Peter Gardner

Bio: Peter Gardner is an academic researcher from University of Birmingham. The author has contributed to research in topics: Antenna (radio) & Antenna efficiency. The author has an hindex of 8, co-authored 28 publications receiving 207 citations.

Rain Attenuation at Millimeter Wave and Low-THz Frequencies

Abstract: Wave attenuation through rain with different rainfall rates at millimeter wave ( $f = 77$ GHz) and low-terahertz (Low-THz) ( $f = 300$ GHz) frequencies is studied in this article. Rain has pronounced impacts on electromagnetic wave propagation and one of the well-known effects is attenuation of the transmitted wave. Attenuation at both frequencies and hydrometeor properties [rainfall rate and drop size distribution (DSD)] are measured simultaneously. The measured DSD is fit with gamma and Weibull distributions and is also compared to the frequently used distribution Marshall and Palmer (MP) model; Weibull is shown to be a better fit to the measured DSDs. Theoretical prediction of attenuation as a function of rainfall rate (up to about 20 mm/h) is determined using Mie scattering theory, and the fit gamma and Weibull, and MP distribution models; as well as using the International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation. The calculations are evaluated by comparing them to the experiment. The measured results at 77 GHz best agree with the ITU-R recommendation whereas at 300 GHz, the calculation based on Mie scattering and the Weibull distribution exhibits the best fit to the measured data. The measured data that exceed the theoretical prediction are analyzed and interpreted based on their corresponding observed drop size properties, for the first time.

Low-THz Dielectric Lens Antenna With Integrated Waveguide Feed

Abstract: A novel dielectric lens antenna with a broadband integrated waveguide-based feed and an optimized tapered extension is presented for low terahertz frequencies. The antenna consists of an extended hemispherical lens fed by a standard WR-3 rectangular waveguide fitted directly at the bottom of the lens. The antenna has been designed for high-resolution imaging radar systems requiring very wide bandwidth performance and highly directive beams. A novel matching technique based on an air pocket etched off the lens dielectric is employed to obtain broadband antenna operation covering the entire dominant-mode bandwidth of the waveguide. In addition, a new taper shaped lens extension is proposed for the first time and optimized to achieve improved sidelobe level and gain performance. The antenna is compatible with newly developed waveguide-based automotive radar and communications systems. The operating 3 dB gain bandwidth is 30% (230–310 GHz) achieving a maximum of 30 dB measured gain. The measured S 11 is well below –14 dB across the WR-3 band.

Tunable Double-Layer EBG Structures and Application to Antenna Isolation

Abstract: A novel electronically tunable two-layer slot-patch one-dimensional electromagnetic band-gap (EBG) structure with significantly simplified biasing network is presented. The proposed structure consists of apertures (slots or slits) etched off a metallic ground, and a varactor-loaded patch printed on a thin dielectric substrate, placed on top of each aperture. The apertures are initially designed using microstrip line excitation and a stop-band is produced in the ${\text{S}_{{21}}}$ response. Tuning of the stop-band is achieved by changing the voltage applied to the varactors which are electrically isolated from the metallic ground, resulting in a simple biasing configuration. As a practical application, the proposed tunable EBG structures are employed in the common ground plane of two closely spaced printed monopole antennas, significantly reducing the mutual coupling between them. Simulation results and measurements of fabricated prototypes are presented.

Millimeter-Wave Slotted Waveguide Array With Unequal Beamwidths and Low Sidelobe Levels for Vehicle Radars and Communications

Abstract: A low profile, high gain 32 × 64-slot array antenna with unequal beamwidths in the E- and H-planes and low sidelobes is proposed for vehicular applications in the 71–81 GHz band. The antenna is composed of 512 (16 × 32) 2 × 2-slot subarrays arranged with equal spacing and excited by a nonuniform corporate-feed-network. A two dimensional amplitude-tapering (complying with Taylor distribution) is used to achieve the low sidelobe levels (SLLs). Combined with the different dimensions of the array, the sidelobes and the beamwidths in the E- and H-planes are independently controlled. A prototype slotted waveguide array is fabricated to verify the array properties. Measurements show that the matching of the array is better than −14 dB over the entire bandwidth. The first SLL is lower than −18.9 dB/−24 dB with the maximum 3-dB beamwidth of 2.3°/1.3° in the E-/H-plane, respectively. The peak gain of over 39.4 dBi and the cross-polarization discrimination (XPD) of below −36.2 dB are also achieved. The demonstrated features of high gain, low SLL, and independent controllability of the beam in the E- and H-planes are most desirable for vehicular communications and radars.

