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A metasurface reflector unit cell is proposed for achieving near-complete-range of complex reflectance (i.e., magnitude and phase) for versatile beamforming capabilities. The unit cell is based on coplanar coupled resonators: a split ring resonator (SRR) with a lumped capacitor and a lumped resistor, and a dipole ring resonator (DRR) with another lumped capacitor. The DRR inserted inside the SRR creates a coupled resonance configuration which results in an enhanced complex reflectance range at the desired frequency. To provide a physical insight and explain the operation principle of the structure, the response of the unit cell is modeled as a coupled Lorentz oscillator via the effective surface susceptibilities, where a unique plasma, damping constant, and resonant frequency can be attributed to each resonator. The proposed unit cell is demonstrated in an array configuration for linear-polarized beamforming, where full-wave simulations are used to demonstrate beam-steering, gain control, side-lobe level control and dual- and triple-beam generation, as illustrative examples. Finally experimental demonstration is performed to validate the full-wave results and obtain in-depth electrical characterization of the reflectors.

A simple method is proposed to characterize metasurface unit cells using rectangular waveguide. The method maps the S-parameters obtained using a dominant-mode waveguide to the S-parameters of fundamental Floquet mode for a plane wave incident at any desired angle. The mapping between the dominant waveguide mode and the fundamental Floquet mode is executed by extracting the equivalent surface susceptibilities of the metasurface unit cell. The results obtained from the proposed method show good agreement with the full-wave simulation results of the metasurface unit cell.

Novel Fabry–Perot resonator-based compound Huygens’ structure with two all-dielectric metasurface layers is proposed and experimentally demonstrated. This design consists of two dielectric layers with about a quarter-wavelength separation at the center frequency. Each layer is a 2-D lattice of dielectric resonators. To realize the structure mechanically, each dielectric resonator is connected with its neighboring resonators using four interconnections or “two bridges.” The two bridges allow for a mechanically strong design with low fabrication tolerances. The two layers are used to cancel the reflections from the bridges, and hence achieve low backscattering in a wide bandwidth. Full-wave simulations are used to realize various beam transformations in the millimeter-wave (mm-wave) band, such as refracted and difference-pattern (DP) beams. The proposed structure is also successfully demonstrated using experiments for the uniform and DP beams at the mm-waves.

An all-dielectric Fabry–Perot compound Huygens’ structure is proposed for beam-forming at the millimeter-wave (mm-wave) band for circularly polarized (CP) waves. The proposed structure is based on a symmetric unit cell in the plane of the structure, which allows for CP wave transmission, and is demonstrated in the near field of a 60 GHz right-hand CP slot array antenna. Full-wave demonstration of a uniform structure shows a negligible effect on the reflection and radiation of the antenna from 59 to 62 GHz. Full-wave simulations were further used to demonstrate a phase-gradient structure for beam-steering from 59 to 61 GHz. Finally, a difference-pattern structure was fabricated and experimentally demonstrated for operation from 61 to 62 GHz, exhibiting low reflection and good axial ratio (AR) performance across the bandwidth.

A novel millimeter-wave (mm-wave) amplitude-only direction finding (DF) antenna front-end is proposed and experimentally demonstrated based on multiport leaky-wave antennas (LWAs). The multiport LWA is realized using an array of $N$ linearly polarized slot antennas. Each slot antenna is engineered to produce a beam pointing along a specific direction, exploiting the beam scanning law of LWAs. Realizing progressively shifted beams angularly in space by controlling the slot geometry of each antenna, the multiport LWA becomes sensitive to a large finite angular sector. Using this architecture, a unique mapping between the angle of arrival (AoA) and the port locations is achieved. Using detailed full-wave simulations, the DF operation of the slot-based LWA is successfully demonstrated for several examples involving single and multiple signals illuminating the antenna. It is demonstrated that the AoA can be determined by measuring the received power at each of the ports and the known radiation patterns of the LWAs. The DF antenna front-end is demonstrated experimentally at 60 GHz using a ten-port slot array antenna fabricated using substrate integrated waveguide (SIW) technology and tested in various incoming signal scenarios.

An all-dielectric Huygens’ transmit-array is proposed and experimentally demonstrated in the 120-GHz-band. The proposed transmit-array is fabricated using a high-precision laser-drilling process providing high fabrication precision and accuracy. A non-uniform Huygens’ surface is next placed on top of a planar high gain slot-array antenna for far-field beamforming. Full-wave simulations are first used to demonstrate the beamforming capability by generating difference-pattern beams as an example. A uniform transmit-array was then fabricated and characterized to investigate the effect of the transmit-array on the antenna performance, along with showing very low fabrication tolerances and minimal dimensional variation due to the laser drilling process. Next, a phase-gradient transmit-array for beam-tilting is experimentally demonstrated as a practical example of beamforming. The proposed all-dielectric structure is the first Huygens’ structure to be demonstrated at these frequency bands, and represents an attractive alternative to conventional metallic Huygens’ metasurfaces based on standard printed circuit board (PCB) solutions.

