Bandwidth enhancement and size reduction of microstrip slot antennas

Reduced size microstrip monopole slot antennas with different slot shapes-straight, L and inverted T, and placed on a small ground plane, are investigated. The ground plane size is 50 mm/spl times/80 mm, which is about the size of a typical PC Wireless card. Detailed simulation and experimental investigations are conducted to understand their behavior and optimize for broadband operation. It is shown that, the variation in the slot shape, from straight to L and T shapes, helps in generating additional resonances, which when coupled to the original resonances of the slot, further increases impedance bandwidths. The bent shapes of the L and T slots reduce their height and provide more space on the ground plane for electronics. A mirror image dual L-slot antenna, placed at two adjacent corners of the ground plane, is also investigated and optimized for the polarization diversity. They provide an impedance bandwidth of 87%, with near orthogonal radiation characteristics. The measured impedance bandwidths (S/sub 11/=-10 dB) of up to 60%, 84%, and 80% are achieved for these straight, L and inverted T slots respectively, by suitably selecting their design parameters. The simulation results are in good agreement with the experimental data considering several practical issues.     

Size reduction of cavity-backed slot antennas

A technique for reducing the dimensions of the cavity of a cavity-backed slot antenna (CBSA) is presented, which facilitates proper fabrication and integration of miniaturized slot antennas on multilayer substrates. This is accomplished by replacing the solid metal around the traditional slot antennas with a specific metallic pattern that can be viewed as a series of parallel strip lines placed around the slot antenna. This metallic pattern is then modified by designing the parallel strips in a compact fashion to reduce the overall antenna dimensions and obtain a reduced-size CBSA. It is shown that, for a simple straight slot antenna, the overall occupied volume of the modified cavity backing the slot antenna can be reduced by more than 65% without affecting the high radiation efficiency of the antenna. A number of traditional cavity backed slot antennas and the proposed modified CBSAs are designed, fabricated, and measured. The reduced-size CBSAs show a very low input VSWR, low cross-polarized radiation levels, and high radiation efficiency. Despite their small ground plane size, the proposed cavity backed slot antennas have front-to-back ratio (FTBR) values in the range of 6-7 dB.     

Bandwidth enhancement of microstrip patch antennas using coupledlines

A novel single-layer rectangular patch antenna using a coupled line feed is described. This coupled line matching technique increases the bandwidth of the patch antenna by a factor of more than 2.5 as compared to the normal edge-fed patch with the same geometrical dimension     

Studies of CPW-fed equilateral triangular-ring slot antennas and triangular-ring slot coupled patch antennas

Designs of coplanar waveguide (CPW)-fed equilateral triangular-ring slot antennas with tuning-stub and triangular-ring slot coupled patch antennas are proposed and experimentally investigated. The impedance matching of the resonant frequency can be obtained only by adjusting the tuning-stub length for the proposed triangular-ring slot antenna with tuning-stub. For the design of ring-slot coupled patch antenna, slightly changing the patch size causes the tunable frequency-ratio f/sub 2//f/sub 1/ between the first two operating frequencies to fall in the range of about 1.1-1.42. Details of the proposed designs are investigated by experimental as well as theoretical studies.     

Bandwidth enhancement and broadband noise reduction ininjection-locked semiconductor lasers

Injection locking of a semiconductor laser can significantly improve the broadband modulation characteristics. By adjusting the frequency offset between the master laser and the slave laser, improved modulation bandwidth or flatness of the modulation response can be emphasized. The improved modulation characteristics are accompanied by reduced broadband relative intensity noise. Our calculations predict that the parasitic-free modulation bandwidths can be enhanced above the theoretical limit for the free-running laser     

Design of reconfigurable slot antennas

In this paper the design of a compact, efficient and electronically tunable antenna is presented. A single-fed resonant slot loaded with a series of PIN diode switches constitute the fundamental structure of the antenna. The antenna tuning is realized by changing its effective electrical length, which is controlled by the bias voltages of the solid state shunt switches along the slot antenna. Although the design is based on a resonant configuration, an effective bandwidth of 1.7:1 is obtained through this tuning without requiring a reconfigurable matching network. Four resonant frequencies from 540-890 MHz are selected in this bandwidth and very good matching is achieved for all resonant frequencies. Theoretical and experimental behavior of the antenna parameters is presented and it is demonstrated that the radiation pattern, efficiency and polarization state of the antenna remain essentially unaffected by the frequency tuning     

