Lora Schulwitz

A compact dual-polarized multibeam phased-array architecture for millimeter-wave radar

A broad-band dual-polarized phased array is presented, which allows for independent beam control of the vertical and horizontal polarization with multibeam scanning in azimuth and elevation. The system is based upon a compact tray architecture with element spacing of 0.6/spl lambda/. Using stereolithography, a miniature dual-polarized waveguide front end was fabricated, which provides a low-loss transition to the microstrip phase-shifting circuitry. A p-i-n diode switch followed by a low-noise amplifier is implemented for each tray to allow for the electronically controlled beam scanning with a 49/spl deg/ field of view. The phased array demonstrates broad-band characteristics from 34 to 40 GHz with better than 20-dB cross-polarization signal discrimination.

A New Low Loss Rotman Lens Design Using a Graded Dielectric Substrate

In this paper, a new low loss graded dielectric Rotman lens design is presented. The graded dielectric allows for the enhanced focusing of the energy between the beam ports and the array ports of the lens, thereby minimizing the energy spill-over to the Rotman lens sides. New lens design equations are presented, which account for the change in effective wavelength and ray bending within the lens. The graded dielectric within the lens was fabricated by forming a periodic lattice of voids, with a variable density, in the lens substrate. Compared to a conventional Rotman lens, the new graded dielectric Rotman lens shows a measured insertion loss improvement of up to 2.1 dB. In addition, the degradation in peak power at the extreme scan angles is improved from 1.5 to 0.7 dB.

A New Low Loss Rotman Lens Design for Multibeam Phased Arrays

The design methodology and analysis of a new low loss Rotman lens beam-forming network is presented. With the introduction of dielectric contours of varying permittivity within the lens, enhanced focusing is achieved. The varying permittivity is realized through a synthesized dielectric technique, where a periodic lattice of holes is formed within the dielectric substrate. In comparison to a conventional Rotman lens of similar shape and size, this new enhanced focused Rotman lens shows an insertion loss improvement of 1.2 to 2.0 dB. Also, the decrease in gain at the extreme scan angles is reduced from 1.5dB to 0.7dB

Millimeter-Wave Dual Polarized L-Shaped Horn Antenna for Wide-Angle Phased Arrays

A new broadband dual polarized L-shaped horn antenna and associated waveguide feed structure is presented. The antenna is well suited for millimeter-wave polarimetric phased array systems requiring wide-angle scanning and ease of integration with planar circuits. A stereolithographic fabrication process is employed to obtain the complex angles and intricate features that are essential for the antenna and feed design. Dielectric material is used to fill the horn antenna and waveguide feed, which allows for the desired radiation characteristics as well as low loss transition to the microstrip circuitry. Broadband attributes are demonstrated with measured return losses of better than -10 dB from 34 to 40 GHz. The measured gain is 5.3 dB at 35 GHz, along with 19 dB cross-polarization discrimination

A dual polarized millimetre-wave multibeam phased array

This paper presents a single aperture multibeam spatial power combining system that can support two separate polarizations. A Rotman lens is used as the power dividing network, which also has the ability to scan the beam over discrete angles. 1/spl times/9 dual polarized array was designed to demonstrate the beam steering in azimuth plane. The entire system is designed for the Ka band, with a center frequency of 32.5 GHz. The use of MMIC amplifiers allow for high power multibeam capabilities. Through simulations and measurements, a /spl plusmn/30 degree scan range was achieved for the horizontal and vertical polarizations.

A Monopulse Rotman Lens Phased Array for Enhanced Angular Resolution

A low cost monopulse phased array is described, which is based upon a Rotman lens and switched line phase shifting network. An amplitude comparison monopulse scheme is implemented, where the phased array is capable of scanning the sum and difference beams throughout a 60deg field of view. The sum beam directivity is better than 12 dB within a 6 GHz bandwidth at Ka band. Over 20 dB difference beam nulls were achieved throughout a 1 GHz bandwidth. The entire phase shifting circuit occupies a size of 62 mm by 62 mm, which is no larger than conventional Rotman lens circuitry.

