Analytical Design Procedure for Forward Wave Couplers in RGW Technology Based on Hybrid PEC/PMC Waveguide Model

In this paper, a systematic design methodology of a 0dB and a 3dB forward couplers based on the ridge gap waveguide (RGW) technology is presented. This methodology is based on exact theoretical formulations rather than any approximate or empirical equations. The procedure of the proposed design methodology is mainly to build a virtual equivalent waveguide model. This waveguide has two horizontal upper and lower perfect electric conductor (PEC) walls, while the left and the right walls are made of perfect magnetic conductors (PMC). A detailed analysis for this hybrid PEC/PMC waveguide, a common waveguide for coupling, is introduced as the starting phase for designing the RGW couplers. The equivalent RGW coupler that assures the same operation of the hybrid PEC/PMC waveguide at a specific frequency range is deduced based on detailed theoretical aspects. Moreover, a simple analyzing of transitional bends and phase shifters with accurate calculations is presented in this paper, which are the fundamental building blocks of several mmW components such as the six-port junction and the butler matrix. The possibility of tuning the coupler center frequency is introduced without the need of using any nonlinear elements. The resulting RGW couplers are implemented through well-known full wave simulator (Ansoft HFSS), with verification through prototype measurements in order to confirm the validity of the proposed methodology. A good agreement is achieved between measurement and simulation results

Wideband Printed Ridge Gap Rat-Race Coupler for Differential Feeding Antenna

In this paper, a wideband 3 dB hybrid 180° rat-race coupler is introduced in the printed ridge gap waveguide technology. It has simultaneous wide matching and isolation bandwidth with low output amplitude imbalance. It operates in the millimeter wave band from 25.8 to 34.2 GHz (27.96%) with 15 dB return loss and isolation, and ±0.5 dB output amplitude imbalance. The proposed design employing an open stub at the middle of the 3λ/4 branch line and quarter wavelength lines at all the ports of the coupler. The objective of the added open stub is to separate the output ports amplitudes around the -3 dB level by certain values depending on the required amplitude imbalance. The analytical derivation for the role of the added open stub is presented along with a parametric study on its effect on amplitude imbalance, matching, and isolation. This results in having two intersection points for the output ports instead of one of the conventional coupler and hence the amplitude imbalance bandwidth increases. The objective of the added quarter wavelength lines is to improve the matching and isolation bandwidths. First, the conventional rat-race coupler is presented and a bandwidth of 14.25% at 30 GHz is achieved. After that the rat-race with the added quarter wavelength lines is presented to illustrate the objective of the added quarter wavelength lines and a bandwidth of 19.44% is achieved. Finally, the rat-race with the quarter wavelength lines and the added stub is presented and a prototype is fabricated and measured. The s-parameters measurements are in a good agreement with the simulated ones

4×4 -Element Cavity Slot Antenna Differentially-Fed by Odd Mode Ridge Gap Waveguide

A differential feeding for a cavity slot antenna is presented. The proposed feeding is based on a simple mechanism rather than the traditional complex networks that suffer from high losses. It is based on exciting the first higher order mode (TE10) of the ridge gap waveguide (RGW) by enlarging the ridge width. This enlargement would excite some undesired even modes that are suppressed by inserting a vertical perfectly electric conducting (PEC) wall in the middle of the waveguide based on the concept of magic tee operation. The proposed 4 × 4 cavity slot antenna is implemented using substrate integrated waveguide (SIW) technology. Two horizontal slots on the top of proposed wide RGW, representing the differential feeding approach, are implemented to feed the cavity slot antenna. The slots couple the fields with same amplitudes and 1800 phase difference to the cavity. The electric fields of the two coupling slots have odd symmetry in the x-axis, and subsequently, uniform electric field distribution of the TE440 mode of a cavity can be excited. The 4/4 radiating slots are etched on the top of the cavity in a specific distribution to ensure having in-phase fields for broadside radiation with low-cross-polarization levels. The measurement and simulation results of the proposed cavity slot antenna are in a good agreement. The obtained results confirm that the proposed antenna achieves a relative bandwidth of 7.1% for -10-dB return loss, a gain of about 16.5 dBi, and a side lobe level about -17 dB in E-plane and -13.8 dB in H-plane. Moreover, the proposed antenna provides low cross-polarization levels (-35 dB in E-plane and -27 dB in H-plane) within the operating frequency band of 32.5 to 34.9 GHz. With this achieved low profile, high gain, and high efficiency of the proposed cavity slot antenna, it may have a great potential for millimeter-wave (MMW) applications

High Gain and Wideband High Dense Dielectric Patch Antenna Using FSS Superstrate for Millimeter-Wave Applications

