A New Type of Ultra-Wide Band Conical Antenna Ridged with a Novel Finline Radiator

A new type of ultra-wide band(UWB) conical antennas ridged by a novel taper finline radiator(TFR) used as radiation and receiving of the short pulse are developed. In which, a new UWB feed structure of a coplanar waveguide to finline and a TFR ridge are used initially. The experiment results show the characteristics of high fidelity, high efficiency, and high gain compared with some common broad-band antennas such as the biconical antennas, V-conical antennas, logarithm periodic antennas, and the other TEM horns.     

Theoretical and experimental research on nonradiative dielectric waveguide directional couplers

A practical design of nonradiative dielectric (NRD) waveguide directional couplers is presented. The dispersion characteristics of coupled NRD-guides and the scattering coefficients of NRD-guide directional couplers are studied as well as the transitions from metal rectangular wave-guide to NRD-guide couplers. Experiments of 3-dB and 10-dB NRD-guide couplers in ka-band show that the couplers are of good performance and promise in millimeter-wave integrated circuits.     

Coupling of NRD-Guide Filled with Low Permittivity Dielectric Between Waveguides

A new version of NRD-guide coupling structure is proposed in which a low permittivity dielectric is filled between the coupling waveguides. It takes full advantage of the common NRD-guide with more flexibility. The choice of different dielectric materials can optimize the required performance. The corresponding coupling characteristics are analyzed. Some examples are given to show the new coupling characteristics. An important feature is the enhanced coupling between the waveguides and increased attenuation in the transverse direction, and this implies a size reduction and enhanced EMC capability. Furthermore, the filling of the low dielectric material between the coupling waveguides makes the structure an integrated unit and especially suitable for realization by micro-electromechanical system (MEMS) or by microwave integrated circuits.     

Steady State Responses of NRD-Guide Crossbar Balanced Mixer in MM-Wave Band

The periodic and quasi-periodic steady states of the nonradiative dielectric waveguide (NRD-guide) crossbar single-balanced mixer excited by single tone or dual tones in mm-wave band are deeply researched in the paper. Based on the wideband dispersion characteristics, the mode self-contained property and the modes orthogonality and a series of modes excitation criterions of the NRD-guide, a novel mixer is designed and analyzed. Two important parameters, the local oscillator and incident wave inductive electromotive forces corresponding to the LSE/LSM mode-converter and LSM-mode probe respectively, are calculated firstly by using the wire-antenna theory and the moment method. According to the theorem of band-pass signal sampling, a kind of integrated and general quasi-periodical steady-state responses algorithm for the nonlinear microwave/mm-wave circuits excited by multiple tones, the inter-modulation balance method based on the multi-dimension discrete Fourier transformation (MDFT-IMB), is designed and then successfully applied to calculate the performances of the above NRD-guide mixer.     

A new type NRD-guide receiving front-end in Ka-band

A new type millimeter-wave receiving frond-end using NRD-guide as internal transmission line is presented in this paper. The receiving frond-end consists of a NRD-guide crossbar balanced mixer, a NRD-guide LSE mode local oscillator and two impedance-converters at two input ports of the mixer circuit. Firstly, the propagation characteristics of some transmission modes often used in NRD-guide are given, and the conditions which these modes are applied as the operating modes are discussed. Secondly, the principle of the balanced mixed which is regarded as the key circuit unit in the receiving frond-end is analysed by using vector Green's function, and the conversion loss of the mixer is computed with an equivalent circuit in Ka-band. And then, from the view of obtaining the optimum performances of the whole receiving frond-end, some methods of designing local oscillator are expound. Some experimental results of the receiving frond-end at Kaband are given in the paper lastly. Because the frond-end have the impedance matching and converting circuits, it possesses better electrical performance. The integrated frond-end which have compact size and excellent shock strength is suitable for varied millimeter-wave system.     

