Leaky CPW-based slot antenna arrays for millimeter-wave applications

A uniplanar leaky-wave antenna (LWA) suitable for operation at millimeter-wave frequencies is introduced. Both unidirectional and bidirectional versions of the antenna are presented. The proposed structure consists of a coplanar waveguide fed linear array of closely spaced capacitive transverse slots. This configuration results in a fast-wave structure in which the n=0 spatial harmonic radiates in the forward direction. Since the distance, d, between adjacent elements of the array is small d/spl Lt//spl lambda//sub o/, the slot array essentially becomes a uniform LWA. A comprehensive transmission line model is developed based upon the theory of truncated periodic transmission lines to explain the operation of the antenna and provide a tool for its design. Measured and simulated radiation patterns, directivity, gain, and an associated loss budget are presented for a 32-element antenna operating at 30 GHz. The uniplanar nature of the structure makes the antenna appropriate for integration of shunt variable capacitors such as diode or micro-electromechanical system varactors for fixed frequency beam steering at low-bias voltages.     

Efficiency and gain of slot antennas and arrays on thick dielectric substrates for millimeter-wave applications: a unified approach

A unified approach for representing the surface-wave fields and for computing the corresponding radiation efficiencies from arbitrarily shaped slot-type antennas on thick dielectric substrates at millimeter-wave (mm-wave) frequencies is presented. In this approach, two different representations of the surface-wave fields, i.e., the one based on the idea that the surface-wave power can be associated with a substrate radiation pattern and the other based on the cylindrical wave expansion, are linked together in a unified way. The developed theory is then applied for investigating the surface wave characteristics of printed twin offset slots and uniform linear slot arrays. Based on the developed theory, new insight into the mechanism with which surface-wave power is coupled by the slot pair is presented. Subsequently, the optimum number of elements and corresponding interelement spacing for linear, uniformly excited, slot dipole arrays is explored for achieving maximum radiation efficiency and gain. In order to provide guidance on practical mm-wave integrated slot antenna array design, supportive numerical results are presented for Substrates of dielectric constant /spl epsi//sub r/ = 4.0 and /spl epsi//sub r/ = 12.0.     

Microstrip dipoles on electrically thick substrates

Certain basic radiation properties of microstrip dipoles on electrically thick substrates are investigated, and a comparison is made with the case of dipoles printed on a dielectric half-space. It is concluded that the microstrip dipole radiation properties become sensitive to substrate loss as the substrate thickness increases, with the half-space properties obtained for an adequate amount of loss. Asymptotic formulas for radiated power and efficiency are given for both the thick substrate and half-space problems, showing the behavior with increasing dielectric constant. The method of moments is used to extend the analysis to center-fed strip dipoles, and a method of improving both the efficiency and gain of a printed antenna by using a superstrate layer is discussed.     

Characterization of IMPATT diodes at millimeter-wave frequencies

In order to evaluate the quality of a microwave device and to design a suitable circuit for it, the device must be characterized in terms of an equivalent circuit. At low microwave frequencies L through X bands, devices can be characterized in a relatively simple manner in conjunction with a coaxial transmission line network analyzer. At higher frequencies, such as millimeter-wave frequencies, however, the characterization must be carried out in a waveguide. This paper presents a technique for characterizing an IMPATT diode mounted in a waveguide and the associated circuit parasitics at millimeter-wave frequencies. The passive and active device parameters and the circuit parasitics, which have increased effects particularly at millimeter-wave frequencies, are evaluated by means of a computer-aided iterative curve-fitting method from the measured variation of the input impedance (VSWR) as a function of position of a movable short placed behind the device. The accuracy of the technique and the computer program are first checked by comparing the characteristics of anX-band IMPATT diode measured by the present technique and those measured by the network analyzer method. The characterization of a millimeter-wave IMPATT diode is then presented. A technique to achieve the stabilization required for the measurement of active parameters of the diode is also described. Comparison of the performance of an IMPATT diode amplifier calculated from the measured diode characteristics with the experimentally observed amplifier performance is then presented. It is shown that the device characterization technique can effectively be used for the analysis and design of a millimeter-wave circuit in which the device is used.     

