Intrinsic modes of radiation in ferrite patch antennas

We have found two types of radiation modes for patch antennas loaded with ferrite materials. Each mode of radiation is a linear combination of normal modes of propagation in parallel plate waveguide separated by a slab of ferrite material. We have introduced new boundary conditions in which only TE modes of oscillation in the patch antenna cavity result. According to different propagation directions relative to the applied DC field these TE modes are distinguished as transverse modes and longitudinal modes, and they possess mutually perpendicular radiation polarizations. While the longitudinal TE modes are found to form discrete modes in the frequency domain, the radiation frequency of a transverse TE mode can be continuously tuned over a wide frequency range by varying the biasing magnetic field. Circularly polarized radiations may result from simultaneous excitations of these two modes. Ferrite patch antennas of square geometry have been fabricated and tested. The measured resonant frequencies compared very well with our theory     

Radiation modes in circular patch antennas

We have formulated exact solutions of the normal modes in the microstrip patch antenna possessing circular geometry. The theory makes use of a new Green's function in conjunction with current potential analysis. The calculations demonstrate that the magnetic wall confinement boundary conditions as formulated in past theories hold approximately true if the surface wave loss is minimal compared to other losses: dielectric loss, conductor loss, and radiation loss. For practical path antennas the normal modes are not confined locally near the microstrip patch. Rather, they are composed of propagation surface waves which extend far beyond the region containing the patch antenna. We term these normal modes as leaky modes, since they resemble the leaky modes found in dielectric image guides. Measurements by us of the radiation mode frequencies and the intrinsic Q-values of the microstrip patch antennas compared very well with theory     

Radiation characteristics of slotted oversize patch antennas

A novel integrated antenna with low loss and medium gain is designed. It is composed of a driven oversize slotted patch, backed by a metallic ground plane. Its radiation occurs from the slots and some of its edges. By a suitable optimisation, an excellent field distribution over the antenna aperture is obtained, that provides high gain and low crosspolarisation at far field     

Microwave sintered Mg-Cd ferrite substrates for microstrip patch antennas in X-band

The ferrites with chemical formulae MgFe₂O₄, Mg_0.6Cd_0.4Fe₂O₄ and Mg_0.2Cd_0.8Fe₂O₄ specified with Ferrite S1, S2 and S3 were prepared by the oxalate co-precipitation method using AR grade sulphates under microwave sintering technique. The single phase cubic spinel structure formation of all the ferrites was confirmed by XRD and FTIR techniques. The dielectric parameters such as permittivity (ε_r), dielectric loss tangent (tan δ_e), permeability (µ_r) and magnetic loss tangent (tan δ_m) were determined from parameters S₁₁ and S₂₁ by using material measurement software with VNA. The synthesized ferrites S1, S2 and S3 with determined dielectric parameters were used as substrate to design rectangular microstrip patch antenna by simulation using Ansoft Designer SV 2.2. The designed antennas were fabricated by using screen printing technique. The return loss (RL), 10 dB % bandwidth and VSWR of these fabricated antennas were measured on vector network analyzer. The simulated and measured values of resonating frequency, return loss (RL), 10 dB % bandwidth and VSWR were nearly matched with each other. Mg_0.2Cd_0.8Fe₂O₄ (Ferrite S3) can be used as substrate of antenna for better results.     

Improved formulae for the resonant frequencies of triangular microstrip patch antennas

In this article, an improved formula for the effective side length (a _eff) of the equilateral triangular patch antenna is presented. The computed resonant frequencies for the first five modes, using this formula, are compared with the available experimental and theoretical results in the literature. It is shown that the proposed formula has better accuracy than other available expressions. Moreover, the 30°–60°–90° and 30°–30°–120° triangular patch antennas are studied. Specifically, improved formulae for the effective dielectric constant of these patches are derived.     

Radiation and scattering features of patch antennas with bianisotropic substrates

The analysis of patch antennas residing in cavities filled by general inhomogeneous and lossy bianisotropic substrates is presented. The theoretical study is based on a variational formulation associated with the boundary value problem under analysis, and a hybrid finite element-boundary integral method is employed to solve the electromagnetic field inside and outside cavities numerically. Initially, the general formulation presented is applied to some particular cases known in the literature. Then, the main scattering and radiation features of cavity backed patch antennas with chiral, anisotropic, and bianisotropic materials are presented. Particularly, it is shown that complex media allow for frequency control and for a reduced antenna size at a given operating frequency.     