Characteristic impedance of nonradiative dielectric waveguide and its application

In this paper a formula for determining the characteristic impedance of the nonradiative dielectric waveguide (NRD-guide) is presented. The numerical results are obtained, which are very useful for designing NRD waveguide components, such as impedance transformers, filters, branch-line hybrids, and active circuits. As a practical example for applying the formula, a 3 dB brainched NRD-guide directional coupler was designed and fabricated. The experiments show good consistency with the theory.     

超宽带匹配馈电结构的设计与实验

设计研制了一种低阻抗传输线向高阻抗超宽带天线馈电的馈电结构,理想情况下,该馈电方法可实现特性阻抗为50Ω的同轴传输线向特性阻抗为200Ω的超宽带天线匹配馈电。分别用TEM喇叭天线和抛物反射面天线进行了实验验证,结果表明,与同轴线直接馈电相比,采用该匹配馈电结构后,TEM喇叭天线的辐射场强提高了15%,反射面天线的辐射场强提高了27%。     

The development of nonradiative dielectric waveguide transmitting front-end in Ka-band

The operating theory,design method and experimental results of the nonradiative dielectric waveguide (NRD-guide) transmitting front-end in millimeter wave band are related in details in this paper. As a kind of dielectric waveguide,the NRD-guide possesses fine transmission performances, and it can be used to fabricate the millimeter wave hyterodyne integrated circuits. The two kinds NRD-guide transmitting front-ends substantiated in the paper, the voltage controlling oscillator(VCO) and twin-Gunn-diode power-combiner,have very similar structures to each other and possess compact sizes, fine machinery and electric performances.For the VCO front-end in Ka-band, the frequency modulation band is greater than 150MHz, the output power is larger than 20mW.For the power-combiner, the output power is larger than 40mW,the combination efficiency is better than 90%,the frequency stabilization reaches 1.68×10^–5. Combined with the receiving front-end reported before,the transmitter and receiver can be composed to a dielectric waveguide R/T module to be applied in some millimeter wave sub-systems.     

A double constrained robust capon beamforming based imaging method for early breast cancer detection

Ultra-wideband （UWB） microwave images are proposed for detecting small malignant breast tumors based on the large contrast of electric parameters between a malignant tumor and normal breast tissue. In this study, an antenna array composed of 9 antennas is applied to the detection. The double constrained robust capon beamforming （DCRCB） algorithm is used for reconstructing the breast image due to its better stability and high signal-to-interference-plus-noise ratio （SINR）. The successful detection of a tumor of 2 mm in diameter shown in the reconstruction demonstrates the robustness of the DCRCB beamforming algorithm. This study verifies the feasibility of detecting small breast tumors by using the DCRCB imaging algorithm.     

超宽带天线辐射中心的时域测量方法

 采用时域方法测量超宽带天线的辐射中心时,找出一个参考点,使天线以此点为中心的辐射波在辐射主轴某一范围内的波形时延最小,该参考点即为天线的辐射中心。该方法无需考虑馈入脉冲的频率,仅需观察天线辐射场各方向的波形时延。用时域测量方法测量了超宽带TEM喇叭天线的辐射中心,并用TEM喇叭做为馈源的抛物反射面天线进行了验证,结果证明了该方法的可行性与准确性。     

Analysis and application of NRD-guide excitors

In this paper, the NRD-guide excitors using a length of coaxial line which consists of a rectangle external conductor and a thin round inner conductor are presented, and the characteristics of the input impedances of LSE ₁₁ ^o mode and LSM ₁₁ ^o mode at the insertion points are analysed and calculated by using the method of the rector Green's function respectively. The computation results show that the mode excitors are able to improve the operating modes matching between NRD-guide and the quasi-TEM transmission line. The structures are suitable for fabrication LSE ₁₁ ^o mode oscillator and LSM ₁₁ ^o mode oscillator to compose millimeter wave NRD-guide integrated front ends. An example of an LSE ₁₁ ^o mode oscillator in Ka-band is given. Its oscillation frequency and output power could be easily adjusted by changing the parameters of the excitor.     