YBCO superconducting ring resonators at millimeter-wave frequencies

Superconducting microstrip ring resonators operating at 35 GHz have been fabricated from laser ablated YBa₂Cu₃O _7-x (YBCO) films on lanthanum aluminate substrates. The circuits consisted of superconducting strips over normal metal ground planes. The circuits are measured from 20 K to 90 K and with microwave input powers ranging from 0.25 mW to 10 mW. The superconducting resonators show significant improvement in Q over identical gold resonators at 20 K, but only marginal improvement at 77 K. No variation in the superconductor performance is observed with varying input power. The lowest microwave surface resistance of the superconductors at 77 K is 9 mΩ. The change in the resonant frequency with temperature is analyzed and a value for the penetration depth computed. Double resonances were observed in some superconducting ring resonators and an explanation is advanced. Factors limiting millimeter-wave high-temperature superconductor circuits are explored and potential performance levels calculated based on current reported values for high-temperature superconductor surface resistances     

The design of small slot arrays

The differences in mutual coupling for a central slot and a peripheral slot cannot be ignored in small arrays if good patterns and impedance are to be obtained. A theory has been developed whereby the length and offset of every slot in the array can be determined, in the presence of mutual coupling, for a specified aperture distribution and impedance match. The theory enlarges on Stevenson's method, and uses a modified form of Booker's relation based on Babinet's principle to treat nonresonant longitudinal shunt slots in the broad wall of a rectangular waveguide. A general relation between slot voltage and mode voltage is developed, and then formulas are derived for the active, self-, and mutual admittances among slots. These formulas result in a design procedure. Analogous treatments of inclined series slots in rectangular guide and of strip-line-fed slots are possible. Comparison between various experiments and the theory is presented. Tests of the theory include the resonant length of a zero offset slot, resonant conductance versus offset and resonant conductance versus frequency for a single slot, and self- and mutual admittances for two staggered slots. The design and performance of a two-by-four longitudinal shunt slot array is also described.     

High-gain low-cost microstrip antennas and arrays based on FR4 epoxy

In this work, two previously reported low-cost design techniques for high-gain microstrip antennas are compared based on detailed parameter study. Both of these methods exploit a combination of a spacer and a layer of FR4 epoxy. The distinguishing feature of the said methods is the position of the metallization. A parameter study is performed on the thickness of the FR4 layer and its effect on the antenna gain, efficiency and pattern symmetry is reported. Capability of these methods is designing high-gain arrays is studied and specific design examples are provided. It is shown that the first method has superior performance in the sense of gain and efficiency. Especially, the first method supersedes the second one for high-gain arrays. As well, it is shown that the first method is a pure microstrip alternative to another previously reported technique wherein a CNC milled waveguide structure is exploited as the feed network.     

Scan-independent slot arrays with parasitic wire arrays in astratified medium

The effect of a parasitic wire array on the scan admittance of a slot array has been investigated. Structures considered can consist of an infinite slot array and an arbitrary number of parasitic infinite arrays of piecewise linear wires, all arrays being embedded in a stratified medium. These include, as particular cases, phased arrays of Clavin elements. Expressing the fields from the arrays as plane waves, a procedure similar to the periodic moment method for infinite periodic structures is set up to obtain the scan admittance of the slot array. Scan admittances are presented for a slot array with monopole arrays in free space, and a slot array with a tilted dipole array in a stratified medium. Blind spots at which the incident energy is mainly reflected rather than transmitted were found. Results obtained indicate the possibility of using parasitic wire arrays for scan compensation of active slot arrays     

Dipole and slot elements and arrays on semi-infinite substrates

The printed dipole or slot antenna on a semi-infinite substrate and infinite phased arrays of these elements are investigated. The solution is based on the moment method in the Fourier transform domain. The generalized impedance or admittance matrix can be expressed in rapidly converging infinite-integral or infinite-summation forms, allowing the accurate determination of the current distributions. Using the present formulation, the input impedance, resonant length, and radiation pattern for the isolated antennas, and the reflection coefficient for infinite phased arrays, are calculated.     

Some effects of dielectric loading on periodic slot arrays

The applications of arrays of rectangular slots have been severely limited since their resonant frequency (where unity transmission occurs) and bandwidth change with incident angle. By utilizing a modal analysis solution which includes the effects of dielectric slabs on both sides of the array, we show that these dielectric effects can, with proper design, reduce or eliminate the unwanted changes in resonant frequency and bandwidth. The presence of the dielectric slabs also cause other changes in the transmission curves. Two of these changes are the occurrence of the Wood's anomaly ("blind angle") null at a lower frequency, and additional narrow resonances in the transmission curves. These phenomena are explained by considering the behavior of the Floquet modal impedances in the presence of the dielectric layer.     