A novel low-profile grooved-dielectric choke ring with dual-band surface impedance resonance is proposed and experimentally demonstrated. The proposed structure is designed by engineering the surface impedance of a dielectric-based choke ring to introduce two resonant frequencies around the global navigation satellite system (GNSS) bands of L2 (1227.60 MHz) and L1 (1575.42 MHz). This provides capacitive surface impedances around both bands simultaneously, which is required for efficient surface wave suppression for higher multipath rejection performance. To demonstrate the proposed principle of surface impedance engineering, an in-house choke ring prototype of the proposed design is tested with the widely used Dorne and Margolin antenna. A high multipath rejection in both GNSS bands is experimentally confirmed with comparable performances to an otherwise bulky, heavy, and expensive conventional metallic choke ring.

Accuracy and precision of positioning, navigation, and timing using the Global Navigation Satellite System (GNSS) is important for current and future applications such as autonomous vehicles and Internet of Things. A major threat to the accuracy and precision of GNSS is multipath interference from reflections around the antenna. To combat this issue, reference station antennas use corrugated ground planes to suppress multipath signals. In this paper, a comparative study of performance, size, and weight of six corrugated ground plane solutions is presented.

The conditions for broadside radiation with no open stop-band are derived using a field based metasurface model of a general leaky-wave antenna (LWA). Using the Generalized Sheet Transition Conditions (GSTCs), the unique set of surface susceptibilities describing the metasurface to enable broadside radiation is obtained and it is found that the LWA must exhibit orthogonal electric and magnetic field dipole moments forming a Huygens' source configuration. The susceptibilities must further be lossy and satisfy a unique amplitude and phase relationship between the two.

A simple stacked dielectric structure is presented to achieve a broadband filtering response at millimeter-wave (mm-wave) frequencies. The structure consists of alternative slabs of different dielectric materials (non-periodic designs possible) to exhibit a bandpass response. The structure is designed using a transmission line model and confirmed with full-wave simulations. Compared to standard printed circuit board (PCB) fabrication, stacked dielectric structures are expected to exhibit better loss performance, due to absence of metallic patterns, and be easier to fabricate at mm-waves because of the absence of constraints from PCB line-width/gap dimension tolerances. An example structure was designed, fabricated, and measured with a center frequency 57 GHz consisting of three dielectric slabs and two air gaps. ANSYS FEM-HFSS simulations of this structure show well-matched bandpass performance, insertion loss of less than 1 dB, and a 3-dB bandwidth of 4.5 GHz. Measurement of the fabricated structure shows excellent performance and correlation with simulation.

A novel all-dielectric Huygens’ metasurface pair capable of circularly-polarized beam-forming is proposed. The proposed structure consists of two layers of dielectric resonators separated by approximately one quarter-wavelength at the design frequency. Each dielectric resonator is symmetrical to allow for the transmission of circularly-polarized waves. In order to physically design the structure, each resonator is connected to neighboring resonators using four symmetrical bridges. The second dielectric layer is added to cancel reflections caused by the bridges, allowing for the achievement of perfect matching. Fullwave simulations are used to demonstrate the full phase range achieved by varying unit cell dimensions. The operation of the proposed metasurface is further demonstrated by obtaining refracted and difference-pattern beams from a circularly-polarized slot array antenna.

A novel analog and real-time spectral decomposition system for signal processing at millimeter-wave (mmwave) frequencies is proposed and demonstrated using full-wave simulations. The system is based on a multi-port leaky-wave antennas (LWAs) structure formed using an array of $N 1-D$ LWAs with $2 N$ ports. When this structure receives a broadband time-domain signal from a single direction, the signal’s various spectral components are separated in real-time. They subsequently appear at the various ports of the LWAs following their respective beam-scanning laws. The proposed concept is demonstrated using frequency and time-domain full-wave simulations of two slot array antennas to decompose a transient pulse into four frequencies. The frequency outputs are then correlated back to the beam-scanning laws of the antennas.