Steady-State Responses of NRD-Guide LSE/LSM Mode Oscillators in MM-Wave Bands

The analysis methods for the steady-state responses of the mm-wave band NRD-guide negative impedance oscillators based on nonlinear microwave autonomous circuits harmonic balanced method are presented in the paper in details. Firstly, the large-signal nonlinear lumped equivalent circuits of the Gunn diode are studied in mm-wave bands. Then, the performances of two kinds of NRD-guide autonomous circuits, the probe-exciting LSM ₁₁ ^o-mode oscillator and the LSE ₁₁ ^o-mode oscillator, are analyzed by the way of extracting the large-signal dynamic harmonic admittance (conductance) of the Gunn diode or directly configuring the harmonic balance equations for the oscillator. The input impedance of the exciting probe in the oscillator and the performances of the load-pulling and the local stability of the NRD-guide oscillator are also involved.     

Discontinuity of NRD-Guide and Its Application in Millimeter Wave Circuits

In this paper, the performances of two typical discontinuous structures of the NRD-guide, the traverse metallic rod to disturb an incident wave and the traverse probe to excite required modes, are analyzed and computed by utilizing the theory of modes orthogonality of the NRD-guide. The moment method is used to evaluate the current distribution on the rod and probe and the affection of some higher-order modes is taken into account simultaneously. On these bases, the multitone exciting steady states of two kinds of important circuits that employ the above discontinuous structures, the NRD-guide crossbar balanced mixer and the LSM ₁₁ ⁰ -mode oscillator, are simulated by the harmonic balance technique based on the multi-dimensional discrete Fourier transformation (MDFT-HB method).     

Nonlinear Frequency-Modulation Distortion Analysis for VCO Based on Harmonic Balance Method

The analysis methods for the steady-state responses of the voltage tuning negative resistance oscillator (voltage-controlling oscillator, VCO) by the microwave nonlinear autonomous circuit harmonic balance method in millimeter-wave bands are studied in the paper. Firstly, the quasi-periodic characteristic of the steady-state response of the VCO modulated by a periodic signal is proved. Then, on the bases of the harmonic balance analysis and the inter-modulation balance analysis, a novel method for obtaining the steady-state tuning performance and the nonlinear frequency-modulation distortion characteristic of the VCO is presented. The total analysis process is aimed to a kind of NRD-guide Gunn diode VCO. The large-signal lumped equivalent circuit model of the millimeter-wave P⁺N-junction varactor is also given for explaining the algorithm and the principle of the NRD-guide VCO.     

Compact NRD-Guide Switch by Using Schottky Barrier Diodes

Based on a miniaturized NRD-guide coupling structure, a new switch circuit is proposed. The 3dB coupler and two schottky barrier diodes with improved diode mounts and matching circuits are used. It features with wideband performance and compact size. The high isolation performance can also be realized using the same circuit by adjusting the bias currents of the diodes. An experimental prototype is implemented and the tested characteristics are supplied.     

All-optical switchable UWB pulses generation,modulation and transmission

We proposed and demonstrated all-optical polarity- and shape-switchable ultrawideband (UWB) Gaussian pulses generation schemes using a single polarization interferometer (PI) or a semiconductor optical amplifier (SOA) cascaded by a PI. When an optical signal with dark return-to-zero (RZ) format propagates directly through a single PI, a pair of polarity-reversed UWB monocycle pulses and a positive UWB doublet pulse is acquired respectively only by adjusting the polarization controllers, without changing the bias of the intensity modulator. If a SOA is connected at the input of the PI to firstly implement the first-order differential function to the input dark RZ pulse utilizing gain saturation effect of the SOA, both polarity- and shape-switchable UWB Gaussian monocycle and doublet pulses are all acquired from the cascaded system. Moreover, if a nonreturn-to-zero control signal is introduced into the SOA, utilizing the cross-gain modulation (XGM) effect of the SOA and the differential characteristic of PI, all-optical shape modulation to UWB signals can be realized, and the polarity of the modulated UWB pulses can also be switched. Also, UWB signal transmission characteristics in fiber link were investigated.     

