A switched-capacitor delta-sigma modulator with reduced sensitivityto op-amp gain

Low operational amplifier (op-amp) gain can degrade the performance of a switched-capacitor delta-sigma modulator (ΔΣM). A ΔΣM that incorporates a new gain-compensated switched-capacitor integrator is described. The resulting ΔΣM topology has reduced sensitivity to op-amp gain. Simulation and measurement results for an experimental ΔΣM that demonstrate the advantages of the new architecture are presented     

Uniplanar monopulse antenna based on odd/even mode excitation ofcoplanar line

A uniplanar microstrip antenna, finding application in monopulse radars, is proposed. Two series-fed slot arrays are fed by a coplanar waveguide transmission line excited either in its coplanar mode, or coupled slot line mode, which provide the difference (Δ) and sum (Δ) patterns, respectively     

A single chip Δ-Σ ADC with a built-in variable gainstage and DAC with a charge integrating subconverter for a 5 V 9600-b/smodem

A 12-b, 19.2-ksamples/s Δ-Σ A/D and D/A converter for a 9600-b/s facsimile modem analog front end is described. In the proposed Δ-Σ ADC, the reference voltage is varied to adjust the signal gain, thus, eliminating the need of a variable gain amplifier. The Δ-Σ DAC uses a 4-b charge integrating subconverter which is insensitive to process variations     

Design and demonstration of polarization-insensitive Mach-Zehnderswitch using a lattice-matched InGaAlAs/InAlAs MQW and deep-etchedhigh-mesa waveguide structure

The authors have designed and demonstrated a 2×2 Mach-Zehnder switch in view of polarization independence as well as low propagation loss (α) and absorption change (Δα). To obtain polarization-insensitive refractive index change (Δn), a lattice-matched InGaAlAs-InAlAs multiple quantum-well (MQW) with a large detuning wavelength was used. Moreover, to reduce the insertion loss difference between polarizations, we applied a multimode-interferometer 3-dB coupler and a deep-etched high-mesa waveguide structure. This switch, therefore, can provide polarization-independent operation about both driving voltage and insertion loss, which is indispensable to practical optical switching applications. We also paid attention to Δα suppression when we decided the value of wavelength detuning and the length of the phase shift region. We also investigated the wavelength dependence of the switch. Within 1530-1560 nm, which is the erbium-doped fiber amplifier (EDFA) gain band, polarization independence in the driving voltage and the crosstalk was maintained. This result shows that the switch is also applicable in wavelength division multiplexing (WDM) applications     

High transmission gain integrated antenna on extremely high resistivity Si for ULSI wireless interconnect

We have demonstrated the highest transmission gain integrated dipole antenna on Si reported so far, to use as an integrated antenna for the purpose of ULSI on-chip wireless interconnection. A 2-mm long and 10-/spl mu/m wide dipole antenna pair at a distance of 1 cm shows a transmission gain of -36.5 dB at 18 GHz, which is 20 dB higher than the previously reported gain. This large increase in gain is achieved by proton implantation on the Si substrate, which increased the resistivity from 10 /spl Omega/-cm to 0.1 M/spl Omega/-cm. It is also found that transmission gain can be maximized for a given resistivity by optimizing the Si substrate thickness or by inserting a low-k dielectric layer below the substrate.     

Antenna-gain measurement of handheld terminals at 900 MHz

This paper presents antenna-gain measurements of handheld terminals by the random-field measurement (RFM) method. We have measured the relative antenna gain for different-sized terminal boxes in indoor and outdoor environments to show a gain decrease caused by the box size. The measured results are explained by calculating the average gain of the horizontal radiation pattern. To find the effect by a different human carrier, we also measured the antenna gain for several parameters, such as weight, height, head parameters, and the antenna protruding length from the head. We present a correlation factor of the antenna-gain deviation due to different human carriers     

Compact and miniaturized microstrip antenna based on fractal and metamaterial loads with reconfigurable qualification

