A highly integrated phased array transmit/receive architecture is presented. Multilayer microstrip antennas with a scanning potential up to 60° are combined, on a common manifold, with SiGe MMICs including four RF channels each, together with the necessary digital control circuits. Power distribution and combining are realised by the concept of a folded planar reflectarray. This study also includes the necessary solutions for multilayer interconnects and efficient heat removal from the active circuits. To prove the concept, passive arrays with different fixed beam positions have been tested successfully; followed by a first active array demonstrating excellent scanning performance up to 60° both in E- and H-plane.

In this work, one-dimensional (1D) and 2D scan phased array antennas for 60 GHz radio communication and radar sensing systems are proposed, studied and experimentally validated in the substrate-integrated waveguide technology. A linearly polarised phased array with 1D scanned beams in the first part of this study and a right-hand circularly polarised (CP) array with 2D scanned beams in the second part are presented and discussed in detail. In the demonstrated 1D phased array, dielectric rod antenna is used as radiating elements to form 1 × 4 linear array and then a planar Butler matrix is integrated along with the array to obtain phase-steered beams. In the 2D phased array, CP radiating elements are used to form 2 × 4 array and then a folded Butler matrix is used to feed the CP array. Simulated and measured characteristics of these two phased array antenna radiation parameters are compared. The proposed phased arrays can be integrated into 60 GHz and other millimetre-wave radar and radio systems as an integrated antenna front-end.

A novel technique for tuning periodic phase shifting surfaces at millimetre-waves is presented. The proposed structure consists of a periodic surface placed over a ground plane creating an air cavity. The periodic surface is formed by a two-dimensional array of metallic square loop elements printed on a 0.8 mm thick dielectric substrate. When excited by a plane wave, the structure is acting as an artificial impedance surface, reflecting the incident wave with a wide range of phase values within a specific frequency band. The tuning is achieved by means of a small number of piezoelectric actuators which support the periodic surface. The actuators are placed around the periodic surfaces thereby not interfering with the radiation performance and introducing no losses. They produce a displacement between the periodic surface and the ground plane when voltage is applied, which in turn changes the reflection phase response of the structure. Full wave periodic simulations have been carried out in three-dimensional electromagnetic simulation software (CST Microwave Studio^TM) to extract the reflection characteristics and evaluate the expected tuning range of the proposed structure. A prototype has been fabricated and measured validating the concept.

This study presents the implementation of a microelectromechanical systems (MEMS)-based active phase shifter (APS) by using vector sum method. The proposed phase shifter comprises of two variable gain amplifiers (VGAs), a Wilkinson power divider with 90° phase shift lines, a Wilkinson power combiner and two 1-bit (0°/180°) MEMS phase shifters. First, all the components were designed and fabricated individually to check for their proper functionality, then they were brought together in a novel vector sum topology to work as a full-360° span phase shifter. Fabricated VGAs function properly at designed frequency (77 GHz) with gain variation from 0 to 14 dB with the tuned base voltages from 1.8 to 2.3 V. The VGAs not only serve for providing the weighted amplitudes but also compensate 4.3 dB loss from 1-bit MEMS phase shifter and 0.8 dB loss from each power divider and combiner. Active/passive components and MEMS switches are all integrated at one single chip of 3.74 mm² and manufactured with IHP 0.25 µm SiGe BiCMOS technology. As to the author's knowledge, this is the first demonstration of an APS using integrated active components and MEMS technology. Presented phase shifting mechanism can be used at automotive radar system for beam steering purpose.