Radiation and scattering characteristics of microstrip antennas onnormally biased ferrite substrates

Radiation and scattering characteristics of microstrip antennas and arrays printed on ferrite substrates with a normal magnetic bias field are described. The extra degree of freedom offered by the biased ferrite can be used to obtain a number of novel characteristics, including switchable and tunable circularly polarized radiation from a microstrip antenna having a single feed point, dynamic wide-angle impedance matching for phased arrays of microstrip antennas, and a switchable radar cross section reduction technique for microstrip antennas. Results are obtained from full-wave moment method solutions for single microstrip antennas and infinite arrays of microstrip antennas. A cavity model solution for a circular patch antenna on a biased ferrite substrate is also presented, to aid in understanding the operation of these antennas     

Ku波段宽频带双极化微带天线阵的设计

提出一种新型双频(Ku/Ka)双圆极化平板缝隙天线.三层平行平板构成双层的径向波导, 缝隙对螺旋排布于最上层平板, 低频与高频缝隙对分别逆时针和顺时针排布, 对应实现右旋圆和左旋圆极化辐射.低频与高频段分别采用单根探针与多根探针的馈电形式.在组成高频径向波导的平板外围加上一圈金属通孔使低频馈电端口易于阻抗匹配.仿真结果表明:该新型双频天线在Ku和Ka频段最高的辐射效率达到60.5%和55.7%, -1 dB增益带宽分别为8.3%和6.2%, 具有较宽的轴比带宽以及较高的端口隔离度, 该天线具有很好的工程应用价值.     

Dual-frequency patch antennas

Dual-frequency patch antennas may provide an alternative to large-bandwidth planar antennas, in applications in which large bandwidth is really needed for operating at two separate transmit-receive bands. When the two operating frequencies are far apart, a dual-frequency patch structure can be conceived to avoid the use of separate antennas. In this paper, a critical overview of possible solutions for dual-frequency patch antennas is presented, and future perspectives are outlined. Geometries are discussed in particular     

Meshed patch antennas

Conventional microstrip patch antennas are printed with continuous solid copper shapes and ground planes. The general properties of meshed patches are presented in this paper where both the patch itself and the ground plane are meshed. The gain, cross-polarization, bandwidth and radiation patterns are discussed for different combinations of patch and ground plane. The radiation patterns are not significantly affected by meshing the patch alone, but meshing the ground plane increases the back radiation. The gain can suffer by up to 3 dB or more when compared to a standard patch. Cross-polarization is improved providing that the correct mesh line geometry is chosen for the excitation mode. Meshing lowered the resonant frequency in some cases by up to 30% and also improves the bandwidth by a factor of up to 2.5 in some modes. Overall, the meshed patch offers a complex tradeoff between parameters but gives opportunities for improving the bandwidth and reducing the cross polarization and the antenna dimensions at the expense of the gain.     

Micromachined patch antennas

This paper presents the use of selective lateral etching based on micromachining techniques to enhance the performance of rectangular microstrip patch antennas printed on high-index wafers such as silicon, GaAs, and InP. Micromachined patch antennas on Si substrates have shown superior performance over conventional designs where the bandwidth and the efficiency have increased by as much as 64% and 28%, respectively. In this work, the silicon material is removed laterally underneath the patch antenna to produce a cavity that consists of a mixture of air and substrate with equal or unequal thicknesses. Characterization of the micromachined patch antenna is presented herein and includes a discussion on the bandwidth improvements, radiation patterns, and efficiency of the patch. In addition, antenna placement on the reduced index cavity with respect to the high-index substrate is described to achieve efficiency improvements over conventional patch antennas     

Circular-waveguide-fed microstrip patch antennas

A microstrip patch antenna fed by a circular waveguide is presented. The microstrip patch built on a foam substrate is laid on the flange of the circular waveguide's open mouth. The waveguide feeds the patch by coupling energy to the patch through a narrow slot underneath the patch. Two operating frequency bands were observed and the characteristics of the antenna were measured.     

