A. Zamanifekri

Beam Squint Compensation in Circularly Polarized Offset Reflector Antennas Using a Sequentially Rotated Focal-Plane Array

The problem of beam squinting in circularly polarized offset reflector antennas is solved by using a novel focal-plane array concept that consists of sequentially rotated linearly polarized elements. This concept can be used to facilitate beam steering in full-duplex communication with satellite Internet (VSAT) operating in the Ka-band. A prototype consisting of a 75-cm offset dish illuminated by a 2 ×2 array of sequentially rotated aperture-coupled microstrip antennas was developed and tested at 20 GHz. Experimental results clearly demonstrate the removal of the beam-squint and resulted in an axial ratio (AR) below 1 dB within the 1-dB beamwidth of the main beam.

Optimum configuration of focal plane arrays for satellite communication

This paper describes an investigation of the focal plane field distribution of an offset reflector antenna. A physical-optics model is developed to calculate the near-field data at the focal plane. A 70 cm offset reflector antenna comparable to a standard satellite TV set has been our study case. As a starting point in our design process, we have investigated the optimal size of the focal plane array (FPA) for offset reflector antennas and achievable scan ranges. This study gives the guidance to the antenna designer for optimal FPA size, the proper F/DP and the required number of array elements.

A Millimeter-Wave Tunable Hybrid-Transformer-Based Circular Polarization Duplexer With Sequentially-Rotated Antennas

This paper presents a millimeter-wave tunable hybrid-transformer-based duplexer concept with dual-antenna configuration. By using orthogonal sequentially-rotated linearly-polarized antennas and the hybrid-transformer-based duplexer, the transmitter and receiver duplexes the two antennas with orthogonal circular-polarized signals. An on-chip tuning technique using magnetic coupling is introduced to improve the isolation of the duplexer in case of impedance imbalances. An alternative duplexer with a similar principle using an on-board rat-race coupler is also proposed and designed for comparison. In order to demonstrate the isolation with practical antenna connections, prototypes have been developed to integrate the on-chip duplexer and the rat-race coupler with on-board aperture-coupled microstrip antennas with sequential rotation technique. Measurement results demonstrate the orthogonal circular polarizations for the receiver and transmitter modes on both prototypes. The achieved isolation by the on-chip tunable duplexer is better than 50 dB between 30.2 and 31.2 GHz, while the achieved isolation by the rat-race version is about 20 dB in the same bandwidth.

Dual-frequency filtenna using defected ground structure for VSAT applications

This paper presents the design of a dual-frequency filtenna using a defected ground structure (DGS). A shared aperture coupled microstrip antenna operating at 20/30 GHz (Ka band) is integrated with a coupled-line bandpass filter to increase the isolation between the transmit and receive channels. It is shown that the presence of slots in the ground plane can significantly increase the coupling between the coupled lines. The proposed technique allows for the design of tightly coupled lines without the necessity of using very narrow gaps. The integrated module can be made small enough to fit within an array unit cell for satellite communication applications.

A 30/35GHz phased array transmitter front-end with >+14dBm Psat and 10° phase/5-bit amplitude resolution for advanced beamforming

A 30/35 GHz dual-band phased array transmitter (TX) front-end is demonstrated in a 0.25um SiGe:C BiCMOS process. The front-end provides variable phase shifts from 0°~360° with a ~10° resolution. A 5-bit amplitude resolution is achieved for advanced beamforming algorithms. Accurate transmitted beam patterns can be generated by applying a genetic algorithm with the achieved phase and amplitude resolution. The front-end transmits a >+14dBm saturation output power with >+15dB gain and >+22dBm OIP3 at 30/35GHz.

An Active Ka-Band Shared-Aperture Antenna With 50 dB Isolation for Satellite Communication

An active hybrid shared-aperture concept (employing both active and passive circuits) is presented. This active shared aperture realizes the required isolation level of 48 dB between transmit (TX) (30 GHz) and receive (RX) (20 GHz) channels of a ground terminal for two-way satellite communication. It can be applied in very small aperture terminals. The dual-frequency shared aperture can be used as a building block for a linearly or circularly polarized phased-array feed in a focal-plane array system. It includes a 20-GHz low-noise amplifier with on-chip notch filtering realized in a 0.25-μm SiGe:C BiCMOS technology. The on-chip filter achieves 30 dB of attenuation at 30 GHz with only 0.4 dB noise figure degradation. The isolation is further enhanced by a novel dual-frequency shared-aperture concept based on defected ground structures in the printed circuit board. Experimental results from the prototype show an overall isolation between TX and RX channel of more than 50 dB at 30 GHz.

Fast pattern synthesis for focal plane arrays using an iterative Gram-Schmidt orthogonalization

In this study, a method for amplitude and phase constrained focal plane array pattern synthesis based on the intersection approach and Gram-Schmidt orthogonalization is presented. A new formulation for alternation projection, which leads to a efficient and simple algorithm, is given. The basic idea of the method is to utilize Gram-Schmidt orthogonalization as the projection operator in the iteration step of the alternating projection method. A number of examples are presented to highlight various aspects of the proposed method.