Kenneth A. Hummer

High power four-way power divider/combiner

A four-way waveguide power divider/combiner has been developed using a radial waveguide. The divider has an insertion loss of less than 0.5 dB and a power balance of +or-0.2 dB over a bandwidth of 2.5 GHz at X-band. A power combiner using this circuit and four Gunn oscillators has been demonstrated with over 70% combining efficiency. The circuit should have applications in millimeter-wave power combining and high-power microwave systems.<<ETX>>

Theoretical and experimental study of the input impedance of the cylindrical cavity-backed rectangular slot antennas

The authors study the input impedance of a cylindrical cavity-backed slot antenna based on mode matching and the complex Poynting theorem. Two cavity-backed slot antennas were fabricated to verify the theory. The numerical results agree very well with measurements. Two resonant frequencies were found from the input impedance. One resonant frequency is attributed to the rectangular slot and the other is due to the cavity. The slot length controls the first resonant frequency and has a much stronger effect on the input impedance at the antenna operating frequency as compared with the cavity length. >

Microstrip active antennas and arrays

A description is presented of active antennas and arrays fabricated using microstrip patch antennas and Gunn diodes. Injection-locking experiments were carried out on these X-band antennas to achieve frequency coherency and to calculate the circuit Q-factor. An electronic tuning range of over 9% has been achieved for the single active patch element. A two-element active array was also developed. The output power levels from the two elements were combined in free space, resulting in higher power in the main beam. The tuning range was much narrower and the antenna pattern broke from a single beam into two separate beams as the DC bias voltage was varied. The breakup limits the practical tuning range.<<ETX>>

Slot antennas fed by circular waveguides

Slot antennas fed by a circular waveguide or a cylindrical cavity have been developed. The slot antennas can be rectangular slots or cross slots. Radiation patterns have been measured for both slot configurations. The use of circular waveguides has many advantages, such as a symmetrical feeding arrangement and the realization of cross polarization feeding.<<ETX>>

Integrated Circuit Active Arrays And Spatial Power Combiners Using Aperture Coupled Patch Antennas

Integrated circuit active arrays and spatial power combiners using aperture coupled patch antennas have been developed. Results from a prototype element and a two-element combiner are very encouraging. Methods for achieving phase coherency have been developed.

Resonant frequency and antenna pattern of a dielectrically filled, circular waveguide fed slot antenna

The effects of a dielectric filling material on the characteristics of a circular waveguide fed slot antenna are given. The antenna pattern is found using a sinusoidal aperture E-field distribution. The resonant frequency is found by using a theory for cavity backed slot antennas. The theoretical and experimental resonant frequency and antenna pattern of a dielectric-filled, circular waveguide fed slot antenna are presented. The error in resonant frequency was always less than 1% while the error in half-power beamwidth was less 2.61%. The good agreement between the theory and experiments implies that the main effect of the dielectric is in changing the propagation constant in the slot and not the slot aperture field distribution.<<ETX>>

Input impedance of the slot antennas backed by cylindrical cavity

The input impedance of a cylindrical cavity-backed slot antenna has been derived based on the mode matching method and the complex Poynting theorem. Two cavity-backed slot antennas were fabricated to verify the theory. Numerical results agree very well with measurements. It is pointed out that the results should have many applications in conformal antennas and arrays.<<ETX>>

Microwave Active Array Elements

Two types of active antenna elements have been investigated. One type uses a microstrip antenna with an active device mounted directly on the antenna. The other uses an active device coupled to a microstrip patch antenna through an aperture. Microstrip active antenna elements and two-element arrays have been demonstrated for both types of circuits. Injection locking of the antenna elements has been achieved through space and mutual coupling. The circuit Q-factor was calculated based on the locking gain and locking bandwidth. The power outputs from two elements have been successfully combined in free space with a combining efficiency of over 90 percent. An analytical method based upon the aperture coupling theory and the derivation of S-parameter matrix has been developed for modeling a microstrip line coupled to a microstrip patch antenna using a circular coupling aperture. The results should have many applications in low cost active arrays, active transmitters, and spatial power combiners.