This paper presents a novel design of a Fabry-Perot (FP) resonator antenna with a wide gain bandwidth in X band. The bandwidth enhancement of the antenna is attributed to the positive reflection phase gradient of an electromagnetic band gap (EBG) structure, which is constructed by the combination of two complementary frequency selective surfaces (FSSs). To explain well the design procedure and approach, the EBG structure is modeled as an equivalent circuit and analyzed using the Smith Chart. Experimental results show that the antenna possesses a relative 3 dB gain bandwidth of 28%, from 8.6 GHz to 11.4 GHz, with a peak gain of 13.8 dBi. Moreover, the gain bandwidth can be well covered by the impedance bandwidth for the reflection coefficient ( ${\rm S} _{11}$ ) below $-10~{\rm dB}$ from 8.6 GHz to 11.2 GHz.

Wideband Fabry-Perot Resonator Antenna With Two Complementary FSS Layers

Based on a transformation optics method, a flat compact dual-polarized Luneburg lens antenna is proposed and implemented using the printed-circuit-board-stacked gradient-index metamaterials for beamscanning and multibeam applications at X-bands. The transformed material properties of the planar Luneburg lens are designed with 17-layered permittivity distribution of polynomials. Each layer is discretized into $41 \times 41$ pixels made of broadband and less polarization-dependent unit cells responsible for desired index distributions. The effects of transformation, approximation, and discretization on the lens performance are analyzed comprehensively. Also, to validate the implementation method, a flat Luneburg lens with a thickness of 14.1 mm, a focal length of 28 mm, and an aperture size of $98.9 \times 98.9$ mm2 is designed and tested. A stacked aperture-coupled patch antenna operating at 10 GHz is applied as a feeder. The measured results show that the proposed antenna can operate over a bandwidth of ~20% with an antenna efficiency of 32%, a cross-polarization level of <−17.1 dB, as well as the maximum gain of 15.9/16.35 dBi and a scanning angle of ±32°/±35° for two orthogonal polarizations, respectively. The presented flat Luneburg lens antenna featuring broad bandwidth, high gain, wide scanning angle, and easy fabrication has a high potential in 5G wireless communication, imaging, and remote sensing applications.

A Flat Dual-Polarized Transformation-Optics Beamscanning Luneburg Lens Antenna Using PCB-Stacked Gradient Index Metamaterials

This paper presents a novel design of cylindrical modified Luneberg lens antenna at millimeter-wave (mm-wave) frequencies in which no dielectric is needed as lens material. The cylindrical modified Luneberg lens consists of two air-filled, almost-parallel plates whose spacing continuously varies with the radius to simulate the general Luneberg's Law. A planar antipodal linearly-tapered slot antenna (ALTSA) is placed between the parallel plates at the focal position of the lens as a feed antenna. A combined ray-optics/diffraction method and CST-MWS are used to analyze and design this lens antenna. Measured results of a fabricated cylindrical modified Luneberg lens with a diameter of 100 mm show good agreement with theoretical predictions. At the design frequency of 30 GHz, the measured 3-dB E- and H-plane beamwidths are 8.6° and 68°, respectively. The first sidelobe level in the E-plane is -20 dB, and the cross-polarization is -28 dB below peak. The measured aperture efficiency is 68% at 30 GHz, and varies between 50% and 71% over the tested frequency band of 29-32 GHz. Due to its rotational symmetry, this lens can be used to launch multiple beams by implementing an arc array of planar ALTSA elements at the periphery of the lens. A 21-element antenna array with a -3-D dB beam crossover and a scan angle of 180° is demonstrated. The measured overall scan coverage is up to ±80° with gain drop less than -3 dB.

Air-Filled Parallel-Plate Cylindrical Modified Luneberg Lens Antenna for Multiple-Beam Scanning at Millimeter-Wave Frequencies

This communication presents the design and experimental verification of a substrate integrated waveguide fed lens antenna for 79 GHz automotive radar applications. The proposed integrated lens antenna consists of a six layer cylindrical Luneburg lens illuminated by 17 source elements of substrate integrated waveguide fed by a planar log periodic dipole antenna array. The Luneburg lens is developed by using a unique foam material AirexR82 ( $\varepsilon _{r} = 1.12$ ), which is drilled and pressed to achieve the different dielectric constant needed to follow the index law inside the lens. The return loss and the radiation characteristics of the proposed integrated lens antenna are investigated and validated by measurements. A good agreement between the measured and simulated results is observed. The measured results confirm the beam scanning capability of the proposed integrated lens antenna for a wide scan angle of ±85° in azimuth plane having a maximum antenna gain of 15 dBi at 82.5 GHz and gain drop of less than 2.75 dB for the edge feeds. The estimated radiation efficiency of the antenna is found to be 67% at 82.5 GHz.