Low-THz Transmission Through Water-Containing Contaminants on Antenna Radome

Abstract: In this paper, signal reduction due to the presence of water content formed on a radome has been studied at low-THz frequencies. The effect of obscurants on signal reduction has been characterized by measuring the ratio of reflected signals from a reference target through the radome, with contaminant and without contaminant. All the measurements have been compared to theoretical models, demonstrating a reasonable agreement. Water is the most common obscurant in outdoor applications and the main cause of performance deterioration in rainy, snowy, and foggy weather. This paper concentrates on the attenuation caused by different forms of distribution of water as a radome contaminant. Both a thin uniform layer of water and randomly distributed water droplets are studied at 150 and 300 GHz. The results show strong signal reduction due to the presence of uniform thickness of water and higher signal reduction with increasing frequency. However, the measured transmissivity through distributed water droplets, which occur in practice due to the surface tension of water, shows lower transmission loss at the shorter wavelength, due to transmission through the distribution of gaps between droplets.

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Dual-Band Base Station Array Using Filtering Antenna Elements for Mutual Coupling Suppression

Abstract: This paper presents a novel dual-band base station antenna array using filtering antenna elements for size miniaturization. It consists of two $1 \times 6$ subarrays arranged side by side, which are designed for Digital Cellular System (DCS: 1710–1880 MHz) and Wideband Code Division Multiple Access (WCDMA: 1920–2170 MHz) applications. The two subarrays are composed of filtering antenna elements with high in-band radiation efficiency and out-of-band radiation rejection levels. The radiation of the DCS subarray is suppressed in the WCDMA band and vice versa. Mutual coupling between the two subarrays, therefore, can be suppressed and high isolation can be obtained with reduced subarray spacing. For demonstration, a dual-band filtering antenna array is designed and fabricated. The overall width of the array is only 206 mm, which is much narrower than that of typical industrial products ( $\sim 290$ mm). An isolation of 35 dB is obtained between the two subarrays without any decoupling network. The measured antenna gains are about 14.2 and 14.5 dBi for DCS and WCDMA bands, respectively, and the 3-dB beamwidths of the horizontal radiation patterns are 65° ± 5°. In addition, null filling below the main beam in the vertical radiation patterns is realized by elaborately designing a feed network to manipulate the output magnitude and phase of each array element. The proposed array is suitable for potential base station applications.

Broadband Double-Layered Huygens’ Metasurface Lens Antenna for 5G Millimeter-Wave Systems

Abstract: A double-layered Huygens’ unit cell is proposed to design a broadband metasurface lens (meta-lens) for 5G millimeter-wave antennas. The Huygens’ unit cell consists of a pair of antisymmetric conducting semicircle arc elements on both surfaces of a thin dielectric substrate. The surface currents flowing at the opposite directions on both conducting elements form an electric current loop to induce the orthogonal magnetic current, and then the Huygens’ resonances are stimulated. The Huygens’ unit cell provides the transmission phase coverage of over 400° with transmission amplitude better than −2.3 dB. This breaks through the phase shift limitation of a conventional double-layer frequency-selective surface (FSS) element. It shows that induced magnetism makes such a Huygens-based meta-lens very compact with only one printed circuit board. As an example, a double-layered meta-lens on a 1.5 mm-thick dielectric substrate is designed and experimentally verified. The meta-lens antenna achieves the measured peak gain of 30.7 dBi at 26.2 GHz with an aperture efficiency of 42.25% over the 3 dB bandwidth of 15.7% from 24.1 to 28.2 GHz, fully covering the proposed 5G spectrum from 24.25 to 27.5 GHz. This proposed method greatly helps in the application of promoting planar lightweight low-cost broadband lens antennas in the coming 5G systems.

State-of-the-art in terahertz sensing for food and water security – A comprehensive review

Abstract: Background Recently, there has been a dramatic change in the field of terahertz (THz) technology. The recent advancements in the THz radiation sector considering generation, manipulation and detection have brought revolution in this field, which enable the integration of THz sensing systems into real-world. The THz technology presents detection techniques and various issues, while providing significant opportunities for sensing food and water contamination detection. Scope and approach Many researchers around the world have exploited the potential of invaluable new applications of THz sensing ranging from surveillance, healthcare and recently for food and water contamination detection. The microbial pollution in water and food is one the crucial issues with regard to the sanitary state for drinking water and daily consumption of food. To address this risk, the detection of microbial contamination is of utmost importance, since the consumption of insanitary or unhygienic food can lead to catastrophic illness. Key findings and conclusions This paper presents a first-time review of the open literature covering the advances in the THz sensing for microbiological contamination of food and water, in addition to state-of-the-art in network architectures, applications and recent industrial developments. With unique superiority, the THz non-destructive detection technology in food inspection and water contamination detection is emerging as a new area of study. With the great progress, some important challenges and future research directions are presented within the field.