Muaad Hussein

This paper presents a comprehensive study of a groove gap waveguide (also known as a waffle-iron) bandpass filter at Ka-band (26.5-40 GHz), fabricated using high resolution polymer jetting (Polyjet) 3-D printing technology. The same filter was previously fabricated using brass CNC milling technology. The metalized Polyjet 3-D printed filter is lower loss, lighter in weight and more cost-effective, when compared to the solid metal case. The filter operates at a center frequency of 35.65 GHz and has a 500 MHz bandwidth (1.4% fractional bandwidth), having a transmission zero below and above the passband. Without any design iterations, the measured S-parameters for the Polyjet 3-D printed filter are presented and compared with simulated results, showing excellent agreement. A comparison is then made between the measured results and that of its brass machined counterpart. The new Polyjet 3-D printed filter is 85% lighter than the conventional machined version. All these features prove the important potential of 3-D printing technology for millimeter-wave applications, which include aerospace.

In high‐order (N > 1) frequency selective surfaces (FSSs), the surfaces are usually cascaded vertically and separated by a dielectric substrate to achieve desired responses. The dielectric substrate thickness is a critical parameter in designing such structures. It is usually high for most traditional designs. In this article, we present a novel approach for designing extremely low‐profile high‐order bandpass FSSs. The structure is built by using the coupling of the third harmonics instead of the fundamentals of the resonators to achieve a bandpass response. By using the proposed design method, the coupling between the third harmonics can be very weak with a very thin substrate, and a flat response can be achieved. The thickness of the structure is reduced to one third in term of wavelength when compared with the structure using the fundamental mode. The overall thickness of a second‐order FSS can be reduced to λ/75, where λ is the free space wavelength. A prototype of the proposed bandpass FSS is designed, fabricated, and experimentally characterized. The measurement results of this device show a very good and stable frequency response with respect to the angle of incidence up to ±45° as predicted.

A novel hybrid ultra-high frequency radio frequency identification tag is proposed in this paper. The tag offers the advantage of both dipole type and patch antenna depending on the object it is placed on. The label-type dipoles are not functional on metallic objects and patch antennas are not efficient on non-metallic objects, whereas the proposed tag is a dual port design thus it is capable of working in two different modes in off-metal and on-metal scenarios. In off-metal mode, the tag works as a dipole antenna designed on an FR-4 substrate with 3.2 mm thickness. The wide capacitive loaded dipole arms and optimum tuned impedance matching between the chip and the antenna increase the robustness and limit the detuning effect in off-metal mode. The metallic surface of the host material acts as the ground plane in on-metal mode and the tag transforms into a short-ended quarter wavelength patch antenna. The measurement result confirms a long read range between 8 and 12 m in off-metal mode depending on the host material and 5.6 m in on-metal mode.

This paper proposes a new approach to implement Frequency Selective Surfaces (FSSs) with sharp transition edges and almost flat bandpass responses. The design is suitable for submillimetre wave and terahertz applications. The proposed structure exhibits a low insertion loss in the desired band. The structure is realized by combining bandstop and bandpass FSS structures on the same plane. By cascading more than one layers of surfaces, separated by dielectric slabs, the response with the desired flat passband characteristics can be achieved. The structure is polarization independent and exhibits low insertion loss at the passband around 170 GHz.

This paper presents a new type of cross coupled low loss and high selectivity bandpass filter operating at millimeter wave band. The filter is designed based on groove gap waveguide technology. A Ka-band 4^th-order bandpass filter is proposed, designed and fabricated. Cross coupling between a one pair of non-adjacent resonators has been introduced to produce two transmission zeros at the frequencies below and above the passband. The designed filter, which operates at a central frequency of 35.65 GHz with a fractional bandwidth of 1%, is fabricated using CNC milling machine. A reasonable agreement between the measured and simulated results has been obtained. Most design specifications are met although the measured insertion loss and return loss are not as good as the predicted which may be due to discrepancy between the material properties and fabrication errors.

High-order bandpass frequency selective surfaces (FSSs) (N ≥ 1) can achieve high performance with a flat in-band frequency response and fast roll-off. One particular practical issue of designing bandpass FSSs using resonant surfaces is that the thickness of the substrate would be around a quarter of a wavelength. On the other hand, the size of a nonresonant FSS array element is usually large. A new miniaturized FSS capable of exhibiting a second-order bandpass response is proposed in this letter. Two miniaturized resonant surfaces coupled by a nonresonant inductive layer are used to build the proposed FSSs. An FSS operating at around 3.8 GHz is designed to verify the method. The element size is smaller than 0.076λ × 0.076λ for the proposed structure. This is significantly smaller than the element size of second-order FSSs designed using conventional approaches. The overall thickness is less than λ/24, where λ is the free-space wavelength at the resonant frequency. The method could be particularly useful for the design of FSSs at lower frequencies with longer wavelengths.

In this paper, a new miniaturized frequency selective surface (FSS) structure is proposed. Compared with previous FSSs, the proposed structure has promising miniaturization features. The array element is implemented by using vias to connect structures on two surface layers. The dimensions of the proposed array element are only 0.035λ×0.035λ. The top layer is constructed by four spiral-shaped structures; the bottom is made of four square-shaped patches. They are connected in series by vias. In so doing, the values of the resonant component values are increased; thus the resonant frequency is shifted downwards. The frequency response is insensitive to the oblique incidence angle. Also, the proposed design is symmetric rotationally on the xy (the surface) plane and can be applied for circular polarization applications.

This paper proposes a new method to implement Frequency Selective Surfaces (FSSs) with sharp band edge transitions suitable for millimetres wave applications. A bandpass FSS can be realized by combining two bandstop FSS structures on the same plane. By choosing appropriate dimensions of the structures, the passbands and stopbands of the FSS can be controlled to obtain desired characteristics. With this method, multiple passbands and stopbands of an FSS can be achieved simultaneously. A prototype FSS is designed at the Ka band. The FSS is fabricated and then tested in free space to verify the proposed design. The structure is polarization independent and has a very low insertion loss at around 40 GHz.

Traditionally, the element of a frequency selective surface (FSS) is rotationally symmetrical and the element arrays in a multi-layer FSS are aligned with each other. A new approach to miniaturize the size of the FSS array element is proposed in this paper by interconnecting array elements only in one direction in a two-layer FSS structure. One layer acts as an enhanced inductor while the other layer provides capacitance. The interconnection between adjacent array elements changes the equivalent circuit and produces a strong cross-layer capacitance, which lowers the resonant frequency significantly. The dimensions of the miniaturized FSS element are much smaller than the wavelength at the resonant frequency (periodicity << λ). The element can also have a low profile since the cross-layer capacitance is stronger with a thinner substrate. The sensitivity to the incident angle of the proposed structure is comparable with traditional ones. A theoretical equivalent circuit model is developed to characterize the structure, based on analysis of the geometrical configuration of the FSS structure and the electric field distribution on it. The theory was verified by experimental results.