Tunable circular patch antennas

A method to control the resonant or operating frequencies of circular patch antennas has been investigated experimentally and theoretically. It consists of the placement of passive metallic or tuning posts at approximate locations within the input region of the antenna. Comparison of measured and analytical results seems to establish the validity of a theoretical model proposed to determine the input performance of such circular patch antennas.     

Characteristics of switchable ferrite microstrip antennas

Switchable antennas consisting of microstrip elements with an in-plane biased ferrite cover layer are introduced. Their radiation and radar cross section (RCS) properties are examined through a full-wave moment-method analysis. For microstrip antennas with a ferrite cover layer, the presence of a decaying extraordinary wave in the ferrite layer can reduce or prohibit incident fields from reaching the antenna resulting in significant RCS reduction. For antenna radiation, most of the power will be converted into magnetostatic waves and little radiates into the air. Under such circumstances, the antennas are “off,” in the sense that they are effectively absent as radiators or scatterers. The aim of this paper is, through the use of an accurate full-wave analysis, to investigate the properties of the switchable microstrip antennas. Both the cases of strip dipoles and rectangular patches are analyzed. The effects of the cover-layer thickness, bias-field strength, and the existence of both ordinary and extraordinary waves on the switchable antenna properties are discussed     

L-probe proximity-fed short-circuited patch antennas

Experimental results for L-probe proximity-fed short-circuited quarter-wavelength patch antennas are presented. Using a foam layer of thickness ~0.1λ₀, as a supported substrate, an impedance bandwidth of 39% and a gain of >7.0 dBi have been obtained. The far field patterns are stable across the passband     

Crosspolarisation characteristics of rectangular patch antennas

Theoretical results describing the crosspolarisation characteristics of rectangular patch antennas are presented. Of particular interest is the result that the copolarisation radiation is not sensitive to resonant frequency and substrate thickness while the crosspolarisation component increases with resonant frequency and/or substrate thickness     

Cross polarization of microstrip patch antennas

The cross-polarization level of circular and rectangular patches is evaluated by finding the peak value angles. The peak value is strongly dependent on substrate dielectric constant, varying roughly as1/epsilon. Aspect ratio of a rectangular patch has little effect on peak values or location. Patch thickness also has little effect; results are limited to thin patches as surface waves are not included.     

Correction to “Radiation and scattering characteristics ofmicrostrip antennas on normally biased ferrite substrates”

The authors correct several errors appearing in their paper (see Pozar, IEEE Trans. Antennas. Propagat., vol. 40, p. 1084, 1992). First, the sign assumption for κ in the Green's function is opposite that given in equation (1) for the permeability tensor. The sign of κ is directly related to the polarity of the bias field, and is sometimes defined differently by different workers. The convention used in the present work was modified after the derivation of the Green's function, and this change was accounted for in the computer program, but mention of this was neglected in the paper. Thus,κ should be replaced by -κ in equations (21)-(23). Next, the μ that appears in the denominator of equation (24) should actually be μ₀, and the term Y should be dropped from the second parenthetical terms in both equations (16) and (17). Also, the 1/β² terms in equations (30a) and (30b) should be changed to 1/β. These errors are only in the printed paper, and do not affect the results presented therein     

Polygonal patch antennas for wireless communications

An effective design of polygonal patch antennas with multifrequency or broad-band operation modes for wireless communications is presented in this paper. It is shown how polygonal patches with suitable features may be obtained after a proper perturbation of conventional rectangular geometries, which inherently present poor bandwidth performances. These perturbed irregular geometries may support multiple resonances and, thus, may present a broad-band or multifrequency operation mode, even employing conventional patch antennas with a single dielectric substrate. These polygonal patches are efficiently analyzed through a numerical code based on the method of moments, with entire domain basis functions that accurately describe the radiation mechanism. After the presentation of the analysis and design techniques, some antenna layouts for modern wireless communication systems will be proposed. Such antennas are designed for both universal mobile telecommunication system and wireless local area network portable equipment with real-life finite ground planes.