voltage characteristic of a single varactor and an anti-series-connected varactor pair are analyzed and compared. The effect of linear and parabolic terms of nonlinearity to harmonics outputs and distortions is discussed. It is shown that an anti-series-connected varactor pair has a completely suppressed linear term and reduced parabolic term. The advantage of an anti-series-connected varactor pair is theoretically explained.

This paper presents Q factor analysis for FET oscillators employing distributed-constant elements. We replace the inductor of a lumped constant Colpitts circuit by a shorted microstrip transmission line for high frequency applications. Involving the FET's transconductance and the transmission line's loss due to both conducting metal and dielectric substrate, we deduce the Q factor formula for the entire circuit in the steady oscillation state. We compared the computed results from the oscillator employing an uniform shorted microstrip line with that of the original LC oscillator. For obtaining even higher Q factor, we modify the shape of transmission line into nonuniform, i.e., step-, tapered-, and partially-tapered stubs. Non-uniformity causes some complexity in the impedance analysis. We exploit a piecewise uniform approximation for tapered part of the microstrip stub, and then involve the asymptotic expressions obtained from both stub's impedance and its frequency derivatives into the active Q factor formula. Applying these formulations, we calculate out the value of capacitance for tuning, the necessary FET's transconductance and achievable active Q factor, and then finally explore oscillator performances with a microstrip stub in different shapes and sizes.

Nonlinear distortions in an anti-series varactor pair (ASVP) are analyzed by a perturbation method. To the authors' knowledge, this paper presents the first derivation of an analytical expression that explicitly shows intermodulation and harmonic distortions of the ASVP. In addition to canceling the expected even-order distortion, the third-order distortion can be suppressed simultaneously when a certain condition is satisfied. We also find that the second- and third-order distortions can be greatly suppressed without dependence on dc bias voltage if the varactors in the ASVP have an ideal abrupt p-n junction. These theoretical predictions are verified by measuring the second- and third-order harmonic distortions of an ASVP. The experimental results show that the second-order harmonic distortion is suppressed by approximately 20 dB. The third-order harmonic distortion is suppressed to the same extent in the theoretically predicted dc bias voltage range.

The time delay of magnetostatic wave in a YIG slab has been studied experimentally, where the nonuniform dc magnetic field is applied normal to a slab surface by using the artificially sharpened magnetic pole piece. The non-dispersive group delay characteristics are found, and the effect of nonuniform magnetic field on the propagation loss is also investigated.

Harmonic distortions of a recently developed lightweight film-type ESPAR (Electronically Steerable Passive Array Radiator) antenna are investigated experimentally. These distortions arise from the nonlinearity of the varactor diodes that are directly integrated with the parasitic radiator elements to control the antenna's radiation pattern. A reactive-near-field measurement technique that employs low-interference probes in an ultra-small anechoic box is used to reduce experimental time and cost. An anti-series varactor pair is introduced and compared with the conventional single varactor. Consequently, an ESPAR antenna equipped with the anti-series varactor pair exhibits remarkable suppression of nonlinear distortion. In particular, the second- and the third-order harmonic is reduced by approximately 20 dB and 12 dB from the level of a single varactor type ESPAR antenna, respectively.

Conventional adaptive array antenna processing must access signals on all of the array antenna elements. However, because the low-cost electronically steerable passive array radiator (ESPAR) antenna only has a single-port output, all of the signals on the antenna elements cannot be observed. In this paper, a technique for adaptively controlling the loaded reactances on the passive radiators, thus forming both beam and nulls, is presented for the ESPAR antenna. The adaptive algorithm is based on the steepest gradient theory, where the reactances are sequentially perturbed to determine the gradient vector. Simulations show that the ESPAR antenna can be adaptive. The statistical performance of the output SIR of the ESPAR antenna is also given.

In this paper, we report on our recent work in designing and developing an optical waveguide and optical integrated circuit for optical BFN in adaptive multibeam array antenna. We introduce a new integrated Ti:LiNbO3 waveguide and prove that it is able to yield large birefringence and birefringence dispersion. We present a new technique using a microwave-modulated optical wave to measure the birefringence in integrated Ti:LiNbO3 optical waveguides. The measuring results show that the new waveguide has a birefringence of 0.08 and birefringence dispersion of 0.05 µm-1 at optical wavelength of 1.55 µm. When the new Ti:LiNbO3 is applied to form a integrated optical waveguide array in optical beamforming network, it is shown that microwave phase shifts within the range of [-180, +180] is achieved by tuning the optical wavelength 10 nm around 1.55 µm.