A frequency-tunable lens-coupled annular-slot antenna (ASA) with a nearly 50 GHz tuning range has been designed, fabricated and characterised at the G-band (140–220 GHz). Initial numerical electromagnetic simulation results show that the resonant frequency of the antenna can be tuned effectively, with a tunability of ∼2.5 GHz/fF associated with the capacitive loading from the varactor. In addition, simulated far-field antenna patterns have demonstrated that the addition of the varactor used to implement the capacitive loading does not strongly affect the antenna's radiation properties. This design has been demonstrated experimentally, using a Schottky varactor diode with a zero-bias junction capacitance of ∼16 fF mounted on a 200 GHz ASA fabricated on a semi-insulating silicon wafer. Measurement at G-band shows a frequency tuning range of nearly 50 GHz by varying the voltage bias of the Schottky varactor diode from −5 to 1 V. The measurement results agree well with simulations based on an equivalent circuit model for the Schottky diode and the antenna. Measured far-field radiation patterns of the lens-coupled tunable ASA at 203 GHz show good agreement with calculations based on the ray-tracing technique, verifying that the diode mounting does not affect the antenna radiation properties significantly. This type of tunable ASA is very promising for realising reconfigurable detectors and focal-plane arrays at terahertz (THz) frequencies, and may find applications in future adaptive submillimetre-wave/THz communication systems.

A compact frequency, pattern and polarisation reconfigurable planar ultra-wideband antenna is presented. The antenna is frequency reconfigurable to allow flexible functionality such as limiting the impact of out-of-band interferers if required in certain applications. Moreover, it provides basic pattern reconfiguration to enhance the scanning or the communication performance in future wireless applications by sensing interferers in the space domain and achieving pattern diversity to mitigate fading and increase signal-to-noise ratio. Another special feature of the proposed antenna is that its polarisation is reconfigurable at specific frequencies to generate circular polarised (CP) radiation. The antenna performance characteristics are verified through parametric simulations and measurements. The proposed antenna presents significant degrees of freedom in providing reconfigurable properties in frequency, radiation patterns and polarisation as compared to standard single-parameter reconfigurable antennas; therefore providing a flexible radio front-end for smart radio and wireless applications such as cognitive radio.

A new cognitive radio antenna system is presented and discussed in this study. The antenna system is composed of a wideband antenna that is used for channel sensing and a communicating antenna that is used for dynamic transmission over various frequencies. The communicating antenna is a software controlled reconfigurable antenna that can tune its frequency response by changing the height and angular position of its ground plane. This antenna is composed of a rectangular patch and three ground planes. Two ground planes are fixed while the third one moves and tilts based on the user's demand. The antenna's moving ground plane is controlled by an Arduino board and two linear actuators. The wideband sensing antenna is composed of a printed monopole patch that searches the spectrum for idle frequencies. A prototype of the complete antenna system is fabricated and tested. Both experimental and simulated results show good agreement.

In this study, a novel reconfigurable antenna using a PIN diode is proposed for multiband (GSM900/1800/1900/UMTS/LTE2300/2500) operation in mobile handsets. By adjusting the on/off state of the PIN diode, the reconfigurable antenna operates in a planar inverted-F antenna (PIFA) mode as well as a loop mode. The operating bandwidth at a low band is attributed to the PIFA mode. The broad bandwidth at a high band is easily achieved in the PIFA mode as well as the loop mode. It is observed from the measured results that this planar antenna exhibits an impedance bandwidth of ∼8.7% at the 920-MHz band and ∼48.3% at the 2250-MHz band. With the reconfigurable technology, the antenna can achieve a compact size of 27 × 10 × 1.6 mm³.

An omnidirectional microstrip patch antenna, capable of reconfiguring both polarisation and radiation pattern is proposed. It operates with two orthogonal ±45° slanted linear polarisations and can produce two dipole-like radiation patterns, providing 360° coverage in either the horizontal or elevation plane. With appropriate steering, this enables a single antenna to provide full spherical coverage for any polarisation. The reconfiguration is realised by phase shifting, thus does not require switching elements, such as microelectromechanical system or pin diodes embedded into antenna. The basic principles of operation are discussed and validated by numerical and measured data.

In this study, an approach for making electrically small antennas is proposed. In this technique, a two port configuration is utilised in which one port is exploited (the secondary port) in order to match the other port (the primary port) to the source. Based on the proposed approach a microstrip patch antenna is designed and fabricated. The simulated and measured results show that utilising the proposed technique allows the patch antenna to resonate at a frequency much lower than its intrinsic resonance frequency. Moreover, not only it considerably improves the bandwidth of operation, but also it allows frequency reconfiguration in a wide range.