A novel application of leaky-wave antennas (LWAs) as integrated antennas and multiplexers/demultiplexers is proposed and experimentally demonstrated in the millimeter-wave band at 60~GHz. The first application is demultiplexing of an oblique-incident free-space wideband plane wave into $2N$ channels using $N$ LWAs with different beam-scanning laws. The second application is $N$--channel multiplexing and demultiplexing using $N$ pairs of identical LWAs in each other's far-field, where each LWA pair is designed such that the broadside frequency is the center frequency of its respective channel. Friis transmission equation is used to analytically demonstrate the two proposed applications using Gaussian radiation beams. The LWAs are then implemented using reflection-cancelling slot pairs using substrate integrated waveguide (SIW) technology. Full-wave simulations are used to demonstrate the first application by demultiplexing an incident plane wave into two and four channels using two LWAs. Finally, the two proposed applications are experimentally demonstrated by conducting horn-to-LWA and LWA-to-LWA transmission measurements and successfully showing broadband frequency discrimination. The proposed LWAs provide a simple, compact, high-efficiency, and low-profile multiplexing/demultiplexing solution with high-integration capability with other circuitry. Compared to conventional multiplexers, the proposed solution does not require matching networks and can be directly scaled to higher frequencies using the same architecture., Comment: 11 pages, 9 figures

An analog, low-profile and shielded spectrum analyzer is proposed for operation at mm-wave frequencies around the 60 GHz band based on a novel side-fire Leaky-Wave Antenna (LWA) configuration. The proposed side-fire periodic LWA is systematically developed from a conventional 3-port waveguide T-junction which is modified to a LWA unit cell with an internal matching mechanism to suppress the stop-band and enable broadside radiation based on unit cell symmetry considerations. The resulting periodic side-fire antenna radiates in the plane of the antenna, whereby the leakage power be either be allowed to radiate in free-space or kept confined inside a PPW structure. The proposed side-fire structure thus can be completely shielded useful as an analog broadband spectrum analyzer using Substrate Integrated Waveguide (SIW) Technology. Furthermore, a convex side-fire antenna is demonstrated to focus the radiated beams in the near-field of the structure to make the entire system compact. The integrated spectrum analyzer is experimentally demonstrated between 59 GHz - 66 GHz providing 1 GHz frequency resolution. Furthermore, a simple mathematical model consisting of array of line sources is proposed to efficiently model the beam-scanning characteristics of the curved side-fire LWA in the near-field of the structure., Comment: 11 pages, 11 figures

A novel all-dielectric metasurface based on reflection cancelling Huygens’ source pair is proposed for mm-wave beam-forming applications, and demonstrated using full-wave simulations. The metasurface is realized using an elliptical resonator connected with its neighbor using four dielectric bridges to provide mechanical stability. The quarter-wavelength spaced resonator pair is next used to achieve reflection cancelling, thereby matching the structure over a large bandwidth. By exploiting resonator ellipticities, transmission phase is engineered. Its application in beam-forming is next illustrated by realizing a monopulse pattern as an example.

A low-cost light-weight 3D-printed copper coated choke ring is presented and experimentally demonstrated to have similar performance to a fully metallic choke ring. The conventional metallic choke ring is the standard ground plane used in global navigation satellite systems (GNSS) reference antennas to reject multipath signals. While the choke ring greatly enhances the performance of the antenna, it has the disadvantage of being heavy, bulky, and expensive. One method to reduce the weight and cost of the choke ring, while maintaining the same performance as the metallic structure, is to build the structure using a low-cost, light-weight dielectric material and coating the outside with an electric conductor. In this paper, a prototype of a novel 3D-printed choke ring made from polylactic acid (PLA) plastic and coated with copper tape is fabricated and tested. The novel choke ring is demonstrated to have the same performance as an otherwise heavy and expensive metallic choke ring.

An active phaser based on co-directional couplers is proposed for achieving a flat magnitude transmission while preserving its strong dispersive delay response. The phasers are realized using Half-Mode Substrate Integrated Waveguide (HMSIW) structures, and are successfully demonstrated using full-wave simulations. Due to the non-TEM nature of the device, the proposed phasers are ideally suitable for mm-wave real-time analog signal processing systems.

An active microwave C-section phaser is proposed which provides a flat magnitude transmission in a wide frequency band along with a frequency-dependent group delay response considering practical dissipation losses. The key lies in integrating a constant gain amplifier inside a microwave C-section, which perfectly compensates the distributed conductor and dielectric losses of the coupler, while preserving the intrinsic dispersion of the C-section. The operation of the proposed device is confirmed using numerical analysis and full-wave simulations.

A novel low-profile dual-band tunable artificial magnetic conductor (AMC) structure based on the choke ring is presented in this paper. The structure is tuned to the Global Navigation Satellite System (GNSS) frequencies of L2 (1227.60 MHz) and L1 (1575.42 MHz). Using full-wave simulations for the Dorne & Margolin (DM) antenna mounted on the AMC structure, it is demonstrated that the proposed dual-band structure provides good multipath performance at both L2 and L1. Compared to the conventional choke ring, the novel design provides a 52% reduction in height and a 26% reduction in diameter.