Gain and bandwidth enhancement of low profile, linearly polarized square dense dielectric patch antennas using a frequency selective surface (FSS) superstrate layer is proposed. A high dense dielectric patch antenna is utilized as a radiating element instead of a metallic patch in order to gain several significant advantages, including low profile, wide bandwidth, and high radiation efficiency. The implemented antenna is excited by an aperture-coupled feeding technique. The antenna gain is enhanced by using a highly reflective FSS superstrate layer, realizing an antenna gain enhancement of 11 dBi. The implemented antenna acquired a measured gain of about 17.78 dBi at 28 GHz with a 9% bandwidth and radiation efficiency of 90%. The bandwidth of the proposed antenna is improved by using a unit cell printed on two sides, as it provides a positive phase gradient over the desired frequency range. The antenna impedance bandwidth is broadened and the measured impedance matching S11 exhibited a 15.54% instead of 9% bandwidth while maintaining a high-gain characteristic of about 15.4 dBi. The implemented antenna presents a solid radiation performance with good agreement between the measured and simulation results. For some attractive advantages such as low profile, low cost, lightweight, small size, and ease of implementation, the proposed antenna is a very good candidate for millimeter-wave wireless communications

Green's Function of a Dielectric Slab Grounded by Carbon Fiber Composite Materials

The exact solution is obtained for Green's function of an infinitesimal horizontal electric dipole on a dielectric slab backed by a ground plane of carbon fiber composite (CFC) material. We consider both reinforced continuous carbon fiber (RCCF) CFC and carbon nanotube (CNT) CFC. RCCF is modeled by an electrically anisotropic surface impedance tensor whereas CNT is modeled as isotropic. The spectral domain method is used and the asymptotic part of the integrand is treated by adding and subtracting that for a perfect electric conductor ground, leaving a rapidly-converging term for numerical integration. Numerical results based on this method compare well with results based on a time-domain finite integration technique. The effect of conductivity and anisotropy of the composite ground plane on electric field is investigated

Electromagnetics Waveguide Tubes Coated With Inhomogeneous Lossy Materials for Superior Shielding Above and Below Cutoff Frequency

Abstract-A new approach for enhanced electromagnetic interference shielding of metallic waveguide (WG) tubes coated with inhomogeneous lossy materials is proposed based on numerical simulation. Shielding enhancement is achieved by using stepped variations of complex permittivity and complex permeability coating materials along the WG transverse direction. Such variation in the coating layer provides multiple wave reflections below and above the WG cutoff frequency. The underlying principle is applied to a rectangular WG operating in the dominant TE 10 mode. Simulation examples of rectangular WGs coated with uniform and stepped lossy materials are demonstrated. The proposed approach shows remarkably better performance when compared with WGs coated with uniform lossy materials

Analysis and Design of a Wideband Coaxial Transition to Metal and Printed Ridge Gap Waveguide

In this paper, a wideband coaxial to ridge gap transition is proposed and implemented. The transition has a compact size, wide bandwidth, and simple structure. It can be used to excite ridge gap waveguides implemented by the printed circuit board or computer numerical control (CNC) technologies. A similar circuit model for a coax-to-microstrip junction is proposed and used to establish a systematic design procedure for the proposed transition. Perfect electric conductor and perfect magnetic conductor (PMC) boundaries are used to make the procedure independent of the fabrication technology. The PMC is replaced by a bed of nails for ridge gap realized by CNC technology and mushroom-shaped structure in the case of PCB technology. The proposed transition based on the PCB technology is fabricated and measured. There is a good agreement between simulated and measured results which validates the proposed design. The transition has a 59.22% bandwidth with S11−0.5 dB

Ka-Band Linear to Circular Polarization Converter Based on Multilayer Slab With Broadband Performance

In this paper, a Ka-band polarization converter is presented, which is based on multilayer slab. In order to improve impedance matching, metallic circular traces are printed periodically on each dielectric multilayer slab. Simulated results of the polarizer show that it can transform linearly polarized (LP) to circularly polarized (CP) fields over a frequency band from 23 to 35GHz (42%) with an insertion loss less than 0.5 dB. The transmitted CP wave by the polarizer is approximately robust under oblique illuminations. The polarizer is fabricated and measured by a wideband horn antenna satisfying the simulated results. Next, in order to design a high-gain CP structure around 30 GHz, an 8-element LP array antenna with Chebyshev tapered distribution is designed and integrated with the polarizer. Obviously, the antenna limits the overall bandwidth (nearly 28 to 31.5 GHz) due to the narrowband nature of the LP antenna array. When the polarizer is illuminated by an incident LP wave, the two linear components of the transmitted wave with approximately equal amplitudes and 90° phase difference on the frequency band of interest are produced. Experimental results of the proposed structure show a pure CP with a gain of 13 dBi at 30 GHz, which can be suitable for millimeter wave communication

Low Loss and Ultra Flat Rectangular Waveguide Harmonic Coupler

Recently, communication networks are evolving dramatically to meet the human dynamic needs as well as provide the required support for the massive expansion in future applications. This fosters the research in the mm-wave components to create a new infrastructure for these applications. As a result, the electrical characteristics of the designed components in terms of the bandwidth and the linearity have to be evaluated in an accurate way. The linearity of the mm-wave components is evaluated through the assessment of the inter-modulation of these components, especially at the second harmonic band. In this paper, a −17-dB harmonic coupler is designed to pick a strong sample at the second harmonic, while suppressing the fundamental signal at the coupled port. A design procedure for the proposed harmonic coupler is presented and illustrated. The fabricated unit is silver plated to minimize the losses, where the measured coupling at the second harmonic band shows an excellent agreement with the simulated ones. In addition, the measured coupling level at the fundamental band is below −75 dB