Theory of miniaturized shorting-post microstrip antennas

An analytical theory for the eigenfrequencies and eigenmodes of shorting-post microstrip antennas (MPA's) is presented. These antennas are seen as promising candidates for miniaturized mobile telecommunication handsets. In particular, it is shown that the zero mode of the unloaded MPA plays a central role for reducing the lowest operation frequency of the loaded MPA. The theory allows a complete calculation of all relevant antenna parameters and can easily be extended to the case of multiple shorting posts. Applications to the examples of rectangular and circular shorting post MPA's are illustrated     

Self and mutual admittance of slot antennas on a dielectric half-space

In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ _r =3.80), crystal quartz (∈ _r =4.53), silicon (∈ _r =11.9) and GaAs (∈ _r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies.     

Bandwidth enhancement of a microstrip-line-fed printed wide-slotantenna

Printed wide-slot antennas fed by a microstrip line with a fork-like tuning stub for bandwidth enhancement are proposed and experimentally investigated. Both the impedance and radiation characteristics of this antenna are studied. Experimental results indicate that a 1:1.5 VSWR bandwidth of 1 GHz is achieved at operating frequencies around 2 GHz, which is nearly ten times that of a conventional microstrip-line-fed printed wide-slot antenna. It also achieved a 2-dB gain bandwidth of at least 0.5 GHz     

Design of single layer broadband slot antennas

A novel design for single layer slot antennas is presented. The antenna consists of a rectangular slot on the top of a substrate and two parasitic patches with a coplanar feed-line on the opposite side. The simulated and experimental data show good performances in terms of bandwidth and unidirectional radiation.     

RCS reduction and gain enhancement of SRR inspired circularly polarized slot antenna using metasurface

In this work, a novel Circularly Polarized (CP) slot antenna is proposed for low RCS and high gain applications. The proposed antenna is designed in two phases. Initially, a metasurface is designed, which is composed of two similar artificial magnetic conductor (AMC) unit cells arranged orthogonally in chessboard-like configuration for broadband RCS reduction. Then, the CP slot antenna is designed by placing dual SRR on the backside of the slot for impedance matching and to achieve circular polarization. Detailed analysis is conducted to investigate the performance of metasurface loaded CP slot antenna. The proposed antenna shows 10 dB RCS reduction over the bandwidth of 41.3% at boresight direction compared to CP slot antenna. The maximum in-band and out-of-band RCS reduction achieved is 24 dB and 20 dB, respectively. The maximum gain of the antenna is also increased by 2.7 dB as a result of parasitic radiation of the metasurface and an improvement in overall performance of the antenna is observed by the employment of metasurface. Measured results of the fabricated prototype are in good agreement with the simulated results.     

Simulation and experiment on SIW slot array antennas

By etching longitudinal slots on the top metallic surface of the substrate integrated waveguide (SIW), an integrated slot-array antenna is proposed in this letter. The whole antenna and feeding system are fabricated on a single substrate, which takes the advantage of small size, low profile, and low cost, etc. The design process and experimental results of a four-by-four SIW slot array antenna at X-band are presented.     

Bandwidth improvement for a microstrip-fed series array ofdielectric resonator antennas

The impedance and pattern bandwidth of an array of dielectric resonator antennas series fed by a microstrip line was significantly improved by replacing individual DRAs with paired DRAs. The DRAs in each pair are spaced slightly <λ_g/4 apart so that their input reflections cancel. An array of eight DRA pairs was designed and fabricated, and its performance was compared to an array of eight single elements. The 10 dB return loss bandwidth improved from 2 to 18% and the 3 dB gain pattern bandwidth improved from 12 to 17%     

Bandwidth enhancement of aperture-coupled reflectarrays

An aperture-coupled reflectarray element with a reduced inter-element spacing is proposed. Bandwidth improvements are demonstrated by a smooth and similar behaviour of the phase design curves when properly decreasing the unit cell size. Experimental validations are reported for the measured radiation patterns of two reflectarray prototypes with different element spacings     