A broadband millimeter-wave dual polarized phased array for radar front end applications

A broadband millimeter-wave phased array system is presented which allows for independent control of vertically and horizontally polarized beams in azimuth and elevation. The complete system is based upon a low profile tray architecture with compact spacing between adjacent elements and ease of integration with multiple linear arrays. Using stereolithography, a dual polarized waveguide structure was fabricated which allowed for a low loss transition between an array of miniature horn antennas and the array ports of the phase shifting network. A broadband switch network with low noise amplifier was designed to achieve a compact electronically controlled phased array. Recent advances in radar imaging and sensor systems have led to the necessity of compact, low cost, and robust phased array front ends. In particular, dual polarized phased arrays are becoming increasingly popular for identifying targets with various polarization signatures. Polarimetric radar systems must extract both the amplitude and phase information to correctly characterize the position and polarization signature of targets. This information can only be obtained through the independent processing of two orthogonal polarizations. In addition, communication systems can effectively double the bandwidth of the transmitted and received signals by taking advantage of the polarization diversity. In this paper, a low profile phased array front end system is presented which allows for the independent control and characterization of the vertical and horizontal polarizations. With the ever more highly developed MMIC technologies for Ka band, a very compact and broadband phased array front end can be realized. Here, a tray based architecture is implemented, where additional low profile trays are stacked upon each other to form a two dimensional phased array. In this way, a compact three dimensional imaging system can be implemented. A new yet complex dual polarized waveguide structure is presented, which feeds an array of miniature horn antennas, forming a compact single aperture element. Fabricating such a complex structure is often a challenge, especially for millimeter-wave frequencies where fabrication of extremely small shapes with complex angles is difficult. To address this challenge, stereolithography is used in a layer by layer process to form a rigid polymer structure, which is then electroplated with metal. As shown in (1), recent advances in the stereolithography process have allowed for an inexpensive and reliable way to fabricate truly three dimensional structures, where methods such as CNC machining or silicon micromachining may fail. Here, several trays of waveguides and horn antennas were fabricated through stereolithography, where each tray allowed for the control of either the vertical or horizontal polarization. To demonstrate the capabilities of the system, a complete dual polarized 1x10 linear array was fabricated, and the associated beam controlling circuitry was implemented on a single low profile tray. The entire phased array front end was designed for broadband operation from 34 to 40 GHz. This system is ideally suited for applications such as imaging systems, automotive collision avoidance radar, remote sensing, and communication systems.

Packaging Method for Increased Isolation Using a Microstrip to Waveguide Transition

A new technique to decrease crosstalk within high frequency packages, which is based on a microstrip to waveguide transition, is presented. The waveguide based packaged circuit demonstrates well over 40% bandwidth and the insertion loss throughout the designed frequency band is comparable to that of the conventional packaging approaches. In contrast to the conventional implementations, this new packaging method achieves approximately 20-dB isolation improvement for a test circuit as presented here. In addition, to suppress low frequency interference, a dc and low frequency filter is implemented as part of the waveguide transition

Miniature dual polarized L-shaped horn antenna array for broadband millimeter-wave electronically scanned arrays

In this paper, a miniature dual polarized L-shaped horn antenna array is presented for millimeter-wave electronically scanned array radar. Through measurements of the L-shaped horn antenna and waveguide feed, the 10 dB return loss for both waveguide ports showed better than 16% bandwidth for 34 to 40 GHz operation. In addition, better than 15 dB isolation was achieved throughout this frequency range. The measured gain of the antenna at 35 GHz is 5.3 dB with 19 dB cross-polarization discrimination. The L-shaped horn antenna demonstrates approximately 96 degree beamwidth in the E-plane and 70 degree beamwidth in the H-plane, which therefore allows for the wide-angle beam scanning for phased arrays. Finally, the L-shaped horn antenna array was implemented as part of a broadband millimeter-wave phased array.

Millimeter-wave dual polarized L-shaped horn antenna array

A new broadband dual polarized L-shaped horn antenna and associated waveguide feed structure is presented. The horn antenna and waveguide feeds are filled with dielectric material, where a small aperture area of 0.5lambda square is achieved. Using stereolithography, the miniature antennas and waveguides were fabricated as sets of cavity filled blocks. Broadband attributes are demonstrated with a measured return loss of better than -10 dB from 34 to 40 GHz. The measured gain is 5.3 dB at 35 GHz, with 19 dB cross-polarization discrimination