We have described a compact antenna based on fractal and metamaterial loads techniques. The microstrip patch antenna is assumed as a basic antenna and then the effect of fractal structures is implemented. The fractal patch is considered as a right-handed element and then by adding a left-handed element, the antenna miniaturization is achieved by using the metamaterial loads technique. The equivalent circuit is also used to describe the element effect on miniaturization and parametric models clarify them. The proposed antenna is modified for wireless applications and experimental results confirm our simulation results. In addition, we show that the proposed antenna is suitable for reconfigurable. By joining the unit cells together with various arrangements and changing the effective length, the various inductances can be obtained. Finally, by adding reconfigurable characteristic to the proposed antenna, the gain and radiation pattern can be controlled as shows in this paper. The patch antenna has low bandwidth and gain and so we have developed the patch antenna with defected ground to improve the bandwidth and the Frequency Selective Surface (FSS) is used to achieve higher gain and bandwidth. The final antenna is covering 2.4, 3.5 and 5.5 GHz with higher gain than the patch antenna.     

Rejection of an FH signal in a DS spread-spectrum system usingcomplex adaptive filters

The performance of a direct sequence QPSK spread-spectrum receiver using adaptive filters in the presence of frequency hopped interference is analyzed. The analysis includes both the adaptive prediction error filters and the adaptive transversal filters with two-sided taps. If the product of the instantaneous frequency offset Ω_l, between the jamming signal and the carrier of the spread-spectrum signal, and the sampling period Δ is 360° (Ω_l·Δ=360°), the filter gain is reduced to zero. The filter gain G highly depends on the filter adaptation rate μ. Depending on μ, G can vary from zero to more than 20 dB for a jammer/signal power ratio (J/S) of 20 dB. If Ω _l·Δ is small enough (⩽10°), the performance of the transversal filter is better than that of the prediction error filter, in the case when μ is small. For larger values of μ or Ω_l·Δ, these performances are approximately the same. Numerical results for the hopping sequence of the jamming signal are also presented. Besides the filter gain the analysis of the adaptation rate (time constant) filter misadjustment and the system bit error probability is also included     

手动VSAT站天线接收增益的诊断测量

阐述了利用卫星信标和高增益标准喇叭天线,测量手动VSAT站天线接收增益的方法。由测量的天线接收增益计算天线接收效率,从而实现对天线发射增益进行估算。最后,给出了工程测量实例,证明了该方法的可行性,并对增益测量误差进行了分析,其均方根误差±0.28dB。     

Effect of grating phase difference on single-mode yield incomplex-coupled DFB lasers with gain and index gratings

In complex-coupled DFB lasers with both index and gain gratings, I have studied the effect of the phase difference between index and gain gratings on the single-mode yield considering the threshold gain difference (side-mode suppression ratio) and the optical field uniformity (spatial hole burning). I have obtained the optimum values of: (1) the phase difference ΔΩ between index and gain gratings, (2) the coupling strength (ℵL)_i of gain grating, and (3) the coupling strength (ℵL)_r of index grating, in order to obtain a high single-mode yield regardless of the relative positions of both facets, The used theory is based on the coupled-mode theory and includes the spatial hole burning correction and the standing wave effect. ΔΩ=π/4 (and 3π/4) DFB lasers with HR-AR facets have the highest single-mode yield and should have ~0.6⩽(ℵL)_i⩽~1.5 and (ℵL)_r<~1.25 in order to obtain above 50% yields. Even above 90% yields can be obtained with the range of ~1.1⩽(ℵL)_i⩽~1.4 and ~0.5⩽(ℵL)_r ⩽~0.85. The superior yield characteristics of ΔΩ=π/4 (and 3π/4) DFB lasers, which is above 2.4 times higher than that of ΔΩ=0 (and π) DFB lasers, comes from their better field intensity uniformity. The results presented in this paper provide insight into the variation of the threshold gain difference and the optical field uniformity with ΔΩ, (ℵL)_r, (ℵL)_i, and (ρ_l, ρ_r)     

Optimizing antenna configuration for MIMO systems with imperfect channel estimation

We study the optimal antenna configuration (i.e. number of transmit and receive antennas) for multiple-input multiple-output systems in pilot-symbol-assisted modulation schemes with imperfect channel estimation. We assume block flat-fading channels and focus on a practical range of high signal-to-noise ratio. An ergodic capacity lower bound is used as the objective function to be maximized. We analytically study the capacity gain from adding extra antennas to the transmitter or to the receiver in two different scenarios. Our numerical results show that the optimal antenna configuration under imperfect channel estimation can be significantly different from that under perfect channel estimation assumption. In addition, we investigate the capacity gain from optimizing antenna configuration and find that the gain can be larger than that achieved by optimizing transmit power over pilot and data symbols, particularly for large block lengths.     

