Yasuto Mushiake

A report on Japanese development of antennas: from the Yagi-Uda antenna to self-complementary antennas

The self-complementary antenna structure was originated and its constant-impedance property was discovered by the author in 1948. He pursued investigations of this type of antenna for many years, and he attained many extensions of the principle of self-complementarity, from the simplest planar structure to various other cases. In parallel with these studies, extensive developmental investigations of extremely broadband antennas have been carried out in Japan, based on this principle. This article succinctly describes a long history of these studies on self-complementary antennas, including the background of its origination. In connection with the extremely broadband property of this type of antenna, the non-constant-impedance property of incorrectly arranged log-periodic antennas is clearly shown, based on the results of experiments. This experimental fact indicates that the log-periodic shape in an antennas structure does not guarantee a broadband property for the antenna. Most of experimental details and all of the theoretical treatments are omitted from this article.

Stacked Self-Complementary Antennas

In order to improve the radiation characteristics of antennas, especially to increase their directivities or power gains, the stacked antenna technique is often utilized effectively in practice. In such cases, there are mutual interactions between the element antennas, mainly owing to the effects of the mutual impedances. Accordingly, the constant-impedance property of self-complementary antennas is not necessarily preserved when they are introduced as element antennas into a stacked antenna. However, the author has proposed various types of stacked self-complementary antenna, where all the element antennas have constant impedance, independently of the source frequency and their shapes.

Origination of Self-Complementary Planar Structures and Discovery of Their Constant-Impedance Property

According to the result obtained in Chapter 3, section 3.1, the input impedances, Z1and Z2, for mutually complementary planar structures are given by relationship (3.3), that is (Z_{1}Z_{2}= (Z_{0}/2)^{2}) where Z0 is the intrinsic impedance of the medium, which is approximately equal to 120 π[Ω] in free space. This relationship was derived by the author in 1948 [1.1–1.3]. As mentioned in section 3.1, however, the same expression had already been obtained by several other investigators, after making various assumptions, as the relationship between the input impedances for a slot antenna and its complementary wire antenna [3.1–3.4]. However, expression (4.1) in the present theory is derived without any assumptions being made, and it is always exact for any shape of mutually complementary structure. Therefore, expression (4.1) is an innovative and generalized relationship for a pair of arbitrarily shaped complementary planar structures. Nevertheless, the originality or novelty of the author’s theory was not appreciated when it first appeared.

Fundamental Theories of Complementary Structures

For the purpose of developing the theory of self-complementary antennas, some preliminary considerations will be made in this chapter, and electromagnetic fields for a pair of mutually dual structures will be discussed in this section.

Notes on the history of the yagi-uda antenna [historical corner]

This issue hosts a very special researcher, Yasuto Mushiake, Professor Emeritus at Tohoku University and at Tohoku Institute of Technology, born on March 28, 1921. He first studied at the Hiroshima Higher Technical School, (presently, Hiroshima University), and then at the Tohoku Imperial University during World War II.

Monopole-Slot Type Modified Self-Complementary Antennas

The radiation of the three-dimensional SCA shown in Fig. 6.7 is separated into two portions which are respectively in the upper and the lower half-spaces divided by the infinite horizontal plane of the conducting sheet. By taking this property into account, a practical application of this antenna is conceivable, where only the upper half of its radiation is utilized.

Impedance Relationships for Complementary Planar Structures

For the purpose of investigating the relationship between the input impedances for mutually complementary planar structures, an arbitrarily shaped plate antenna and its complementary hole antenna, as shown in Figs 3.1(a) and (b) are considered.

Developmental Studies of Rotationally Symmetric Self-Complementary Antennas

As an example of an axially symmetric self-complementary antenna for practical application, an equally spaced unipole (or monopole)-notch type array antenna with tapered distribution of the unipole-lengths as shown in Fig. 10.1 has been experimentally studied [8.1–8.3, 10.1–10.4]. According to the theory described in Chapter 4, this has a constant input impedance of 607π Ω under the condition that the end terminals are terminated by a lumped resistance or a transmission line with 60πΩ. However, the end terminals of the tested structure are opened as shown in the same figure.

General Considerations about Approximations and Modifications of Self-Complementary Antennas

According to the theory of the self-complementary antenna (SCA), the basic structures of this type of antenna consist of infinitely extended planar sheets of perfect electric conductors. In addition, in the case of stacked antennas, an infinite number of element antennas are arranged periodically. Therefore, the theoretically obtained self-complementary antenna can only be approximated by limited size of structure and limited number of element antennas, when this principle is applied to extremely broad-band practical antennas.

Multi-Terminal Self-Complementary Planar Structures

A simple and typical example of a rotationally symmetric multi-terminal selfcomplementary planar structure is shown in Fig. 5.1, where all of the eight contour Unes of the four conducting planar sheets are generated with a single bent line by rotating it by 45° steps.