A High-Power Reflector Impulse Antenna with Dual-Tem Source

There are different demands on radiation efficiency and direction pattern according to various ultra-wideband (UWB) antennas and high power applications. To obtain more radiating gain on bore-sight of paraboloidal reflector and centralized radiating direction, a novel feeding structure called dual-TEM source has been designed and applied in half-paraboloidal reflector impulse radiating antenna (IRA) applications. Simulation results proved that this proposed half-paraboloidal reflector IRA with dual-TEM source provided greater radiation performance on bore-sight as a result of the synthesized power in the aperture space of paraboloid. Moreover, lots of simulation work and comparison have been done in different feeding models to summarize a relative optimal feeding structure.     

Dependence of terahertz radiation on gap sizes of biased multi-energy arsenic-ion-implanted and semi-insulating GaAs antennas

We investigate the characteristics of terahertz radiation pulses using biased multi-energy arsenic-ion-implanted and semi-insulating GaAs photoconductive antennas with different gap sizes in terahertz time-domain spectroscopy. At a specific fluence excitation, with increasing antenna gap size, the absolute values of the (peak) normalized terahertz waveform minimum (valley), as well as the bandwidth, reveal an increasing trend for multi-energy arsenic-ion-implanted GaAs antennas and a decreasing trend for semi-insulating GaAs antennas. We find that the largest reachable bias fields applied to arsenic-ion-implanted GaAs antennas are higher than those applied to semi-insulating GaAs antennas. On the basis of pump fluence dependences of peak terahertz amplitude, we deduce that multi-energy arsenic-ion-implanted GaAs antennas have the ability to acquire higher THz power at even higher pump fluence in comparison with semi-insulating GaAs antennas.     

Terahertz generation and detection of LT-GaAs thin film photoconductive antennas excited by lasers of different wavelengths

A new method of generating and detecting terahertz waves is proposed. Low-temperature-grown gallium arsenide (LT-GaAs) thin films are prepared by etching a sacrificial layer (AlAs) in a four-layer epitaxial structure constituted with LT-GaAs, AlAs, GaAs, and semi-insulating gallium arsenide (SI-GaAs). The thin films are then transferred to clean silicon for fabricating the LT-GaAs thin film antennas. The quality and transmission characteristics of the films are analyzed by an 800-nm asynchronous ultrafast time domain spectroscopy system, and the degree of bonding between the film and silicon wafer is determined. Two LT-GaAs thin film antennas for generating and detecting the terahertz waves are tested with a 1550-nm femtosecond laser. The terahertz signal is successfully detected, proving the feasibility of this home-made LT-GaAs photoconductive antennas. This work lays a foundation for studying the mechanism of terahertz wave generation in GaAs photoconductive antennas below the semiconductor band gap.     

墙体对微波脉冲的衰减特性

 研究墙体对微波脉冲的衰减特性，测量了微波脉冲垂直入射墙体后的脉冲信号，经过计算得到普通砖混墙、普通钢筋混凝土墙、钢筋网混凝土墙对窄带微波和超宽带微波的衰减值；分析了微波脉冲穿越不同墙体的频谱变化。研究结果表明，普通钢筋混凝土墙和普通砖混墙对窄带微波脉冲的衰减为0.342～0.699 dB/cm，对超宽带信号的衰减为0.134～0.183 dB/cm。钢筋网混凝土墙（厚65 cm）对超宽带信号的衰减较大（29.07～45.79 dB），同时使穿透墙体的超宽带信号频率分布向高频位移。