Radio Propagation Model Considering Antenna Beam Tilt with Application to Small Cells

Antenna beam tilting techniques are commonly used to deploy small cells with reduced coverage compared than macrocells. This paper proposes a new statistical propagation model for small cells with electrical and mechanical antenna tilt. The proposed model combines the dual slope path loss model with the departure angle spread model for considering antenna beam tilt. The proposed departure angle spread model introduces a new parameter reflecting the azimuth spread of departure (ASD) angles in order to account for the change of transmit antenna gain by electrical and mechanical tilt. Through this approach, the antenna gain for each ray is separately computed by considering the transmit antenna beam pattern as well as the antenna beam tilt. We perform field tests to measure the receive signal power in the downlink of commercial Long-Term Evolution small cells with antenna tilt. Based on the measurement data, we find the statistically optimal ASD parameter using a grid search and calculate the antenna gain for each ray. Also, the overall transmit antenna gain is obtained by averaging antenna gains for multiple rays. To assess the accuracy of the proposed model, the estimation error is evaluated by comparing the measured receive signal power with the estimated value using a propagation model, and the performance of the proposed propagation model is compared with those of existing path loss models in terms of root mean square error deviation. Then, it is shown that the proposed model provides more accurate propagation estimation for small cells than existing models.     

High Gain Patch Antenna with Composite Right-Left Handed Structure and Dendritic Cell Metamaterials

We present a novel high-gain patch antenna utilizing composite right-left handed (CRLH) structure and dendritic cell metamaterials. The proposed CRLH antenna, composed of modified Sievenpiper mushroom unit-cells, is based on the positive first-order resonance mode for high gain. In addition, the dendritic cell metamaterials are used to surround the proposed antenna to further increase the antenna directivity and gain due to suppressing the surface waves. The experimental results show that the gain and the directivity of the proposed antenna with CRLH and dendritic cells can be improved by 3.88 dB and 8.82, respectively, in comparison with a conventional patch antenna. Moreover, a 10-dB bandwidth with 9.55% is achieved. The measured results are in good agreement with the simulated ones.     

A 42‐GHz Wideband Cavity‐Backed Slot Antenna with Thick Ground Plane

We investigate the characteristics of a wideband and high‐gain cavity‐backed slot antenna in terms of the reflection coefficients, radiation patterns, and gain. A cavity‐backed slot antenna structure includes baffles, reflectors, and thick ground planes. The measured gain and bandwidth of a 10‐dB return loss in a cavity‐backed 2 × 2 array slot antenna with h₁=2 mm, d = 2 mm are 15.5 dBi and nearly 27% respectively, at 42 GHz. Baffles and reflectors are used to increase antenna gain, thus reducing the coupling among the slots on the thick ground plane.     

Receive antenna selection for unitary space-time modulation over semi-correlated Ricean channels

Receive antenna selection for unitary space-time modulation (USTM) over semi-correlated Ricean fading channels is analyzed (this work generalizes that of Ma and Tepedelenlio-glu for the independent and identically distributed (i.i.d.) Rayleigh fading case). The antenna selection rule is that the receive antennas with the largest signal powers are chosen. For single antenna selection, we derive the maximum likelihood decoding for the correlated Ricean case. We also derive the Chernoff bound on the pairwise error probability for the high signal to- noise ratio (SNR) region and obtain the coding gain and diversity order. Our results show that even when there are transmitter side correlations and a line of sight component, receive antenna selection with USTM preserves the full diversity order if the USTM constellation is of full rank. We also give an approximation to the distribution function of a quadratic form of non-zero mean complex Gaussian variates (from Nabar et al.) at the high SNR region. Based on this approximation, a closed-form expression for the coding gain is also obtained and compared with that of the i.i.d. Rayleigh case. We also analyze the case of multiple receive antenna selection and derive the coding gain and diversity order. We show that USTM constellations, which have been proposed for the i.i.d. Rayleigh channel, can be used with the correlated Ricean channel as well.     