A novel approach for miniaturization of slot antennas

With the virtual enforcement of the required boundary condition (BC) at the end of a slot antenna, the area occupied by the resonant antenna can be reduced. To achieve the required virtual BC, the two short circuits at the end of the resonant slot are replaced by some reactive BC, including inductive or capacitive loadings. The application of these loads is shown to reduce the size of the resonant slot antenna for a given resonant frequency without imposing any stringent condition on the impedance matching of the antenna. A procedure for designing this class of slot antennas for any arbitrary size is presented. The procedure is based on an equivalent circuit model for the antenna and its feed structure. The corresponding equivalent circuit parameters are extracted using a full-wave forward model in conjunction with a genetic algorithm optimizer. These parameters are employed to find a proper matching network so that a perfect match to a 50 /spl Omega/ line is obtained. For a prototype slot antenna with approximate dimensions of 0.05/spl lambda//sub 0//spl times/0.05/spl lambda//sub 0/ the impedance match is obtained, with a fairly high gain of -3dBi, for a very small ground plane (/spl ap/0.20/spl lambda//sub 0/). Since there are neither polarization nor mismatch losses, the antenna efficiency is limited only by the dielectric and ohmic losses.     

Impedance and polarization characteristics of H and IHI slot antennas

Slot antennas can be end loaded to tune input impedance for use with active devices and to decrease overall slot length at a given resonant frequency. Cross polarization and impedance of end-loaded slots in an H configuration are analyzed. For an H antenna of approximately equal height and width, D-plane cross polarization was found to be -20 dB, and the resonant frequency decreased by 34% over a slot with a length equal to the width of the H. The cross polarization can be reduced with our new IHI configuration, which is introduced. The impedance at the second resonance can be tuned over a range of 26-82 /spl Omega/.     

Bandwidth and Q of antennas radiating TE and TM modes

The time-domain Poynting theorem is used to develop a general expression for the complex Poynting vector applicable to any single-frequency electromagnetic radiation field. It is found that the traditional complex Poynting vector applies to TE or TM fields, which we call simple fields, but that it does not apply to TE and TM fields, which we call compound fields. Either TE or TM fields are generated by most antennas. We show that previously imposed theoretical minimum size-to-wavelength ratios for useful antenna operation apply to simple fields but not always to compound ones. We conclude that electrically small, efficient compound antennas may be possible. As an example, the general form of the Poynting vector is used to analyze a compound source consisting of four antenna elements; idealized, superimposed, properly phased and oriented, coherent, electric and magnetic, dipole and quadrupole radiators. When properly driven, the antenna supports zero reactance on a circumscribing virtual surface of radius a, even in the limit as the radius-to-wavelength ratio of that surface goes to zero. The directivity pattern has a fixed 9 dB gain; the radiative Q of the surface is less and the bandwidth more by a factor of (ka)², where k is the wave number, than for similarly sized radiators of simple fields     

Experimental determination of the mutual admittance of slot antennas

The mutual admittance of two X band radiators are measured, using three different methods of measurement. The results, both for free space and ionised environment, are in qualitative agreement with previous theoretical computations.     

Experimental study of the impedance of cavity-backed slot antennas

The impedance of a simple open slot antenna was measured as a function of frequency and was then compared with the theoretical values obtained through Babinet's principle from the known values of the admittance of its complementary antenna, the strip dipole. A careful experimental study was then made of the impedance of the same slot with several different cavity backings. The impedance was found both as a function of frequency and of the various parameters of the cavity, namely, the cross-sectional size of the cavity, the medium filling the cavity, and the type of termination of the cavity.     

Design of cavity-backed slot antennas using the finite-differencetime-domain technique

A cavity-backed slot antenna is thought to be one of the most suitable elements for the wireless transmission of microwave energy. A design technique is developed for the cavity-backed slot antenna using the finite-difference time-domain (FDTD) method. The technique is effective in characterizing antenna performance such as the input impedance and the far-field pattern since it takes into account the geometry of the feeder as well as the cavity. We present a method that overcomes difficulties when the FDTD method is used to design the antenna. Moreover, we discuss how to determine the calculation parameters used in the FDTD analysis. Several numerical results are presented, along with measured data, which demonstrate the validity, efficiency, and capability of the techniques. The paper proposes a new prediction method for the frequency characteristics of the cavity-backed slot antenna, which applies computational windows to time-sequence data. It is emphasized that windowing the slow decaying signal enables the extraction of accurate antenna characteristics. We also discuss how to estimate the antenna patterns when we use a sinusoidal voltage excitation