A survey of microstrip antenna elements is presented, with emphasis on theoretical and practical design techniques. Available substrate materials are reviewed along with the relation between dielectric constant tolerance and resonant frequency of microstrip patches. Several theoretical analysis techniques are summarized, including transmission-line and modal-expansion (cavity) techniques as well as numerical methods such as the method of moments and finite-element techniques. Practical procedures are given for both standard rectangular and circular patches, as well as variations on those designs including circularly polarized microstrip patches. The quality, bandwidth, and efficiency factors of typical patch designs are discussed. Microstrip dipole and conformal antennas are summarized. Finally, critical needs for further research and development for this antenna are identified.

Microstrip antenna technology

A multiple access, spread spectrum communication system and method for providing high capacity communications to, from, or between a plurality of system users, using code-division-spread-spectrum communication signals. The communication system uses means for providing marginal isolation between user communication signals. The marginal isolation is provided by generating simultaneous multiple steerable beams; using an omni-directional antenna with polarization enhancement; using power control devices to adjust the output power for user generated communication signals either in response to their input activity level, or in accordance with a minimum allowable power for maintaining a communication link. The communication system can also employ a means for transmitting a predetermined pilot chip sequence contiguous with the code-division-spread-spectrum communication signals. In further embodiments the communication system employs a plurality of user terminals linked to each other or to other services through one or more terrestrial or satellite repeaters. Multiple satellite repeaters are operable in a new communication mode to obtain further gains in signal isolation.

Spread spectrum multiple access communication using satellite or terrestrial repeaters

A repeater and associated method of use includes at least one antenna element for communicating in one direction and at least one antenna element for communicating in another direction. A radio frequency uplink path and a radio frequency downlink path are coupled between the antennas. At least one of the radio frequency uplink path or the radio frequency downlink path includes an adaptive cancellation circuit. The adaptive cancellation circuit is configured to generate a cancellation signal without requiring an injected signal. The cancellation signal, when added to a radio frequency signal in the respective uplink and downlink paths, substantially reduces feedback signals present in the radio frequency signal.

Repeaters for wireless communication systems

Dual-frequency patch antennas may provide an alternative to large-bandwidth planar antennas, in applications in which large bandwidth is really needed for operating at two separate transmit-receive bands. When the two operating frequencies are far apart, a dual-frequency patch structure can be conceived to avoid the use of separate antennas. In this paper, a critical overview of possible solutions for dual-frequency patch antennas is presented, and future perspectives are outlined. Geometries are discussed in particular.

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Dual-frequency patch antennas

The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured.

An experimental investigation of electrically thick rectangular microstrip antennas

A technique is investigated for controlling the operating frequency and polarization of microstrip antennas. The control is achieved by placing shorting posts at appropriate locations within the antenna's boundaries. By changing the number and locations of the posts, the operating frequency can be tuned over a 1.5-to-1 range, and the polarization can be changed from horizontal to vertical, right-hand circular, or left-hand circular. All of these changes are obtained without significantly altering the input impedance or radiation patterns of the antenna and without increasing the complexity of the external microwave feed network. The frequency and polarization can be electronically controlled by using microwave switching diodes for the shorting posts. Antennas that have two feeds and operate simultaneously in two orthogonal polarizations have been constructed with the capability to switch between linear and circular polarization. Also, a thin frequency-scanned array has been built with the frequency-agile microstrip elements.

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Microstrip antennas with frequency agility and polarization diversity

An inexpensive, flush mounted microstrip antenna which is frequency agile d has polarization diversity. The frequency and polarization of the antenna can be selected by selecting the location of shorting posts in the antenna. The use of switching diodes in place of shorting posts provides the means of electronically switching the frequency and polarization characteristics of the antenna. Frequency-agility provides frequency scannable microstrip antenna arrays which also have polarization diversity. Frequency-agility, polarization diversity and frequency scannable arrays are controllable by digital means such as a computer.

Frequency-agile, polarization diverse microstrip antennas and frequency scanned arrays

A dual radiating system where one radiating element is placed atop the ot in a piggyback fashion. The elements can be a pair of microstrip or dielectric-loaded parallel plate radiators, or it can be a combination of the two. Separate coaxial lines feed each of the radiators, and there is a minimum of coupling from one antenna to another. The antenna can be used alone or more effectively in a linear or planar conformal array.

Flush-mounted piggyback microstrip antenna

An inexpensive, flush mounted selectable mode microstrip antenna which is equency-agile and has polarization diversity. The mode, frequency and polarization of the antenna can be selected by selecting the location of shorting posts in the antenna. The use of switching diodes in place of shorting posts provides the means of electronically switching the mode, frequency and polarization characteristics of the antenna. The selectable mode microstrip antenna arrays are also provided. The selection of mode, frequency and polarization can be selected and controlled by digital means such as a computer.

Selectable-mode microstrip antenna and selectable-mode microstrip antenna arrays

This invention comprises sn inexpensive, flush-mounted microstrip antenna e polarization of which is easily changed from vertical linear to horizontal linear, left-circular, right-circular or any desired elliptical sense. This enables the designer to select the polarization by selecting the proper location of shorting posts in the antenna. The use of rf switching diodes in place of conventional shorting posts provides a means of electronically switching the polarization.

Daniel H. Schaubert

Papers

Microstrip antennas with frequency agility and polarization diversity

Frequency-agile, polarization diverse microstrip antennas and frequency scanned arrays

Flush-mounted piggyback microstrip antenna

Selectable-mode microstrip antenna and selectable-mode microstrip antenna arrays

Microstrip antenna with polarization diversity