The electronically steerable passive array radiator (ESPAR) antenna is one kind of the parasitic elements based single-port output antennas with several variable reactances. It performs analog aerial beamforming and none of the signals on its passive elements can be observed. This fact and one that is more important--the nonlinear dependence of the output of the antenna from adjustable reactances--makes the problem substantially new and not resolvable by means of conventional adaptive array beamforming techniques. A novel approach based on stochastic approximation theory is proposed for the adaptive beamforming of the ESPAR antenna as a nonlinear spatial filter by variable parameters, thus forming both beam and nulls. Two learning rate schedule were examined about output SINR, stability, convergence, misadjustment, noise effect, bias term, etc., and the optimal one was proposed. Further development was traced. Our theoretic study, simulation results and performance analysis show that the ESPAR antenna can be controlled effectively, has strong potential for use in mobile terminals and seems to be very perspective.

To realize S-band mobile satellite communications and broadcasting systems, the onboard mission system and equipment were designed for the Japanese Engineering Test Satellite VIII. The system performs voice communications using handheld terminals, high-speed data communications, and multimedia broadcasting through a geostationary satellite. To enhance system efficiency and flexibility, the onboard mission system features phased-array-fed reflector antennas with large antenna diameter and baseband switching through onboard processors. Configurations and performance of the subsystems and key onboard equipment, large deployable reflectors, feed arrays, beam forming networks and onboard processors, are presented. The S-band mobile systems and onboard equipment will be verified through in-orbit experiments scheduled for 2002.

An optically controlled beamforming technique is a very effect procedure for phased array antenna control. We have built a Fourier optical processing beamforming network. In the optical processor, we use optical waveguide arrays and a GRIN micro lens in order to reduce the size and weight of the processor, optical coupling losses, mechanical destabilization, and optical alignment difficulties. This paper describes the characteristics of a one-dimensional Fourier optical processor, and shows the configurations of both its transmitting and receiving modes, which we have constructed. We demonstrate multiple signal generation, and beam steering for transmission in the X-band. Furthermore, we configure the beamformer for reception using the phase information of local signals form the optical processor. We additionally demonstrate the beam steering of the received X-band RF signal. Experimental results confirm the feasibility of the Fourier optical processing beamforming network.

Phase noise generation in varactor-tuned oscillators is analyzed by an asymptotic perturbation technique. It is found out that 1/f noise and AM noise are converted into phase noise by first- and higher-order nonlinearities of the varactor. The deduced formula can be utilized in CAD for circuit evaluation/optimization of varactor-tuned osicillators.

This paper introduces a theory for fast optimization of the circuit topology and parameters in sinusoidal oscillators. The theory starts from a system model composed of standard active and passive elements. We then include even the output load in the circuit, so that there is no longer any interaction with the outside of the system through the port. This model is thus called no-input-no-output (NINO) oscillator. The circuit is cut at an arbitrary branch, and is characterized in terms of the scalar impedance from the cut point. This is called active impedance because it is a function of not only the stimulating frequency but also the active device gain. The oscillation frequency and necessary device gain are estimated by solving impedance-domain Barkhausen equilibrium equations. This estimation works for the adjustment of circuit elements to meet the specified oscillation frequency. The estimation of necessary device gain enables us to maximize the oscillation amplitude, thanks to the inherent negative-slope nonlinearity of active devices. The active impedance is also used to derive the oscillation Q (quality) factor, which serves as a key criterion for sideband noise minimization i.e. frequency spectrum purification. As an alternative measure to active impedance, we also introduce branch admittance matrix determinant. This has the same numerical effect as the scalar impedance but can be used to formulate oscillator characteristics in a more elegant fashion, and provides a lucent picture of the physical behavior of each element in the circuit. Based on the proposed theory, we provide the tabled formulas of oscillation frequency, necessary device gain, active Q factor for a variety of typical Colpitts, Hartley, and cross-coupled twin-FET (field-effect transistor) oscillators.