Lens Antenna for Wide Angle Beam Scanning at 79 GHz for Automotive Short Range Radar Applications

In this paper, a balanced-to-balanced power divider is proposed, for the first time, with arbitrary power division, which can be regarded as the balanced form of a Gysel power divider. The constraint rules are provided for its mixed-mode and single-ended S-parameters. The six-port network is analyzed by simplifying it to two-port networks with other ports matched at the central frequency. Its critical characteristic impedances are then calculated analytically by our derived equations according to the desired differential-mode power division ratio. The maximum achievable power division ratio is 1:4.692 when the characteristic impedances are limited within the realizable range of 20-120 Ω. The impacts of several freely selected design parameters on the operating bandwidth are explored numerically. A prototype is realized by microstrip lines and lumped resistors with the power division ratio of 1:32. The balanced-to-balanced performances of unequal power division, low differential-mode insertion loss, good suppression of common-mode noises, and mode conventions have been demonstrated by the simulated and measured results of the balanced-to-balanced power divider prototype.

A Balanced-to-Balanced Power Divider With Arbitrary Power Division

-A novel unequal Wilkinson power divider is presented. A coupled-line section with two shorts is proposed to realize the high characteristic impedance line, which cannot be implemented by conventional microstrip fabrication technique due to fabrication limitation. The proposed coupled-line structure is compatible with single layer integration and can be easily designed based on an even-odd mode analysis. As a design example, a 10:1 Wilkinson power divider at 2 GHz is fabricated and measured. The measured -10 dB bandwidth of S11 is about 16%, and the isolation S32 is better than -20 dB. The measured amplitude balance between output port 2 and port 3 is between -10.20 dB and -9.52 dB, and the corresponding phase difference is between 0deg and 4.6deg.

A 10:1 Unequal Wilkinson Power Divider Using Coupled Lines With Two Shorts

This paper presents dual-band equal/unequal Wilkinson power dividers based on a coupled-line section with short-circuited stub (called as the \coupled-line section" for short), which consists of a pair of parallel coupled lines and a short-circuited stub. With the analyses of the phase shift and equivalent characteristic impedance, the coupled-line section is used to replace the quarter-wavelength branch line in the conventional equal/unequal Wilkinson power divider to obtain excellent dual-band operation. The closed-form equations and design procedures of dual-band Wilkinson power divider are given, where one degree of design freedom is obtained and design ∞exibility is shown. As two examples, a dual-band equal Wilkinson power divider with the frequency ratio of 1:8 : 1 and an unequal one with the high power dividing ratio of 7 : 1 and frequency ratio of 1:8 : 1 are designed, fabricated and measured. The measurements are in good agreement with the simulations. It is shown that the proposed power dividers have simple topologies, and can be easily fabricated with small frequency ratios and high power dividing ratios.

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Dual-band equal/unequal wilkinson power dividers based on coupled-line section with short-circuited stub

In this letter, a circularly polarized (CP) waveguide antenna with dual pairs of slots is presented for Ka-band applications. Circular polarization is realized by combining two orthogonal linear polarizations, which are generated by two pairs of radiation slots on a cavity surface, respectively. Two approaches of radiation slots, i.e., edge slots and corner slots, are discussed. The corner slots approach is employed to design a CP waveguide antenna at Ka-band. The measured axial ratio (AR) is below 3 dB from 29.69 to 30.06 GHz, or 1.2% relative bandwidth, with a minimal value of 0.4 dB at 29.9 GHz. The measured antenna gain is 9.8 dBi at 30 GHz, and the return loss is below –13 dB within the 3 dB AR bandwidth. The all-metal structure of the proposed antenna is very appropriate for tough environment applications.

Circularly Polarized Waveguide Antenna With Dual Pairs of Radiation Slots at Ka-Band

A novel step-index cylindrical homogeneous lens at millimeter-wave (MMW) frequencies is designed by using the technique of parallel plates propagating the TE1 mode. The cylindrical homogeneous lens, which is sandwiched between two parallel conducting plates, has an H-shaped cross section to give the desired step-index of refraction. For a given aperture size, the focal length of the cylindrical homogeneous lens can be adjusted by changing the cross-section structural parameters rather than the dielectric material itself, which should be highlighted for cylindrical homogeneous lens for the first time. A planar linearly tapered slot antenna (LTSA) is chosen to feed the cylindrical homogeneous lens. The ray-tracing and transverse resonance methods are used to analyze and design this lens antenna at 30 GHz. Measured results of the fabricated lens antenna show good agreement with simulations. At 30 GHz, the measured 3-dB E- and H-plane beamwidths are 6.1° and 50.2°, respectively, and the first sidelobe level in the E-plane is -16.3 dB. The measured gain is 17.9 dB, corresponding to a radiation efficiency of 67.2%.

Xidong Wu

Papers

Air-Filled Parallel-Plate Cylindrical Modified Luneberg Lens Antenna for Multiple-Beam Scanning at Millimeter-Wave Frequencies

A 10:1 Unequal Wilkinson Power Divider Using Coupled Lines With Two Shorts

Dual-band equal/unequal wilkinson power dividers based on coupled-line section with short-circuited stub

Circularly Polarized Waveguide Antenna With Dual Pairs of Radiation Slots at Ka-Band

Millimeter-Wave Fan-Beam Antenna Based on Step-Index Cylindrical Homogeneous Lens