Coherent optical beam forming with passive millimeter-wave arrays

Passive millimeter-wave imaging requires large apertures to achieve an angular resolution comparable to that of typical infrared imagers. Aperture synthesis offers a route to achieving high resolution without using a single large aperture, by interferometrically combining the signals from a number of smaller distributed apertures. In such a system the individual millimeter-wave signals must be transported to a common location with good phase fidelity and combined to form the image. This paper discusses a technique called coherent optical beam forming which performs optical transport of the up-converted millimeter-wave signal and direct image formation at the optical frequency. Proof of principle experiments are described that demonstrate coherent optical beam forming with a point source and a method of self-calibrating the array to remove phase errors     

Quasi-equispaced slot arrays with extremely low crosspolarisation

Crosspolarisation well below the prescribed side-lobe level of a travelling-wave array may be achieved, without using additional discriminating structures, by applying a circular, dielectric-filled waveguide with a sequence of circumferential gaps. Operated in the TM01 mode, a computer-designed X band prototype having a directivity of 27 dB was found to secure crosspolarisation of less than ?34 dB.     

渐变开槽相控阵天线的FDTD分析

对UHF波段无限大开槽阵列天线进行了时域分析,应用Floquet原理对阵列的结构进行区域划分,同时采用时域有限差分法（FDTD）进行数值仿真,研究了作为相控阵天线应用时的频率和空间扫描特性,给出了数值计算结果,得到一些有参考价值的结论。     

Multi-layer epitaxially grown silicon impatt diodes at millimeter-wave frequencies

Complementary (N⁺PP⁺) and double-drift (N⁺NPP⁺) silicon IMPATT diodes were prepared and investigated as oscillators in the millimeter-wave frequency region of 50 to 70 GHz. All the diodes were fabricated from multi-layer epitaxially grown silicon structures. A maximum CW output power level of 198 mW at 62.9 GHz and a maximum conversion efficiency of 7.3% have been measured for the complementary diodes. The double-drift IMPATT diodes have a maximum CW output power of 400 mW at 56.3 GHz and a maximum conversion efficiency of 8.5%.     

An architecture for electrically configurable gate arrays

An architecture for electrically configurable gate arrays using a two-terminal antifuse element is described. The architecture is extensible, and can provide a level of integration comparable to mask-programmable gate arrays. This is accomplished by using a conventional gate array organization with rows of logic modules separated by wiring channels. Each channel contains segmented wiring tracks. The overhead needed to program the antifuses is minimized by an addressing scheme that utilizes the wiring segments, pass transistors between adjacent segments, shared control lines, and serial addressing circuitry at the periphery of the array. This circuitry can also be used to test the device prior to programming and observe internal nodes after programming. By providing sufficient wiring tracks segmented into carefully chosen lengths and a logic module with a high degree of symmetry, fully automated placement and routing is facilitated     

Electronic and electromagnetic devices for millimeter-wave beam control arrays

Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays.     

Planar multimode detector arrays for infrared and millimeter-wave applications

A new type of detector array is described. By means of a suitably designed metallic network, many detector elements (each individually small compared to wavelength) are assembled into an impedance-matched termination for radiation incident normally on the plane of the device. Residual reactance is tuned out by means of a movable backshort. An array of 400 bismuth-film microbolometers with a total area of 1 cm²has been tested at 215 GHz. A coupling efficiency of approximately 60 percent was observed. The detector has aD*of4 times 10^{8}cm . Hz^1/2/W at room temperature with response time on the order of2 times 10^{-7}s. Similar arrays of Schottky and SIS diodes can probably be constructed.     

A sheet impedance approximation for electrically thick materialshields

This paper describes a simple extension of the sheet impedance concept to treat electromagnetic (EM) shields that may be thick in terms of material shield wavelengths. For magnetic shields, a simple relation between the equivalent electric and magnetic currents representing the shield is obtained, and the electric current is found as the solution of a single surface integral equation that is shown to be a simple perturbation of that for a perfect electric conducting (PEC) surface. Finally, it is shown that the computation of the small interior fields of good shields requires the use of the proper PEC interior equivalent problem     

Design of shunt slot arrays without weak excitations

By using an appropriate objective function, simulated annealing is found to prevent the presence of weakly excited slots in feedmatched waveguide slot arrays designed to produce demanding power patterns     

On the design of nonuniformly spaced slot arrays

A technique for the design of nonuniformly spaced waveguide slot arrays is proposed. The slots are in active resonance, and their position is adjusted so that the sources of the array will have the desired amplitudes and phases. The conductances of the slots depend on the desired pattern and the efficiency. Applications on Taylor and cosec ²&thetas; patterns have shown the validity of the method