Classical antenna array synthesis techniques such as Fourier, Dolph-Chebyshev and Taylor synthesis efficiently obtain array current distributions for equally spaced arrays that generate a desired far-field radiation pattern function or keep important parameters like beamwidth and sidelobe level within prescribed performance bounds. However, the concept of optimization of the field pattern (e.g., by decreasing sidelobes or beamwidth) of an given equally spaced array realization by altering its element spacings still represents a challenging problem having considerable practical advantages. These include reduction in size, weight, and number of elements of the array. This paper describes a new approach to synthesis of unequally spaced arrays utilizing a simple inversion algorithm to obtain the element spacings from prescribed far-zone electric field and current distribution, or current distributions from prescribed far-zone electric field and element spacings.

Design of unequally spaced arrays for performance improvement

An effective method for optimizing the performance of a fixed current distribution, uniformly spaced antenna array has been to adjust its element positions to provide performance improvement. In comparison with the default uniform structure, this approach yields performance improvements such as smaller sidelobe levels or beamwidth values. Additionally, it provides practical advantages such as reductions in size, weight and number of antenna elements. The objective of this paper is to describe a unified mathematical approach to nonlinear optimization of multidimensional array geometries. The approach utilizes a class of limiting properties of sinusoidal, Bessel or Legendre functions that are dictated by the array geometry addressed. The efficacy of the method is demonstrated by its generalized application to synthesis of rectangular, cylindrical and spherical arrays. The unified mathematical approach presented below is a synthesis technique founded on the mathematical transformation of the desired field pattern, followed by the application of limiting forms of the transformation, and resulting in the development of a closed form expression for the element positions. The method offers the following advantages over previous techniques such as direct nonlinear optimization or genetic algorithms. First, it is not an iterative, searching algorithm, and provides element spacing values directly in a single run of the algorithm, thereby saving valuable CPU time and memory storage. Second, It permits the array designer to place practical constraints on the array geometry, (e.g., the minimum/maximum spacing between adjacent elements)

Generalized analytical technique for the synthesis of unequally spaced arrays with linear, planar, cylindrical or spherical geometry

A reconfigurable microstrip antenna is proposed for low-cost adaptive beam-switching applications. A small patch-slot ring structure is used as the radiating element where an asymmetrical arrangement of p-i-n diodes is employed to switch the pattern in four directions. The antenna provides pattern switching of 65° and 45° in its fundamental mode for the elevation and azimuth planes, respectively. By maintaining the resonant frequency and beamwidth as relatively constant, beam switching is realized using a single feed point.

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Reconfigurable Antenna With Elevation and Azimuth Beam Switching

A joint field/circuit model is proposed in this paper to characterize a class of line-to-ring coupling structures for design and optimization of microstrip dual-mode filters and ring resonator circuits. The generic model is derived from field theory and presented in terms of circuit elements by applying a newly developed numerical deembedding technique called "short-open calibration" in a deterministic method-of-moments scheme. It provides a new design strategy for characterizing and optimizing electrical performance of the line-to-ring coupling structures. Such three-port topologies are explicitly formulated by using an equivalent network having circuit elements calculated by the proposed joint field/circuit model. Three microstrip tightly coupling geometries and their related ring resonators are studied with the extracted J-inverter susceptance parameters. Experiments are performed to validate the joint model and also show coupling characteristics of the three types of line-to-ring circuit for the design of ring resonators and dual-mode filters. With this new technique, an optimized microstrip dual-mode filter is successfully designed and the prediction agrees well with our measurements.

A joint field/circuit model of line-to-ring coupling structures and its application to the design of microstrip dual-mode filters and ring resonator circuits

A transmission-line model is used to extract the equivalent lumped-element circuits for the closed- and open-loop ring resonators. The unloaded Q values of the ring resonators can be calculated from the equivalent lumped elements G, L, and C. Four different configurations of microstrip ring resonators fabricated on low and high dielectric-constant substrates are used to investigate the lumped elements and unloaded Qs. The largest difference between the measured and calculated unloaded Q is 5.7%, which is due to measurement uncertainties and accuracies of the calculation. These simple expressions introduce an easy method for analyzing ring resonators in filters and provide, for the first time, a means of predicting their unloaded Q.

Equivalent lumped elements G, L, C, and unloaded Q's of closed- and open-loop ring resonators

The resonant frequencies of a microstrip-ring resonator capacitively coupled to a feed line are accurately analyzed using a transmission-line model. By making use of ABCD- and Y-admittance matrices, a compact closed-form expression for the input impedance of the ring alone is analytically derived and shows that the ring ran be equivalently viewed as a frequency-dependent capacitor. The coupling gap is then modeled by an equivalent L-network comprising a parallel and a series gap capacitance obtained by modifying Garg and Bahl's closed-form expressions for an end-to-end microstrip gap. By simplifying the parallel and series combinations of the overall equivalent circuit, the total input impedance looking from the feed line to the gap is analytically derived to predict the resonant frequencies. To verify the analysis, the resonant frequencies of the capacitively coupled ring resonator have been accurately measured, with the experimental results showing very good agreement with the theoretical predictions.

Transmission-line analysis of a capacitively coupled microstrip-ring resonator

The sidelobe reduction of asymmetric linear arrays by tuning element spacings is presented. Using appropriate point matching and least square error approximation of the radiation power distribution, further sidelobe reduction may be achieved with slight beamwidth broadening. Two simulation results are given to show the feasibility of the proposed technique.

Sidelobe reduction of asymmetric linear array by spacing perturbation

A shortened dipole antenna using meander line is designed for the personal communication network (PCN) handset operating at center frequency f0 = 880 MHz. The shortened dipole antenna is printed on a Duroid 6010 substrate with dielectric constant er = 10.5 and thickness = 25 mils. A shortening ratio (SR) of 45.9% is experimentally achieved with the printed-circuit dipole antenna (PCDA) of 9.2-cm length as compared to the λ0/2 linear dipole antenna. Owing to the planar, lightweight, thin, and small characteristics, the PCDA using meander line is well suited for signal transmission and reception of the PCN handset, in which it may be built in, and various antenna diversity schemes for fading reduction may be utilized. © 1992 John Wiley & Sons, Inc.

Printed-circuit dipole antenna for personal communication network handset

In this article calculations of power components transmitted and reflected at the step discontinuities in dielectric-slab and dielectric-loaded waveguides are presented using the geometric-optics approach. Step discontinuities regarding the dielectric slab thickness and refractive index are considered. Numerical results are shown to be in good agreement with those of other rigorous methods. The computation involved in this approach is efficient since the associated mathematical formulation can be analytically expressed from the geometric optics point of view. © 1992 John Wiley & Sons, Inc.

Analysis of step discontinuities in dielectric‐slab and dielectric‐loaded waveguides using geometric‐optics approach

An analysis is developed for a patch antenna coupled to a transmission line. The coupling port is placed on the same side and the opposite side of the feeding end. A transmission line method is used to model the circuit. Experimental results are presented to verify the simulated results. Whether the coupling port is placed on the same side or the opposite side of the feeding end, the coupled power levels from the patch to the transmission line are almost the same. The coupling characteristics as a function of the gap and length variations are also identical for these two configurations.

Cheng-Cheh Yu

Papers

Transmission-line analysis of a capacitively coupled microstrip-ring resonator

Sidelobe reduction of asymmetric linear array by spacing perturbation

Printed-circuit dipole antenna for personal communication network handset

Analysis of step discontinuities in dielectric‐slab and dielectric‐loaded waveguides using geometric‐optics approach

Analysis of a patch antenna coupled to a transmission line