A Compact Rectangular Dual Patch Antenna for Multiple Satellite Communication Applications

At present, with the advances in satellite communication systems and their increasing importance, wideband antennas are in great demand for both military and commercial applications. Most of the communication systems need a wideband antenna that operates on multi-octave frequencies. In patch antenna, diverse techniques played a vital role in enhancing the antenna parameters such as gain or bandwidth. A new design concept of a compact rectangular dual patch antenna has been developed for both high gain and wider bandwidth. In this work, a compact rectangular dual patch antenna is proposed as a wideband antenna for multiple satellite communication applications such as Global Positioning System, Global Navigation Satellite System, Indian Regional Navigation Satellite System, and S-Band Satellite Communication. The designed rectangular dual patch antenna is simulated and fabricated. Based on the performance, the fabricated antenna is compared with the simulated results in terms of VSWR, gain, axial ratio, and 3 dB beam width. Increased gain and wider bandwidth have been achieved with the developed rectangular patches and their energy distributed on the surface of the dual patches simultaneously. Finally, the proposed rectangular dual patch antenna shows improved performance for the multiple satellite communication applications.

     

An analysis of space-charge-region recombination in HBT's

The importance of including recombination in the base side of the emitter-base space-charge-region (SCR) in the computation of the current gain in AlGaAs/GaAs HBT's is investigated. Recombination due to Shockley-Read-Hall, Auger and radiative processes is considered. The interaction of the base-side SCR recombination currents with the neutral-base current and the collector current, which occurs via their dependence on the quasi-Fermi level splitting (ΔE_fn) at the base-emitter junction, is not found to be a significant factor in the computation of ΔE_fn. However, it is confirmed that the quasi-Fermi level splitting, as calculated from a balancing of the thermionic/tunnel current with the neutral base and collector currents, must subsequently be included in the computation of the base-side SCR currents if the current gain is not to be severely underestimated. A discussion of why the ideality factor is ≈1 for the base-side SCR currents is given. Finally, simple analytical expressions for ΔE _fn and the SCR recombination currents are presented and should prove useful for HBT device- and circuit-simulation purposes     

Exact SEP and performance bounds for orthogonal space‐time block codes in cooperative multiantenna AF relaying networks

In this paper, we derive a moment generating function (MGF) for dual‐hop (DH) amplify‐and‐forward (AF) relaying networks, in which all nodes have an arbitrary number of antennas, with orthogonal space‐time block code (OSTBC) transmissions over Rayleigh fading channels. We present an exact error rate expression based on the derived MGF and another analytical approach to derive achievable performance bounds as closed‐forms of symbol error rate, outage probability, and normalized channel capacity. Furthermore, we derive the asymptotic behavior of symbol error rate and outage probability. From this asymptotic behavior, it is shown that the diversity order and its dependence on antenna configurations can be explicitly determined. Simulation results are also presented to verify their accuracy by comparing with numerical results and to provide an insight to the relationship between relaying networks' antenna configuration and diversity order. It is confirmed that the transmit antenna gain of the source node and the receive antenna gain of the relay node can be obtained only when the relay is close to the destination, and then, the transmit antenna gain of the relay node and the receive antenna gain of the destination node can be obtained only when the relay is close to the source.     

0.3 THz紧凑型反射面天线

介绍了一部工作在0.3 THz的紧凑型高增益反射面天线。该天线包括馈源喇叭、分光片以及反射面三个部分,天线的组成部件集成在一块底板之上,底板尺寸为19.4 cm×16.8 cm。首先,通过理论设计确定天线各个组成部分参数和布局;进而,通过精密机加工手段得到一体化的天线样机;最终,利用平面近场测试系统完成方向图测试。测试结果表明,天线增益大于40 dB,副瓣低于-10 dB,从而在紧凑空间内实现太赫兹高增益天线。     

Effects of non-ideal Hadamard modulators on the performance ofΠΔΣ ADC

A non-ideal Hadamard modulator in the front-end of ΠΔΣ ADC can be modelled as an ideal Hadamard modulator with gain error in parallel with an offset error. The effects of non-ideal Hadamard modulators can be partially removed by using chopper stabilisation and adaptive channel gain equalisation